Structure and life history of Wucheria bancrofti

Structure ofWucheria Bancroft:

The adult worm is long, hair, like, transparent and often creamy white in colour. They are filiform and cylindrical in shape and body ends terminate bluntly .Sexes are separated and there is sexual dimorphism is distinct. The male worm measure 2.5 to 4 cm in length and 0.1 mm in diameter heaving a ventrally curved tail-end containing a number genital papillae and two spicules of unequal copulatory spicules.The female worm measure 8 to 10 cm in length and 0.2 to o.3 mm in diameter leaving a narrow and abruptly pointed tail. The female genital pore or valve is located ventrally in the pharyngeal region and is characterised provided with a pyriform objector The male and female coiled together ; females are usually more in number than the males. Its mouth is simple without lips, the pharynx is divided into an interior muscular and posterior glandular part, the oesophageal bulb is not found and the intestine is like those of other nematodes. The microfilaria is covered in a hyaline sheath followed by cuticula being lined by flattened subcuticular cells or epidermis and an inner column of cytoplasm containing nuclei.However, various structure from anterior end downward is further mouth or oral stylet, nerve ring band, nephridiopore, rented cells and a dark coloured inner mass and four cells of the further anus. The microfilariae do not undergo further development in the human body unless they are taken up by their suitable secondary host. If these microfilariae are not sucked up by the mosquito, they die in the course of time. Their life span in the human body is probably 7o days.

Life history of Wucheria Bancroft

Wucheria Bancroft is a digenetic parasite i.e life history is complete in two hosts. Final host is the man who harboring the adult worm, while the intermediate host is the blood sucking insect usually a mosquito. Life history takes place by copulation, larval development in man, development in insect , infection of a new host, which is discussed below.

1.Copulation: Copulation takes place when individual of both sexes are present in the same lymph gland.

2.Larval development in man:Female is viviparous mostly ovoviviparous releasing numerous of juveniles called microfilaria.They are microscopic about 0.2 to 0.3 mm long, surrounded by a dedicated cuticular sheath and containing rudiment of a various adult structure.The body of microfilaria consists of a surface covering of flattened epidermal cells and an inner column of cytoplasm containing nuclei. Microfilaria, discharge into lymph vessels soon enter the blood vessel and circulate with blood showing active movement. They migrate to reside ultimately in a deeper blood vessel to the thorax. But they do not migrate further development until sucked by the intermediate host.Mosquito

In the blood of man microfilaria show day and night periodicity,/ called diurnal rhythm. By they live in the larger deep-seated blood vessel, but at night or during sleep they came into a superficial or peripheral vessel in skin, to be sucked by the doctoral mosquito (culex or Aedes) which serve as intermediate host.In the place where there are diurnal mosquitoes, they reverse this periodicity.Microfilaria in human blood eventually dies unless ingested by the intermediate host sucking blood from infected humans.

3.Development of mosquito:In the stomach of mosquito microfilaria loses their sheaths, penetrate the stomach wall and migrate to thoracic muscle or wing musculature where they undergo metamorphosis and grow.They change first to a plump sausage shaped organism, later to a more elongated form, and finally to a long slender juvenile of the third infective stage. Microfilaria undergoes two moults in about 10 days to reach the third stage larva which is about 1.5mm long. Infective juveniles now migrate into mosquito's labium.

4. Infection of a new human host:When this mosquito pierces its proboscis into another potential human host, the infective juveniles come out of labium on the skin of victim and enter it.They probably penetrate through the wound made by the mosquito and enter blood of a human host. In the new human host, juveniles pass into lymph glands and lymph passages, where they coil up and develop into the adult form. Adults copulate and female develop microfilariae.

Diagnosis:

Diagnosis of microfilaria involves the study of microfilariae after staining. Microfilariae of different species are identified after their specific shape and morphological character.

Pathogenesis and symptom:

It causes several fever mental depression, headache etc. In heavy infection lead to accumulation of living or dead worms eventually blocks the lymphatic vessel and glands, resulting in various pathological condition. Most spectacular is the immense swelling of the affected body parts, termed elephantiasis.Due to the lymphatic obstruction lump cannot get back into the circulatory system, accumulated into an organ and causes lower limbs scrotum in male legs and mammary gland is affected.

Treatment and control

Treatment:Treatment of infected patient done using a drug called diethylcarbamazine(DEC). The medicine killed the microfilaria and sometimes adult worm in the lymph vessels. It has also some side effect. DEC only be used , if Uche ria is identified. Another drug ,ivermectin ,can also be used, although it kills the only microfilaria.

Prevent:To prevent new infections, avoid infective mosquito between dusk and dawn (the time when they mostly feed). A mosquito net can be applied all around the bed. Mosquito repellent applied on your skin or the use of long trousers and sleeves might keep the mosquito away. Mass treatment is given to the whole community in some endemic countries . Programs to eliminate lymphatic filariasis in more than forty countries are decreasing the risk of infection.

Control: No proper or satisfactory treatment is known yet. Infection may be reduced by eradication of microfilaria from circulatory by administering hetero and compound of antimony and arsenic.An important preventive measure from mosquito bites.

Reference:

Aggarwal Sarita. A Text Book of Biology,New Delhi.: Madhuban Educational Books, 2011.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L., Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

http://www.biologydiscussion.com/

http://www.parasitesinhumans.org/

https://web.stanford.edu/class/

https://en.m.wikipedia.org/wiki/Wucheria-bancrofti