Onze ans de chimioprophylaxie par la diéthylcarbamazine de la filariose lymphatique apériodique à Tahiti.

Publication Type  Journal Article
Year of Publication  1966
Authors  Laigret, J.; Kessel, J-F.; Bambridge, B.; Adams, H.
Journal Title  Bull Wld Hlth Org
Volume  34
Pages  925-38
Journal Date  1966

Les auteurs exposent leur expérience de l'utilisation au long cours de la diéthylcarbamazine pour la chimioprophylaxie de l'endémie filarienne (filariose à Wuchereria bancrofti) dans la population rurale de l'île de Tahiti.L'efficacité du médicament, remarquable pendant les premières années de traitement, semble limitée dès que le niveau d'infection, évalué par les indices microfilariens, diminue et atteint une certaine valeur critique. Cette stagnation tient sans doute à l'impossibilité de traiter tous les individus, mais elle est aussi due à l'insuffisance d'action de la diéthylcarbamazine sur les filaires adultes. D'autre part, bien que des essais comparatifs de divers schémas de traitement montrent la supériorité des doses mensuelles, la posologie idéale du produit doit encore être précisée et l'on ignore toujours sur quel stade du parasite il agit.
La lutte contre la filariose bénéficiera certainement des recherches visant à définir un traitement associant la diéthylcarbamazine et un macrofilaricide, arsénical ou stibié.
The paper analyses the results of an eleven-year study of the application of diethylcarbamazine to the entire rural population (25000 persons) of Tahiti for treatment of non-periodic bancroftian filariasis. Preliminary work from 1948 to 1953 established a treatment schedule of 6 mg diethylcarbamazine citrate per kilogram of body-weight on one day per month for 12 months. Because of the high endemicity, all those over 1 year old were treated in 1953 ; subsequently, only those found in the course of periodic blood surveys to be carriers of microfilariae were traeted. In 1961 the treatment was modified, each carrier being given 6 mg diethylcarbamazine per kilogram of body-weight per day for six successive days, repeated every six months. The chemical control measures were accompanied by the mechanical destruction of the breeding and resting places of the mosquito vector, Aedes polynesiensis, which cannot be effectively and economically controlled by means of insecticides.
The results of the campaign were evaluated by studying (a) the presence of microfilariae in the blood, (b) the prevalence of symptoms of bancroftian filariasis and (c) the infectivity of the vector.
In 1949, 29.9% of the population were microfilaria carriers, the average density of microfilariae per 20 mm3 of blood being 23.4 for all persons examined and 78.4 for carriers. By 1953, these figures had been reduced to 20.6%, 11 and 53.6 respectively, and by two to three years after the mass treatment to 6%, 1.5 and 24.1. Subsequent changes were much smaller, the figures for 1964 being 6.8%, 1.3 and 19.6, practically the same as nine years previously.
The symptoms of bancroftian filariasis studied were (a) enlarged epitrochlear glands, (b) lymphangitis, (c) hydrocele, (d) elephantiasis and (e) all other symptoms. Surveys were carried out in 1949, 1958 and 1964. For all the symptoms there were pronounced falls in the prevalence between 1949 and 1958 and then further slight decreases, except in regard to enlarged epitrochlear glands, where there was an increase ; possible explanations for this are advanced. The percentage of people with no symptoms of bancroftian filariasis increased from 29.5% in 1949 to 75.3% in 1958 and 80.9% in 1964.
With regard to the vectors, before mass chemoprophylaxis began, 5% of mosquitos were carrying larvae at all stages and 1.2% were carrying infective larvae, the respective densities (larvae per mosquito) being 1.1 and 0.31. These figures fell by 1955 to 2.9%, 0.7%, 0.12 and 0.022, respectively, and have since remained fairly steady, the 1964 figures being 3%, 0.5%, 0.13 and 0.017.
The results indicate that, whatever the schedule of treatment employed, diethylcarbamazine is very effective when first used on a heavily infected population. There is evidence that, particularly when the limits of effectiveness are being reached, dosing for one day per month for 12 months is more efficient than dosing for six consecutive days every six months. The drug apparently acts mainly by decreasing the transmission of the parasite because of the great decrease in the number of microfilariae in circulation. The effectiveness of the treatment was such that, within less than five years after mass chemoprophylaxis, bancroftian filariasis was no longer a public health problem in Tahiti.
However, the fact still remains that, once the infection rate is brought down to a certain level, any further reductions becomes very difficult and the slightest relaxation of control measures leads to a renewed rise in microfilaria rates. Below this critical level, the clinical rates continue to improve slowly. In conclusion the authors pose several questions in relation to the treatment schedule and dose and to the desirability for mass treatment as against treatment of carriers ; the answers to these questions should lead to more effective use of diethylcarbamazine and other drugs in the chemoprophylaxis of bancroftian filariasis in the future.

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