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AbstractIn February 2014, the Malaria Elimination Working Group, in partnership with the Peruvian Ministry of Health (MoH), hosted its first international conference on malaria elimination in Iquitos, Peru. The 2-day meeting gathered 85 malaria experts, including 18 international panelists, 23 stakeholders from different malaria-endemic regions of Peru, and 11 MoH authorities. The main outcome was consensus that implementing a malaria elimination project in the Amazon region is achievable, but would require: 1) a comprehensive strategic plan, 2) the altering of current programmatic guidelines from control toward elimination by including symptomatic as well as asymptomatic individuals for antimalarial therapy and transmission-blocking interventions, and 3) the prioritization of community-based active case detection with proper rapid diagnostic tests to interrupt transmission. Elimination efforts must involve key stakeholders and experts at every level of government and include integrated research activities to evaluate, implement, and tailor sustainable interventions appropriate to the region.

Long-term antimalarial chemoprophylaxis is currently used by deployed U.S. military personnel. Previous small, short-term efficacy studies have shown variable rates of side effects among patients taking various forms of chemoprophylaxis, though reliable safety and tolerability data on long-term use are limited. We conducted a survey of troops returning to Fort Drum, NY following a 12-month deployment to Operation Enduring Freedom, Afghanistan from 2006 to 2007. Of the 2,351 respondents, 95% reported taking at least one form of prophylaxis during their deployment, and 90% were deployed for > 10 months. Compliance with daily doxycycline was poor (60%) compared with 80% with weekly mefloquine (MQ). Adverse events (AEs) were reported by approximately 30% with both MQ and doxycycline, with 10% discontinuing doxycycline compared with 4% of MQ users. Only 6% and 31% of soldiers reported use of bed nets and skin repellents, respectively. Compliance with long-term malaria prophylaxis was poor, and there were substantial tolerability issues based on these anonymous survey results, though fewer with MQ than doxycycline. Given few long-term antimalarial chemoprophylaxis options, there is an unmet medical need for new antimalarials safe for long-term use., (© The American Society of Tropical Medicine and Hygiene.)

Individuals with glucose 6-phosphate dehydrogenase (G6PD) deficiency are at risk for the development of hemolytic anemia when given 8-aminoquinolines (8-AQs), an important class of antimalarial/antiinfective therapeutics. However, there is no suitable animal model that can predict the clinical hemolytic potential of drugs. We developed and validated a human (hu)RBC-SCID mouse model by giving nonobese diabetic/SCID mice daily transfusions of huRBCs from G6PD-deficient donors. Treatment of SCID mice engrafted with G6PD-deficient huRBCs with primaquine, an 8-AQ, resulted in a dose-dependent selective loss of huRBCs. To validate the specificity of this model, we tested known nonhemolytic antimalarial drugs: mefloquine, chloroquine, doxycycline, and pyrimethamine. No significant loss of G6PD-deficient huRBCs was observed. Treatment with drugs known to cause hemolytic toxicity (pamaquine, sitamaquine, tafenoquine, and dapsone) resulted in loss of G6PD-deficient huRBCs comparable to primaquine. This mouse model provides an important tool to test drugs for their potential to cause hemolytic toxicity in G6PD-deficient populations.

The majority of malaria rapid diagnostic tests (RDTs) detect Plasmodium falciparum histidine-rich protein 2 (PfHRP2), encoded by the pfhrp2 gene. Recently, P. falciparum isolates from Peru were found to lack pfhrp2 leading to false-negative RDT results. We hypothesized that pfhrp2-deleted parasites in Peru derived from a single genetic event. We evaluated the parasite population structure and pfhrp2 haplotype of samples collected between 1998 and 2005 using seven neutral and seven chromosome 8 microsatellite markers, respectively. Five distinct pfhrp2 haplotypes, corresponding to five neutral microsatellite-based clonal lineages, were detected in 1998-2001; pfhrp2 deletions occurred within four haplotypes. In 2003-2005, outcrossing among the parasite lineages resulted in eight population clusters that inherited the five pfhrp2 haplotypes seen previously and a new haplotype; pfhrp2 deletions occurred within four of these haplotypes. These findings indicate that the genetic origin of pfhrp2 deletion in Peru was not a single event, but likely occurred multiple times.

Anti-malarial 8-aminoquinolines drugs cause acute hemolytic anemia in individuals with glucose-6-phosphate dehydrogenase deficiency (G6PDD). Efforts to develop non-hemolytic 8-aminoquinolines have been severely limited caused by the lack of a predictive in vivo animal model of hemolytic potential that would allow screening of candidate compounds. This report describes a G6PDD mouse model with a phenotype closely resembling the G6PDD phenotype found in the African A-type G6PDD human. These G6PDD mice, given different doses of primaquine, which used as a reference hemolytic drug, display a full array of hemolytic anemia parameters, consistently and reproducibly. The hemolytic and therapeutic indexes were generated for evaluation of hemotoxicity of drugs. This model demonstrated a complete hemolytic toxicity response to another known hemolytic antimalarial drug, pamaquine, but no response to non-hemolytic drugs, chloroquine and mefloquine. These results suggest that this model is suitable for evaluation of selected 8-AQ type candidate antimalarial drugs for their hemolytic potential.

