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We evaluated routine testing with SARS-CoV-2 Delta variant-specific RT-PCR in regional hospital laboratories in addition to centralised national genomic surveillance in the Netherlands during June and July 2021. The increase of the Delta variant detected by RT-PCR correlated well with data from genomic surveillance and was available ca 2 weeks earlier. This rapid identification of the relative abundance and increase of SARS-CoV-2 variants of concern may have important benefits for implementation of local public health measures.

Background: Real-time PCR methods are increasingly used in routine patient care settings not only to determine the presence or absence of pathogens in patient materials, but also to obtain semiquantitative results to estimate the pathogen load. However, it is so far unknown how well these methods are harmonized among different laboratories. Methods: Sets of stool samples were distributed three to four times per year to ca. 25–40 participating laboratories within the European Union as part of an external quality assessment scheme (EQAS) for the detection of gastrointestinal protozoa. This paper presents the results obtained over a 3-year period for Entamoeba histolytica, Entamoeba dispar, Giardia lamblia, Cryptosporidium species and Dientamoeba fragilis. Results: Although both false-positive and false-negative results were reported, the overall sensitivity and specificity were high. The substantial differences in the quantitative output of the real-time PCR assays could be traced back to differences in DNA isolation procedures between different laboratories. Conclusions: Participation in an EQAS proved to be important as it provides information on how the real-time PCR methods used by the participant compares to the generally reported results and indicates how procedures could be improved. Semiquantitative results of real-time PCR methods are not exchangeable between laboratories as long as the diagnostic procedures are not harmonized. Intralaboratory comparison of semiquantitative real-time PCR results seems only possible by the use of calibration curves derived from well-validated standards in clinical material and not by spiking solutions with purified DNA.

Graphical abstract Research highlights ► Gametocyte density is positively associated with mosquito infection rates. ► Autologous plasma reduces the transmission of malaria parasites. ► Transmission reducing activity is associated with indicators of recent exposure to gametocytes., Malaria-infected individuals can develop antibodies which reduce the infectiousness of Plasmodium gametocytes to biting Anopheles mosquitoes. When ingested in a bloodmeal together with gametocytes, these antibodies reduce or prevent subsequent parasite maturation in the insect host. This transmission-blocking immunity is usually measured in human sera by testing its effect on the infectivity of gametocytes grown in vitro. Here we evaluate evidence of transmission-blocking immunity in eight studies conducted in three African countries. Plasmodium falciparum gametocytes isolated from each individual were fed to mosquitoes in both autologous plasma collected with the parasites, and permissive serum from non-exposed donors. Evidence of transmission reducing effects of autologous plasma was found in all countries. Experiments involving 116 Gambian children (aged 0.5–15 years) were combined to determine which factors were associated with transmission reducing immune responses. The chances of infecting at least one mosquito and the average proportion of infected mosquitoes were negatively associated with recent exposure to gametocytes and sampling late in the season. These results suggest that effective malaria transmission-reducing antibodies do not commonly circulate in African children, and that recent gametocyte carriage is required to initiate and/or boost such responses.

BACKGROUND: Tuberculosis (TB) in Africa is increasing because of the human immunodeficiency virus (HIV) epidemic, and in HIV/AIDS patients it presents atypically. Pulmonary tuberculosis (PTB) in Africa is mainly diagnosed clinically, by chest radiograph or by sputum smear for acid fast bacilli (AFB). METHODS: We evaluated in 120 HIV-infected patients with chest infection the diagnostic accuracy of AFB smear of sputum and bronchoalveolar lavage (BAL) fluid, sputum Mycobacterium tuberculosis (MTB) culture, real-time PCR and MycoDot serological test, using MTB culture of BAL fluid as gold standard. We correlated PCR cycle threshold values (C(T)) to the culture results. Retrospectively, we evaluated the development of active TB in patients with positive PCR but negative culture. RESULTS: Culture of BAL fluid identified 28 patients with PTB. Fifty-six patients could not produce adequate sputum. Sputum AFB smear and the serological test had sensitivities of 66.7% and 0%, respectively. PCR with C(T) 40 was positive in 73 patients, 27 of whom were also TB culture positive (96.4% sensitivity and 52.3% specificity of PCR). PCR with C(T) 32 had sensitivity of 85.7% and specificity of 90.9% to diagnose PTB in BAL. No patients with positive PCR but negative culture developed active TB during 18 months follow-up. CONCLUSION: In these HIV-infected patients, AFB smear and serology had very low sensitivities. PCR of BAL with C(T) value 32 had improved specificity to diagnose active PTB. A prospective follow-up study is warranted in TB/HIV endemic settings, applying real time PCR to both sputum and BAL.

