Mansonella streptocerca

Mansonella streptocerca, (formerly Diptalonema streptocerca), is a filarial (arthropod-borne) nematode (roundworm) causing the disease streptocerciasis. It is a common parasite in the skin of humans in the rain forests of Africa, where it is thought to be a parasite of chimpanzees, as well.^[1]

Mansonella streptocerca is one of three filarial nematodes that cause subcutaneous filariasis in humans. The other two filarial nematodes are Loa loa (the African eye worm), and Onchocerca volvulus (river blindness).

The worm is distributed across West and Central Africa.^[2]

Morphology

The adult form of M. streptocerca was discovered by Dr. Wayne M Meyers while working as a medical missionary in Africa. M. streptocerca adults have a unique posterior end that is bent, resembling the shape of a shepherd’s crook. This feature makes it possible for laboratory workers to distinguish M. streptocerca from other species of roundworms.^[2]

Life cycle

Life cycle of Mansonella streptocerca

The contraction of an M. streptocerca infection can be better understood through an understanding of its life cycle. The life cycle involves two stages: one involving a midge (genus Culicoides) and another involving a human host. First, a midge ingests a blood meal from a human host. This allows third-stage filarial larvae to enter the bite wound. Once inside the dermis, the larvae develop into adults, usually less than 1 mm from the surface of the skin. In terms of size, the females can reach 27 mm in length, whereas the males can be around 50 μm in diameter. These adults then produce nonperiodic microfiliariae, which habitate in the skin, but can also travel to the peripheral blood. These microfilariae are then passed onto the midge when the insect ingests a blood meal. Following the blood meal, microfilariae travel to the midge’s midgut through the hemocoel to the thoracic muscles. In the thoracic muscles, the microfiliariae develop into first-stage larvae, followed up by third-stage development. In this latter stage, the larvae travel to the midge’s proboscis, where it can subsequently infect another human host upon another blood meal ingestion. ^[3]

Infection

Distribution of Mansonella streptocerca based on published reports before the year 2000.

The infection of these roundworms typically causes no symptoms but may sometimes cause a mild dermatitis of the thorax and shoulders. M. streptocerca infections fortunately do not cause any nodules, skin disease, or ocular infections like that of Onchocerca volvulus. Due to the absence of nodules, differentiating between M. streptocerca and O. volvulvus infections are easier to diagnose.^[2]

See also

• Mansonelliasis.
• List of parasites (human)

References