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During November 2008-July 2009, we investigated the origin of unknown fever in Senegalese patients with a negative malaria test result, focusing on potential rickettsial infection. Using molecular tools, we found evidence for Rickettsia felis-associated illness in the initial days of infection in febrile Senegalese patients without malaria.

Background: Studies on human genetic factors associated with malaria have hitherto concentrated on their role in susceptibility to and protection from disease. In contrast, virtually no attention has been paid to the role of human genetics in eliciting the production of parasite transmission stages, the gametocytes, and thus enhancing the spread of disease., Methods and Findings: We analysed four longitudinal family-based cohort studies from Senegal and Thailand followed for 2-8 years and evaluated the relative impact of the human genetic and non-genetic factors on gametocyte production in infections of Plasmodium falciparum or P. vivax. Prevalence and density of gametocyte carriage were evaluated in asymptomatic and symptomatic infections by examination of Giemsa-stained blood smears and/or RT-PCR (for falciparum in one site). A significant human genetic contribution was found to be associated with gametocyte prevalence in asymptomatic P. falciparum infections. By contrast, there was no heritability associated with the production of gametocytes for P. falciparum or P. vivax symptomatic infections. Sickle cell mutation, HbS, was associated with increased gametocyte prevalence but its contribution was small., Conclusions: The existence of a significant human genetic contribution to gametocyte prevalence in asymptomatic infections suggests that candidate gene and genome wide association approaches may be usefully applied to explore the underlying human genetics. Prospective epidemiological studies will provide an opportunity to generate novel and perhaps more epidemiologically pertinent gametocyte data with which similar analyses can be performed and the role of human genetics in parasite transmission ascertained.

Background: In 2006, the Senegalese National Malaria Control Programme (NMCP) has recommended artemisinin-based combination therapy (ACT) as the first-line treatment for uncomplicated malaria and, in 2007, mandated testing for all suspected cases of malaria with a Plasmodium falciparum HRP-2-based rapid diagnostic test for malaria (RDT(Paracheck). Given the higher cost of ACT compared to earlier anti-malarials, the objectives of the present study were i) to study the accuracy of Paracheck compared to the thick blood smear (TBS) in two areas with different levels of malaria endemicity and ii) analyse the cost-effectiveness of the strategy of the parasitological confirmation of clinically suspected malaria cases management recommended by the NMCP., Methods: A cross-sectional study was undertaken in the villages of Dielmo and Ndiop (Senegal) nested in a cohort study of about 800 inhabitants. For all the individuals consulting between October 2008 and January 2009 with a clinical diagnosis of malaria, a questionnaire was filled and finger-prick blood samples were taken both for microscopic examination and RDT. The estimated costs and cost-effectiveness analysis were made considering five scenarios, the recommendations of the NMCP being the reference scenario. In addition, a sensitivity analysis was performed assuming that all the RDT-positive patients and 50% of RDT-negative patients were treated with ACT., Results: A total of 189 consultations for clinically suspected malaria occurred during the study period. The sensitivity, specificity, positive and negative predictive values were respectively 100%, 98.3%, 80.0% and 100%. The estimated cost of the reference scenario was close to 700 euros per 1000 episodes of illness, approximately twice as expensive as most of the other scenarios. Nevertheless, it appeared to us cost-effective while ensuring the diagnosis and the treatment of 100% of malaria attacks and an adequate management of 98.4% of episodes of illness. The present study also demonstrated that full compliance of health care providers with RDT results was required in order to avoid severe incremental costs., Conclusions: A rational use of ACT requires laboratory testing of all patients presenting with presumed malaria. Use of RDTs inevitably has incremental costs, but the strategy associating RDT use for all clinically suspected malaria and prescribing ACT only to patients tested positive is cost-effective in areas where microscopy is unavailable.

Background: Q fever is a worldwide zoonotic disease caused by Coxiella burnetii. Epidemiologically, animals are considered reservoirs and humans incidental hosts., Methodology/principal Findings: We investigated Q fever in rural Senegal. Human samples (e.g., sera, saliva, breast milk, feces) were screened in the generally healthy population of two villages of the Sine-Saloum region. Ticks were collected in four regions. Seroprevalence was studied by immunofluorescence, and all other samples were tested by two qPCR systems for detection of C. burnetii. Positive samples were genotyped (multispacer typing) by amplification and sequencing of three spacers. Strains were isolated by cell culture. We found that the seroprevalence may be as high as 24.5% (59 of 238 studied) in Dielmo village. We identified spontaneous excretion of C. burnetii by humans through faeces and milk. Hard and soft ticks (8 species) were infected in 0-37.6%. We identified three genotypes of C. burnetii. The previously identified genotype 6 was the most common in ticks in all studied regions and the only one found in human samples. Three strains of genotype 6 of C. burnetii were also recovered from soft tick Ornithodoros sonrai. Two other genotypes found in ticks, 35 and 36, were identified for the first time., Conclusions/significance: Q fever should be considered a significant public health threat in Senegal. Humans, similar to other mammals, may continuously excrete C. burnetii.

Background: Effective vaccines to combat malaria are urgently needed, but have proved elusive in the absence of validated correlates of natural immunity. Repeated blood stage infections induce antibodies considered to be the main arbiters of protection from pathology, but their essential functions have remained speculative., Methodology/principal Findings: This study evaluated antibody dependent respiratory burst (ADRB) activity in polymorphonuclear neutrophils (PMN) induced by Plasmodium falciparum merozoites and antibodies in the sera of two different African endemic populations, and investigated its association with naturally acquired clinical protection. Respiratory bursts by freshly isolated PMN were quantified by chemiluminescence readout in the presence of isoluminol, which preferentially detects extra-cellular reactive oxygen species (ROS). Using a standardized, high throughput protocol, 230 sera were analyzed from individuals of all age groups living in meso- (Ndiop) or holo-endemic (Dielmo) Senegalese villages, and enrolled in a cross-sectional prospective study with intensive follow-up. Statistical significance was determined using non-parametric tests and Poisson regression models. The most important finding was that PMN ADRB activity was correlated with acquired clinical protection from malaria in both high and low transmission areas (P = 0.006 and 0.036 respectively). Strikingly, individuals in Dielmo with dichotomized high ADRB indexes were seventeen fold less susceptible to malaria attacks (P = 0.006). Complementary results showed that ADRB activity was (i) dependent on intact merozoites and IgG opsonins, but not parasitized erythrocytes, or complement, (ii) correlated with merozoite specific cytophilic IgG1 and IgG3 antibody titers (P<0.001 for both), and (iii) stronger in antisera from a holo-endemic compared to a meso-endemic site (P = 0.002), and reduced in asymptomatic carriers (P<0.001)., Conclusions/significance: This work presents the first clearly demonstrated functional antibody immune correlate of clinical protection from Plasmodium falciparum malaria, and begs the question regarding the importance of ADRB by PMN for immune protection against malaria in vivo.

Sulfadoxine-pyrimethamine with amodiaquine (SP-AQ) is a highly efficacious regimen for intermittent preventive treatment to prevent malaria in children (IPTc), but the amodiaquine component is not always well tolerated. We determined the association between amodiaquine dosage by body weight and mild adverse events (AEs) and investigated whether alternative age-based regimens could improve dosing accuracy and tolerability, using data from two trials of IPTc in Senegal, one in which AQ dose was determined by age and the other in which it was determined by weight category. Both dosage strategies resulted in some children receiving AQ doses above the recommended therapeutic range. The odds of vomiting increased with increasing amodiaquine dosage. In one study, incidence of fever also increased with increasing dosage. Anthropometric data from 1,956 children were used to predict the dosing accuracy of existing and optimal alternative regimens. Logistic regression models describing the probability of AEs by dosage were used to predict the potential reductions in mild AEs for each regimen. Simple amendments to current AQ dosing schedules based on the child's age could substantially increase dosing accuracy and thus improve the tolerability of IPTc using SP-amodiaquine in situations where weighing the child is impractical.

