Loa loa filaria
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Filaria loa Cobbold, 1864 |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Loa loa is the filarial nematode (roundworm) species that causes Loa loa filariasis. Its geographic distribution includes Africa and India.[1] L. loa is one of three parasitic filarial nematodes that cause subcutaneous filariasis in humans. The two other filarial nematodes are Mansonella streptocerca and Onchocerca volvulus (causes river blindness). Maturing larvae and adults of the eye worm occupy the subcutaneous layer of the skin ; the fat layer; of humans, causing disease. The young larvae develop in horseflies of the genus Chrysops (deer flies, yellow flies), including the species C. dimidiata and C. silacea, which infect humans by biting them.
Pathophysiology
Morphology
Loa loa worms have a simple body including a head, body, and tail. Males range from 20mm to 34mm long and 350μm to 430μm wide. Females range from 20mm to 70mm long and are about 425μm wide.[1]
Life Cycle
The vector for Loa loa filariasis are flies from two species of the genus Chrysops, C. silacea and C. dimidiata. During a blood meal, an infected fly (genus Chrysops, day-biting flies) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1). The larvae develop into adults that commonly reside in subcutaneous tissue (2). The female worms measure 40 to 70 mm in length and 0.5 mm in diameter, while the males measure 30 to 34 mm in length and 0.35 to 0.43 mm in diameter. Adults produce microfilariae measuring 250 to 300 μm by 6 to 8 μm, which are sheathed and have diurnal periodicity. Microfilariae have been recovered from spinal fluids, urine, and sputum. During the day they are found in peripheral blood, but during the noncirculation phase, they are found in the lungs (3). The fly ingests microfilariae during a blood meal (4) . After ingestion, the microfilariae lose their sheaths and migrate from the fly's midgut through the hemocoel to the thoracic muscles of the arthropod(5). There the microfilariae develop into first-stage larvae (6) and subsequently into third-stage infective larvae (7). The third-stage infective larvae migrate to the fly's proboscis (8) and can infect another human when the fly takes a blood meal (1).
References
- Taxonomy Browser: Loa Loa. National Center for Biotechnology Information (NCBI).