Background: There is a need for a simple and efficacious treatment for cutaneous leishmaniasis with an acceptable side-effect profile., Methods: We conducted a randomized, vehicle-controlled phase 3 trial of topical treatments containing 15% paromomycin, with and without 0.5% gentamicin, for cutaneous leishmaniasis caused by Leishmania major in Tunisia. We randomly assigned 375 patients with one to five ulcerative lesions from cutaneous leishmaniasis to receive a cream containing 15% paromomycin-0.5% gentamicin (called WR 279,396), 15% paromomycin alone, or vehicle control (with the same base as the other two creams but containing neither paromomycin nor gentamicin). Each lesion was treated once daily for 20 days. The primary end point was the cure of the index lesion. Cure was defined as at least 50% reduction in the size of the index lesion by 42 days, complete reepithelialization by 98 days, and absence of relapse by the end of the trial (168 days). Any withdrawal from the trial was considered a treatment failure., Results: The rate of cure of the index lesion was 81% (95% confidence interval [CI], 73 to 87) for paromomycin-gentamicin, 82% (95% CI, 74 to 87) for paromomycin alone, and 58% (95% CI, 50 to 67) for vehicle control (P<0.001 for each treatment group vs. the vehicle-control group). Cure of the index lesion was accompanied by cure of all other lesions except in five patients, one in each of the paromomycin groups and three in the vehicle-control group. Mild-to-moderate application-site reactions were more frequent in the paromomycin groups than in the vehicle-control group., Conclusions: This trial provides evidence of the efficacy of paromomycin-gentamicin and paromomycin alone for ulcerative L. major disease. (Funded by the Department of the Army; ClinicalTrials.gov number, NCT00606580.).

There remains a need for new drugs to prevent relapse of Plasmodium vivax or P. ovale infection. The relapsing primate malaria P. cynomolgi has been used for decades to assess drugs for anti-hypnozoite activity. After sporozoite inoculation and blood-stage cure of initial parasitemia with chloroquine, rhesus macaques were treated on subsequent relapses with chloroquine in conjunction with test regimens of approved drugs. Tested drugs were selected for known liver or blood-stage activity and were tested alone or in conjunction with low-dose primaquine. Tinidazole and pyrazinamide prevented relapse when used in conjunction with chloroquine and low-dose primaquine. Triamterene and tinidazole administered without primaquine achieved radical cure in some animals. All other tested drugs or combinations failed to prevent relapse. The rhesus macaque-P. cynomolgi model remains a useful tool for screening drugs with anti-hypnozoite activity. Tinidazole and pyrazinamide require further investigation as agents to enable dose reduction of primaquine.

Background: We conducted a randomized, placebo-controlled, double-blind trial to establish the efficacy of atovaquone-proguanil to prevent malaria with the goal of simulating weekly dosing in a human Plasmodium falciparum challenge model., Methods: Thirty volunteers randomly received 1 of the following dose regimens: (1) 250 milligrams of atovaquone and 100 milligrams of proguanil (250/100 milligrams) 1 day prior to infectious mosquito challenge (day -1), (2) 250/100 milligrams on day 4 after challenge, (3) 250/100 milligrams on day -7, (4) 500 milligrams of atovaquone and 200 milligrams of proguanil (500/200 milligrams) on day -7 or, (5) 1000 milligrams of atovaquone and 400 milligrams of proguanil (1000/400 milligrams) on day -7. All regimens included matching placebo such that all volunteers received identical pill numbers. Six volunteers served as open-label infectivity controls. Volunteers underwent mosquito sporozoite challenge with P. falciparum 3D7 strain. Follow-up consisted of serial microscopy and close clinical monitoring for 90 days., Results: Six of 6 infectivity controls developed parasitemia as expected. Two of 5 evaluable volunteers receiving 250/100 milligrams 7 days prior to challenge and 1 of 6 volunteers receiving 1000/400 milligrams 7 days prior to challenge were microscopically diagnosed with malaria. All other volunteers were protected. Atovaquone exposure (area under the curve) during liver stage development was low in 2 of 3 volunteers with prophylactic failure (423 and 199 ng/mL × days compared with a mean for protected volunteers of 1903 ng/mL × days), as was peak concentration (165 and 81 ng/mL compared with a mean of 594 ng/mL in volunteers with prophylactic success). Elimination half-life was short in volunteers with prophylactic failure (2.4, 2.0, and 3.3 days compared with a mean of 4.1 days in volunteers with prophylactic success)., Conclusions: Single-dose atovaquone-proguanil provides effective malaria chemoprophylaxis against P. falciparum challenge at dosing intervals supportive of weekly dosing. Postexposure prophylaxis 4 days after challenge was 100% effective.

Because of recent declining malaria transmission in Latin America, some authorities have recommended against chemoprophylaxis for most travelers to this region. However, the predominant parasite species in Latin America, Plasmodium vivax, can form hypnozoites sequestered in the liver, causing malaria relapses. Additionally, new evidence shows the potential severity of vivax infections, warranting continued consideration of prophylaxis for travel to Latin America. Individualized travel risk assessments are recommended and should consider travel locations, type, length, and season, as well as probability of itinerary changes. Travel recommendations might include no precautions, mosquito avoidance only, or mosquito avoidance and chemoprophylaxis. There are a range of good options for chemoprophylaxis in Latin America, including atovaquone-proguanil, doxycycline, mefloquine, and--in selected areas--chloroquine. Primaquine should be strongly considered for nonpregnant, G6PD-nondeficient patients traveling to vivax-endemic areas of Latin America, and it has the added benefit of being the only drug to protect against malaria relapses.

A sensitive biomarker of malaria infection would obviate the need for placebo control arms in clinical trials of malaria prophylactic drugs. Antibodies to the 42-kDa fragment of merozoite surface protein-1 (MSP1(42)) have been identified as a potential marker of malaria exposure in individuals receiving prophylaxis with mefloquine. We conducted an open-label trial to determine the sensitivity of seroconversion to MSP1(42), defined as a fourfold rise in enzyme-linked immunosorbant assay (ELISA) titer, among 23 malaria naïve volunteers receiving mefloquine prophylaxis and 6 controls after Plasmodium falciparum sporozoite challenge. All members of the control cohort but none of the mefloquine cohort developed patent parasitemia. Four of six controls but zero of the mefloquine cohort seroconverted to MSP1(42). We conclude that malaria infection during suppressive prophylaxis does not induce antibody response to the blood-stage antigen MSP1(42) in a malaria-naïve study population.