Background: Genetic evidence for diversifying selection identified the Merozoite Surface Protein1 block2 (PfMSP1 block2) as a putative target of protective immunity against Plasmodium falciparum. The locus displays three family types and one recombinant type, each with multiple allelic forms differing by single nucleotide polymorphism as well as sequence, copy number and arrangement variation of three amino acid repeats. The family-specific antibody responses observed in endemic settings support immune selection operating at the family level. However, the factors contributing to the large intra-family allelic diversity remain unclear. To address this question, population allelic polymorphism and sequence variant-specific antibody responses were studied in a single Senegalese rural community where malaria transmission is intense and perennial., Results: Family distribution showed no significant temporal fluctuation over the 10 y period surveyed. Sequencing of 358 PCR fragments identified 126 distinct alleles, including numerous novel alleles in each family and multiple novel alleles of recombinant types. The parasite population consisted in a large number of low frequency alleles, alongside one high-frequency and three intermediate frequency alleles. Population diversity tests supported positive selection at the family level, but showed no significant departure from neutrality when considering intra-family allelic sequence diversity and all families combined. Seroprevalence, analysed using biotinylated peptides displaying numerous sequence variants, was moderate and increased with age. Reactivity profiles were individual-specific, mapped to the family-specific flanking regions and to repeat sequences shared by numerous allelic forms within a family type. Seroreactivity to K1-, Mad20- and R033 families correlated with the relative family genotype distribution within the village. Antibody specificity remained unchanged with cumulated exposure to an increasingly large number of alleles., Conclusion: The Pfmsp1 block2 locus presents a very large population sequence diversity. The lack of stable acquisition of novel antibody specificities despite exposure to novel allelic forms is reminiscent of clonal imprinting. The locus appears under antibody-mediated diversifying selection in a variable environment that maintains a balance between the various family types without selecting for sequence variant allelic forms. There is no evidence of positive selection for intra-family sequence diversity, consistent with the observed characteristics of the antibody response.

A comparative study between the Enzyme-Linked Immuno Sorbent Assay (ELISA-CSP) for circumsporozoitic antigen detection method, the direct observation after dissection and the polymerase chain reaction (PCR) technique used to identify Plasmodium falciparum genomic DNA markers was carried out. This to evaluate the sensibility and the specificity of the PCR, for the determination of both sporozoitic index (ICSP) and the entomological inoculation rate (EIR). The study is conducted in laboratory on eighty six specimens of Anopheles gambiae M infected after being fed with the blood of a gametocytes carrier from Dielmo (Senegal). Salivary glands of forty-eight specimens randomly selected (test A) among the infected eighty six are microscopically observed after manual dissection for the sporozoites detection. The content of these salivary glands and the crushed head/thorax of the remaining 38 specimens (test B) are tested in ELISA-CSP and PCR. The positive and negative results obtained were recorded and summarized for each method. A pair-comparison of the results obtained with each method generally revealed a good sensibility and an excellent specificity The kappa coefficient (K) of test A indicated a "moderate" to "excellent" concordance between the three different methods performed. By using the crushed head/thorax sample, generally used to determine the transmission parameters (ICSP and EIR), the PCR/ELISA-CSP concordance was excellent. In the light of the values of sensibility and specificity obtained, this PCR is comparable to the other methods for the assessment of sporozoitic index and entomological inoculation rate.

Background: The long terminal half life of piperaquine makes it suitable for intermittent preventive treatment for malaria but no studies of its use for prevention have been done in Africa. We did a cluster randomized trial to determine whether piperaquine in combination with either dihydroartemisin (DHA) or sulfadoxine-pyrimethamine (SP) is as effective, and better tolerated, than SP plus amodiaquine (AQ), when used for intermittent preventive treatment in children delivered by community health workers in a rural area of Senegal., Methods: Treatments were delivered to children 3-59 months of age in their homes once per month during the transmission season by community health workers. 33 health workers, each covering about 60 children, were randomized to deliver either SP+AQ, DHA+PQ or SP+PQ. Primary endpoints were the incidence of attacks of clinical malaria, and the incidence of adverse events., Results: 1893 children were enrolled. Coverage of monthly rounds and compliance with daily doses was similar in all groups; 90% of children received at least 2 monthly doses. Piperaquine combinations were better tolerated than SP+AQ with a significantly lower risk of common, mild adverse events. 103 episodes of clinical malaria were recorded during the course of the trial. 68 children had malaria with parasitaemia >3000/microL, 29/671 (4.3%) in the SP+AQ group, compared with 22/604 (3.6%) in the DHA+PQ group (risk difference 0.47%, 95%CI -2.3%,+3.3%), and 17/618 (2.8%) in the SP+PQ group (risk difference 1.2%, 95%CI -1.3%,+3.6%). Prevalences of parasitaemia and the proportion of children carrying Pfdhfr and Pfdhps mutations associated with resistance to SP were very low in all groups at the end of the transmission season., Conclusions: Seasonal IPT with SP+PQ in children is highly effective and well tolerated; the combination of two long-acting drugs is likely to impede the emergence of resistant parasites., Trial Registration: ClinicalTrials.gov NCT00529620.

Background: The time necessary for malaria parasite to re-appear in the blood following treatment (re-infection time) is an indirect method for evaluating the immune defences operating against pre-erythrocytic and early erythrocytic malaria stages. Few longitudinal data are available in populations in whom malaria transmission level had also been measured., Methods: One hundred and ten individuals from the village of Ndiop (Senegal), aged between one and 72 years, were cured of malaria by quinine (25 mg/day oral Quinimax in three equal daily doses, for seven days). Thereafter, thick blood films were examined to detect the reappearance of Plasmodium falciparum every week, for 11 weeks after treatment. Malaria transmission was simultaneously measured weekly by night collection of biting mosquitoes., Results: Malaria transmission was on average 15.3 infective bites per person during the 77 days follow up. The median reappearance time for the whole study population was 46.8 days, whereas individuals would have received an average one infective bite every 5 days. At the end of the follow-up, after 77 days, 103 of the 110 individuals (93.6%; CI 95% [89.0-98.2]) had been re-infected with P. falciparum. The median reappearance time ('re-positivation') was longer in subjects with patent parasitaemia at enrolment than in parasitologically-negative individuals (58 days vs. 45.9; p = 0.03) and in adults > 30 years than in younger subjects (58.6 days vs. 42.7; p = 0.0002). In a multivariate Cox PH model controlling for the sickle cell trait, G6PD deficiency and the type of habitat, the presence of parasitaemia at enrolment and age >/= 30 years were independently predictive of a reduced risk of re-infection (PH = 0.5 [95% CI: 0.3-0.9] and 0.4; [95% CI: 0.2-0.6] respectively)., Conclusion: Results indicate the existence of a substantial resistance to sporozoites inoculations, but which was ultimately overcome in almost every individual after 2 1/2 months of natural challenges. Such a study design and the results obtained suggest that, despite a small sample size, this approach can contribute to assess the impact of intervention methods, such as the efficacy vector-control measures or of malaria pre-erythrocytic stages vaccines.

