ORIGINAL RESEARCH ARTICLE Role of asymptomatic carriers and weather variables

Background: Malaria transmission is perennial in the AssamArunachal Pradesh interstate border areas in the Sonitpur district of Assam, India. A yearlong study was carried out on the incidence of symptomatic and asymptomatic malaria and the role of asymptomatic malaria carriers in persistent transmission of the disease. The relationships between malaria incidence and weather parameters were also investigated. Methods: Active and mass blood surveys were conducted on a monthly basis in Bengenajuli, Sapairaumari Pathar, and Nigam villages near the AssamArunachal Pradesh border. Epidemiological indices were estimated for malaria-positive cases. Multiple linear regression between monthly malaria incidence and monthly average temperature, and relative humidity along with monthly total rainfall was carried out. The known malariavectors collected in CDC light traps were identified and recorded. Results: Slide positivity rate (SPR) and Plasmodium falciparum percent (Pf %) for symptomatic malaria were 26.1 and 79.8, respectively. Prevalence of malaria vectors was observed throughout the year with varying density. Anopheles philippinensis/nivipes and A. annularis were predominant among the seven known vector species recorded currently. Asymptomatic parasitemiawas detected throughout the year with SPR ranging from 4.8 to 5.3. Monthly rainfall with 1-month lag had the highest correlation (r0.92) with SPR. The relationship between SPR and weather factors was established as SPR114.220.58 Tmin1.38 RH0.03 R