Mansonelliasis - Vectors and The Masonelliasis Life Cycle

Vectors and The Masonelliasis Life Cycle

During a blood meal, an infected midge (genus Culicoides) or blackfly (genus Simulium) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound. They develop into adults that reside in body cavities, most commonly the peritoneal cavity or pleural cavity, but also occasionally in the pericardium (M. perstans), subcutaneous tissue (M. ozzardi) or dermis (M. steptocerca) (3).

In M. perstans, size range for female worms is 70 to 80 mm long and 120 μm in diameter, and the males measure approximately 45 mm by 60 μm. In M. steptocerca, the females measure approximately 27 mm long. Their diameter is 50 μm at the level of the vulva (anteriorly) and ovaries (near the posterior end), and up to 85 μm at the mid-body. Males measure 50 μm in diameter. In M. ozzardi, adult worms are rarely found in humans. The size range for females worms is 65 to 81 mm long and 0.21 to 0.25 mm in diameter but unknown for males. Adult worms recovered from experimentally infected Patas monkeys measured 24 to 28 mm long and 70 to 80 μm in diameter (males) and 32 to 62 mm long and .130 to .160 mm in diameter (females) (3).

Adults produce unsheathed and non-periodic (sub-periodic in M. perstans) microfilariae that reach the blood stream. A midge or black fly ingests microfilariae during a blood meal. After ingestion, the microfilariae migrate from the midgut through the hemocoel to the thoracic muscles of the arthropod. There the microfilariae develop into first-stage larvae and later into third-stage infective larvae. The third-stage infective larvae migrate to the arthropod’s proboscis where they can then infect another human when the midge or blackfly takes a blood meal (3). Asymptomatic humans serve as a significant reservoir for the disease. Little is known about other reservoirs of the disease.

Life Cycles of Various Mansonella