This report of an accidental exposure to Mycobacterium tuberculosis in a microbiological laboratory illustrates the value of gamma interferon enzyme-linked immunospot assay using peptides of ESAT-6, CFP-10, TB37.6, and TB7.7 for the diagnosis of latent infection. In particular, positive responses to peptides 2 to 6 of TB37.6 were observed exclusively in recently infected persons.

Contains fulltext : 58663.pdf (Publisher’s version ) (Closed access) Transmission blocking immunity (TBI) was studied in relation to age, gametocyte density and transmission intensity. subjects with high gametocytaemias were selected in a hypo-endemic urban district and a hyper-endemic rural area in South Cameroon. TBI was determined in blood from gametocyte carriers in a bioassay (Direct Membrane Feeding Assay), with either autologous plasma (OWN) or control serum (AB). Mosquito infection rates (IR) were compared. infection rates correlated positively with gametocyte and oocyst densities. Three TBI indicators were analysed: the proportion of transmission reducers (IRAB > IROWN, P < 0.01), the mean intensity of TBI (IRAB - IROWN), and the contribution of TBI to total inhibition [(IRAB-IROWN)/(100-IROWN)]. we could not discriminate between areas with regard to either the proportion of transmission reducers (urban 15% and rural 29%) or the mean levels of TBI (urban 10% and rural 9%), or contribution of TBI to total inhibition (urban 10% and rural 13%). there was no relationship between TBI indicators and age, but a trend of increasing values was observed with rising gametocytaemia, which was considered as a confusing factor. a multivariable analysis showed that the probability of being a reducer was 4.6 fold higher in the rural area than in the urban district.

Glutathione S-transferases (GST) are a family of enzymes involved in phase-II detoxification of endog- enous and xenobiotic compounds. Polymorphisms in GST genes have been associated with susceptibility to different diseases. In this study we determined the frequencies of polymorphisms in GSTM1, GSTT1, and GSTP1 in DNA of 138 children from Cameroon, presenting with uncomplicated malaria (N 19), malaria with minor complications (N 81), or severe malaria (N 38). Analyses of GSTM1 and GSTT1 were performed using PCR-multiplex procedure, while GSTP1 was done by PCR-RFLP. Subjects presenting with malaria with complications were found more often of the GSTM1-null genotype (58-64%) as compared with those with uncomplicated malaria (32%), a difference that was statistically significant. We conclude that the GSTM1-null genotype is associated with malaria with complications. In severe malaria, release of oxygen free radicals and a variety of pro-inflammatory cytokines can lead to increased vascular permeability, leakage of colloid from intravascular space, pathologic vasodilation, and myocardial depression with ultimate hypovolemia and impaired organ perfusion. In children with malaria, lipid peroxidation in both blood plasma and erythrocytes is increased, while erythrocytic antioxidants such as glutathione (GSH), catalase, and tocopherol were shown to be lower in patients with malaria than in control subjects. 1 The intracellular parasite digests hemoglobin, thereby releasing free ferroprotoporphyrin or heme, which in the presence of oxygen oxidizes to ferriprotoporphyrin or hemin. This process produces superoxide, which decomposes into H2O2 and O2. Antimalarials like chloroquine and amo- diaquine inhibit this reaction, thus building up a toxic con- centration of ferro/ferriprotoporphyrin (FP) leading to para- site death. 2,3 Indeed, several studies have suggested that an increase in oxidative stress in parasitized red blood cells (RBCs) offers an advantage to parasite clearance rather than exacerbating the pathology. 2-4 Glucose-6-phosphate dehy- drogenase (G6PD)-deficient individuals for instance, are par- tially protected against malaria. G6PD is essential for NADPH production, which reduces oxidized glutathione. Glutathione as an antioxidant is required for growth of the parasite 2,5 but also for maintenance of the redox state of the host cell. Altered redox metabolism of the host cells, particu- larly the endothelial cells, may exacerbate disease complica- tions, for example by enhancing endothelial damage, brain inflammation, and development of cerebral malaria. Several studies document escape of FP from the parasite's food vacu- ole with consequent damage to erythrocyte membrane through oxidation of proteins and lipids with eventual lysis of the host cell. 6-8 To maintain the integrity of the erythrocyte

