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. Named for Otto Wucherer and Joseph Bancrofti. If the infection is
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| W. Brancrofti (m.scopic view) |
Limited treatment modalities exist and no vaccines have been developed.
It belongs to phylum Aschelmenthes, Class Nematoda and it is
a dreadful endoparasite of men. It is largely confined to trophic and subtrophic,
in India, Japan, Central Africa and South Africa.
Structure:-
The adult worm are long hair like transferent often creamy white in colour.
They are thread like in shape having tapering end but head and terminates in a
slightly rounded swelling.
The male measures 2.5-4 cm in length. In male tail end is curved
ventrally and contain spicules of unequal length and a number of genital papillae.
The female measures 8-10 cm in length and 0.2-0.3 mm in thickness
having an pointed and narrow tail end.
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| Computerized view |
with difficulty. The female genital pore or valva located ventrally in the pharyngeal
region which is provided with a pyriform ovijector. its mouth is simple without lip.
pharynx is divisible into an anterior muscular and posterior glandular part.
Oesophagus bulb is absent.
The microfilaria are developing stage in human body. They are very active
and can move both with and against the blood stream. They have colourless
transparent body with blunt head and rather pointed tail. they are covered by a
hyaline sheath, which is much longer than their body. In addition it shows various
structure such as the future mouth, nerve ring band, nephridiopore and dark coloured
inner mass and 4 cell of future anus.
The microfilaria do not undergo any further development in human body
unless they are taken up by the suitable secondary host. If these are not sucked up
by mosquitoes, they die out as they have a life span of about 70 days in human body.
Life History:-
The life history of W. Bancrofti is digenetic as it involve a secondary host, the female
mosquito of this genus culex, Anophilish.
Mature male and female worm copulate in the lymph gland of men and the
female liberate active embryo but are ovoviviparous. the microfilaria are born very immature.
However, they find their way into the blood stream where they can live for a considerable
time without undergoing any developmental changes.
In the oriental countries, the microfilaria show nocturnal periodicty, appear
in the peripheral circulation at night between 10 pm to 4 am.
If and when it is sucked up by its intermediate host the mosquito, the
microfilaria goes to further development and became infective to man. Immediately
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| Plasmodium life cycle of W.B |
penetrate the gut within an hour or two and migrate to the thoracic muscle. In the
two days they changes thick short souges shaped from with short spicules measuring
124-250(meu) in length and 10-70(meu) in breadth. it possesses a rudimentary
digestive track. Within 3-7 days the first stage larva grows rapidly, moult once or twice
to become second stage larva measuring in length of 15-30 cm .
By the 10th or 11th day the process of metamorphosis became complete.
The tail lost, the digestive system, the body cavity and genital organ are fully developed.
This is the infective stage to man which enter in proscis sheath of mosquito. There may
several larval coiled up in mosquito labium waiting for an opportunity to infect man while
it having its blood meal.
They creeps out of the labium of mosquito and penetrate into skin and came to
settle in lymphatic gland. Here they grow and become sexually mature within a period of
5-10 months.
The time taken for complete development in mosquito varies from 10 - 20 days
or more depending on atmosphere, temperature, humidity and also to a certain extent on
the series of mosquito.
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| Life cycle of W. Bancrofti |
Pathogenecity:-
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| a lady suffering from elephantiasis |
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 occur accumlation of lymph in the effected organs due to which they swell
fantastically, a condition called lymphoedema. When they infect lymph nodes then they
cause lymphadenities, in lymph vessells they cause lymphangities and after infecting
epididymis and related areas they cause hydrocele. However, the affected organs
sometimes become enormously enlarged, producing a tumor like ugly look; this condition
is called elephantiasis; the elephantiasis of feet, hands, scrotum etc are of common
occurance in the areas where Wuchereria Bancrofti is prevalent
Source:- Zoology-Vertebrate (Jordan)