Background: Urbanization has a great impact on the composition of the vector system and malaria transmission dynamics. In Dakar, some malaria cases are autochthonous but parasite rates and incidences of clinical malaria attacks have been recorded at low levels. Ecological heterogeneity of malaria transmission was investigated in Dakar, in order to characterize the Anopheles breeding sites in the city and to study the dynamics of larval density and adult aggressiveness in ten characteristically different urban areas., Methods: Ten study areas were sampled in Dakar and Pikine. Mosquitoes were collected by human landing collection during four nights in each area (120 person-nights). The Plasmodium falciparum circumsporozoite (CSP) index was measured by ELISA and the entomological inoculation rates (EIR) were calculated. Open water collections in the study areas were monitored weekly for physico-chemical characterization and the presence of anopheline larvae. Adult mosquitoes and hatched larvae were identified morphologically and by molecular methods., Results: In September-October 2007, 19,451 adult mosquitoes were caught among which, 1,101 were Anopheles gambiae s.l. The Human Biting Rate ranged from 0.1 bites per person per night in Yoff Village to 43.7 in Almadies. Seven out of 1,101 An. gambiae s.l. were found to be positive for P. falciparum (CSP index = 0.64%). EIR ranged from 0 infected bites per person per year in Yoff Village to 16.8 in Almadies. The An. gambiae complex population was composed of Anopheles arabiensis (94.8%) and Anopheles melas (5.2%). None of the An. melas were infected with P. falciparum. Of the 54 water collection sites monitored, 33 (61.1%) served as anopheline breeding sites on at least one observation. No An. melas was identified among the larval samples. Some physico-chemical characteristics of water bodies were associated with the presence/absence of anopheline larvae and with larval density. A very close parallel between larval and adult densities was found in six of the ten study areas., Conclusion: The results provide evidence of malaria transmission in downtown Dakar and its surrounding suburbs. Spatial heterogeneity of human biting rates was very marked and malaria transmission was highly focal. In Dakar, mean figures for transmission would not provide a comprehensive picture of the entomological situation; risk evaluation should therefore be undertaken on a small scale.

Background: Malaria is one of the main motives for outpatient consultation and hospitalization in Mauritania. However, its incidence remains unclear because of diagnostic problems and insufficient epidemiological data., Methods: Between April and August 2007, a study on malaria incidence was carried out in Nouakchott city. A total of 237 febrile outpatients, from all Nouakchott districts, attending the two main hospitals of the city were investigated. Finger prick and blood dried filter paper samples were performed to prepare thick and thin films and nested-PCR for malaria parasite species identification and density. The accuracy of diagnosis of 'presumptive malaria', assigned by clinicians and based on fever and other malaria suggestive symptoms, was assessed. Entomological investigations based on morphological and molecular characterization of Anopheline species were conducted in Dar Naïm district., Results: Malaria prevalence rate was 25.7% (61/237), the majority of positive blood slides as well as nested-PCR products were due to Plasmodium vivax 70.5% (43/61) and Plasmodium ovale 24.6% (15/61). Two malaria patients, both with P. vivax, have never travelled out of Nouakchott and seem likely to have been autochthonous (3.3%). Of the 237 individuals included in the survey, 231(97.5%) were clinically diagnosed and treated as malaria cases. 26.4% of clinically diagnosed cases were positive for Plasmodium using microscopic examination and PCR. Thus, false positive cases constituted 73.6% (170/231) of the clinically diagnosed malaria cases. The search for mosquito vectors in Dar Naïm district allowed morphological and molecular identification of Anopheles arabiensis and Anopheles pharoensis., Conclusion: This study demonstrates that, during the hot and dry season, Plasmodium species responsible of recurrent malaria (P. vivax and P. ovale) are the dominant species in Nouakchott city and autochthonous malaria cases exist but are rare. Clinical diagnosis of malaria has a very low positive predicted value. The systematic use of microscopy-based diagnosis and/or rapid diagnostic tests should be considered to appropriately manage malaria and non-malaria cases.

Relapsing fever, caused by spirochaetes belonging to the genus Borrelia, was once the cause of worldwide epidemic disease. This was largely through infection with the louse-borne form of the disease, caused by Borrelia recurrentis (louse-borne relapsing fever (LBRF)). During the last century, we have witnessed the demise of this infection, largely owing to improved standards of living and the introduction of the insecticide DDT, resulting in a reduction in the incidence of the body louse, the vector for relapsing fever. In areas of extreme poverty this disease persists, causing a significant burden of disease. It is now looking probable that this infection is caused by a louse-adapted variant of Borrelia duttonii, transmitted by Ornithodoros moubata 'soft' ticks in East Africa. Like LBRF, infection still causes impact, particularly affecting young children and pregnant women. Over recent years, the true burden of relapsing fever caused by infection with the closely related Borrelia crocidurae, transmitted by Ornithodoros sonrai ticks, has only just begun to emerge. Here, the current state of knowledge concerning relapsing fever in Africa is reviewed.

For decades malarial control has been implemented to control the impact of the disease on the health of populations living in endemic zones. The use of artemisinine combination therapy, intermittent preventive treatment for children and pregnant women, vector-control methods such as long-lasting insecticide-impregnated mosquito nets and indoor remanent insecticide spraying has proven to be effective. These practices have lead to such an extensive reduction of the malaria burden in some endemic areas that the objective of eradication that was unimaginable a few years ago is now back to the forefront. Regardless of the method chosen, careful evaluation and surveillance of its effectiveness in man is necessary. Achieving epidemiologic impact is the main goal of malaria control methods. The main measures for evaluation involve parasitological and clinical aspects of human malaria. The purpose of this article is to review methods used for epidemiologic evaluation of malaria burden.

Between June and December 2004, snake collections were undertaken in eight villages of the vicinity of Kindia, an area of Guinea Conakry where the incidence of snakebite is among the highest reported in the world. A total of 916 specimens were collected, including 90 Elapidae (9.8 %) and 174 Viperidae (19.0%). The Black Mamba Dendroaspis polylepis was represented by eight specimens, i.e. almost 1% of the snakes collected. This species, which is considered as very rare in West Africa, appears common in this area of Guinea. The current difficulties for the treatment of snakebite due to the high increase of the cost of antivenom therapy are discussed.

The distribution and range of 50% inhibitory concentrations (IC(50)s) of doxycycline were determined for 747 isolates obtained between 1997 and 2006 from patients living in Senegal, Republic of the Congo, and Gabon and patients hospitalized in France for imported malaria. The statistical analysis was designed to answer the specific question of whether Plasmodium falciparum has different phenotypes of susceptibility to doxycycline. A triple normal distribution was fitted to the data using a Bayesian mixture modeling approach. The IC(50) geometric mean ranged from 6.2 microM to 11.1 microM according to the geographical origin, with a mean of 9.3 microM for all 747 parasites. The values for all 747 isolates were classified into three components: component A, with an IC(50) mean of 4.9 microM (+/-2.1 microM [standard deviation]); component B, with an IC(50) mean of 7.7 microM (+/-1.2 microM); and component C, with an IC(50) mean of 17.9 microM (+/-1.4 microM). According to the origin of the P. falciparum isolates, the triple normal distribution was found in each subgroup. However, the proportion of isolates predicted to belong to component B was most important in isolates from Gabon and Congo and in isolates imported from Africa (from 46 to 56%). In Senegal, 55% of the P. falciparum isolates were predicted to be classified as component C. The cutoff of reduced susceptibility to doxycycline in vitro was estimated to be 35 microM.

