OBSERVATIONS ON THE TRANSMISSION OF FILARIASIS IN URBAN CALCUTTA

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Abstract
Rozeboom, L E. (Dept. of Pathobiol., The Johns Hopkins Univ. Schl. Hygiene, Baltimore, Md. 21205), N. C. Bhattacharya (Calcutta Schl. Trop. Med.) and S. K. Gilotra. Observations on the transmission of fllariasis in urban Calcutta. Amer. J. Epid., 1968, 87: 616–632.—For a period of 14 months (January, 1966— February, 1967) the factors in the transmission of Wuchereria bancrofti by Culex fatigans in a small, densely populated neighborhood in Howrah, a suburb of Calcutta, were studied. Mosquito densities were highest during the cold, dry months, at low levels during the hot, dry months (April–June) and again relatively high throughout the rainy months of July to November. Natural infection rates of mosquitoes with mature larvae of W. bancrofti ranged from 0 to 1.0% during the cold months, and from 1.8 to 4.3% during the warm months. From biting rates, infective larva rates and intensities of infections, it is estimated that any one living in the area would risk being bitten about 50 times during the year by infective mosquitoes carrying a total of at least 180 stage III larvae. There are two transmission seasons, late February to early April, and during the warm rainy weather from July to November. An important factor inhibiting higher transmission rates is the high daily mortality rates of the mosquito, which range around 20 to 30 per cent through most of the warm, rainy months. During the cold season, in spite of high mosquito densities, only a few females are able to survive the longer incubation period required for complete development of the parasite. During the hottest part of the year, the parasites themselves undergo degeneration in the mosquitoes.

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