The name elephantiasis refers to the extreme swelling of human body parts affected by this roundworm (nematode). Elephantiasis occurs in a broad equatorial belt around the world, and was present historically in tropical Australia.
The infection is carried by mosquitoes which take up the juvenile worms while biting an infected human. After development in the mosquito the parasite is then able to be transmitted to another human host.
The larval stage worms are deposited on the skin while the mosquito is biting. The larvae enter the skin via the wound made by the mosquito, migrate through the tissues and into the peripheral lymphatic system. The worms typically mature in the larger lymph vessels, usually in the lower limbs and the genital region.
Three stages of infection follow:
- incubation or asymptomatic phase
- acute inflammatory phase
- obstructive phase.
After mating the adult female worms release many juvenile worms, called microfilariae, which are carried in the lymph back to the heart and then circulate through the bloodstream. They are first detected during the acute inflammatory phase and the number of microfilariae in the peripheral blood varies according to the time of day. The greatest number of microfilariae are found at the times when their vector, the mosquito, is most likely to be feeding, generally during the night.
During the obstructive phase the changes in the lymphatic system caused by the adult worms become most apparent. The normal flow of lymph becomes greatly restricted and results in swelling of the lymph ducts, secondary bacterial infections and infiltration of the affected areas with fibrous connective tissue development. If the afflicted person is subjected to repeated infections then the condition may progress to the classical manifestation of elephantiasis with thickened skin and grossly swollen body parts.
Joseph Bancroft, a Brisbane physician, recognised in 1876 that Elephantiasis is caused by round worms. His discovery was later honoured when the parasite was named Wuchereria bancrofti.
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