Academic journal article Bulletin of the World Health Organization

Efficacy of Five Annual Single Doses of Diethylcarbamazine for Treatment of Lymphatic Filariasis in Fiji

Academic journal article Bulletin of the World Health Organization

Efficacy of Five Annual Single Doses of Diethylcarbamazine for Treatment of Lymphatic Filariasis in Fiji

Article excerpt

Introduction

Diethylcarbamazine citrate (DEC) has been widely used for the treatment of lymphatic filariasis since its filaricidal effect was first reported (1). A series of trials designed to find the most suitable treatment regimen in endemic areas showed that a 12-dose course of treatment (12 x 6mg/kg body weight) was necessary to treat infection with Wuchereria bancrofti (2, 3). This scheme has been employed worldwide with success, but repeating 12 doses can pose considerable operational difficulties. However, a satisfactorily strong effect from a single 6mg/kg dose was reported in French Polynesia (4) and Samoa (5). In Samoa, when assessed 12 months after treatment, the single dose reduced the mf rate by 54% and mf density by 94%. A study in Fiji (6) revealed that five rounds of annual treatment with 6 mg/kg were as effective as a 28-dose course of treatment delivered over 2 years (total dose, 140mg/kg) when assessed 5 years after commencement of treatment. A single-dose scheme was shown to be effective against Brugia malayi as well (7, 8).

A single dose of DEC (6mg/kg) has been reported to reduce mf counts by 85-95% in a cohort of mf-positive individuals (5, 9, 10). This implies that high-count carriers will remain mf positive after treatment, and therefore that a single treatment will not effectively reduce the mf rate in a community with many high-count carriers. It has been reported that the recurrence rate of microfilaraemia within a year of DEC treatment was higher where pretreatment mf density had been higher (11). A possible explanation is that juvenile parasites present during treatment were not affected and later began reproduction. It is possible that a high mf density facilitated filarial transmission by vector mosquitos and resulted in the accumulation of juvenile forms (3rd and 4th larval stages and young adults) in the human population. However, no study has compared the efficacy of annual single-dose treatment in areas with different endemicity. This article reports the influence of pretreatment levels of mf density and rate on reduction in mf rate after annual single-dose treatment.

Materials and methods

Sample villages, blood examinations, and treatments

The study was carried out on Kadavu Island, Fiji, and included 43 villages with a total population of 7600. Of these, 5799 (76.3%) persons were registered in the 1985 pretreatment survey. Eleven villages were excluded from the study because less than 30 persons were examined in each of them as a result of small size and/or poor compliance. All of those registered in 1985 (4686 people in 32 villages) were examined for mf using a 60-[micro]l finger-prick (thick smear method). Single-dose mass treatment with DEC (6mg/kg) was given in early 1986. Annual blood examinations and subsequent mass treatments were then performed in 1987, 1988, 1989, and 1990, with the final blood survey taking place in 1990-91. Villages were informed about a week before the arrival of the filariasis team. Residents gathered in the village community hall where names were called by household. Any new arrivals were included for treatment. Blood was collected and clinical examinations conducted where necessary. All slides were brought to the Filariasis Office in Suva for processing, microscopic examination, and recording. Only the results of those registered in 1985 were enumerated. Details of the villages, mass treatments, and blood examinations have been described (6). The village mf rates before and after treatment, and the pretreatment mf density (geometric mean of mf counts per 60 [micro]l of blood) are shown in Table 1, together with data on the numbers of people examined and those found positive for mf.

Table 1: Microfilariae (mf) rate before (1985) and after five annual treatments (1987-91) with diethylcarbamazine citrate

                         mf rate as % (No. mf positive/No, examined)
               mf density
Village        (a) 1985       1985             1987

Muani             1. … 
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