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.