In this article we will discuss about Wuchereria Bancrofti:- 1. Structure of Wuchereria Bancrofti 2. Morphology of Wuchereria Bancrofti 3. Pathogenesis 4. Treatment of Disease 5. Control of Disease.
Structure of Wuchereria Bancrofti:
Wuchereria Bancrofti are filarial worms are long, thin tapering worms without lips around mouth. The oesophagus does not possess a bulb. The life cycle involves a blood sucking insect. Adults are filarial worms and they produce microfilariae.
This is also called as Filaria bancrofti. It lives in man in warm countries such as Arabia, India, Malaya, China, Korea, Japan, West Indies, Brazil and South Pacific Islands. In India, it mainly occurs along sea coast and along the banks of large rivers except Indus. It causes elephantiasis or wuchereriasis or Bancrofti’s filariasis. The filarial worm is a dreaded human parasite.
Morphology of Wuchereria Bancrofti:
The adult worm lives coiled up in the lymph glands and lymph passages of man. Adult female averages 82 mm long and 0.25 mm wide,. The male is smaller, average 40 mm in length by 0.1 mm in width. The head end is slightly enlarged. The mouth is a simple hole without lips. The mouth leads directly into oesophagus with a buccal cavity.
The oesophagus does not possess the bulges and constrictions. The vulva opens to the outside of the body in the midregion of the oesophagus. The male possesses two spicules of unequal length and a gubernaculum.
Microfilariae:
The females are ovo-viviparous, lay eggs with well developed embryos. The embryos are known as microfilariae having a length 275 um. They pass through lymph nodes and reach the main lymphatic trunks into the circulating blood.
Microfilaria stops further development in human beings. If they are not sucked by the mosquito (intermediate host) they die. The life span of microfilaria is about 70 days.
Microfilaria occurs as two biologically different forms. Larvae of oriental countries like India and China, show marked nocturnal periodicity i.e. they appear in peripheral blood during night (between 10 p.m. to 4 p.m.) They are transmitted by night-biting mosquitoes, Culex fatigans. Larvae of Pacific Islands like Polynesia show diurnal periodicity and they are transmitted by day-biting mosquitoes, Aedes polynesiensis.
In the larvae of oriental countries, microfilarial periodicity depend on alternate:
1. accumulation of the microfilariae in the lung capillaries, usually by day (active phase) and
2. approximately even distribution throughout all the circulating blood usually by night (negative phase).
Wuchereria bancrofti is a digenetic endoparasite, and complete life cycle in man, the definite host and mosquito (Culex & Aedes), intermediate host.
Stages in Mosquito:
Microfilaria is sucked from peripheral blood of man. The sheath of microfilaria digests in the stomach of mosquito. Then larvae penetrate stomach wall and reach thoracic and wing muscles. In next couple of days slender microfilaria changes to a thick, short sausage form with a short spiky tail. It has a rudimentary alimentary tract and is the first stage larva.
In 3 to 7 days, it grows and moults twice giving rise to second stage larva. Development proceeds forming body cavity, digestive system, genital organs etc. It is the third stage larva. It measures 1500 to 2000 um in length and migrate into the mosquito’s labium as infective stages.
When mosquito bites a fresh human host, infective juveniles comes out the labium on the skin of the victim. Filariform larvae penetrate through the wounds made by the mosquito. Worm larvae travel from the point of entry into human skin to the lymphatics. They grow and moult twice before becoming adults.
Pathogenesis of Wuchereria Bancrofti:
The pathogenic effect of Wuchereria bancrofti are produced by the adult either living or dead. Light infection produces no serious symptoms. It causes filarial fever, head ache and mental depression. In heavy infection, the adult, living or dead blocks lymphatic vessels and glands, resulting in various pathological conditions.
When the disease has caused the enlargement of such organs as the scrotum, breasts or legs, it is called elephantiasis. The adult worm causes an inflammatory reaction of lymphatic system or lymphangitis, obstruction of lymph in the organs results in their enlargement called lymphedema. The enlargement of lymphatic glands also lead to lymphadentis. Adult and microfilariae produce lesions in lymph node and also granulomas in spleen.
Occasionally hyperplasia of muscle fibres may be observed. Symptoms of filarial infection include fever, tenderness of infected parts, eosinophilia inflammation and transient swelling. Anxiety caused by fear is of considerable importance. Thick blood smears are preferable in examinations for microfilariae.
Treatment of Disease Caused by Wuchereria Bancrofti:
No proper medicine is available to eradicate the filaria worms.
However, following filarial drugs can be used:
1. Mel, W. It is an arsenical preparation effective on adult worms.
2. Heterazan compound (Diethyl carbamaide) can be used to check microfilariae.
3. MSb (Paramelaminyl phenyl stibonate) is effective on infective larvae and immature adult worm.
Control of Disease Caused by Wuchereria Bancrofti:
1. Eradication of mosquito by insecticide or by other control measures.
2. Reducing infection amongst mosquitoes.
3. Treatment of carriers by using heterozon and cyanine.
4. Movement from areas of infection.
5. Protection from mosquitoes, using mosquito net or mosquito repellent while sleeping in night, and
6. Control of breeding of mosquitoes.