Loiasis

Life Cycle and Morphology

Life Cycle

The lifecycle of Loa loa is very similar to that of any other filarial parasite. The parasite is transmitted to humans via the bite of an infected tabanid (for specifics, please refer to the transmission and vector page). The infective larva enters the wound and develops into maturity within the subcutaneous tissue of the human. These adult worms then migrate throughout the subcutaneous tissue causing Calabar swellings, and occasionally migrate across the conjunctiva of the eyes or around the nose, causing quite a lot of pain. Males and females mate, and the females produce microfilariae that circulate throughout the blood with a diurnal periodicity that peaks during mid day. These microfilariae are then ingested by the vector, i.e. the mango fly, and develop into infective larvae within them.

Incubation Period

The incubation period is ten to twelve days to reach infective stage in mango fly. infection is long lived and the prepatent period in humans in some cases may be as long as ten years, although it is generally closer to one year

Morphology

The picture to the left is of a microfilaria, and these are 250 - 300 micrometers long and sheathed, with a body nuclei continuous to the tip of the tail, unlike W. bancrofti.

Adult males are 2 - 3.5 centimeters long, and adult females are 5 - 7 centimeters long. Neither of them is wider than 0.5 millimeters.

Information is mostly taken from Markell and Voge's Medical Parasitology, 8th Ed.

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