Item does not contain fulltext A young female health professional was diagnosed with pulmonary tuberculosis caused by Mycobacterium bovis. Source finding and contact tracing was initiated by the regional municipal health service using both tuberculin skin test and QuantiFERON((R))-TB Gold (QFT-GIT (IGRA). The strain appeared near-identical to that of an elderly Dutch patient. 01 augustus 2012

Contains fulltext : 108727.pdf (Publisher’s version ) (Open Access) INTRODUCTION: In the era of malaria elimination and eradication, drug-based and vaccine-based approaches to reduce malaria transmission are receiving greater attention. Such interventions require assays that reliably measure the transmission of Plasmodium from humans to Anopheles mosquitoes. METHODS: WE COMPARED TWO COMMONLY USED MOSQUITO FEEDING ASSAY PROCEDURES: direct skin feeding assays and membrane feeding assays. Three conditions under which membrane feeding assays are performed were examined: assays with i) whole blood, ii) blood pellets resuspended with autologous plasma of the gametocyte carrier, and iii) blood pellets resuspended with heterologous control serum. RESULTS: 930 transmission experiments from Cameroon, The Gambia, Mali and Senegal were included in the analyses. Direct skin feeding assays resulted in higher mosquito infection rates compared to membrane feeding assays (odds ratio 2.39, 95% confidence interval 1.94-2.95) with evident heterogeneity between studies. Mosquito infection rates in membrane feeding assays and direct skin feeding assays were strongly correlated (p

OBJECTIVES: To determine the aetiological agents of pulmonary infections in HIV-infected Tanzanians and to correlate the causative agents with clinical, radiographic features, and mortality. DESIGN: A prospective study. SETTING: Kilimanjaro Christian Medical Centre (KCMC), Tanzania. SUBJECTS: Bronchoalveolar lavage fluid (BAL) were obtained from 120 HIV infected patients with pulmonary infections. BAL for causative agents was analysed and correlated with clinical and radiographic features, and one-month outcome. RESULTS: Causative agents were identified in 71 (59.2%) patients and in 16 of these patients, multiple agents were found. Common bacteria were identified in 35 (29.2%) patients, Mycobacterium tuberculosis in 28 (23.3%), Human Herpes Virus 8 (HHV8) in 12 (10%), Pneumocystis jiroveci in nine (7.5%) and fungi in five (4.2%) patients. Median CD4 T cell count of the patients with identified causes was 47 cells/microl (IQR 14-91) and in the 49 patients with undetermined aetiology was 100 cells/ microl (IQR 36-188; p = 0.01). Micronodular chest radiographic lesions were associated with presence of M. tuberculosis (p = 0.002). The one-month mortality was 20 (16.7%). The highest mortality was associated with HHV8 (41.7%) and M. tuberculosis (32.1%). Mortality in patients with undetermined aetiology was 11.3%. No death occurred in patients with PCP. CONCLUSION: In this population of severely immunosuppressed HIV-infected patients with pulmonary infection a variety of causative agents was identified. Micronodular radiographic lesions were indicative of TB. High mortality was associated with M. tuberculosis or HHV8. No death occurred in patients with P. jiroveci infection.

A real-time polymerase chain reaction (PCR) method targeting the 5.8S ribosomal RNA gene was developed for the detection of Dientamoeba fragilis in stool samples. The PCR also included an internal control to detect inhibition of the amplification by fecal constituents in the sample. The assay was performed on species-specific DNA controls ( n =29) and a range of stool samples ( n =85), and achieved high specificity and sensitivity. D. fragilis DNA could be detected in unpreserved fecal samples up to 8 weeks after storage at 4 °C. The use of this assay in a diagnostic laboratory offers the possibility of introducing DNA detection as a feasible technique for the routine diagnosis of intestinal D. fragilis infections.