Doxycycline, a synthetically derived tetracycline, is a partially efficacious causal prophylactic (liver stage of Plasmodium) drug and a slow acting blood schizontocidal agent highly effective for the prevention of malaria. When used in conjunction with a fast acting schizontocidal agent, it is also highly effective for malaria treatment. Doxycycline is especially useful as a prophylaxis in areas with chloroquine and multidrug-resistant Plasmodium falciparum malaria. Although not recommended for pregnant women and children < 8 years of age, severe adverse events are rarely reported for doxycycline. This report examines the evidence behind current recommendations for the use of doxycycline for malaria and summarizes the available literature on its safety and tolerability.

In an attempt to separate the antimalarial activity of tafenoquine (3) from its hemolytic side effects in glucose-6-phosphate dehydrogenase (G6PD) deficiency patients, a series of 5-aryl-8-aminoquinoline derivatives was prepared and assessed for antimalarial activities. The new compounds were found metabolically stable in human and mouse microsomal preparations, with t(1/2) > 60 min, and were equal to or more potent than primaquine (2) and 3 against Plasmodium falciparum cell growth. The new agents were more active against the chloroquine (CQ) resistant clone than to the CQ-sensitive clone. Analogues with electron donating groups showed better activity than those with electron withdrawing substituents. Compounds 4bc, 4bd, and 4be showed comparable therapeutic index (TI) to that of 2 and 3, with TI ranging from 5 to 8 based on IC(50) data. The new compounds showed no significant causal prophylactic activity in mice infected with Plasmodium berghei sporozoites, but are substantially less toxic than 2 and 3 in mouse tests.

In 2003, 44 U.S. Marines were evacuated from Liberia with either confirmed or presumed Plasmodium falciparum malaria. An outbreak investigation showed that only 19 (45%) used insect repellent, 5 (12%) used permethrin-treated clothing, and none used bed netting. Adherence with weekly mefloquine (MQ) was reported by 23 (55%). However, only 4 (10%) had serum MQ levels high enough to correlate with protection (> 794 ng/mL), and 9 (22%) had evidence of steady-state kinetics (MQ carboxy metabolite/MQ > 3.79). Tablets collected from Marines met USP identity and dissolution specifications for MQ. Testing failed to identify P. falciparum isolates with MQ resistance. This outbreak resulted from under use of personal protective measures and inadequate adherence with chemophrophylaxis. It is essential that all international travelers make malaria prevention measures a priority, especially when embarking to regions of the world with high transmission intensity such as west Africa..

Patients with clinical manifestations of leishmaniasis, including cutaneous leishmaniasis, have limited treatment options, and existing therapies frequently have significant untoward liabilities. Rapid expansion in the diversity of available cutaneous leishmanicidal chemotypes is the initial step in finding alternative efficacious treatments. To this end, we combined a low-stringency Leishmania major promastigote growth inhibition assay with a structural computational filtering algorithm. After a rigorous assay validation process, we interrogated approximately 200,000 unique compounds for L. major promastigote growth inhibition. Using iterative computational filtering of the compounds exhibiting > 50% inhibition, we identified 553 structural clusters and 640 compound singletons. Secondary confirmation assays yielded 93 compounds with EC(50)s < or = 1 microM, with none of the identified chemotypes being structurally similar to known leishmanicidals and most having favorable in silico predicted bioavailability characteristics. The leishmanicidal activity of a representative subset of 15 chemotypes was confirmed in two independent assay formats, and L. major parasite specificity was demonstrated by assaying against a panel of human cell lines. Thirteen chemotypes inhibited the growth of a L. major axenic amastigote-like population. Murine in vivo efficacy studies using one of the new chemotypes document inhibition of footpad lesion development. These results authenticate that low stringency, large-scale compound screening combined with computational structure filtering can rapidly expand the chemotypes targeting in vitro and in vivo Leishmania growth and viability.

Background: Sulfadoxine-pyrimethamine was a common first line drug therapy to treat uncomplicated falciparum malaria, but increasing therapeutic failures associated with the development of significant levels of resistance worldwide has prompted change to alternative treatment regimes in many national malaria control programs. METHODOLOGY AND FINDING: We conducted an in vivo therapeutic efficacy trial of sulfadoxine-pyrimethamine at two locations in the Peruvian Amazon enrolling 99 patients of which, 86 patients completed the protocol specified 28 day follow up. Our objective was to correlate the presence of polymorphisms in P. falciparum dihydrofolate reductase and dihydropteroate synthase to in vitro parasite susceptibility to sulfadoxine and pyrimethamine and to in vivo treatment outcomes. Inhibitory concentration 50 values of isolates increased with numbers of mutations (single [108N], sextuplet [BR/51I/108N/164L and 437G/581G]) and septuplet (BR/51I/108N/164L and 437G/540E/581G) with geometric means of 76 nM (35-166 nM), 582 nM (49-6890- nM) and 4909 (3575-6741 nM) nM for sulfadoxine and 33 nM (22-51 nM), 81 nM (19-345 nM), and 215 nM (176-262 nM) for pyrimethamine. A single mutation present in the isolate obtained at the time of enrollment from either dihydrofolate reductase (164L) or dihydropteroate synthase (540E) predicted treatment failure as well as any other single gene alone or in combination. Patients with the dihydrofolate reductase 164L mutation were 3.6 times as likely to be treatment failures [failures 85.4% (164L) vs 23.7% (I164); relative risk = 3.61; 95% CI: 2.14 - 6.64] while patients with the dihydropteroate synthase 540E were 2.6 times as likely to fail treatment (96.7% (540E) vs 37.5% (K540); relative risk = 2.58; 95% CI: 1.88 - 3.73). Patients with both dihydrofolate reductase 164L and dihydropteroate synthase 540E mutations were 4.1 times as likely to be treatment failures [96.7% vs 23.7%; RR = 4.08; 95% CI: 2.45 - 7.46] compared to patients having both wild forms (I164 and K540)., Conclusions: In this part of the Amazon basin, it may be possible to predict treatment failure with sulfadoxine-pyrimethamine equally well by determination of either of the single mutations dihydrofolate reductase 164L or dihydropteroate synthase 540E., Trial Registration: ClinicalTrials.gov NCT00951106.

