EFFECT OF IVERMECTIN ON 2 FILARIA-VECTOR PAIRS - BRUGIA-MALAYI AEDES-AEGYPTI - LITOMOSOIDES SIGMODONTIS-BDELLONYSSUS BACOTI

The effect of ivermectin was studied on two filaria-vector pairs, Brug ia malayi-Aedes aegypti and Litomosoides sigmodontis-Bdellonyssus baco ti. The rodent hosts, respectively Mastomys coucha and Meriones unguic ulatus, were treated with ivermectin doses of 0.05 mg/kg, or 0.2 mg/kg or 2 mg/kg. Batches of vectors were fed on rodents, infected or not, treated or not, from H7 to D43 post-ivermectin. Vector survival was ob served and dissections were performed to study the filarial developmen t. It appears that ivermectin has no systemic effect on vectors, or ve ry little. The drug acts on transmission because it affects the microf ilariae. Transmission of L. sigmodontis is blocked because microfilari ae are eliminated from the blood. Transmission of B. malayi is blocked although microfilaremia remains present at a low level. Two particula r features are observed: microfilariae are hyper-ingested, but they do not cross the stomach wall (in contrast, they cross at a high rate in the control batch of Aedes, due to the << stomach wall limitation >>) . These events might be explained by a muscular passivity of the micro filariae treated with ivermectin. Transmission of the two filarioid sp ecies is restored normally about D25-40 post ivermectin because a new population of microfilariae has appeared. These ivermectin experiments emphasize the diversity and complexity of two important phases of the filarial cycle in the vector: the ingestion of microfilariae and the passage through the stomach wall.