Background Tuberculosis (TB) is a major health problem and HIV is the major cause of the increase in TB. Sub-Saharan Africa is endemic for both TB and HIV infection. Determination of the prevalence of M. tuberculosis strains and their drug susceptibility is important for TB control. TB positive culture, BAL fluid or sputum samples from 130 patients were collected and genotyped. The spoligotypes were correlated with anti-tuberculous drug susceptibility in HIV-infected and non-HIV patients from Tanzania. Results One-third of patients were TB/HIV co-infected. Forty-seven spoligotypes were identified. Fourteen isolates (10.8%) had new and unique spoligotypes while 116 isolates (89.2%) belonged to 33 known spoligotypes. The major spoligotypes contained nine clusters: CAS1-Kili 30.0%, LAM11- ZWE 14.6%, ND 9.2%, EAI 6.2%, Beijing 5.4%, T-undefined 4.6%, CAS1-Delhi 3.8%, T1 3.8% and LAM9 3.8%. Twelve (10.8%) of the 111 phenotypically tested strains were resistant to anti-TB drugs. Eight (7.2%) were monoresistant strains: 7 to isoniazid (INH) and one to streptomycin. Four strains (3.5%) were resistant to multiple drugs: one (0.9%) was resistant to INH and streptomycin and the other three (2.7%) were MDR strains: one was resistant to INH, rifampicin and ethambutol and two were resistant to all four anti-TB drugs. Mutation in the kat G gene codon 315 and the rpo B hotspot region showed a low and high sensitivity, respectively, as predictor of phenotypic drug resistance. Conclusion CAS1-Kili and LAM11-ZWE were the most common families. Strains of the Beijing family and CAS1-Kili were not or least often associated with resistance, respectively. HIV status was not associated with spoligotypes, resistance or previous TB treatment.

Monoclonal antibodies (mAbs) and human sera from gametocyte carriers were applied in the bio-assay to test for their transmission-blocking capacity. Competition ELISA's have been developed for the detection of natural transmission blocking antibodies. Approximately 55% of the sera blocking in the bio-assay gave positive results in these competition ELISA's.

Financial support was provided by The Wellcome Trust (grant ref. 055487), the European Commission, and the University of London Central Research Fund London School of Hygiene and Tropical Medicine. Department of Infectious and Tropical Diseases. Keppel St, London, UK. London School of Hygiene and Tropical Medicine. Department of Infectious and Tropical Diseases. Keppel St, London, UK. London School of Hygiene and Tropical Medicine. Department of Infectious and Tropical Diseases. Keppel St, London, UK. London School of Hygiene and Tropical Medicine. Department of Infectious and Tropical Diseases. Keppel St, London, UK. London School of Hygiene and Tropical Medicine. Department of Infectious and Tropical Diseases. Keppel St, London, UK. London School of Hygiene and Tropical Medicine. Department of Infectious and Tropical Diseases. Keppel St, London, UK. London School of Hygiene and Tropical Medicine. Department of Infectious and Tropical Diseases. Keppel St, London, UK. University of Ibadan. College of Medicine. Ibadan, Nigeria. Organisation de Coordination pour la lutte contre les End?mies en Afrique Centrale. Malaria Department. Yaounde, Cameroon. Minist?rio da Sa?de. Funda??o Nacional de Sa?de. Instituto Evandro Chagas. Bel?m, PA, Brasil. Universiti Malaysia Sarawak. Kota Samarahan. Sarawak, Malaysia. Biomedical Primate Research Centre. Rijswijk, The Netherlands. The origin and geographical spread of Plasmodium falciparum is here determined by analysis of mitochondrial DNA sequence polymorphism and divergence from its most closely related species P. reichenowi (a rare parasite of chimpanzees). The complete 6 kb mitochondrial genome was sequenced from the single known isolate of P. reichenowi and from four different cultured isolates of P. falciparum, and aligned with the two previously derived P. falciparum sequences. The extremely low synonymous nucleotide polymorphism in P. falciparum (pi=0.0004) contrasts with the divergence at such sites between the two species (kappa=0.1201), and supports a hypothesis that P. falciparum has recently emerged from a single ancestral population. To survey the geographical distribution of mitochondrial haplotypes in P. falciparum, 104 isolates from several endemic areas were typed for each of the identified single nucleotide polymorphisms. The haplotypes show a radiation out of Africa, with unique types in Southeast Asia and South America being related to African types by single nucleotide changes. This indicates that P. falciparum originated in Africa and colonised Southeast Asia and South America separately.