In sub-Saharan Africa, malaria and malnutrition are major causes of morbidity and mortality in children less than five years of age. To explore the impact of malnutrition on subsequent susceptibility to malaria, a cohort of 874 rural preschool children in Senegal was followed-up during one malaria transmission season from July through December. Data on nutritional status and Plasmodium falciparum parasitemia were collected at baseline. Malaria morbidity was monitored through weekly home visits. Wasted children (weight-for-height z-score < -2) were at lower risk of having at least one subsequent clinical malaria attack (odds ratio = 0.33; 95% confidence interval = 0.13-0.81, P = 0.02), whereas stunting (height-for-age z-score < -2) or being underweight (weight-for-age z-score < -2) was not associated with clinical malaria. Although non-biological explanations such as overprotection of wasted children by their mothers should be considered, immunomodulation according to nutritional status could explain the lower risk of malaria attack among wasted children.

Background: According to entomological studies conducted over the past 30 years, there was low malaria transmission in suburb of Dakar but little evidence of it in the downtown area. However; there was some evidence of local transmission based on reports of malaria among permanent residents. An entomological evaluation of malaria transmission was conducted from May 2005 to October 2006 in two areas of Dakar., Methods: Mosquitoes were sampled by human landing collection during 34 nights in seven places in Bel-air area (238 person-nights) and during 24 nights in five places in Ouakam area (120 person-nights). Mosquitoes were identified morphologically and by molecular methods. The Plasmodium falciparum circumsporozoïte indexes were measured by ELISA, and the entomological inoculation rates (EIR) were calculated for both areas. Molecular assessments of pyrethroid knock down resistance (Kdr) and of insensitive acetylcholinesterase resistance were conducted., Results: From May 2005 to October 2006, 4,117 and 797 Anopheles gambiae s.l. respectively were caught in Bel-air and Ouakam. Three members of the complex were present: Anopheles arabiensis (> 98%), Anopheles melas (< 1%) and An. gambiae s.s. molecular form M (< 1%). Infected mosquitoes were caught only during the wintering period between September and November in both places. In 2005 and 2006, annual EIRs were 9,5 and 4, respectively, in Bel-air and 3 and 3, respectively, in Ouakam. The proportion of host-seeking An. gambiae s.l. captured indoors were 17% and 51% in Bel air and Ouakam, respectively. Ace 1 mutations were not identified in both members of the An. gambiae complex. Kdr mutation frequency in An. arabiensis was 12% in Bel-air and 9% in Ouakam., Conclusion: Malaria is transmitted in Dakar downtown area. Infected mosquitoes were caught in two subsequent years during the wintering period in two distant quarters of Dakar. These data agree with clinical data from a Senegalese military Hospital of Dakar (Hospital Principal) where most malaria cases occurred between October and December. It was the first detection of An. melas in Dakar.

Background: The adaptation of Anopheles gambiae to humans and its environment involves an ongoing speciation process that can be best demonstrated by the existence of various chromosomal forms adapted to different environments and of two molecular forms known as incipient taxonomic units., Methods: The aim of this study was to compare the epidemiologic role of Anopheles arabiens is and the molecular forms M and S of Anopheles gambiae in the transmission of Plasmodium in a rural areas of southern Senegal, Dielmo. The sampling of mosquitoes was carried out monthly between July and December 2004, during the rainy season, by human volunteers and pyrethrum spray catches., Results: Anopheles arabiensis, An. gambiae M and S forms coexisted during the rainy season with a predominance of the M form in September and the peak of density being observed in August for the S form. Similar parity rates were observed in An. arabiensis [70.9%] (n = 86), An. gambiae M form [68.7%] (n = 64) and An. gambiae S form [81.1%] (n = 156). The circumsporozoite protein (CSP) rates were 2.82% (n = 177), 3.17% (n = 315) and 3.45% (n = 405), with the mean anthropophilic rates being 71.4% (n = 14), 86.3% (n = 22) and 91.6% (n = 24) respectively for An. arabiensis and An. gambiae M and S forms. No significant difference was observed either in host preference or in Plasmodium falciparum infection rates between sympatric M and S populations., Conclusion: No difference was observed either in host preference or in Plasmodium falciparum infection rates between sympatric M and S populations, but they present different dynamics of population. These variations are probably attributable to different breeding conditions.

Background: The burden of Plasmodium falciparum malaria has worsened because of the emergence of chloroquine resistance. Antimalarial drug use and drug pressure are critical factors contributing to the selection and spread of resistance. The present study explores the geographical, socio-economic and behavioural factors associated with the use of antimalarial drugs in Africa., Methods: The presence of chloroquine (CQ), pyrimethamine (PYR) and other antimalarial drugs has been evaluated by immuno-capture and high-performance liquid chromatography in the urine samples of 3,052 children (2-9 y), randomly drawn in 2003 from the general populations at 30 sites in Senegal (10), Burkina-Faso (10) and Cameroon (10). Questionnaires have been administered to the parents of sampled children and to a random sample of households in each site. The presence of CQ in urine was analysed as dependent variable according to individual and site characteristics using a random - effect logistic regression model to take into account the interdependency of observations made within the same site., Results: According to the sites, the prevalence rates of CQ and PYR ranged from 9% to 91% and from 0% to 21%, respectively. In multivariate analysis, the presence of CQ in urine was significantly associated with a history of fever during the three days preceding urine sampling (OR = 1.22, p = 0.043), socio-economic level of the population of the sites (OR = 2.74, p = 0.029), age (2-5 y = reference level; 6-9 y OR = 0.76, p = 0.002), prevalence of anti-circumsporozoite protein (CSP) antibodies (low prevalence: reference level; intermediate level OR = 2.47, p = 0.023), proportion of inhabitants who lived in another site one year before (OR = 2.53, p = 0.003), and duration to reach the nearest tarmacked road (duration less than one hour = reference level, duration equal to or more than one hour OR = 0.49, p = 0.019)., Conclusion: Antimalarial drug pressure varied considerably from one site to another. It was significantly higher in areas with intermediate malaria transmission level and in the most accessible sites. Thus, P. falciparum strains arriving in cross-road sites or in areas with intermediate malaria transmission are exposed to higher drug pressure, which could favour the selection and the spread of drug resistance.

Plasmodium falciparum malaria episodes may vary considerably in their severity and clinical manifestations. There is good evidence that host genetic factors contribute to this variability. To date, most genetic studies aiming at the identification of these genes have used a case/control study design for severe malaria, exploring specific candidate genes. Here, we performed a family-based genetic study of falciparum malaria related phenotypes in two independent longitudinal survey cohorts, as a first step towards the identification of genes and mechanisms involved in the outcome of infection. We studied two Senegalese villages, Dielmo and Ndiop that differ in ethnicity, malaria transmission and endemicity. We performed genome-scan linkage analysis of several malaria-related phenotypes both during clinical attacks and asymptomatic infection. We show evidence for a strong genetic contribution to both the number of clinical falciparum malaria attacks and the asymptomatic parasite density. The asymptomatic parasite density showed linkage to chromosome 5q31 (LOD = 2.26, empirical p = 0.0014, Dielmo), confirming previous findings in other studies. Suggestive linkage values were also obtained at three additional chromosome regions: the number of clinical malaria attacks on chromosome 5p15 (LOD = 2.57, empirical p = 0.001, Dielmo) and 13q13 (LOD = 2.37, empirical p = 0.0014 Dielmo), and the maximum parasite density during asymptomatic infection on chromosome 12q21 (LOD = 3.1, empirical p<10(-4), Ndiop). While regions of linkage show little overlap with genes known to be involved in severe malaria, the four regions appear to overlap with regions linked to asthma or atopy related traits, suggesting that common immune related pathways may be involved.

