Anopheles barbirostris/campestris as a probable vector of malaria in Aranyaprathet, Sa Kaeo Province.

As a result of dramatic increase in malaria cases in Sa Kaeo Province from 666 cases in 1995 to 4,381 in 1997, a brief entomological study was carried out during January 1998 to December, 1999 in Pa Rai subdistrict where most malaria cases were reported. Of fourteen species of mosquitos found, only Anopheles barbirostris group was the most abundant species throughout the year. Adult identification was not able to confirm species within An. barbirostris group, particularly between An. barbirostris and An. campestris because of morphological resemblance. Therefore, the barbirostris group captured in this study is reported to be either An. barbirostris or An. campestris. The seasonal prevalence of barbirostris/campestris was bimodal in distribution (September and November) and coincided well with malaria occurrence in this area. Human landing collections revealed high adult densities with 20 bites/person-night for mean indoor density and 53.5 bites/person-night for mean outdoor density. The biting peak was during 21.00-24.00 hours. Among 223 barbirostris/campestris dissected for oocysts and sporozoites only one gut from the outdoor collection in November was infected with oocysts. There were no sporozoites detected in salivary glands of all mosquitos collected. This appears to indicate that in the absence of major vectors local species may serve as potential transmitters of malaria in Thailand.