The effect of natural malaria transmission-blocking factors in the blood of Plasmodium falciparum gametocyte carriers was assessed in two types of functional bioassays. In the direct membrane feeding assay (DMFA), a comparison is made between the infectivity of gametocytes from a naturally infected gametocyte carrier in the presence of autologous plasma and the infectivity in the presence of replacement plasma from nonimmune donors. In the standard membrane feeder assay (SMFA), cultured NF54 gametocytes are used to measure the capacity of endemic sera to block transmission. In the DMFA, 18 out of 48 sera (37.5%) from Cameroonian gametocyte carriers reduced transmission significantly, while in the SMFA 22 out of 48 sera (45.8%) produced transmission reduction. There was a positive correlation between both assays (r + 0.41, P < 0.05). Antibodies against epitopes of transmission-blocking target antigens Pfs48/45 and Pfs230 were measured in competition ELISAs and compared with the results of DMFA and SMFA. Serological reactivity in competition ELISAs against three epitopes of Pfs48/45 was significantly higher in the group of transmission-reducing sera in both the DMFA and the SMFA, especially for epitope III. No significant difference was found for Pfs230 antibodies (epitope I). Sensitivity of the serological assays was approximately 60%, with a specificity of around 70%. Serological tests cannot replace the functional bioassay in field situations as yet, but can contribute in the selection of sera for SMFA evaluation.

This study investigated the successive losses in the parasite densities of Plasmodium falciparum stages during the early sporogony in laboratory-reared Anopheles gambiae infected by membrane feeding with blood from naturally infected gametocyte carriers (>50 gametocytes/mm3). The developmental stages of P. falciparum in the mosquito were studied from zygote to oocyst, by immunofluorescent method using monoclonal antibodies against the Pfs25 protein present on the surface of newly formed gametes. This method allows for assessment of the various sporogonic stages before, during and after passage of the midgut wall. Parasite densities were determined within the entire blood meal at 3 h (zygotes and macrogametes) and 24 h (ookinetes) post-infection. At 48 h after the mosquito blood meal, midguts were checked for the presence of early oocysts. For the mid-size oocysts count, classic microscopy examination was used at day 7 postinfection. The parasite efficacy was estimated by following successive losses in parasite densities between different early stages of the sporogonic cycle in A. gambiae. Thirty-seven experimental infections were realized with high gametocyte densities, ranging from 64 to 2392 gametocytes/mm3. All gametocyte carriers showed infection with round forms 100%; ookinetes were found in 91.9%. The prevalences of infections with oocysts were 48.6% at day 2 (young oocyst) and 37.8% at day 7 (mid-size oocyst). The mean densities per mosquito for each parasite stage were 12.6 round forms, 5.5 ookinetes, 1.8 young oocyst and 2 mid-size oocysts. Significant correlations were found between two consecutive parasite stages (round forms/ookinetes, ookinetes/young oocysts, young oocysts/mid-size oocysts) and between round forms and mid-size oocysts. The mean parasite density significantly decreased between round forms and ookinetes (yield Y1 = 41.6%) and between ookinetes and young oocysts (Y2 = 61.4%). By contrast, no significant decrease was observed between young oocysts and mid-size oocysts (Y3 = 91.2%). The overall yield of the early sporogonic cycle (from round form to oocyst at day 7) was equal to 25.7%, indicating that almost 3/4 of the total parasites were lost during the early step of the sporogonic cycle, from 3 h post-infection to day 7.

