| Summary: | Background & objectives: Malaria is an important public health problem in northwestern desert partof Rajasthan. Since desert malaria is seasonal or unstable, there is a need to study its epidemiology inthe totality to address factors like how malaria is introduced into desert every year and what are desertspecifictransmission risk factors leading to epidemics?Methods: Twenty-six villages in irrigated, semi-irrigated and non-irrigated settings of the desert havebeen selected. Periodic investigations were undertaken in all the seasons from 2001 through 2002 todetermine causes of introduction of disease, the factors involved in its transmission and the epidemicrisk factors. Standard methods/procedures for mosquito collection, preservation and identification andfor parasitological studies were employed. Rainfall data were analysed and correlated.Results: Importation of malaria infection through individuals was the major cause of introduction ofdisease in all the 12 villages showing some initial load of infection. Areas having higher populationof cattle in relation to humans (human to cattle ratio of 1:25) had less transmission of disease (ratioof 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. Introducedthrough migration, prospective transmission of malaria was observed as a resultant interaction ofdensity of three components namely malaria cases, vector density and cattle to human ratio. Rainfallmore than average when coupled with more cases of imported malaria leads to the eruption of malariaepidemics.Interpretation & conclusion: Importation of malaria cases was the major cause of seasonal introductionof malaria in the desert. This initial or primary parasitic load available in a village leads to aparticular transmission quantum depending upon the density of vectors, human and cattle populationat a particular time. Areas with more imported cases when coupled with profuse vector population leadto epidemic malaria situations in the desert.
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