Previous studies have shown that antibodies from humans exposed continuously to malaria recognize the Plasmodium falciparum asexual blood-stage antigen Pf332. Here we analysed the antibody responses to a C-terminal fragment of Pf332, designated C231, in individuals from Senegal, by measuring the serum levels of immunoglobulin M (IgM), IgG class and subclass and IgE antibodies. IgG antibody reactivity with crude P. falciparum antigen was detected in all the donors, while many of the children lacked or had low levels of such antibodies against C231. The antibody levels increased significantly with age for both crude P. falciparum antigen and C231, and in the older age groups most of the donors displayed antibodies to C231. This was also true for IgM, IgE and IgG subclass reactivity against C231. Moreover, the ratio of IgG1/IgG2 was considerably lower for C231 than for crude P. falciparum antigen, and in age groups 10-14 and 15-19 years the levels of IgG2 against C231 even exceeded that of IgG1. The IgG2/IgG3 ratios suggest that C231 gives similar levels of IgG2 and IgG3, except for children aged 4-9 years, where IgG3 was higher. Raw IgM, IgG class and subclass and IgE antibody levels to C231 tended to be higher in those who did not experience a malaria attack, but following linear multivariate analysis the trends were not significant.

Unlabelled: In the Sahel, most malaria deaths occur among children 1-4 years old during a short transmission season. A trial of seasonal intermittent preventive treatment (IPT) with sulfadoxine-pyrimethamine (SP) and a single dose of artesunate (AS) showed an 86% reduction in the incidence of malaria in Senegal but this may not be the optimum regimen. We compared this regimen with three alternatives., Methods: 2102 children aged 6-59 months received either one dose of SP plus one dose of AS (SP+1AS) (the previous regimen), one dose of SP plus 3 daily doses of AS (SP+3AS), one dose of SP plus three daily doses of amodiaquine (AQ) (SP+3AQ) or 3 daily doses of AQ and AS (3AQ+3AS). Treatments were given once a month on three occasions during the malaria transmission season. The primary end point was incidence of clinical malaria. Secondary end-points were incidence of adverse events, mean haemoglobin concentration and prevalence of parasites carrying markers of resistance to SP., Findings: The incidence of malaria, and the prevalence of parasitaemia at the end of the transmission season, were lowest in the group that received SP+3AQ: 10% of children in the group that received SP+1AS had malaria, compared to 9% in the SP+3AS group (hazard ratio HR 0.90, 95%CI 0.60, 1.36); 11% in the 3AQ+3AS group, HR 1.1 (0.76-1.7); and 5% in the SP+3AQ group, HR 0.50 (0.30-0.81). Mutations associated with resistance to SP were present in almost all parasites detected at the end of the transmission season, but the prevalence of Plasmodium falciparum was very low in the SP+3AQ group., Conclusions: Monthly treatment with SP+3AQ is a highly effective regimen for seasonal IPT. Choice of this regimen would minimise the spread of drug resistance and allow artemisinins to be reserved for the treatment of acute clinical malaria.

Background: Surrogate markers of protective immunity to malaria in humans are needed to rationalize malaria vaccine discovery and development. In an effort to identify such markers, and thereby provide a clue to the complex equation malaria vaccine development is facing, we investigated the relationship between protection acquired through exposure in the field with naturally occurring immune responses (i.e., induced by the parasite) to molecules that are considered as valuable vaccine candidates., Methods and Findings: We analyzed, under comparative conditions, the antibody responses of each of six isotypes to five leading malaria vaccine candidates in relation to protection acquired by exposure to natural challenges in 217 of the 247 inhabitants of the African village of Dielmo, Senegal (96 children and 121 older adolescents and adults). The status of susceptibility or resistance to malaria was determined by active case detection performed daily by medical doctors over 6 y from a unique follow-up study of this village. Of the 30 immune responses measured, only one, antibodies of the IgG3 isotype directed to merozoite surface protein 3 (MSP3), was strongly associated with clinical protection against malaria in all age groups, i.e., independently of age. This immunological parameter had a higher statistical significance than the sickle cell trait, the strongest factor of protection known against Plasmodium falciparum. A single determination of antibody was significantly associated with the clinical outcome over six consecutive years in children submitted to massive natural parasite challenges by mosquitoes (over three parasite inoculations per week). Finally, the target epitopes of these antibodies were found to be fully conserved., Conclusions: Since anti-MSP3 IgG3 antibodies can naturally develop along with protection against P. falciparum infection in young children, our results provide the encouraging indication that these antibodies should be possible to elicit by vaccination early in life. Since these antibodies have been found to achieve parasite killing under in vitro and in vivo conditions, and since they can be readily elicited by immunisation in naïve volunteers, our immunoepidemiological findings support the further development of MSP3-based vaccine formulations.

We use phylogenetic analysis of 1333 bp of mitochondrial DNA sequence to investigate the phylogeny and historical biogeography of the cobra-like elapid snakes, with special reference to the evolution of spitting and the phylogeography of the African spitting cobras, a radiation widespread in open vegetational formations throughout sub-Saharan Africa. Our results suggest that spitting adaptations appear to have evolved three times in cobras, but alternative scenarios cannot be rejected. The Asiatic Naja are monophyletic and originate from a single colonization of Asia from Africa. The radiation of the African spitting Naja appears to date back to the early Miocene and many speciation events in the group predate the Pliocene expansion of grasslands and the radiation of large grazing mammals in Africa. The cladogenic events in this complex appear to have been triggered by both ecological changes and tectonic events associated with the formation and expansion of the African Rift Valley. Taxonomically, our data confirm the inclusion of Boulengerina and Paranaja within Naja, and reveal a clade of African rainforest cobras including N. melanoleuca, Paranaja multifasciata and Boulengerina that constitutes the sister clade of the African open-formation non-spitting cobras. Naja nigricollis is polyphyletic, and we therefore recognize N. nigricincta as a separate species, more closely related to N. ashei and N. mossambica than to N. nigricollis.

Negative consequences of malaria might account for seasonality in nutritional status in children in the Sahel. We report the impact of a randomized, double-blind, placebo-controlled trial of seasonal intermittent preventive anti-malarial treatment on growth and nutritional status in 1,063 Senegalese preschool children. A combination of artesunate and sulfadoxine-pyrimethamine was given monthly from September to November. In the intervention arm, mean weight gain was significantly greater (122.9 +/- 340 versus 42.9 +/- 344 [SD] g/mo, P < 0.0001) and losses in triceps and subscapular skinfold measurements were less (-0.39 +/- 1.01 versus -0.66 +/- 1.01 mm/mo, and -0.15 +/- 0.64 versus -0.36 +/- 0.62 mm/mo, respectively, P < 0.0001 for both). There was no difference in height increments. The prevalence of wasting increased significantly in the control arm (4.6% before versus 9.5% after, P < 0.0001), but remained constant in intervention children: 5.6% versus 7.0% (P = 0.62). The prevention of malaria would improve child nutritional status in areas with seasonal transmission.