Malaria is of continuing concern in nonimmune traveling populations. Traditionally, antimalarial drugs have been developed as agents for dual indications (treatment and prophylaxis). However, since 2000, when the 5th Amendment to the Declaration of Helsinki (DH2000) was adopted, development of new malaria prophylaxis drugs in this manner has ceased. As a consequence, there may not be any new drugs licensed for this indication in the foreseeable future. Major pharmaceutical companies have interpreted DH2000 to mean that the traditional development paradigm may be considered unethical because of doubt over the likelihood of benefit to endemic populations participating in clinical studies, the use of placebo, and the sustainability of post-trial access to study medications. In this article, we explore the basis of these concerns and suggest that the traditional development paradigm remains ethical under certain circumstances. We also consider alternative approaches that may be more attractive to sponsors as they either do not use placebo, or utilize populations in endemic countries who may unambiguously benefit. These approaches represent the way forward in the future, but are at present unproven in clinical practice, and face numerous regulatory, logistical and technical challenges. Consequently, in the short term, we argue that the traditional clinical development paradigm remains the most feasible approach and is ethical and consistent with the spirit of DH2000 under the appropriate circumstances.

To help mitigate the expanding global impact of malaria, with its associated increasing drug resistance, implementation of prompt and accurate diagnosis is needed. Malaria is diagnosed predominantly by using clinical criteria, with microscopy as the current gold standard for detecting parasitemia, even though it is clearly inadequate in many health care settings. Rapid diagnostic tests (RDTs) have been recognized as an ideal method for diagnosing infectious diseases, including malaria, in recent years. There have been a number of RDTs developed and evaluated widely for malaria diagnosis, but a number of issues related to these products have arisen. This review highlights RDTs, including challenges in assessing their performance, internationally available RDTs, their effectiveness in various health care settings, and the selection of RDTs for different health care systems.

In our laboratory, a series of antimicrobial peptides have been developed, where the resulting 3D-physicochemical properties are controlled by the placement of amino acids with well-defined properties (hydrophobicity, charge density, electrostatic potential, and so on) at specific locations along the peptide backbone. These peptides exhibited different in vitro activity against Staphylococcus aureus (SA) and Mycobacterium ranae (MR) bacteria. We hypothesized that the differences in the biological activity is a direct manifestation of different physicochemical interactions that occur between the peptides and the cell membranes of the bacteria. 3D-QSAR analysis has shown that, within this series, specific physicochemical properties are responsible for antibacterial activity and selectivity. There are five physicochemical properties specific to the SA QSAR model, while five properties are specific to the MR QSAR model. These results support the hypothesis that, for any particular AMP, organism selectivity and potency are controlled by the chemical composition of the target cell membrane.

A series of acid-stable carboxamide derivatives of 2-guanidinoimidazolidinedione (5a-c and 6a-c) were prepared as potential malaria prophylactic and radical cure agents. The new compounds showed moderate to good causal prophylactic activity in mice infected with Plasmodium yoelii sporozoites. Three compounds were further tested for causal prophylactic activity in Rhesus monkeys infected with Plasmodium cynomolgi sporozoites, and all showed a delay in patency from 13 to 40 days at 30 mg/kg/day x 3 days by IM dosing. Two out of four compounds tested for radical curative activity in Rhesus showed cure at 30 mg/kg/day x 3 days. The other two compounds showed delay in relapse from 16 to 68 days. Conversion of new carboxamides (5 and 6) to s-triazine derivatives (7) was demonstrated in mouse and human microsomal preparations and in rat plasma. The results suggest the metabolites, s-triazine derivatives 7, may be the active species of the new carboxamides 5a-c and 6a-c prepared in this study.

To determine whether antibodies to the 19-kDa fragment of merozoite surface protein 1 (MSP1(19)) help to control blood-stage Plasmodium falciparum infection, we performed a rechallenge experiment of previously infected Aotus monkeys. Monkeys previously exposed to the FVO strain of P. falciparum that did or did not develop high antibody titers to MSP1(19) and malaria-naïve monkeys were challenged with erythrocytes infected with the same strain. Prepatent periods were prolonged in previously infected monkeys compared with malaria-naïve monkeys. Previously infected monkeys with preexisting anti-MSP1(19) antibodies showed low peak parasitemias that cleared spontaneously. Previously infected monkeys that had no or low levels of pre-existing anti-MSP1(19) antibodies also showed low peak parasitemias, but because of low hematocrits, all of these animals required treatment with mefloquine. All previously malaria-naïve animals were treated because of high parasitemias. The results of this study suggest that antibody to the 19-kDa carboxy-terminal fragment of MSP1 plays a role in preventing the development of anemia, an important complication often associated with malaria.

