Tuesday, December 22, 2009
wucheraria bancrofti life cycle- fob-animal biology- btechbiotechnology- 1st year
Wuchereria bancrofti or Filaria, is a parasitic filarial nematode worm spread by a mosquito vector. It is one of the three parasites that cause lymphatic filariasis, an infection of the lymphatic system by filarial worms. It affects over 120 million people, primarily in Africa, South America, and other tropical and sub-tropical countries . If the infection is left untreated it can develop into a chronic disease called Elephantiasis. Limited treatment modalities exist and no vaccines have been developed.
Different species of the following genera of mosquitoes are vectors of W. bancrofti filariasis depending on geographical distribution. Among them are: Culex (C. annulirostris, C. bitaeniorhynchus, C. quinquefasciatus, and C. pipiens); Anopheles (A. arabinensis, A. bancroftii, A. farauti, A. funestus, A. gambiae, A. koliensis, A. melas, A. merus, A. punctulatus and A. wellcomei); Aedes (A. aegypti, A. aquasalis, A. bellator, A. cooki, A. darlingi, A. kochi, A. polynesiensis, A. pseudoscutellaris, A. rotumae, A. scapularis, and A. vigilax); Mansonia (M. pseudotitillans, M. uniformis); Coquillettidia (C. juxtamansonia).
During a blood meal, an infected mosquito introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound .
They develop in adults that commonly reside in the lymphatics .
The female worms measure 80 to 100 mm in length and 0.24 to 0.30 mm in diameter, while the males measure about 40 mm by .1 mm. Adults produce microfilariae measuring 244 to 296 μm by 7.5 to 10 μm, which are sheathed and have nocturnal periodicity, except the South Pacific microfilariae which have the absence of marked periodicity.
The microfilariae migrate into lymph and blood channels moving actively through lymph and blood .
A mosquito ingests the microfilariae during a blood meal .
After ingestion, the microfilariae lose their sheaths and some of them work their way through the wall of the proventriculus and cardiac portion of the mosquito's midgut and reach the thoracic muscles .
There the microfilariae develop into first-stage larvae and subsequently into third-stage infective larvae .
The third-stage infective larvae migrate through the hemocoel to the mosquito's prosbocis and can infect another human when the mosquito takes a blood meal .
A blood smear is a simple and fairly accurate diagnostic tool, provided that the blood sample is taken during the period in the day when the juveniles are in the peripheral circulation . Technicians analyzing the blood smear must be able to distinguish between W. bancrofti and other parasites potentially present.
A polymerase chain reaction test can also be performed to detect a minute fraction, as little as 1 pg, of filarial DNA .
Sometimes infected people do not have microfilariae in their blood. As a result, tests aimed to detect antigens from adult worms can be used.
Ultrasonography can also be used to detect the movements and noises caused by the movement of adult worms .
Dead, calcified worms can be detected by X-ray examinations.
The severe symptoms caused by the parasite can be avoided by cleansing the skin, surgery, or the use of therapeutic drugs, such as Diethylcarbamazine(DEC), ivermectin, or albendazole. The drug of choice however, is DEC, which can eliminate the microfilariae from the blood and also kill the adult worms with a dosage of 6 mg/kg semiannually or annually . A polytherapy treatment that includes ivermectin with DEC or albendazole is more effective than each drug alone. Protection is similar to that of other mosquito spread illnesses; one can use barriers both physical (a mosquito net), chemical (insect repellent), or mass chemotherapy as a method to control the spread of the disease.