Leishmania detection in sand flies using a field-deployable real-time analytic system.

We describe here the development and evaluation of advanced vector surveillance analytic technologies for real-time leishmaniasis risk assessment. Leishmania genus and visceral leishmaniasis causative agent--specific dual fluorogenic-probe hydrolysis (TaqMan), thermally stable (freeze-dried) polymerase chain reaction assays were developed using field-durable analytic instrumentation. In laboratory testing with a panel of diverse Leishmania species from culture and infected sand flies, the sensitivity and specificity of both assays were 100% concordant with DNA sequencing. In specificity testing with Leishmania genetic near neighbors, clinically significant organisms, and human genomic DNA, no detectable fluorescence above background was observed. Field evaluation was conducted in southern Iraq using wild sand flies. In field testing, Leishmania genus assay was 100% sensitive and 96% specific with a single false-positive result. The visceral leishmaniasis genotype assay was 100% sensitive and 100% specific compared to DNA sequencing. Thermally stable polymerase chain reaction assays vastly simplified transportation and storage. Assay preparation and analysis required less than 2 hours.

Epidemiology and spatial analysis of malaria in the Northern Peruvian Amazon.

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.

Spatial clustering and epidemiological aspects of visceral leishmaniasis in two endemic villages, Baringo District, Kenya.

Visceral leishmaniasis (VL) seroprevalence in Kenya is unknown because of the lack of a practical and accurate diagnostic test or surveillance system. A novel serological assay was used to estimate the seroprevalence of Leishmania-specific antibodies, and Global Information System and spatial clustering techniques were applied to study the presence of spatial clusters in Parkarin and Loboi villages in Baringo District in 2001. VL seroprevalences were 52.5% in Parkarin and 16.9% in Loboi. Significant associations among seropositivity and house construction, age, and proximity to domestic animal enclosures were found. A significant spatial cluster of VL was found in Loboi. The spatial distribution of cases in the two villages was different with respect to risk factors, such as presence of domestic animals. This study suggests that disease control efforts could be focused on elimination of sand fly habitat, placement of domestic animal enclosures, and targeted use of insecticides.

Evaluation of serological assays based on a novel excreted antigen preparation for the diagnosis of Cutaneous Leishmaniasis in Panama.

The objective of the present study was to determine the efficacy of prototype diagnostic serological assays for American Cutaneous Leishmaniasis (ACL) in Panama. As such, we prospectively sampled 100 cutaneous leishmaniasis case-patients and tested their sera in two serological assays based upon novel soluble antigen preparations made from propagating the parasites in a protein-free, serum free media. Using serum and a Leishmania mexicana antigen preparation to sensitize plates, the assay correctly identified 89% of the case-patients. While using serum with an antigen preparation from Leishmania braziliensis, the assay correctly identified 71% of the patients. Concerning both test formats, performance was near equal in true positive and presumptive positive subsets demonstrating the improved sensitivity of these assays over reference methods of choice. Since the incidence of leishmaniasis in Panama has increased dramatically in the past 10 years, these assays may be useful in clinical and epidemiological studies and control programs.

Evaluation of a dipstick malaria sporozoite panel assay for detection of naturally infected mosquitoes.

The determination of the presence or absence of malaria sporozoites in wild-caught Anopheles mosquitoes remains an integral component to the understanding of the transmission dynamics in endemic areas. To improve that capability, there has been on-going development of a new device using dipstick immunochromatographic technology for simplifying the testing procedure and reducing the time required to obtain results. As part of a larger multi-center effort, we evaluated the sensitivity and specificity of a prototype malaria sporozoite antigen panel assay (Medical Analysis Systems, Camarillo, CA) against three human Plasmodium species/polymorphs. The wicking (dipstick) assay was compared against a standard parasite antigen capture enzyme-linked immunosorbent assay (ELISA) for the detection of human circumsporozoite protein (CSP) in wild-caught mosquitoes. Over 6,800 Anopheles mosquitoes, representing 20 species collected from malaria endemic areas of Indonesia were tested either individually or in pools of up to 10 mosquitoes each. From 1,442 pooled test strip assays and ELISA formats, nine mosquito pools were found reactive for P.falciparum, P. vivax 210, or P. vivax 247 CSP. There was complete concordance between test strip results and ELISA results. Sensitivity was 100% and given some minor problems with false positives or negatives, specificity (n = 488) was 97%. Most strips judged as false positive produced very weak signals compared with negative control blank strips and paired ELISA-negative samples. The dipstick test proved technically simpler to perform and interpret than the ELISA and results were obtained within 15 min of exposure to mosquito suspension. This qualitative assay appears an attractive alternative to the CSP ELISA for detection of sporozoites in fresh or dried mosquitoes.

