An effective programme for the control of filariasis in Tahiti
Kessel, J.F.
Bulletin of the World Health Organization 16(3): 633-664
1957
ISSN/ISBN: 0042-9686 PMID: 13472416 Document Number: 522040
An account is given of the organization and achievements of a campaign for the investigation and control of filariasis caused by Wuchereria bancrofti in Tahiti, where the incidence of microfilarial and clinical infection is high and the chief vector is Aedes polynesiensis Marks . In recent dissections by Bonnet & Chapman, only 1.2 per cent. of 788 females of Gulex pipiens fatigans Wied. (quinquefasoiatus, auct.) taken in houses in which there were carriers of microfilariae were positive for larvae of W. bancrofti in any stage of development and only O.38 per cent. for the third or infective-stage larvae, whereas 25.5 per cent. of A. polynesiensis from the same houses harboured larvae and 7.6 per cent. infective larvae. The procedure followed in the campaign and recommended for future use comprised the making of surveys of the prevalence of the disease in man, of the prevalence and density of the parasite in man and of the species of mosquitos present, their significance as vectors and the bionomics of those likely to be of importance, determination of infection rates in them in nature by means of intensive mosquito surveys, and application of the chosen control measures. In Tahiti, these were administration of Hetrazan to the population and measures directed against A, polynesiensis. As this is essentially a forest-dwelling mosquito, and the females rest outdoors, bite many kinds of hosts and are adaptable in their choice of breeding places and the eggs are very resistant to drying, it is difficult to control. However, it occurs in Tahiti in large numbers close to houses that are near bush areas, has a limited dispersal range and breeds in small containers. The control measure adopted was therefore elimination of breeding places for 110 yards round each dwelling, and for this the co-operation of householders was enlisted. The aim has been to continue Hetrazan treatment until all carriers are negative, but this is not always practicable and evidence is given that it may not be necessary. Once the treatment programme was well launched, incidence of larvae of W. bancrofti, particularly those in the infective stage, diminished rapidly in mosquitos caught in the field. In a district in which 1 per cent. of the population remained positive and the microfilarial density (product of the percentage of people positive and the average number of microfilariae per positive person, based on single samples of 20 cu. mm. of blood), had been reduced to 0.04, no larvae of W. bancrofti were found in standard dissections of mosquitos. It is thought that in a mass-treatment campaign, reduction of persons positive for microfilariae to 5 per cent., with a corresponding maximum microfilarial density of 1, should reduce transmission to a negligible minimum. There were no indications that the administration of Hetrazan to a population positive for W. bancrofti increases the mosquito population of the area. The importance of continuing mosquito control after the programme against microfilariae has ended is emphasised.