Melanization and encapsulation in Aedes aegypti and Aedes togoi in response to parasitization by a filarioid nematode (Breinlia booliati)

Abstract

In A. aegypti (Singapore strain), a refractory host, there was a marked progressive decline of developing larvae of B. booliati [isolated from rats] during the incubation period. In A. togoi, a susceptible host, the filarial larvae developed normally and the number of larvae remained constant throughout the incubation period. Encapsulation and melanization of B. booliati larvae in A. aegypti and A. togoi were studied. A. togoi occasionally mounted a defense reaction to the infection. In A. aegypti, various stages of filarial larvae were frequently affected by the defense mechanisms of the host, and a relatively large number of melanized larvae were recovered in dissections throughout the incubation period. The process of melanization was described and the relationship between melanization and hemocytes of mosquitoes was discussed. Hemocytes of the mosquito host appeared to be involved in the encapsulation of filarial larvae, as evidenced by adherence of cells to the cuticle of the larvae and the formation of a translucent, gelatinous envelope which contained intact cells, necrotic cells, spaces and numerous whitish granules. The possible involvement of a humoral reaction in bringing about the degeneration and retardation of the filarial larvae is discussed.