Concurrent parasitic infections in onchocerciasis and the occurrence of adverse reactions after ivermectin treatment.

Ivermectin is a safe, effective, and relatively well-tolerated drug for the treatment of human onchocerciasis. However, due to side effects of the drug, large-scale ivermectin distribution without medical supervision is not recommended. The mechanisms involved in the pathogenesis of ivermectin-induced adverse reactions are not yet known. Since onchocerciasis patients are likely to have concurrent parasitic infections, we investigated whether side effects that occur after ivermectin treatment could be related to the presence of parasite eggs and cysts in stool samples prior to treatment. One hundred twenty-nine onchocerciasis patients were treated with a single dose of ivermectin (150 micrograms/kg) and side effects were graded according to the classification of Greene and others. Stool samples were collected before and three days after treatment. A high percentage (80.5%) of the patients reported adverse effects (57% mild, 14.1% moderate, and 9.4% severe reactions). Most (95.1%) of the patients had one or more concurrent parasitic infections. No relationship could be found between the occurrence and extent of side effects and the severity of concurrent intestinal parasitic infections. However, side effects were significantly correlated with pretreatment microfilarial counts. Ivermectin treatment did not induce significant short-term changes in Trichuris trichiura or Schistosoma mansoni egg counts. However, a significant reduction in Ascaris lumbricoides egg counts and Entamoeba coli cyst loads was observed; a cure rate of 46% for cysts was reached. In contrast, hookworm egg production increased after ivermectin treatment. Further studies are required to verify ivermectin-induced changes in cyst and hookworm loads as well as the significance of these findings.