Artesunate is a highly effective antimalarial and there is some evidence that it is also active against schistosome infections. We therefore investigated whether treatment with artesunate of acute malaria in Senegalese children had an impact on their level of infection with Schistosoma haematobium. Twenty-seven children who were entered into a clinical trial of antimalaria treatment were excreting S. haematobium eggs in their urine on the day of treatment. Fifteen children received a combination of a single dose of sulfadoxine/pyrimethamine together with three daily doses of artesunate (4 mg/kg); the remaining 12 children received three daily doses of amodiaquine and artesunate. The overall cure rate and reduction in the mean number of excreted eggs at 28 days post treatment were 92.6% and 94.5%, respectively. Our findings indicate that artesunate, in addition to being a very effective treatment for uncomplicated malaria, can also sharply reduce the S. haematobium loads harboured by pre-school African children.

Background: Inadequate treatment practices with antimalarials are considered major contributors to Plasmodium falciparum resistance to chloroquine, pyrimethamine and sulfadoxine. The longitudinal survey conducted in Dielmo, a rural Senegalese community, offers a unique frame to explore the impact of strictly controlled and quantified antimalarial use for diagnosed malaria on drug resistance., Methodology/principal Findings: We conducted on a yearly basis a retrospective survey over a ten-year period that included two successive treatment policies, namely quinine during 1990-1994, and chloroquine (CQ) and sulfadoxine/pyrimethamine (SP) as first and second line treatments, respectively, during 1995-1999. Molecular beacon-based genotyping, gene sequencing and microsatellite analysis showed a low prevalence of Pfcrt and Pfdhfr-ts resistance alleles of Southeast Asian origin by the end of 1994 and their effective dissemination within one year of CQ and SP implementation. The Pfcrt resistant allele rose from 9% to 46% prevalence during the first year of CQ reintroduction, i.e., after a mean of 1.66 CQ treatment courses/person/year. The Pfdhfr-ts triple mutant rose from 0% to 20% by end 1996, after a mean of 0.35 SP treatment courses/person in a 16-month period. Both resistance alleles were observed at a younger age than all other alleles. Their spreading was associated with enhanced in vitro resistance and rapidly translated in an increased incidence of clinical malaria episodes during the early post-treatment period., Conclusion/significance: In such a highly endemic setting, selection of drug-resistant parasites took a single year after drug implementation, resulting in a rapid progression of the incidence of clinical malaria during the early post-treatment period. Controlled antimalarial use at the community level did not prevent dissemination of resistance haplotypes. This data pleads against reintroduction of CQ in places where resistant allele frequency has dropped to a very low level after CQ use has been discontinued, unless drastic measures are put in place to prevent selection and spreading of mutants during the post-treatment period.

The soft tick Ornithodoros sonrai is recognized as the only vector of Borrelia crocidurae causing human relapsing fever in West Africa. Its determination has been exclusively based on morphological features, geographical distribution and vector competence. Some ambiguities persist in its systematics and may cause misunderstanding about West African human relapsing fevers epidemiology. By amplifying and aligning 16S and 18S rDNA genes in O. sonrai specimens collected from 14 distinct sites in Senegal and Mauritania, we showed the existence of four genetically different subgroups that were morphologically and ecologically identified as belonging to the same species. Within O. sonrai, intraspecific polymorphism was high (pairwise divergence from 0.2% to 16.4%). In all cases, these four subgroups formed a monophyletic clade sharing a common ancestor with East African soft ticks that transmit Borrelia duttoni human relapsing fever. From amplification of the flagellin gene of B. crocidurae we verified that all subgroups of O. sonrai were infected by B. crocidurae and may constitute vectors for this pathogen. All flagellin sequences were identical, refuting the hypothesis suggesting parallel evolution between O. sonrai and B. crocidurae. However, differences in infection rates were significant, suggesting different vector competences between subgroups of O. sonrai.

We propose a stochastic model for simulating malaria tolerance. The model relates the probability of a clinical attack of malaria to the peripheral parasite densities via a pyrogenic threshold that itself responds dynamically to the parasite load. The parameters of the model have been estimated by fitting it to the relationship between incidence of clinical episodes and the entomologic inoculation rate, using age-specific incidence data from two villages in Senegal and one village in Tanzania. The model reproduces the shifts in age distribution of clinical episodes associated with variation in transmission intensity, and in keeping with the data, predicts a slightly higher lifetime number of episodes in the mesoendemic village of Ndiop than in the holoendemic village of Dielmo. This model provides a parsimonious explanation of counter-intuitive relationships between the overall incidence of clinical malaria and transmission intensity. In contrast to the theory of endemic stability, recently proposed to apply to P. falciparum, it does not assume any intrinsic age dependence in the outcome of infection. This model can be used to explore the consequences for predictions of the effects of different anti-malarial interventions on the incidence of clinical malaria.

Background: The ongoing drought in sub-Saharan countries has led to the colonisation of west African Savanna by Ornithodoros sonrai; this tick acts as a vector for Borrelia crocidurae, which causes tick-borne relapsing fever (TBRF). Our aim was to ascertain the incidence of TBRF in west Africa., Methods: From 1990 to 2003, we monitored the incidence of TBRF in Dielmo, Senegal, by daily clinical surveillance and by blood testing of individuals with a fever. From 2002 to 2005, we investigated the presence of O sonrai in 30 villages in Senegal, Mauritania, and Mali, and measured by PCR the prevalence of B crocidurae., Findings: The average incidence of TBRF over 14 years was 11 per 100 person-years (range from 4 in 1990 to 25 in 1997). All age-groups presented a high incidence of the disease. In addition to relapses, repeated infections in the same individuals were common, with some affected by up to six distinct infections during the study period. Epidemiological studies indicated that 26 of the 30 studied villages (87%) were colonised by the vector tick O sonrai and that the average B crocidurae infection rate of the vector was 31%., Interpretation: The incidence of TBRF at the community level is the highest described in Africa for any bacterial disease. The presence of the vector tick in most villages investigated and its high infection rate suggest that TBRF is a common cause of fever in most rural areas of Senegal, Mauritania, and Mali.

Objectives: The in vitro activities of FR160, a synthetic catecholate siderophore, and two iron-binding agents, desferrioxamine and doxycycline, were evaluated against Plasmodium falciparum isolates. Correlations between these compounds and standard antimalarial drugs (chloroquine, quinine, amodiaquine, pyronaridine, artemether, artesunate, atovaquone, cycloguanil and pyrimethamine) were assessed to determine any degree of cross-resistance., Methods: Between October 1997 and February 1998, and September and November 1998, 189 P. falciparum isolates were obtained in Dielmo and Ndiop (Dakar). Their susceptibilities were assessed using an isotopic, microwell format, drug susceptibility test., Results: The 137 inhibitory concentrations (IC(50)) values of FR160 ranged from 0.1 to 10 microM and the geometric mean IC(50) was 1.48 microM (95% CI = 1.29-1.68 microM). The geometric mean IC(50) of doxycycline for 121 isolates was 18.9 microM (95% CI = 16.8-21.3 microM) and that of desferrioxamine for 73 isolates was 20.7 microM (95% CI = 17.3-24.8 microM). FR160 was significantly less active against the chloroquine-resistant isolates (P < 0.0001). The mean IC(50)s of doxycycline were significantly higher for the chloroquine-susceptible isolates than for the resistant parasites (P = 0.0447). There was a weak correlation between the responses to FR160, desferrioxamine or doxycycline and those to the other antimalarial compounds (r(2) < 0.22)., Conclusions: The activities of FR160 and desferrioxamine, determined for P. falciparum clones, were confirmed against 137 isolates. The coefficients of determination between the responses to FR160, doxycycline or desferrioxamine and those to all the antimalarial drugs tested are too weak to suggest cross-resistance. FR160 could be a rationale partner to use in combination with doxycycline.

