DIRECT ASSESSMENT OF THE ADULTICIDAL EFFICACY OF A SINGLE-DOSE OF IVERMECTIN IN BANCROFTIAN FILARIASIS

Although the patent microfilaricidal activity of ivermectin is well es tablished, its efficacy against adult Wuchereria bancrofti is unknown. We used longitudinal ultrasound examinations for periods of 3-9 month s to assess directly the macrofilaricidal effect of a single 400 mu g/ kg dose of ivermectin in 15 men from Recife, Brazil who were infected with W. bancrofti. Before treatment, microfilarial densities ranged fr om 3 to 3098 microfilariae per mt of blood, and movements characterist ic of the living adult worm (the 'filaria dance sign') were observed b y ultrasound examination of the scrotal lymphatic vessels in all 15 me n. Following treatment, microfilarial density was markedly reduced in all men, but the filaria dance sign remained unchanged in both locatio n and pattern. Eight months after treatment, a dilated lymphatic vesse l was surgically removed from one patient at the site of the filaria d ance sign, and 3 intact adult worms were released. When given as a sin gle 400 mu g/kg dose, ivermectin had no observable effect on adult W. bancrofti. Therefore, prolonged suppression of microfilaraemia followi ng treatment with ivermectin cannot be explained by a macrofilaricidal effect of the drug. Ultrasound is a valuable new tool for directly an d rapidly assessing the macrofilaricidal efficacy of antifilarial drug s in lymphatic filariasis.