Insectary-reared Anopheles gambiae were experimentally fed with the blood of 90 naturally infected human volunteers carrying gametocytes of Plasmodium falciparum . At least one mosquito was successfully infected in 74% of experiments. The probability that a gametocyte carrier was infective, the probability that a mosquito became infected, and the number of oocysts harboured were related to gametocyte density. The mean proportion of male gametocytes was 0.217 (i.e., 3.6 females for every male). Sex ratios differed significantly between gametocyte carriers. Variation in sex ratio was not related to the probability that a gametocyte carrier was infective. Among infective people whose sex ratio estimates were based on a reasonable number of gametocytes, sex ratio significantly predicted the proportion of infected mosquitoes and mean oocyst load, with infectivity rising as the proportion of male gametocytes increased towards 50%. There was no indication that infectivity reached a peak at some intermediate sex ratio, as would be expected if random mating of gametes was the primary determinant of fertilization success. These results raise 2 interesting questions: why should higher sex ratios be more infective, and why is the observed population sex ratio lower than that which produces the greatest infectivity?

Pfs48/45, a sexual stage parasite protein doublet of P. falciparum, is a target of antibodies which inhibit the development of the parasite in the mosquito. Twenty-eight (54%) out of 52 sera of gametocyte carriers from Cameroon reduced infectivity in the mosquito membrane feeding bioassay to less than 20% of the controls. These 52 sera were analysed by competition ELISAs for the presence of antibodies capable of competing the binding of six monoclonal antibodies (MoAbs) directed against five different epitopes on Pfs48/45. The percentage of these 52 Cameroon sera that competed with one of the MoAbs ranged from 13% (epitope I) to 33% (epitope IIc). Comparison of activity in the transmission-blocking assay (> or = 80%) and in the Pfs48/45 competition ELISA show a relative specificity of 100% (24 of 24) and a relative sensitivity of 75% (21 of 28). Non-blocking sera showed no competition with any of the MoAbs. These MoAbs were further used to study the diversity of epitopes among isolates of P. falciparum using a two-site ELISA. MoAbs against epitope I, III and V reacted with four different isolates whereas epitope II could be subdivided into three epitopes. None of the isolates reacted with MoAb 3G12 (epitope IV). Using these four different isolates, the competition ELISA titre varies from 1/20 to 1/80 and no significant differences are found between the isolates except for epitope II where only three out of 11 positives for epitope IIa were also positive for epitope IIc.

Insect-reared Anopheles gainbiae were experimentally fed with the blood of naturally infected human volunteers carrying gametocytes of Plasmodium falciparuin. Infection of at least one mosquito was successful in 86 experiments. For these gametocyte carriers, the hemoglobin types studied were AA (normal, n = 77), AS (hetero- zygous sickle cell, n = 8), and SS (homozygous sickle cell, n = 1). The mean of the percentages of infected mosquitoes by gametocyte carriers of AS hemoglobin was almost double that of carriers of AA: 30.4% versus 17.5%. The genetic protection in humans conferred by the sS gene in its heterozygous form seems to be associated with an increasing effect on P. falciparuiiz transmission from humans to mosquitoes. The epidemiologic and evolutionary aspects of this finding are discussed. In humans, it is now accepted that sickle cell hemoglobin (HbS) provides selective protection to heterozygote carriers from dying of Plasinodiunz falciparuin malaria.' Further- more, transgenic mice expressing HbS are protected from rodent malaria2 and rodent cerebral malaria.3 Recent case- control studies in The Gambia4 and Kenya5 have indicated that heterozygosity for HbS provides more than 90% pro- , tection from both cerebral malaria and severe malarial ane- mia in children. The effect of hemoglobin HbS on parasite density is less evident. On the other hand, the possible effect of sickle cell he- moglobin on malaria transmission is unknown. Sexual de- velopment of Plasmodium begins in the vertebrate host with the invasion of erythrocytes by merozoites, followed by the differentiation of trophozoites into gametocytes, which is the only stage competent to pursue its development in the mos- quito. When ingested in a blood meal by the anopheline vector, the development of Plasmodium first takes place in the lumen of the mosquito midgut until the ookinete stage, which penetrates through the epithelium of the midgut and transforms into a young oocyst. The goal of our study was to establish the development of the malarial parasite from naturally infected hemoglobin type AA, AS, and SS individuals when ingested by an an- opheline. We postulated that development might be affected by the presence of HbS and consequently have epidemio- logic implications in regions where the prevalence of this variant is substantial. This study was part of broader epidemiologic investiga- tions on malaria transmission, specifically on parasite-vector relationships, in central Africa. Previously, our group has defined the factors influencing the success of the develop- ment of the parasite in as well as their epi- ,+ i!