The evolution of drug-resistant bacteria is one of the most critical problems facing modern medicine and requires the development of new drugs that exhibit their antibacterial activity via novel mechanisms of action. One potential source of new drugs could be the naturally occurring peptides that exhibit antimicrobial activity via membrane disruption. To develop antimicrobial peptides exhibiting increased potency and selectivity against Gram positive, Gram negative, and Mycobacterium bacteria coupled with reduced hemolytic activity, peptides containing unnatural amino acids have been designed, synthesized, and evaluated. These compounds were designed on the basis of the electrostatic surface potential maps derived from the NMR determined SDS and DPC micelle-bound conformations of (Ala8,13,18)magainin-2 amide. Unnatural amino acids were incorporated into the polypeptide backbone to control the structural and physicochemical properties of the peptides to introduce organism selectivity and potency. The methods and results of this investigation are described below.

We report the first safety and immunogenicity trial of the Plasmodium falciparum vaccine candidate FMP2.1/AS02A, a recombinant E. coli-expressed protein based upon the apical membrane antigen-1 (AMA-1) of the 3D7 clone formulated with the AS02A adjuvant. We conducted an open-label, staggered-start, dose-escalating Phase I trial in 23 malaria-naïve volunteers who received 8, 20 or 40microg of FMP2.1 in a fixed volume of 0.5mL of AS02A on a 0, 1, and 2 month schedule. Nineteen of 23 volunteers received all three scheduled immunizations. The most frequent solicited local and systemic adverse events associated with immunization were injection site pain (68%) and headache (29%). There were no significant laboratory abnormalities or vaccine-related serious adverse events. All volunteers seroconverted after second immunization as determined by ELISA. Immune sera recognized sporozoites and merozoites by immunofluorescence assay (IFA), and exhibited both growth inhibition and processing inhibition activity against homologous (3D7) asexual stage parasites. Post-immunization, peripheral blood mononuculear cells exhibited FMP2.1-specific lymphoproliferation and IFN-gamma and IL-5 ELISPOT assay responses. This is the first PfAMA-1-based vaccine shown to elicit both potent humoral and cellular immunity in humans. Encouraged by the potential of FMP1/AS02A to target host immunity against PfAMA-1 that is known to be expressed by sporozoite, hepatic and erythrocytic stages, we have initiated field trials of FMP2.1/AS02A in an endemic population in the Republic of Mali.

A retrospective surveillance study was conducted to examine the micro-geographic variation of malaria incidence in three malaria-endemic communities in the Northern Peruvian Amazon. The annual malaria risk rate (per 100) ranged from 38% to 47% for Plasmodium vivax and from 15% to 18% for P. falciparum. Spatial clusters were found for P. vivax in Padre Cocha, Manacamiri, and Zungaro Cocha, and for P. falciparum only in Padre Cocha. Spatial-temporal clusters showed that the highest monthly number of P. vivax cases varied every year from December to March in 1996-1997 and from February to June in 1998-1999, and for P. falciparum from November to April in 1996-1997 and from January to April in 1998-1999. Our results suggest a constant presence of high-risk areas (hot spots) for malaria infection in periods with high or low malaria incidence. Modest targeted control efforts directed at identified high-risk areas may have significant impact on malaria transmission in this region.

Two expert research microscopists, each blinded to the other's reports, diagnosed single-species malaria infections in 2,141 adults presenting at outpatient malaria clinics in Tak Province, Thailand, and Iquitos, Peru, in May-August 1998, May-July 1999, and May-June 2001. Plasmodium vivax patients with gametocytemia had higher fever and higher parasitemia than those without gametocytemia; temperature correlated with parasitemia in the patients with gametocytemia. Plasmodium falciparum patients with gametocytemia had lower fever than those without gametocytemia, but similar parasitemia; temperature correlated with parasitemia in the patients without gametocytemia. Hematologic data in Thailand in 2001 showed lower platelet counts in P. vivax patients with gametocytemia than in the P. vivax patients without gametocytemia, whereas P. falciparum patients with gametocytemia had similar platelet counts but lower red blood cell counts, hemoglobin levels, hematocrit levels, and higher lymphocyte counts than patients without gametocytemia.

Primaquine phosphate has been used for preventing relapse of Plasmodium vivax and P. ovale malaria since the early 1950s, based on its ability to kill latent (hypnozoite) and developing liver stages of these parasites. There are three uses for primaquine in malaria: radical cure of established infection with P. vivax or P. ovale malaria; presumptive anti-relapse therapy (PART; terminal prophylaxis) in persons with extensive exposure to these parasites; and primary prophylaxis against all malaria species. All persons for whom primaquine is being considered must have a glucose-6-phosphate dehydrogenase (G6PD) enzyme level checked before use, and persons who have a deficiency of G6PD must not take primaquine for prophylaxis or PART. The recommended adult dose for PART based on clinical trials and expert opinion is 30 mg base daily for 14 days, started on return from a malarious region and overlapping with a blood schizonticide. The adult dose for primary prophylaxis is 30 mg daily begun 1 day before travel and continued for 7 days after return. This review will examine the evidence for these recommendations.

Background: Clinical symptoms of mixed-species malaria infections have been variously reported as both less severe and more severe than those of single-species infections., Methods: Oral temperatures were taken from and blood slides were prepared for 2308 adults who presented at outpatient malaria clinics in Tak Province (Thailand) during May-August 1998, May-July 1999, and May-June 2001 with malaria infections diagnosed by 2 expert research microscopists, each of whom was blinded to the other's reports., Results: In each year, temperatures of patients with mixed Plasmodium vivax-Plasmodium falciparum infections were higher than temperatures of patients with P. vivax or P. falciparum infections. In every mixed-species case, P. falciparum parasitemia was higher than P. vivax parasitemia, but patient temperature was not correlated with the parasitemia of either species or with the total parasitemia., Conclusions: Among adults who self-report to malaria clinics in western Thailand, patients with mixed P. vivax-P. falciparum infections have higher fevers than patients with single-species infections, a distinction that cannot be attributed to differences in parasitemia. This observation warrants more detailed investigations, spanning wider ranges of ages and transmission environments.

