Academic journal article Bulletin of the World Health Organization

Long-Term Efficacy of Single-Dose Mass Treatment with Diethylcarbamazine Citrate against Diurnally Subperiodic Wuchereria Bancrofti: Eight Years' Experience in Samoa

Academic journal article Bulletin of the World Health Organization

Long-Term Efficacy of Single-Dose Mass Treatment with Diethylcarbamazine Citrate against Diurnally Subperiodic Wuchereria Bancrofti: Eight Years' Experience in Samoa

Article excerpt

A single-dose of diethylcarbamazine citrate (DEC, 6 mg per kg body weight) was administered in three mass treatment campaigns to >80% of the estimated total Samoan population (160 000) in 1982, 1983, and 1986. The effect of the drug was evaluated before and after each campaign by conducting four blood surveys covering 9600 to 13 700 people from 26-34 villages on each occasion. The drug reduced tghe prevalence of Wuchereria bancrofti microfilariae from 5.6% to 2.5% (a 55% reduction), while the transmission potential (the estimated mosquito infection rate if everyone is equally exposed to mosquito bites) dropped from 2.18 to 0.67 (a 70% reduction). The total number of microfilariae in the Samoan population is estimated to have been reduced by 80%. A spaced, single-dose treatment with DEC at a 1-2-year interval therefore seems to be an effective control measure against diurnally subperiodic W. bancrofti.

Introduction

Diethylcarbamazine has been the most effective, safe and widely used antifilarial drug since Hewitt et al. first reported its efficacy in 1947 [1]. Subsequently, various dosage schedules suitable for the treatment of different species and types of filarial parasites have been compared [2]. In 1974, the importance of administering an adequate total dose (72 mg per kg body weight) of diethylcarbamazine citrate (DEC) for Wuchereria bancrofti infection was stressed by a WHO Expert Committee [3]. Since then a 12-dose treatment (6 mg per kg) has been used worldwide as a standard regimen. However, use of this regimen poses considerable difficulties in large-scale mass treatment campaigns when the administrative backup is reduced or the enthusiasm of local people wanes. In several countries DEC-medicated cooking salt has been used to facilitate mass treatment and has proved to be very effective and safe [4-7]. In the South Pacific, annual single-dose treatments with DEC (6 mg/kg) are effective in decreasing the prevalence of microfilariae (mf), and the treatment schedule is operationally straightforward [8-10]. However, the long-term effect of this reduced dosage treatment has not yet been assessed critically. Meanwhile, ivermectin, the drug of choice for treating onchocerciasis [11-13], has been tested on lymphatic-dwelling filariae with promising results. A single dose of ivermectin has been reported to be as effective as a full course of treatment with DEC [14]. Whether ivermectin can replace DEC is arguable, but it is essential to study the effect of a single dose of DEC rather than the standard 12 doses. Over the period 1981-88, the filariasis control project in Samoa conducted three rounds of single-dose treatment with DEC covering the entire country and evaluated the long-term parasitological effects. This article summarizes the activities carried out during this 8-year period and the results obtained.

Materials and methods

Samoa consists of two main islands (Upolu and Savaii) and has a total population of about 160 000; endemic filariasis occurs, caused by diurnally subperiodic W. bancrofti, which is transmitted by Aedes polynesiensis and A. samoanus vectors. The filariasis control project was inaugurated in Samoa in 1981, when a nationwide mass drug administration (MDA) campaign using a single dose of DEC (6 mg/kg body weight) was adopted as a national strategy to control the disease. It was intended to cover the total Samoan population except infants under 1 year of age, pregnant women, sick people, and the very old.

Three MDAs were carried out: one each in 1982 (MDA-1), 1983 (MDA-2), and 1986 (MDA-3). Before the drug was administered, a population census was carried out in all villages in the country (>400) as well as in Apia, the capital, with the assistance of village women's committees. Based on the census results, the DEC tablets (or syrup for children aged 1-5 years) needed for each village were packed at the project office in Apia, distributed through local health centres, and administered to the inhabitants on the selected date, which was publicized in radio broadcasts. …

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