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Nasty Infectious Diseases You Want To Avoid - Filariasis

Updated on December 31, 2008

This is a group of tropical diseases caused by a range of parasitic roundworms and larvae that transmit disease to humans. About 200 million people are affected by filariasis, which occurs in tropic and subtropic areas of southeast Asia, South America, Africa, and the Pacific. Mosquitoes inject the worm larvae when they bite, which migrate to the lymph nodes where they develop into mature worms in about a year.

Some of the species live in the lymphatic vessels and block them, causing Elephantiasis (swelling of limbs with thickened, coarse skin). Another type of worm can be seen and felt just underneath the skin, which produces irritating and painful swellings called calabar swellings.

Bancroftian filariasis (Wuchereria bancrofti larial nematode) is spread widely throughout Africa, southern and southeastern Asia, the Pacific, and the tropical and subtropical regions of South America. Malayan filariasis (Brugia malayi filarial nematode) is found only in southern and southeastern Asia. Imported cases of the filariases may be found in the United States, especially among immigrants from the Caribbean and Pacific islands.

Cause - Bancroftian and Malayan filariases are transmitted to humans by the bite of an infected mosquito. The infective larvae that are transmitted into humans via the bite pass into the human lymph system, where they develop to maturity during a 6- to 12-month period. Fertilized mature female worms release embryos that develop into moving larvae (microfilariae), which appear in the human blood system at night only.

Symptoms - Initial inflammatory symptoms occur between three months to a year after the mosquito bite, with episodes of chills, headache, and fever. The fever is often associated with inflammation of the lymphatic system. There is swelling, redness, and pain in the arms, legs, or scrotum. An abscess may occur as a result of dying worms and secondary bacterial infection. Repeated episodes of inflammation lead to symptoms lead to obstruction of the lymphatic system, especially in the genital and leg areas. Chronic swelling stimulates the growth of connective tissue in the skin, causing massive permanent enlargement and deformity (elephantiasis). In Bancroftian filariasis the legs and genitalia are most often involved; in the Malayan variety the portion of the legs below the knees are affected, but the genitals are usually spared. The extent of the total enlargement can vary, but in extreme cases the legs or scrotum can expand to constitute almost half of the entire body mass of the infected individual.

Diagnosis - Blood specimen examination for filaria antigen, patient history, and appearance of the patient.

Treatment - The prognosis is good in early or mild cases, and if the patient can avoid reinfection. Three weeks of diethylcarbamazine cures the infection. However, reactions to large numbers of dying parasites are common (fever, malaise, nausea, and vomiting), so doses are usually low at first. Oral antihistamines may help control hives, and elastic stockings may help control swelling. However, no treatment can reverse elephantiasis. Surgery may ease massive enlargement of the scrotum.

Prevention - In infested areas, filariasis can be controlled by taking diethylcarbamazine or ivermectin preventively, and by using insecticides, repellents, nets, and protective clothing.


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