Plasmodium falciparum is responsible for most of the mortality in travelers related to imported malaria. Problems that occur during travel include the inaccuracy of a microscopic diagnosis of malaria, both false positives and false negatives, when ill travelers seek care while abroad. A false positive diagnosis can result in unnecessary parenteral injections that carry a risk of transmission of blood-borne pathogens, receipt of potentially dangerous drugs such as halofantrine, or receipt of fake, counterfeit drugs. Increased morbidity and mortality are associated with delays in diagnosis and initiation of prompt treatment for falciparum malaria. Availability of expert microscopy to confirm the diagnosis of malaria is limited. The presence of splenomegaly and thrombocytopenia are strongly associated with malaria and would justify empiric treatment. The availability of atovaquone-proguanil, a safe and well tolerated oral drug, should prompt a reconsideration of current treatment recommendations that discourage empiric treatment on clinical suspicion alone.

Enumeration of parasites by microscopic examination of blood smears is the only method available for quantifying parasitemia in infected blood. However, the sources and scale of error inherent in this technique have not been systematically investigated. Here we use data collected in outpatient clinics in Peru and Thailand to elucidate important sources of variation in parasite density measurements. We show that discrepancies between readings from two independent microscopists and multiple readings from a single microscopist are inversely related to the density of the infection. We present an example of how differences in reader technique, specifically the number of white blood cells counted, can contribute to the differences between readings. We discuss the implications of this analysis for field studies and clinical trials.

White blood cells (WBCs) were counted in 4697 individuals who presented to outpatient malaria clinics in Maesod, Tak Province, Thailand, and Iquitos, Peru, between 28 May and 28 August 1998 and between 17 May and 9 July 1999. At each site and in each year, WBC counts in the Plasmodium falciparum-infected patients were lower than those in the Plasmodium vivax-infected patients, which, in turn, were lower than those in the uninfected patients. In Thailand, one-sixth of the P. falciparum-infected patients had WBC counts of <4000 cells/microL. Leukopenia may confound population studies that estimate parasite densities on the basis of an assumed WBC count of 8000 cells/microL. For instance, in the present study, use of this conventional approach would have overestimated average asexual parasite densities in the P. falciparum-infected patients in Thailand by nearly one-third.

Infection with protozoan parasites of the genus Leishmania leads to a wide variety of clinical disease syndromes called leishmaniasis, or more appropriately the leishmaniases. The three major clinical syndromes are cutaneous leishmaniasis, mucosal leishmaniasis, and visceral leishmaniasis. All three of these syndromes have been documented in returning travelers. This article focuses on cutaneous leishmaniasis with some comment on mucosal leishmaniasis.

We conducted a randomized, double-blind, phase III yellow fever (YF) vaccine trial among 1,107 healthy children in Sullana in northern Peru. The safety and efficacy (by measurement of geometric mean neutralizing antibody titer responses) were determined for two YF vaccines, ARILVAX (n = 738) and YF-VAX(R) (n = 369). Serocon-version rates were higher (94.9%) in ARILVAX than in YF-VAX (90.6%) recipients. The two-sided 95% confidence interval (YF-VAX-ARILVAX) was (-12.8% to -2.5%), indicating that the higher seroconversion rate for Arilvax was significant. Post-vaccination (30-day) mean log(10) neutralization indices were found to be similar for both products: 1.32 for ARILVAX and 1.26 for YF-VAX (P = 0.1404, by analysis of variance). A similar number of subjects in each group reported at least one adverse event (AE); 441 (59.8%) for ARILVAX versus 211 (59.9%) for YF-VAX. Most (591; 96.7%) of these were of a mild nature and resolved without treatment. There were no treatment-related serious AEs. This is the first randomized, double-blind comparison of two YF vaccines in a pediatric population; both vaccines were shown to be highly immunogenic and well-tolerated.

In vivo antimalarial drug efficacy studies of uncomplicated Plasmodium falciparum malaria at an isolated site in the Amazon basin of Peru bordering Brazil and Colombia showed >50% RII/RIII resistance to sulfadoxine-pyrimethamine but no evidence of resistance to mefloquine.

In vitro drug sensitivity to chloroquine (CQ), mefloquine (MQ) and quinine was investigated in 60 culture-adapted Plasmodium falciparum isolates from malaria patients in Padrecocha, a village in the Amazonian Department of Loreto, Peru. All isolates showed resistance to CQ, decreased susceptibility to quinine, and sensitivity to MQ. These isolates were examined for mutations in the P. falciparum multidrug resistance 1 (pfmdr1) and chloroquine resistance transporter (pfcrt) genes previously linked to CQ resistance. The mutations N86Y and D1246Y, two of the five mutations commonly observed in the pfmdr1 gene of CQ-resistant clones, were not found. The pfcrt mutation K76T, associated with CQ resistance, was identified in all the isolates tested. Sequence analysis of codons 72-76 in the pfcrt gene showed the haplotypes SVMNT and CVMNT.

