Malaria vectors in a traditional dry zone village in Sri Lanka

Malaria transmission by anopheline mosquitoes was studied in a traditional tank-irrigation-base rice-producing village in the malaria-endemic low coun try dry zone of northcentral Sri Lanka during the period August 1994-Februa ry 1997. Adult mosquitoes were collected from human and bovid bait catches, bovid-baited trap huts, indoor catches, and pit traps. Mosquito head-thora ces were tested for the presence of Plasmodium falciparum and P. vivax, and blood-engorged abdomens for the presence of human blood by ELISAs. House s urveys were done at two-day intervals to record cases of blood film-confirm ed malaria among the villagers. A total of 7,823 female anophelines represe nting 14 species were collected. Trends in anopheline abundance were signif icantly correlated with rainfall of the preceding month in An. annularis, A n. barbirostris, An. subpictus, An. vagus, and An. varuna, but were not sig nificant in An. culicifacies and An. peditaeniatus. Malaria parasite infect ions were seen in seven mosquito species, with 75% of the positive mosquito es containing P. falciparum and 25% P. vivax. Polymorph PV247 was recorded from a vector (i.e., Art. varuna) for the first time in Sri Lanka. Computat ions of mean number of infective vector (MIV) rates using abundance, circum sporozoite (CS) protein rate, and human blood index (HBI) showed the highes t rate in An. culicifacies. A malaria outbreak occurred from October 1994 t o January 1995 in which 45.5% of village residents experienced at least a s ingle disease episode. Thereafter, malaria incidence remained low. Anophele s culicifacies abundance lagged by one month correlated positively with mon thly malaria incidence during the outbreak period, and although this specie s ranked fifth in terms of abundance, infection was associated with a high MIV rate due to a high CS protein rate and HBI. Abundance trends in other s pecies did not correlate significantly with malaria. It was concluded that An. culicifacies was epidemiologically the most important vector in the stu dy area.