Introduction, transmission and aggravation of malaria in desert ecosystem of Rajasthan, India.

BACKGROUND & OBJECTIVES: Malaria is an important public health problem in northwestern desert part of Rajasthan. Since desert malaria is seasonal or unstable, there is a need to study its epidemiology in the totality to address factors like how malaria is introduced into desert every year and what are desert-specific transmission risk factors leading to epidemics? METHODS: Twenty-six villages in irrigated, semi-irrigated and non-irrigated settings of the desert have been selected. Periodic investigations were undertaken in all the seasons from 2001 through 2002 to determine causes of introduction of disease, the factors involved in its transmission and the epidemic risk factors. Standard methods/procedures for mosquito collection, preservation and identification and for parasitological studies were employed. Rainfall data were analysed and correlated. Results: Importation of malaria infection through individuals was the major cause of introduction of disease in all the 12 villages showing some initial load of infection. Areas having higher population of cattle in relation to humans (human to cattle ratio of 1:25) had less transmission of disease (ratio of primary to secondary cases 1:3) as compared to relatively less cattle (human to cattle ratio 1:3) resulting into high transmission of disease with 1:47 ratio of primary to secondary cases. Introduced through migration, prospective transmission of malaria was observed as a resultant interaction of density of three components namely malaria cases, vector density and cattle to human ratio. Rainfall more than average when coupled with more cases of imported malaria leads to the eruption of malaria epidemics. INTERPRETATION & CONCLUSION: Importation of malaria cases was the major cause of seasonal introduction of malaria in the desert. This initial or primary parasitic load available in a village leads to a particular transmission quantum depending upon the density of vectors, human and cattle population at a particular time. Areas with more imported cases when coupled with profuse vector population lead to epidemic malaria situations in the desert.

Entomological studies on malaria in irrigated and non-irrigated areas of Thar desert, Rajasthan, India.

BACKGROUND & OBJECTIVES: Malaria is the major health problem in western Rajasthan yet its vector fauna and transmission dynamics thereof is not understood properly. The present investigations report complete profile of qualitative and quantitative aspects of anopheline species occurring in different settings of desert ecosystem. METHODS: Area with irrigation through canal for more than 20 years (setting I), area with irrigation through canal for 10 years (setting II) and area without any irrigation (setting III) have been selected for studies. Species identification and their densities (per man hour) was made as per standard methods. RESULTS: In village of setting I, during rainy season, An. subpictus and An. stephensi were present while during winter season four species--An. subpictus, An. stephensi, An. culicifacies and An. annularis were collected. In all the villages of setting I, II and III no Anopheles mosquito was observed during summer season. In the villages of desert region without any irrigation facilities through any canal, the anopheline species were present only during rainy season. INTERPRETATION & CONCLUSION: An. stephensi is the major malaria vector of desert irrespective of whether the area is canal irrigated or not. During summer season absence of vector species in all the villages require further studies on micro-ecology of the species under desert conditions.