Monoclonal antibodies (MAbs) 32F1 and 32F3 react with two independent epitopes of a protein doublet with molecular weights of 48 and 45 kilodaltons (kD) expressed on the surface of Plasmodium falciparum (Pfs48/ 45) macrogametes and zygotes; only 32F3 blocks transmission. These MAbs were used to develop a Pfs48/45~specific competition enzyme-linked immunosorbent assay (ELISA) using 32F1 to capture antigen and labeled 32F3 for quan­ tification and analysis of the contribution of antibodies in human serum to transmission-blocking activity. A com­ parison analysis was used to determine agreement of competition ELISA titers and transmission-blocking activity as observed in the bioassay in three groups of serum samples: 37 from European travelers with previous exposure to malaria, 56 from gametocyte carriers, and 66 from schoolchildren from a malaria-endemic area in Cameroon. The index of agreement between outcomes of the ELISA and transmission-blocking assay in gametocyte carriers and in travelers was specifically defined as fair-to-moderate; in schoolchildren the agreement was not significant. The com­ bined analysis of all sera showed a significant and fai r-to-moderate agreement between the results of the competition ELISA and the transmission-blocking assay, with a relative specificity of 94% (of 105 cases negative in the trans­ mission-blocking assay, 99 were also negative in the competition ELISA) and a relative sensitivity of 44% (of 54 cases positive in the transmission-blocking assay, 24 were also positive in the competition ELISA). This study shows that a positive C48/45-ELISA is indicative for transmission-blocking activity in the mosquito assay, while a negative result does not exclude transmission-blocking activity. Gametocytes of Plasmodium falciparum synthesize 230- and 48/45-kilodalton (kD) molecules that remain exposed on the surface of macrogametes and zygotes.1" '3 Several mono­ clonal antibodies (MAbs) directed against these molecules block transmission of the parasite to the mosquito vector. One of the targets of transmission-blocking MAbs is the 48/ 45-kD glycoprotein doublet (Pfs48/45). Two independent, nonrepetitive epitopes of this protein react respectively with MAbs designated 32F1 and 32F3. The presence of 32F3 in a mosquito blood meal blocks transmission of the NF54 iso­ late of P. falciparum while 32F1 does not.4 The conventional assay measuring transmission reduction in mosquitoes using a feeder system, as described by Vermeulen and others,1 is costly, labor intensive, and thus limits the number of sera that can be tested. Development of a serologic test predicting transmission-blocking activity would greatly simplify epi­ demiologic studies. A positive correlation between antibody reactivity to Pfs230 and transmission-blocking activity has been found using immunoprecipitation to quantify the anti­ body response. Such a relation was not found for antibody reactivity to This paper describes the development of a two-site com­ petition enzyme-linked immunosorbent assay (ELISA) based on the 32F3 epitope. This competition ELISA was used to analyze several sets of field sera. In addition, the transmis­ sion-blocking activity of these field sera was determined us­ ing the feeder assay1 and the results obtained were compared with those of the competition ELISA using a statistical anal­ ysis for comparison of methods.6'7

Experimental infections of anopheline mosquitoes were carried out with Plasmodium falciparum gametocytes from 65 naturally infected patients in Cameroon. A comparison was made between infections with blood containing autologous plasma and blood in which the plasma was replaced with plasma from a donor without previous malaria exposure. A lower infection rate was observed in 50 of 65 autologous plasma samples. Transmission was significantly blocked in 3 infections. This indicates that, in a population living in an area endemic for malaria, blood plasma factor(s) can reduce the transmission capacity of gametocyte carriers to mosquitoes.

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Contains fulltext : 22984___.PDF (Publisher’s version ) (Open Access)