Background: In the Sahel and sub-Sahelian regions of Africa, malaria transmission is highly seasonal. During a short period of high malaria transmission, mortality and morbidity are high in children under age 5 years. We assessed the efficacy of seasonal intermittent preventive treatment-a full dose of antimalarial treatment given at defined times without previous testing for malaria infection., Methods: We did a randomised, placebo-controlled, double-blind trial of the effect of intermittent preventive treatment on morbidity from malaria in three health-care centres in Niakhar, a rural area of Senegal. 1136 children aged 2-59 months received either one dose of artesunate plus one dose of sulfadoxine-pyrimethamine or two placebos on three occasions during the malaria transmission season. The primary outcome was a first or single episode of clinical malaria detected through active or passive case detection. Primary analysis was by intention-to-treat. This study is registered with , number NCT00132561., Findings: During 13 weeks of follow-up, the intervention led to an 86% (95% CI 80-90) reduction in the occurrence of clinical episodes of malaria. With passive case detection, protective efficacy against malaria was 86% (77-92), and when detected actively was 86% (78-91). The incidence of malaria in children on active drugs was 308 episodes per 1000 person-years at risk, whereas in those on placebo it was 2250 episodes per 1000 person-years at risk. 13 children were not included in the intention-to-treat analysis, which was restricted to children who received a first dose of antimalarial or placebo. There was an increase in vomiting in children who received the active drugs, but generally the intervention was well tolerated., Interpretation: Intermittent preventive treatment could be highly effective for prevention of malaria in children under 5 years of age living in areas of seasonal malaria infection.

In order to complete an exploratory study on the risk of death due to snakebite in a rural zone of South-Eastern Senegal, we have carried out a survey to estimate the incidence of snakebites in the same population. The study made on a sample of almost 600 subjects showed an annual incidence of 677 bites per 100.000 inhabitants, that is one of the most important rate ever reported in the world until now. Based on these results and data collected previously on deaths due to snakebites in this same population, we provide an estimate of snakebite case fatality rate of 2.1% in this area of Senegal.

There are no specific clinical signs or symptoms of malaria. Fever attacks, anemia, or signs of severity like coma or respiratory distress cannot easily be attributed to malaria in people who are infected most of the time. Ascribing clinical manifestations to malaria is problematic in populations that are regularly exposed to the transmission of human plasmodia. The more transmission is intense and regular, the higher the prevalence of asymptomatic infections. In areas of intense and perennial malaria transmission, more than 90% of the population may be infected and the simple detection of a plasmodial infection is not enough to attribute clinical manifestations to malaria. Naturally acquired anti-malaria immunity permitting asymptomatic infections is incomplete and temporary. It is an obstacle to the estimation of the malaria burden in endemic areas. The positive association between parasite density and fever allows the attribution of clinical attacks to malaria. The relationship between parasitaemia and the risk of fever is not continuous. An age- and endemicity-dependent threshold effect of parasite density has been demonstrated and can be used to distinguish clinical attacks due to malaria from others. Clinical diagnosis and evaluation of malaria are problematic in three situations: in public health to estimate the malaria burden for health services, in clinical research to evaluate treatments or prophylactic measures (drug, vaccine, anti-vectorial devices), and in basic research on pathophysiology, immunology or genetic susceptibility to clinical malaria. No one diagnostic definition nor procedure for detecting cases is adequate for all three purposes. Case detection may be passive (in health structures for example) or active (in population). The choice of methods for diagnosis and recruitment depends on the objectives and whether a "pragmatic" or "explicative" approach is used. The radical differences between these approaches are often unsuspected or ignored.

Many genes have been implicated in the risk of severe malaria, generally based on candidate gene studies in case/control populations. Among these genes, there has been conflicting reports for the implication of a variant of the intercellular adhesion molecule 1 (ICAM1), ICAM1(Kilifi), in the risk of severe malaria, while in vitro studies provided independent support for a functional role of this variant. In order to explore the possible implication of ICAM1 in the susceptibility/resistance to malaria and to try to understand its clinical relevance in the disease process, we have conducted linkage and association studies of ICAM1 in two Senegalese villages located in regions of endemic malaria. We explored the full genetic variability of ICAM1, and tested it on several clinical malarial traits which are under genetic control, focusing principally on variables related to the parasite density and the number of malarial attacks. Our study provides no evidence for a role of ICAM1 variability on the malarial phenotypes studied.

Antibodies to Plasmodium falciparum C-terminal merozoite surface protein 1 (PfMSP-1p19) have been correlated with protection against malaria, but this association may apply to many merozoite antigens. To address this question, we conducted a prospective serological study of 205 individuals in an active 5-month clinical survey in a Senegalese village where malaria is mesoendemic. Before the 2000 rainy season, antibody responses specific for recombinant baculovirus PfMSP-1p19 or merozoite extracts were compared with 2 in vitro functional antibody activities (inhibition of parasite grown and erythrocyte invasion) and with the number of clinical episodes during 5 months of follow-up. Antibody levels to PfMSP-1p19 and merozoite extract correlated, respectively, with erythrocyte invasion and parasite growth inhibition. Although antibody levels to both antigen preparations were associated with age, functional parameters were not. High levels of anti-PfMSP-1p19 immunoglobulin G were associated with reduced malaria in an age-adjusted multivariate analysis. These results support baculovirus PfMSP-1p19-based vaccine development.

Plasmodium species, the etiologic agents of malaria, are obligatory sexual organisms. Gametocytes, the precursors of gametes, are responsible for parasite transmission from human to mosquito. The sex ratio of gametocytes has been shown to have consequences for the success of this shift from vertebrate host to insect vector. We attempted to document the effect of chemotherapy on the sex ratio of two different Plasmodium species: Plasmodium falciparum in children from endemic area with uncomplicated malaria treated with chloroquine (CQ) or sulfadoxine-pyrimethamine (SP), and P. vinckei petteri in mice treated with CQ or untreated. The studies involved 53 patients without gametocytes at day 0 (13 CQ and 40 SP) followed for 14 days, and 15 mice (10 CQ and 5 controls) followed for five days. During the course of infection, a positive correlation was observed between the time of the length of infection and the proportion of male gametocytes in both Plasmodium species. No effects of treatment (CQ versus SP for P. falciparum or CQ versus controls for P. vinckei petteri) on the gametocyte sex ratio were found for either Plasmodium species. This indicates that parasites do not respond to chemotherapy by altering their sex allocation strategy, even though, in the case of P. falciparum, they apparently increase their overall investment in sexual stages. This suggests that malaria parasite species respond to different environmental cues for their sex differentiation and sex determination.

To investigate the potential for use of a well-established strain of Plasmodium falciparum as a reference strain for infected red blood cell (IRBC) surface reactivity, we monitored the binding of specific immunoglobulin G (IgG) from immune individuals to the reference Knob-positive FCR3 strain by flow cytometry. To permit interassay comparison for 162 plasma samples drawn after the rainy season, a labeling index (LI) was defined as the percentage of labeled parasites multiplied by the mean peak intensity. An LI ratio (LIR) was then calculated as the LI of the sample divided by the LI of the control. LIRs were calculated for individuals living in Dielmo and Ndiop, two Senegalese villages where P. falciparum is transmitted holoendemically and mesoendemically, respectively. The incidence (persons with an LIR of >3) observed in Dielmo was lower than that observed in Ndiop. Significantly higher LIRs were observed (i) for samples from Ndiop than for samples from Dielmo (P < 0.01) and (ii) in Ndiop, in subjects with hemoglobin AS (HbAS) than in those with hemoglobin AA (P = 0.03). No correlation with the cumulative age-associated immune status of the villagers was evidenced, contrary to antibody (Ab) responses against conserved IRBC-associated antigen (Ag) measured by enzyme-linked immunosorbent assay. These results are consistent with the notions that protection in HbAS individuals may relate to an increased IgG response to IRBC membrane Ags and that cell surface reactivity parallels IgG responses even though it is in itself a distinct indicator of the anti-P. falciparum Ab response. Measures of IgG binding to live IRBC are thus relevant for the functional screening of conserved IRBC-associated Ags that contribute to parasite destruction in vivo, as these Ags might be included in a multitarget vaccine.

