SHORT-TERM AND LONG-TERM ACTION OF MULTIPLE DOSES OF IVERMECTIN ON LOIASIS MICROFILAREMIA

One hundred nine Gabonese patients infected with Loa ion microfilariae were treated with ivermectin (200 mu g/kg of body weight) at the Para sitology, Mycology and Tropical Medicine Department (Faculte de Medeci ne et des Sciences de la Sante, Libreville, Gabon). Each was given one dose per month for six consecutive months. The peripheral blood micro filaria (mf) count before and after each dose showed an average decrea se in the microfilaremia of 87.3% (short-term-single dose). An annual single-dose mass treatment with 200 mu g/kg of ivermectin was sufficie nt to control the parasite in populations with low (< 400/ml) L. loa m f counts. One month after the sixth dose (shortterm-multiple doses), t he average microfilaremia rate had decreased by 99.2% compared with th e initial infection (35 patients). Samples were taken from 28 patients one month after the first dose and one month after the sixth dose. Th e average mf count decreased by 96.4% after the first dose and by 99.6 % after the sixth dose (average residual mf counts = 13.7 and 1.5 mf/m l, respectively). The mf count after the sixth dose was only 11.2% of the count after the first dose. The low mf count persisted for mon tha n six months after the sixth treatment (long-term-multiple doses). Thu s. mass treatment with multiple doses is more appropriate for areas wh ere the blood mf count is very high. These results show that the numbe r of the annual treatments used in mass chemotherapy with ivermectin c an be adapted to each population to provide efficient protection.