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Wuchereria bancrofti

Common name. Bancroft's filaria

Disease. bancroftian filariasis

Geographic distribution. India, Pakistan, Thailand, China, the Philippines, New Guinea, Central Africa and Nile delta, South and Central America

Life cycle. The Culex, Aedes, and Anopheles species of mosquitoes serve as the intermediate host and vectors of W. bancrofti. In the human host the adult worms take up residence in the lymphatics, where they lay their microfilariae. The microfilariae liberated in the lymph, find their way into the thoracic duct and then to the blood circulation.

Morphology. The adults are elongated, thread-like worms, measuring 35 to 40 x 0.1 ㎜(male) and 90 to 100 x 0.25 ㎜ (female). The microfilariae show nuclei in their body after staining and various internal structures can also be seen. A thin and delicate sheath surrounds the organism. The anterior end is blunt and round. The posterior end culminates into a point that is free of nuclei.

Pathology and Clinical Symptoms. Most of the adult patients experience no symptoms. Sometimes lymphangitis is severe and is accompanied by high fever and headache. In addition to lymphatic involvement, some patients may show epididymitis and orchitis. In the intervening period, repeated attacks of acute lymphangitis may continue. The classical symptoms of this stage are elephantiasis, hydrocele and chyluria.

Diagnosis. The examination of fresh Giemsa-stained blood for W. bancrofti microfilariae serves as the laboratory diagnostic method of choice. Samples should be collected during night time, because this organism exhibits nocturnal periodicity. Serologic methods are also available commercially.

Treatment. Diethyl-carbamazine citrate (DEC) and ivermectin (Mectizan) have known effectiveness against W. bancrofti. In patients with elephantiasis, surgical procedures are required as chemotherapy which can not reverse the fibrotic changes.

Prevention. Unlike malaria, a short stay in an endemic area is usually of no significance. Mass chemotherapy with DEC is an effective method of controlling the infection in a given population.