Investigation of malaria outbreak in Rajasthan

Jaisalmer and Barmer districts in the Thar Desert of Rajasthan experienced an unprecedented rains during 1994 leading to an outbreak of malaria. Investigations were carried out at three sites in two districts (i) Pokaran PHC and (ii) Nachana PHC in Jaisalmer district and Dhorimana in Barmer district during November 1994. Epidemiological and entomological studies in Pokaran PHC revealed presence of small foci of stable malaria. These foci were maintained by large bodies of water (ponds/lakes) drained from surrounding areas and spread over 1 to 5 sq km. Slide positivity rate (SPR), slide falciparum rate (SfR) and child spleen rate (SR) were 60.1, 56.9 and 86.9%, respectively with 3 deaths reported. Adjoining villages experienced epidemic reporting deaths fed by the reservoir from these stable foci. An. culicifacies and An. stephensi were the major malaria vectors. Nachana PHC recorded stable malaria foci of irrigation malaria due to introduction of Indira Gandhi Canal (IGC). SPR, SfR and SR recorded were 52.35, 50.58 and 80.8%, respectively. Transmission appeared to be maintained by An. stephensi, An. culicifacies and An. fluviatilis in relays. An. fluviatilis seems to have established breeding in silted grassy margins of IGC. Dhorimana PHC in border district was also found to be a stable malaria foci although with low malaria indices. However, An. culicifacies and expanded breeding potential of An. stephensi were the main factors in maintaining malaria endemicity in the region.