Background: A Recruit Mortality Registry, linked to the Department of Defense Medical Mortality Registry, was created to provide comprehensive medical surveillance data for deaths occurring during enlisted basic military training., Methods: Recruit deaths from 1977 through 2001 were identified and confirmed through redundant sources. Complete demographic, circumstantial, and medical information was sought for each case and recorded on an abstraction form. Mortality rates per 100,000 recruit-years were calculated by using recruit accession data from the Defense Manpower Data Center., Results: There were 276 recruit deaths from 1977 through 2001 and age-specific recruit mortality rates were less than half of same-age U.S. civilian mortality rates. The majority (72%) of recruit deaths were classified as nontraumatic and 70% of these deaths (139 of 199) were related to exercise. Of the exercise-related deaths, 59 (42%) were cardiac deaths, and heat stress was a primary or contributory cause in at least 46 (33%). Infectious agents accounted for only 49 (25%) of the nontraumatic deaths. Nontraumatic death rates increased with age (rate ratio is 2.5 for 25+ v <25 years; p<0.001). The age- and gender-adjusted nontraumatic death rates were 2.6 times higher for African American than non-African American recruits (p<0.001)., Conclusions: Although recruit mortality rates are lower than the same-age U.S. civilian population, preventive measures focused on reducing heat stress during exercise might be effective in decreasing the high proportion of exercise-related death. The availability of 25 years of comprehensive recruit mortality data will permit the ongoing evaluation of cause-of-death trends, effectiveness of preventive measures, and identification of emerging threats during basic military training.

The NOW ICT Malaria P.f./P.v. for Whole Blood (Binax, Inc., Portland, ME) is a new malaria rapid diagnostic device that represents a technical advance over previous assays, such as ICT Malaria P.f./P.v. and ICT Malaria P.f.. We evaluated this device in March 2001 in symptomatic patients at malaria clinics in Maesod, Thailand. Microscopic examination of Giemsa-stained blood smears was the reference standard. In 246 patients, microscopy showed 32 (13.0%) infected with Plasmodium falciparum, 63 (25.6%) with P. vivax, 6 (2.4%) with mixed infections of P. falciparum and P. vivax, 5 (2.0%) with P. malariae, and 140 (56.9%) negative. Sensitivity for P. falciparum was 100% and specificity was 96.2% (200 of 208; 95% confidence interval [CI] = 92-98). For P. vivax, sensitivity was 87.3% (55 of 63; 95% CI = 77-93) and specificity was 97.7% (173 of 177; 95% CI = 95-99), but all the four false-positive results were microscopically positive for P. malariae; thus, specificity for non-falciparum Plasmodium was 100%. These results suggest improved performance over NOW ICT predecessors.

The ParaSight F test was developed as a pioneer industry effort in the large-scale, process-controlled production of a device for the rapid diagnosis of malaria. This device performed well in field settings but was limited to the detection of a single malaria species, Plasmodium falciparum. The ParaSight F+V assay advanced upon the ParaSight F test format by incorporating a monoclonal antibody directed against a proprietary Plasmodium vivax-specific antigen, in addition to the antibody directed against P. falciparum histidine-rich protein 2, which was used in the ParaSight F assay. The modified assay was developed to add the capability to detect P. falciparum and P. vivax in a single-test-strip format. The present study evaluated three distinct ParaSight F+V prototypes with samples from symptomatic patients in regions of Thailand and Peru where malaria is endemic. Over a 2-year enrollment period (1998 and 1999), a total of 4,894 patients consented to participation in the study. Compared with the results for duplicate microscopic examinations of Giemsa-stained blood smears as the reference diagnostic standard, each successive prototype showed substantial improvement in performance. The final ParaSight F+V prototype, evaluated in 1999, had an overall sensitivity for detection of asexual P. falciparum parasites of 98%. The sensitivity of the device was 100% for P. falciparum densities of >500 parasites/ micro l, with a sensitivity of 83% for parasite densities of 5,000/ micro l, 92% for parasite densities of 1,001 to 5,000/ micro l, 94% for parasite densities of 501 to 1,000/ micro l, and 55% for parasite densities of 1 to 500/ micro l. The specificity for the exclusion of P. vivax was 87%. The areas under the receiver operating characteristic curves for the diagnostic performance of the assay for the detection of P. falciparum and P. vivax were 0.8907 and 0.8522, respectively. These findings indicate that assays for rapid diagnosis have the potential to enhance diagnostic capabilities in those instances in which skilled microscopy is not readily available.

Malaria and leptospirosis are both common in the tropics. Simultaneous infections are possible, although not previously reported. We report two cases of malaria from an area of Thailand on the Thailand-Myanmar border with compelling serologic evidence of simultaneous acute leptospirosis. One was a case of infection with Plasmodium falciparum with acute and convalescent microscopic agglutination test (MAT) titers for Leptospira serovar icterohaemorrhagiae of 1:200 and 1:1,600, respectively. The other was a case of infection with P. vivax that seroconverted to a titer of 1:3,200 for Leptospira serovar bataviae. Additionally, there were five probable cases of leptospirosis with patent malaria parasitemia (three P. falciparum and two P. vivax) detected. Management of dual infections is complicated by their similar clinical presentations, and because the confirmatory diagnosis of malaria is readily available as opposed to that of leptospirosis. Treatment focusing on malaria mono-infections instead of dual infections could result in a delay of specific therapy for leptospirosis and possible consequences of serious complications.

Long before the advent of modern chemoprophylaxis drugs, many practitioners successfully prevented the debilitating and fatal outcomes associated with infection by the Plasmodium parasites that cause malaria. Today, with effective insect repellents and several excellent medications available for chemoprophylaxis, there has never been a better array of quality products to prevent mosquito bites and infection and to suppress parasites once in the blood stream; however, there are thousands of imported cases into nonendemic countries and scores of deaths and near-fatal outcomes every year in returning travelers, soldiers, immigrants, and refugees. In this article, the author focuses on practical uses of currently available prevention tools.

