Epidemiology of subperiodic bancroftian filariasis in Samoa 8 years after control by mass treatment with diethylcarbamazine.

In 1979, a microfilarial prevalence study was conducted in a population of 8385 persons inhabiting 28 villages in Samoa using both the nuclepore filtration (NP) method (with 1 ml blood) and the fingerprick (FP) method (with 60 mm(3) blood). The overall prevalence rate was 4.5% by the NP method and 3.8% by the FP method. The average microfilarial prevalence in males was 2.3 times higher than in females, and the rate among males aged 30 years and over was as high as 20%. The positive cases were found to be concentrated in certain households.The median microfilarial density (MfD-50) for the whole of Samoa was 18.6 using 60-mm(3) blood samples (males, 21.4; females 14.2). While the MfD-50 of any village has a positive association with the microfilarial prevalence rate of that village, a relatively high MfD-50 was noticed among young people under 20 years of age together with low prevalence rates.The negative binomial distribution was fitted to the data on the distribution of microfilarial counts in Samoa and gave a better fit than the log-normal distribution. The data having been fitted to the negative binomial, the number of false negatives could be determined as 9% of the estimated number of positives in the survey population when the NP method was employed and about 25% with the FP method.Further studies revealed that 15.1% of the microfilaria carriers presented some clinical manifestation, the most common being an attack of filarial fever (13.1%). The average duration of a fever attack was 3.5 days and the total period with fever/person/year averaged 27.1 days.