Studies on Bancroftian filariasis in Liberia, West Africa. III. Efficacy of repeated treatment with diethylcarbamazine and vector control on the microfilarial reservoir in a rural population.

The population of four villages in the savanna area in Upper Lofa in the hinterland of Liberia was treated with diethylcarbamazine and the decline of the density of microfilariae of Wuchereria bancrofti was studied. It became obvious that even a repeated treatment with the drug did not result in a complete eradication of the parasites, but that about one third of microfilaria carriers who had received two courses of treatment remained infected, showing ultra low densities which could only be-discovered by employing the sensitive membrane filtration technique. Vector control by means of residual spraying with DDT carried out every six months for 2 1/2 years in two villages did not result in a decrease of the microfilaria carrier rates. However, the microfilarial density of the infected persons declined distinctly during the three years of control. Experiences made with the membrane filtration technique under field conditions are described.