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In 1206 man - hours, 1278 specimens of Anopheles vagusDönitz, 1902 were collected in 36 villages of Bastar district, Madhya Pradesh, India. This Anopheles was found resting indoors during the day time. A uniform feeding pattern was not seen all round the year. This insect appeared to be more numerous in the rainy season in the Indravati plains with hot - wet climate and an elevation range from 457 to 609 m. This species was not captured on human bait. In precipitin tests females fed on human blood were detected. None of the females dissected had infection of malaria parasites.

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Key Words : Abundance, Anopheles vagus Dönitz, 1902, Bastar district, bionomics, distribution, diurnal resting sites, epidemiological significance, feeding times, malaria, man - biting rate, ovarioles, precipitin tests, seasonal prevalence, vector

1. Accepted on 5.6.1994.

2. Assistant Entomologist, National Malaria Eradication Programme, Jagdalpur, Bastar district, Madhya Pradesh, India.

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The Thar desert is a highly inhospitable ecosystem for vectors of serious diseases like malaria, filariasis, dengue including dengue haemorrhagic fever and dengue shock syndrome, leishmaniasis and Japanese Encephalitis, although tropical leishmaniasis and dracunculiasis were already prevalent in the Thar. Some of these diseases like malaria, has been only dismally prevailing until about the turn of the eighties when it reemerged with a vengeance causing immense morbidity and misery. Lymphatic filariasis has made inroads in the Thar, largely through mobile population harbouring the parasite. Recent investigations in the Thar desert have shown that vectors of all the above diseases prosper in the changed climate of the Thar, so much so that a species like Anopheles culicifacies, a major vector of malaria in other parts of the country, but never occurring in the interior of the Thar before the existence of extensive canalized irrigation, has now well established along with the traditional vector, A. stephensi. Therefore, it seems reasonable to review the present extent of prevalence and the factors associated with the emergence and reemergence of the various vector-borne diseases in the Thar desert.

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Key Words : Anopheles culicifacies, Anopheles stphensi, dengue shock syndrome, dracunculiasis, epidemics, Japanese encephalitis, leishmaniasis, lymphatic filariasis, malaria, Thar desert

1. Accepted on 5.6.1996

2. Dy. Director, Desert Medicine Research Centre, Jodhpur 342005, India.

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Focal index is a new parameter for the evaluation of malaria control in any area. It is dealing with the relationship between the quantum of malaria parasitic reservoir, its distribution and the transmission. This parameter can easily be calculated from the basic data of epidemiological information collected at different levels of anti epidemic and sanitary stations. The product of total nos. of cases in a district divided by the nos. of villages which are positive for malaria gives the focal index of that area. The probability of a mosquito infected by malaria parasites depend on the volume of the population and the total nos. of malaria cases in the total population of the village. For calculation of focal index in a group of villages with different nos. of reported malaria cases a varying coefficient factor is applied which is the square of the nos. of malaria cases in the given village. An equation for calculation of basic focal index in complex situation is given. These indices were applied on the results obtained in the Napo county of Guangxi Zhuang region of China. It was demonstrated that the effect of foci eradication in these areas with bednets impregnated with deltamethrin was better than DDT residual spraying. It is expected that for testing the validity, these indices will be applied on the results obtained in other parts of the world also.

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KEY WORDS : basic focal index; China, corrected varying focal index; correction factor; epidemiological data; Guangxi Zhuang region, malaria transmission; Napo county; varying coefficient; vector biology

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1. Accepted on 27.9.1993.
2. Guangxi Institute for Parasitic Diseases Control, 80 Tao Yuan Road, Nanning Guangxi 530021, People’s Republic of China.