Wuchereria Bancrofti

Wuchereria bancrofti Wuchereria bancrofti is a dreadful endoparasite of man; adults harbouring the lymphatic vessels and lymph nodes. Its life history is digenetic, as it involves a secondary host, the blood?sucking insects, i.e., the female mosquitoes of the genus Culex, Aedes or Anopheles; the secondary host for W. bancrofti in India and China is Culex pipiens, in Pacific Islands (except Fiji and New Caledonia) is Anopheles punctatus and in Polynesian Islands is Aedes polynesiensis. Periodicity of Microfilariae: The microfilariae of oriental countries like India and China exhibit nocturnal periodicity, as they appear in peripheral circulation periodically at night only generally between 10 pm and 4 am, but disappear inside during the rest of the day. It is believed that during daytime they retire inside the deeper blood vessels. In fact, the nocturnal periodicity of microfilariae is said to be related with the nocturnal feeding habit of their secondary host, Culex pipiens. Life History of Wuchereria Bancrofti: Wucheria bancrofti is digenetic, i.e., its life history is completed in two hosts; man is the main host, while female mosquito, usually Culex pipiens, is the secondary host. Mature male and female worms copulate in the lymph glands of man where they usually live. Since female worm is viviparous or ovoviviparous, it delivers numerous larvae called microfilariae. The microfilariae are born in very immature stage. However, microfilariae find their way into the blood stream where they can live for a considerable time without undergoing any developmental changes. As referred to, due to their nocturnal periodicity they are sucked up by the secondary host when it comes to take its blood-meal from the human body. The microfilariae, after reaching in the body of the secondary host, undergo further development to become infective to man. In fact, immediately after their entry in the stomach of mosquito, the sheaths around their bodies are shed off and then they penetrate the gut wall within an hour or two and migrate to the thoracic muscles. Here they become short and thick like sausages within 2 days having short spiky tails and measure 124 to 250 µm in length and 10 to 17 pm in diameter, they also possess rudimentary digestive tract. These are first stage larvae. Within next 3 to 7 days they grow rapidly and moult once or twice to become the second stage larvae; they measure 225 to 330 µm in length and 15 to 30 pm in diameter. Finally, by 10th or 11th day they become fully grown and are referred to as third stage larvae; they measure about 1500 to 2000 pm in length and 18 to 23 µm in diameter. This stage is infective to man. These larvae are inactive and come to lie in the labium of the mosquito. When the mosquito bites the warm and moist skin of man, the larvae creep out of the labium to the human skin, then they penetrate into the skin and finally come to settle down in the lymphatic’s. Here, they grow and become fully adult and sexually mature within a period of 5 to 18 months. These sexually mature worms start reproduction to repeat the life history again. The life span of adult worms is very long, probably ranging from 5 to 10 years. Diagnosis and Disease of Wuchereria Bancrofti: The infection of Wuchereria bancrofti is diagnosed by the presence of microfilariae in stained blood smear and by the biopsy of lymph nodes. The disease caused by the infection of W. bancrofti is, in general, referred to as wuchereriasis or filariasis. Pathogenicity of Wuchereria Bancrofti: In fact, the pathogenic effects seen during filariasis are caused by living or dead adult worms. A light infection does not produce serious effects; it causes filarial fever, headache and mental depression, etc. But, during heavy infection a large number of pathological effects are observed; in this condition they block the lymphatic vessels and glands causing lymphatic obstruction so that lymph cannot get back to the circulatory system. Hence, there occurs accumulation of lymph in the affected organs due to which they swell fantastically, a condition called lymphoedema. When they infect lymph nodes then they cause lymphadenitis, in lymph vessels they cause lymphangitis and after infecting epididymis and related areas they cause hydrocele. However, the affected organs sometimes become enormously enlarged, producing a tumour-like ugly look, this condition is called elephantiasis; the elephantiasis of feet, hands, scrotum, etc., are of common occurrence in the areas where W. bancrofti is prevalent. Treatment and Prevention of Disease Caused by Wuchereria Bancrofti: So far, no satisfactory treatment has been reported. However, heterazan and compounds of antimony and arsenic are used to reduce or eradicate microfilariae from the circulatory system. The only way of prevention is to protect our bodies from mosquito bite. 1. To control the mosquito population mosquito breeding grounds should be destroyed. This is achieved by spraying D.D.T., Gammaxene etc., clearing the unwanted bushes from the surroundings, spreading oil or kerosene in drain, swamps etc. 2. At the time of sleeping mosquito net should be used. 3. Mosquitoes can be prevented from biting by use of mosquito repellants, lotions etc. No proper medicine is available to eradicate the filaria worms. Mel, W. It is an arsenical preparation effective on adult worms. Heterazan compound (Diethyl carbamaide ) can be used to check microfilariae. MSb ( Paramelaminyl phenyl stibonate ) is effective on infective larvae and immature adult worm. 4. The National Filaria Eradication Programme (NFEP) launched by the Government of India has been effective in reducing the occurrence of filariasis in our country.