Plasmodium falciparum expresses many antigens, which elicit various immune responses in exposed individuals, but no simple surrogate marker for protection has yet been developed. In this prospective survey, we looked for immune responses predictive of protection at various stages of progression from parasite inoculation to onset of disease. We studied 110 Senegalese volunteers from an area in which malaria is mesoendemic after they had received eradication therapy. We evaluated 4 protection-related outcomes (reappearance of parasitemia, duration of asymptomatic carriage, time to first clinical episode, and incidence of clinical episodes) in terms of levels of immunoglobulin G (IgG) against 3 crude parasite extracts and 5 conserved antigens during a 5-month period. Kaplan-Meier estimates and age-adjusted regression models showed these 4 outcomes to be associated with different patterns of IgG response to PfEMP3-cl5 (derived from P. falciparum erythrocyte membrane protein 3), PfEB200, MSP-1(19) (derived from merozoite surface protein-1), [NANP]10, infected red blood cell membrane, and merozoite and schizont extracts. It should, therefore, be possible to develop surrogate markers for each end point on the basis of IgG response to a limited number of conserved antigens.

West African tick-borne relapsing fever is an endemic disease due to Borrelia crocidurae. The tick Alectorobius sonrai is the only known vector of this bacterium. Several species of rodents and insectivores may be reservoir for this spirochete. The geographic distribution of Borrelia crocidurae is not well known. The zone where the presence of the vector has been recorded is situated in Sahelian regions, from Mauritania and northern Senegal up to Chad. In Senegal, it has been shown that the persistence of drought is responsible for a considerable spread of tick-borne relapsing fever to the south. Few epidemiological data are available about West African tick-borne relapsing fever. In Senegal, epidemiological investigations indicate that Borrelia crocidurae is a major cause of morbidity (annual incidence rate of 5.1%). The relapsing nature of tick-borne borreliosis depends on Borrelia's antigenic variability. Except relapsing febrile episodes, this illness presents no pathognomonic signs. Borrelia crocidurae relapsing fever is generally benignant but neurologic or ocular complications can occur. The diagnosis of tick-borne relapsing fever is made by demonstrating the presence of Borrelia in peripheral blood in thick smear, by intraperitoneal inoculation of mice or more recently with quantitative buffy coat method (QBC test). The best treatment for relapsing fever is tetracycline or doxycycline. When tetracyclines are contraindicated, the alternative is erythromycin. In neurologic complications, the effective treatment is intravenous penicillin G or ceftriaxone. West African tick-borne relapsing fever must be systematically mentioned in case of fever in a patient returning from the endemic area.

An epidemiological survey was conducted during a 4-month period of intense malaria transmission in Dielmo, a holoendemic Senegalese village. Two thick blood smears per inhabitant were collected weekly. The sex ratio of Plasmodium falciparum gametocytes (gamete precursors) was studied in 50 gametocyte carriers. All age classes were represented (mean 19.7 years; range: 2 months-75 years); 42 (84%) of them did not receive antimalarial treatment. Overall 668 thick smears were examined until 100 gametocytes had been counted or for 40 min. A total of 11204 gametocytes were observed with a mean sex ratio of 0.346 (95% CI 0.317-0.374), i.e. 2.89 females per 1 male. Among the 284 thick smears in which at least 10 gametocytes were observed, the mean percentage of male gametocytes was 27.8%, with a range of 0-82%. Great variability was observed between gametocyte carriers and also between thick smears from the same gametocyte carrier. A multivariate analysis was performed which highlighted the fact that only 2 variables had a significant effect on the sex ratio. Anaemia was associated with an increased percentage of males (Prevalence Rate Ratio [PPR] of male gametocytes was multiplied by 1.65 if haematocrit rate < 32%) and a wave of gametocytes was associated with an increased percentage of female gametocytes (PRR was multiplied by 0.48 during the peak of gametocytaemia and for the 2 weeks following this peak). The variables without significant effect on sex ratio were: age, sex, clinical status and sickle cell trait status of the gametocyte carrier, density of asexual parasites, quinine treatment, and gametocyte density (when taking account of its waves). These results are discussed in regard of possible differential production, mortality or sequestration of one gametocyte sex and selective advantages for the transmission of parasites.

Blackwater fever (BWF), one of the commonest causes of death of Europeans living in Africa at the beginning of the twentieth century, but rarely diagnosed since the 1950s, is related to Plasmodium falciparum malaria but there is considerable debate and controversy about its aetiology. From 1990 to 2000, the whole population of Dielmo, a village in Senegal, was involved in a prospective study of malaria. Three cases of BWF occurred in 3 children aged 4, 7 and 10 years, belonging to a subgroup of children who suffered malaria attacks every 4 to 6 weeks over many years, who had received repeated quinine treatment. The spread of chloroquine resistance, by increasing the use of more toxic alternative drugs, may expose endemic populations to a high incidence of severe side effects of antimalarials.

The influence of intestinal worm infections on malaria was studied in individuals from Dielmo, Senegal in 1998. Results suggest that, compared with those infected, individuals free of helminths had the same degree of protection against malaria as that provided by sickle-cell trait, the most potent factor of resistance to malaria identified to date.

The relationship between Plasmodii transmission, infection, morbidity, genetic susceptibility and acquisition of natural immunity is studied among two cohorts in the Senegalese villages of Dielmo (300 inhabitants) and Ndiop (350 inhabitants) where malaria is holoendemic (about 200 P. falciparum infective bites/person/year) and mesoendemic (about 20 P. falciparum infective bites/person/year), respectively. The populations are under a daily active clinical survey. Blood samples are collected at least once per month. Plasma and red blood cells are stored in bio-libraries that allow longitudinal studies of the immune responses against plasmodial antigens and the investigation of the natural history of P. falciparum infections by molecular genotyping methods.

The rapid increase in the world's urban population has major implications for the epidemiology of malaria. A review of malaria transmission in sub-Saharan African cities shows the strong likelihood of transmission occurring within these sprawling cities, whatever the size or characteristics of their bioecologic environment. A meta-analysis of results from studies of malaria transmission in sub-Saharan Africa shows a loose linear negative relationship between mean annual entomologic inoculation rates (EIR) and the level of urbanicity. Few studies have failed to find entomologic evidence of some transmission. Our results show mean annual EIRs of 7.1 in the city centers, 45.8 in periurban areas, and 167.7 in rural areas. The impact of urbanization in reducing transmission is more marked in areas where the mean rainfall is low and seasonal. Considerable variation in the level of transmission exists among cities and within different districts in the same city. This article presents evidence from past literature to build a conceptual framework to begin to explain this heterogeneity. The potential for malaria epidemics owing to decreasing levels of natural immunity may be offset by negative impacts of urbanization on the larval ecology of anopheline mosquitoes. Malaria control in urban environments may be simpler as a result of urbanization; however, much of what we know about malaria transmission in rural environments might not hold in the urban context.