Behavior of Microfilariae of Brugia Pahangi in Anopheles Quadrimaculatus

Abstract

Summary A study of the microfilarial behavior and vectorparasite interactions has been made with Anopheles quadrimaculatus during the early phase of infection with the microfilariae of Brugia pahangi. Both living and sectioned mosquitoes with heavy and light infections were examined at 5, 15, 30 and 60 minutes following engorgement. The penetration of the midgut and subsequent migration within the mosquito, including invasion of the indirect flight muscles, is achieved mechanically through the use of the cephalic hook of the microfilaria. The site of penetration of the midgut is most commonly the area adjacent to the attachment of the hindgut; most of the microfilariae escape into the hemocele between 5 and 15 minutes following engorgement. They accumulate within the hemocele at the posterior tip of the abdomen and between 15 and 30 minutes proceed toward the thorax by a route just beneath the abdominal cuticle within the subcuticular fat bodies. Microfilariae first occur in the thorax by 15 minutes and maximum invasion of the indirect flight muscles is reached between 30 and 60 minutes after the blood meal. Penetration of the muscles occurs principally at their insertions on the cuticle. This pattern of behavior is followed in both heavily and lightly infected mosquitoes. Mechanical damage to the midgut epithelium results from the penetrating activity of the microfilariae. The migration to the thorax produces a marked degree of damage and necrosis within the subcuticular fat bodies; this is related to the intensity of infection. The beginning of pigmental encapsulation of microfilariae in the hemocele or fat bodies occurs as rapidly as 15 minutes after engorgement. This phenomenon appears to be a true host reaction to the parasite.