Disabling Effects and Control of Filariasis

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Abstract
Summary This report reviews the distribution and prevalence of clinical filariasis and of microfilaremia in the Pacific, in Africa and in Asia; discusses the disabling effects of filariasis and outlines a control program that is working satisfactorily in the Society Islands, French Oceania. In collecting epidemiologic data for the maps, a lack of standardization in clinical, blood and mosquito surveys was apparent, and comparison had to be limited to prevalence rates for elephantiasis and microfilaremia. Even here, representative numbers in standard age groups and from all segments of the population were seldom available and suitable correction factors had to be employed to adjust the figures to represent the population as a whole. Procedures for performing and reporting standardized clinical, blood and mosquito surveys are recommended and tables are presented which show summaries of certain of these results from the Society Islands before the filariasis control program began. Seven per cent of the population demonstrated elephantiasis 7% of the males had hydrocele and 12% experienced attacks of lymphangitis. A total of 26% of the whole population showed clinical signs of filariasis, and 32% demonstrated microfilaremia. The disabling aspects of filariasis are difficult to evaluate exactly in terms of man-days of work lost annually in a community, but it is concluded that the social and economic aspects of filariasis are such as to constitute a major public health problem in many parts of the tropics. A correlation between prevalence of elephantiasis and microfilaremia in a population as a whole could not always be shown in the south Pacific. A low prevalence of microfilaremia was associated with a low prevalence of elephantiasis but areas with high microfilaremia rates did not always show high elephantiasis rates. However, when the density of microfilariae per unit of blood was calculated, it was found that a definite correlation existed. It is suggested, for at least that part of the Pacific where non-periodic filariasis occurs, that the density of microfilariae in an area may be used as an index to estimate the amount of elephantiasis in that same area. A filariasis control program now in progress in the Society Islands, which combines mosquito control with parasite control by mass treatment with diethylcarbamazine, shows that when practiced thoroughly, these measures reduce microfilaremia, microfilarial density, the mosquito population and larval density in mosquitoes to a minimum. Primary acute filariasis is rare; new cases of elephantiasis together with other forms of chronic filariasis fail to develop; and transmission is reduced to a low point, in some instances to zero.
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