Seasonal prevalence of malaria vectors and its relationship with malaria transmission in three physiographic zones in Uttaranchal state, India

Anopheles minimus (Diptera : Culicidae) has been reported as a principal malaria vector in district Nainital 1 . An. fluviatilis and An. culicifacies (Diptera: Culicidae) were later incriminated as malaria vectors and An. minimus was reported virtually absent 2–4. Recently, in forest ecotype, An. fluviatilis has been incriminated as malaria vector and its sibling species ‘S’, which is a potential vector of malaria, was recorded for the first time in this area 5 . The data collected from District Malaria Office for the years 1998 and 1999 revealed that the annual parasite incidence (API) and slide positivity rate (SPR) was 0.2 and 0.3, and 1.0 and 1.1, respectively in Nainital and 1.0 and 0.6, and 1.3 and 1.0, respectively in Udham Singh Nagar districts. The transmission dynamics of malaria in such geographical zones is also likely to differ requiring specific vector control strategies. Therefore, the present study was undertaken in three different zones in Kumaon region such as hilly, bhabar (foothill area with very low water table) and terai (plain area with high water table) zones from April 1998 to March 1999 to study the seasonal prevalence of vectors and parasite load in the community. One village in each physiological zone was selected for the pilot study. Hilly zone is characterised by sedimentary and igneous rocks with streamlets and lakes. Mehra Gaon village with a population of 1431 persons, situated at an altitude of 4500 ft was selected from hilly zone. The bhabar zone is characterised by very low water table containing porous substratum with dispersed settlements. The village Sultan Nagri with a population of 524 persons, located in the foothill in forest fringe was selected. Terai zone is characterised by plain area, low-lying with high water table, wet and swampy land with high agriculture yield. Chhattarpur village having a population of 785, with few brick-made houses and inhabitants mostly agriculturists, was selected. Mosquito collections were made from five catching stations (5 human dwellings and 5 cattlesheds) in each village by hand capture method from 0600 to 0800 hrs from indoor resting habitats, fortnightly. Percentage composition of the anophelines in three different physiographic zones, per man hour density (MHD) and abdominal condition of vector species were recorded. Fever surveys were conducted monthly in each study village and the treatment was given as per National Vector Borne Disease Control Programme (NVBDCP) policy.