Detection of Plasmodium vivax and Plasmodium falciparum Circumsporozoite Antigen in Anopheline Mosquitoes Collected in Southern Thailand

During a 13-month study on the ecology of malaria vectors in five villages in southern Thailand, Anopheles specimens collected on human-bait, bovid-bait, and in light traps were tested for the presence of Plasmodium vivax and P. falciparum circumsporozoite antigen by enzyme-linked immunosorbent assay. Plasmodium vivax antigen was detected in seven specimens and P. falciparum in 21 specimens, together representing 0.4% of the 7,938 specimens tested. In one village, Palao-U, circumsporozoite antigen was detected in 16 (0.7%) of the 2,196 specimens tested. In this village, combined rates of infection with P. falciparum and P. vivax were 0.6% for An. minimus, 1.1% for An. sawadwongporni, and 1.5% for An. maculatus. Circumsporozoite antigen was also detected in An. dirus, An. nivipes, An. barbirostris group, and An. hyrcanus group specimens. Combined P. falciparum and P. vivax entomologic inoculation rates in the wet season (March-October) were 0.05 for An. minimus, An. maculatus, and An. dirus, but 0 for An. sawadwongporni. Rates were higher in the dry season (November-February): 0.26 for An. minimus, 0.13 for An. maculatus, 0.13 for An. sawadwongporni, and 0 for An. dirus. The vectorial capacity, calculated based on human biting rate and rate of survival, of An. minimus during the dry season was more than two-fold higher than that of An. maculatus, the species with the second highest vectorial capacity.