Wuchereria bancrofti is a filarial parasitic worm (filariworm) that is the major cause of lymphatic filariasis or elephantiasis. They are nematodes belonging to order Filaroidea. The name Wuchereria bancrofti given on the honor of two scientists Otto Wucherer (physician) and Joseph Bancroft (parasitologist), they made a considerable contribution in the study of disease-causing worms.
Filarial worm lives in the lymphatic system of human, in which they interrupt the flow of lymph, causing a serious condition known as elephantiasis. In such condition the affected body part uncontrolled growth of cells occur this result in the accumulation of thick muscle on the diseased lymphatic gland. This was discovered by Monson, in 1878. In this article we specially focus on the habit and habitat, morphology, life cycle and elephantiasis of Wuchereria bancrofti.
Habit and Habitat
Filarial worm is a dreaded parasite, which is found in the blood and lymph of human. They are digenetic means complete its life cycle in two hosts. The intermediate host is usually a mosquito and the final host is adult man. The adult man act as the shelter of filarial worm, the adult filarial worms coiled up in the lymphatic glands and lymph passages of a man, where they often inhibit the flow of lymph.
Wuchereria bancrofti is transmitted by blood sucking insects usually Culex or Aedes mosquito. They are widely distributed throughout the world except Polar regions. It is found in India, Arabia, Malaya, China, Korea, Japan, East Indies, Brazil and south Pacific Islands, but is absent from Europe, North America, and Africa.
Morphology of Wuchereria bancrofti
- The structure of adult worms is filiform and cylindrical in shape.
- Ends of both body forms are terminate bluntly.
- They are coloured and ceramic white.
- Sexes are separate and distinct sexual dimorphism occurred.
- The female filarial worm measures 65 to 100 mm in length and 0.25 mm in diameter, while male filarial worm measures 40 mm in length and 0.1 mm in diameter.
- W. bancrofti has simple mouth apparatus without lips.
- The oesophagus or pharynx is divided into two distinct portions, the anterior muscular portion and posterior glandular portion.
- They do not have oesophageal bulb.
- Intestine of W. bancrofti, is simple as other nematodes.
- The female genital pore or Vulva is ventrally located in the pharyngeal region, which is provided with pyriform ejector mechanism or ovijector.
- The male has sharply curved ventrally structure located at the posterior end, that contain a number of genital papillae, caudal alae and two unequal copulatory spicules.
Life Cycle of Wuchereria bancrofti
The life cycle of Wuchereria bancrofti completed in two hosts. Blood sucking insects usually mosquito are intermediate host and human serve as final host. They include mainly four stages are Copulation, Larval development in man, Development in mosquito, and Infection of new human host.
Copulation: Copulation take place when both sexes (male and female) are present in same lymph gland of a host body. After copulation gametes of both sexes are fussed together to start the process of fertilization.
Larva Development of filarial worm in Human
- Viviparous female (probably ovoviviparous) developing numerous juveniles called microfilariae. They born in a very immature state.
- They are microscopic measuring about 0.2 to 0.3 mm long, surrounded by a thin circular sheath that containing inception of various adult structures.
- The body of microfilaria covered with flat epidermal cells and cytoplasm containing nuclei.
- The important structure seen from anterior end backwards, including future mouth, nerve ring band, nephridiopore, Renette cell, darkly staining inner mass, 4 large cells and future anus.
- Microfilariae released into lymph vessels, after enter in blood vessels, they actively circulated with blood and migrate to exist in deeper blood vessels of thorax. But do not undergoes further development until they sucked by intermediate host. i.e. insects or mosquitoes.
- In human blood, microfilariae show day and night periodicity called diurnal rhythm. During day they live in the deep situated large vessels, but during sleep at night they come in superficial or peripheral blood vessels.
- At this time, when mosquitoes suck the blood of infected person, microfilariae get transferred into the nocturnal mosquitoes which serve as intermediate host.
- After this place mosquitoes reverse the diurnal rhythm. Microfilariae of the human blood eventually dies or may sucked by the nocturnal mosquitoes.
Development of Microfilariae in Mosquitoes
- The development of microfilariae occurs in the thoracic muscular region or musculature wings.
- During development the microfilariae loss their sheath and penetrate into the stomach wall of mosquitoes, after that they migrate to thoracic region where they undergo metamorphosis and grow.
- They change their body forms as first to a plump sausage shaped, later to a more elongated form, and finally they changed into a long slender juvenile of the third infective stages.
- Microfilariae take two months to complete their all stages, with in about 10 days they reach the third stage larvae which are about 1.5 mm long. Infectious larvae now migrate to the mosquitoes’ labium (proboscis).
Infection in New Human Host
- When infected mosquito pierces its proboscis into another healthy human, the larvae come out of labium on the skin of victim and penetrate through wound made by mosquitoes.
- The larvae enter in the blood of new human host, juveniles reach into lymph glands and lymph passages, where they coil up and developed into adult forms.
- After it adults have ability to copulate each other and females deliver new microfilariae.
Filariasis or Elephantiasis
- The filariasis or elephantiasis is infectious parasitic disease caused by the Wuchereria bancrofti commonly known as filarial worm.
- They live in the lymphatic system of man, where they obstruct the flow of lymph, causing a critical condition know as elephantiasis.
- In Elephantiasis the limb or other body parts grow to enormous size.
Diagnosis of Filariods
- Diagnosis of filariods known as the study of microfilariae, it is examined after staining process.
- The different species of microfilariae are identified on the basis of their specific shape and morphological characters.
- A polymerase chain reaction also performed for the detection of minute fraction, as few as 1 pg, of filarial DNA.
- During diagnosis of some infected person microfilariae do not found in their blood. At this situation, test aimed to detect antigens from adult worms can be used.
- Ultrasonography is another method to the movements and noises produced by the movement of adult worms.
- X-ray examination can be also used to detect dead and calcified worms.
Pathogenesis of Wuchereria bancrofti
- Filarial parasites produce light infection but no serious symptoms.
- It causes filarial fever, headache, mental depression, etc.
- Heavy infection occurs when dead worms eventually block the lymphatic vessels and lymphatic glands, this result in the various pathological conditions.
- In such condition, it is mostly found that the immense swelling of the affected body parts, termed as elephantiasis or filariasis.
- Due to interruption in lymphatic vessels, lymph cannot get back in the circulatory system, It accumulates into organs and swells or enlarge the great proportions of the body such condition is called lymphedema.
- Lymphedema, generally affect in the lower limb, scrotum, legs, and mammary glands. If inflammations occur in lymphatic vessels it is termed as lymphangitis, and inflammation of lymphatic glands termed as lymphadenitis.
- In several cases it is noticed that abnormal connective tissue form in the affected areas to further labyrinthine the condition.
Therapy and Prevention
Scientists have not found a proper and satisfactory treatment of elephantiasis, but infection may reduce or eliminated by some eradication of microfilariae from the circulation by administering heterazan and compounds of antimony and arsenic. There are some preventive methods should be used for the protection against mosquito bites. Mosquito net and insect’s repellent are useful to protect against mosquito bites.
If you are interested to read invertebrates, also read this article – Paramecium: Classification, Habitat, Structure, Locomotion, Nutrition