Entomological and epidemiological studies on malaria in Rajmahal range, Bihar

The epidemiological investigations carried out in six tribal villages in Rajmahal range hill in south Bihar revealed average slide positivity rate (SPR) 25.1 ranging between 9.8 and 37.8 per cent. Plasmodium falciparum was the dominant parasite which accounted 64.2 per cent of the total infections. Results of mass blood survey indicated the presence of high percentage of asymptomatic carriers of malaria parasites in the local populace. In an entomological survey, 25 species of mosquitoes under five genera were collected in 20 trap nights. The average density of mosquitoes recorded was 230.6 per trap night. Anopheles mosquitoes alone accounted 72.8 per cent of the total collection whereas malaria vectors Anopheles maculatus, An. minimus, An. philippinensis, An. varuna and An. annularis accounted 32.8 per cent of the total anophelines collected. Both anopheline and culicine mosquitoes were found susceptible to DDT (4 per cent) and malathion (5 per cent) in 30 min exposure. Dissection of malaria vectors An. minimus, An. maculatus and An. philippinensis revealed very high percentage of parity rate (77.8 per cent) which gives a strong indication about their vectorial status in the transmission of malaria. Poor socio-economic condition, lack of sense of hygiene worsen the situation in the presence of asymptomatic carriers.