Main » Infectious diseases » Arthropod-borne Infection » Loaiasis
Loaiasis is confined to Africa, extending from the Gulf of Guinea in the West to the Great Lakes in the East. Infection with an almost identical parasite is common in these areas in certain monkeys such as the mandrill.
Distribution of loaiasis.
Photo 1. Female Chrysops dimidata biting. Tabanid flies of the genus Chrysops, particularly C. dimidiata and C. silacea, transmit loaiasis. The flies (1) (X4) live in the canopy of primary rain forests (2).
Photo 2. Canopy of primary rain forests.
Photo 3. Calabar swelling. Recurrent large swellings lasting about three days are characteristic and indicate the tracks of the migrating adults in the connective tissue. They are most frequently seen in the hand, wrists and forearm. A marked eosinophilia (60 to 90%) accompanies this phase of the infection.
Photo 4. Adult Loa loa in the eye. The movement of the adult worm under the conjunctiva gives rise to considerable irritation and congestion. The adult is arrowed in this figure.
Photo 5. Extraction of worm. The adult worm can be extracted with fine forceps after anaesthetising the conjunctiva.
Photo 6. Tail of male Loa loa.
769 Loa Loa cycle. When the Chrysops fly bites, the infective third-stage larvae (a) enter the vertebrate host (b) where they mature into adults (c) within about one year. The adults live for 4 to 12 years. The females (about 7 cm long) migrate through the subcutaneous tissues and may cross the front of the eye under the conjunctiva (d). Microfilariae (f) develop from larvae (e) in the female and circulate in the blood with which they are picked up by another fly (g). In the gut of the fly the microfilariae (h) exsheath and enter the fat bodies in which they mature first to 'sausage-like' forms (i,j), then infective third-stage larvae (a). The larvae infect a new host when the Chrysops takes another blood meal.
See also: Nematodes — the filariases.
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