Widespread use of antimalarial agents can profoundly influence the evolution of the human malaria parasite Plasmodium falciparum. Recent selective sweeps for drug-resistant genotypes may have restricted the genetic diversity of this parasite, resembling effects attributed in current debates to a historic population bottleneck. Chloroquine-resistant (CQR) parasites were initially reported about 45 years ago from two foci in southeast Asia and South America, but the number of CQR founder mutations and the impact of chlorquine on parasite genomes worldwide have been difficult to evaluate. Using 342 highly polymorphic microsatellite markers from a genetic map, here we show that the level of genetic diversity varies substantially among different regions of the parasite genome, revealing extensive linkage disequilibrium surrounding the key CQR gene pfcrt and at least four CQR founder events. This disequilibrium and its decay rate in the pfcrt-flanking region are consistent with strong directional selective sweeps occurring over only approximately 20-80 sexual generations, especially a single resistant pfcrt haplotype spreading to very high frequencies throughout most of Asia and Africa. The presence of linkage disequilibrium provides a basis for mapping genes under drug selection in P. falciparum.

Plasmodium falciparum-induced anemia was characterized in Aotus monkeys repeatedly immunized by infection with P. falciparum (FVO strain) parasites, then cross-challenged with CAMP strain, or in monkeys receiving blood stage challenges as part of malaria vaccine trials. In 4 studies, 25 (30.5%) of 82 monkeys had at least a 50% reduction in hematocrit; mean day of maximum parasitemia was 12.5, whereas the mean day of minimum hematocrit was 18.8 (P < 0.0009). Decreased hematocrit levels were not associated with reticulocytosis until parasite densities decreased significantly from peak levels. Direct antibody tests to detect IgG and C3d on the surface of erythrocytes were negative. Nonantibody/noncomplement-mediated lysis of uninfected erythrocytes seems to be the principal cause of the anemia, and it also seems that bone marrow suppression and lysis of infected erythrocytes contributed to the anemia. Partial immunity-whether induced by repeated immunization with whole parasites or with vaccine-seems important to the development of anemia.

Microscopic detection of parasites has been the reference standard for malaria diagnosis for decades. However, difficulty in maintaining required technical skills and infrastructure has spurred the development of several nonmicroscopic malaria rapid diagnostic devices based on the detection of malaria parasite antigen in whole blood. The ParaSight F test is one such device. It detects the presence of Plasmodium falciparum-specific histidine-rich protein 2 by using an antigen-capture immunochromatographic strip format. The present study was conducted at outpatient malaria clinics in Iquitos, Peru, and Maesod, Thailand. Duplicate, blinded, expert microscopy was employed as the reference standard for evaluating device performance. Of 2,988 eligible patients, microscopy showed that 547 (18%) had P. falciparum, 658 (22%) had P. vivax, 2 (0.07%) had P. malariae, and 1,750 (59%) were negative for Plasmodium. Mixed infections (P. falciparum and P. vivax) were identified in 31 patients (1%). The overall sensitivity of ParaSight F for P. falciparum was 95%. When stratified by magnitude of parasitemia (no. of asexual parasites per microliter of whole blood), sensitivities were 83% (>0 to 500 parasites/microl), 87% (501 to 1,000/microl), 98% (1,001 to 5,000/microl), and 98% (>5,000/microl). Device specificity was 86%.

We compared two collection devices, IsoCode and FTA, with whole blood for the diagnosis of malaria by PCR (n = 100). Using whole blood as the reference standard, both devices were sensitive for the detection of single-species malaria infections by PCR (> or =96%). However, the detection of mixed infections was suboptimal (IsoCode was 42% sensitive, and FTA was 63% sensitive).

Aotus monkeys received 4 doses of Plasmodium falciparum EBA-175 region II vaccine as plasmid DNA (Dv-Dv) or recombinant protein in adjuvant (Pv-Pv) or as 3 doses of DNA and 1 dose of protein (Dv-Pv). After 3 doses, antibody titers were approximately 10(4) in DNA-immunized monkeys and 10(6) in protein-immunized monkeys. A fourth dose did not significantly boost antibody responses in the Dv-Dv only or Pv-Pv only groups, but titers were boosted to approximately 10(6) in monkeys in the Dv-Pv group. Four weeks after the last immunization, the animals were challenged with 10(4) P. falciparum-parasitized erythrocytes. Peak levels of parasitemia were lower in the 16 monkeys that received region II-containing plasmids or proteins than in the 16 controls (geometric mean: 194,178 and 410,110 parasites/microL, respectively; P=.013, Student's t test). Three of 4 monkeys in the Dv-Pv group did not require treatment. These data demonstrate that immunization with EBA-175 region II induces a significant antiparasite effect in vivo.

A longitudinal study of malariometric indicators and their association with potential risk factors was conducted during August 1997-July 1998 at Padre Cocha, a village of 1,400 residents in the Peruvian Amazon. The incidence of Plasmodium falciparum infections during the study year was 166/1,000 persons; that of P. vivax was 826/1,000 persons. The mean duration of symptoms prior to diagnosis was 2 days; presenting geometric mean parasite densities were 3,976 parasites/microl for P. falciparum infections and 2,282 parasites/microl for P. vivax. There were no malaria-associated deaths. Consistent with the epidemic nature of malaria in the area, the incidence of both parasite species increased with age and there were no age-specific differences in mean parasite densities. No specific occupational risks for malaria were identified. Activities significantly associated with malaria risk reflected local vector behavior and included strolling outdoors after 6:00 PM and arising before 6:00 AM for adults, and attending evening church services for children.