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.