Exsheathment of microfilariae of Brugia pahangi in the susceptible and refractory strains of Aedes aegypti.

Exsheathment of microfilariae of Brugia pahangi was studied in susceptible (Liverpool) and refractory (Bora-Bora) strains of Aedes aegypti. It was found that the microfilariae tend to carry their sheaths into the haemocoel of both strains of Ae. aegypti within two hours after the engorgement of mosquitoes from a rat parasitized by filariae. The percentage of sheathed microfilariae in the haemocoel then progressively decreased to 0% at eight hours and to 1% at 24 hours post-ingestion in the Bora-Bora and Liverpool strains, respectively. Those microfilariae that remained in the midgut more than two hours after ingestion were most likely to cast off their sheaths there. The percentage of microfilariae exsheathed in the midgut progressively increased to about 91 and 78% at 24 hours post-ingestion in the Bora-Bora and Liverpool strains, respectively. These results suggested that the exsheathment of microfilariae occurs both in the haemocoel and in the midgut of two strains of Ae. aegypti.