Evaluation of the VecTest Malaria Antigen Panel assay for the detection of Plasmodium falciparum and P. vivax circumsporozoite protein in anopheline mosquitoes in Thailand.

We evaluated the performance of the VecTest Malaria Antigen Panel (V-MAP) assay for the detection of Plasmodium falciparum and P. vivax (variants 210 and 247) circumsporozoite protein in anopheline mosquitoes in Thailand. The V-MAP assay is a rapid, one-step procedure using a 'dipstick' wicking test strip. The circumsporozoite (CS) ELISA was used as the reference standard. Mosquitoes evaluated in the study included field-collected specimens (n = 930) and laboratory-reared specimens that had been fed on blood collected from patients with and without Plasmodium gametocytes (n = 4,110) or on cultured P. falciparum gametocytes (n = 262). Field-collected mosquitoes were triturated individually or in pools of 2-5 and tested using 613 V-MAP assays. Laboratory-reared specimens were tested individually using 4,372 V-MAP assays. Assay performance depended on the species of Plasmodium and the number of sporozoites used as the cut-off. For P. falciparum, optimal performance was achieved using a cut-off of 150 sporozoites (sensitivity = 100%, specificity = 99.2%, and accuracy = 0.99). For P. vivax variant 210, optimal performance was also achieved using a cut-off of 150 sporozoites (sensitivity = 94.8%, specificity = 94.5%, and accuracy = 0.95). We were unable to develop a standard-curve for the CS-ELISA using P. vivax variant 247 because of a lack of sporozoites; however, using a cut-off of 30 pg P. vivax 247 antigen (mosquitoes with less than this amount of antigen were considered negative), assay performance (sensitivity = 94.3%, specificity = 99.2%, and accuracy = 0.99) was comparable to that achieved for P. falciparum and P. vivax 210. These results clearly demonstrate that the V-MAP assay performs at an acceptable level and offers practical advantages for field workers needing to make rapid surveys of malaria vectors.

Modular laboratories--cost-effective and sustainable infrastructure for resource-limited settings.

High-quality laboratory space to support basic science, clinical research projects, or health services is often severely lacking in the developing world. Moreover, the construction of suitable facilities using traditional methods is time-consuming, expensive, and challenging to implement. Three real world examples showing how shipping containers can be converted into modern laboratories are highlighted. These include use as an insectary, a molecular laboratory, and a BSL-3 containment laboratory. These modular conversions have a number of advantages over brick and mortar construction and provide a cost-effective and timely solution to offer high-quality, user-friendly laboratory space applicable within the developing world.

Immunization with Leishmania major exogenous antigens protects susceptible BALB/c mice against challenge infection with L. major.

The potential of Leishmania major culture-derived soluble exogenous antigens (SEAgs) to induce a protective response in susceptible BALB/c mice challenged with L. major promastigotes was investigated. Groups of BALB/c mice were immunized with L. major SEAgs alone, L. major SEAgs coadministered with either alum (aluminum hydroxide gel) or recombinant murine interleukin-12 (rmIL-12), L. major SEAgs coadministered with both alum and rmIL-12, and L. major SEAgs coadministered with Montanide ISA 720. Importantly and surprisingly, the greatest and most consistent protection against challenge with L. major was seen in mice immunized with L. major SEAgs alone, in the absence of any adjuvant. Mice immunized with L. major SEAgs had significantly smaller lesions that at times contained more than 100-fold fewer parasites. When lymphoid cells from L. major SEAg-immunized mice were stimulated with leishmanial antigen in vitro, they proliferated and secreted a mixed profile of type 1 and type 2 cytokines. Finally, analyses with Western blot analyses and antibodies against three surface-expressed and secreted molecules of L. major (lipophosphoglycan, gp46/M2/PSA-2, and gp63) revealed that two of these molecules are present in L. major SEAgs, lipophosphoglycan and the molecules that associate with it and gp46/M2/PSA-2.