CLASS : PHASMIDIA
Wuchereria bancroftii is commonly called the filarial worm as it causes filariasis in human beings. It is a digenetic , dimorphic , pseudocoelomate , histozoic and pathogenic parasite. It lives in the lymph vessels and lymph nodes of man. It is widely distributed in tropical and subtropical countries like India , west Indies , Southern china ,Japan , West and South Africa and America.
Demarquay (1866) collected the larval stages of the parasite from the hydrocoelic fuid of man . Wucherer (1866) collected the larval stages from Chylorous urine. Lewis (1872) collected larvae from human blood. Bancroft (1876) found the adult female.`
- The body of Wuchereria is long , narrow , thread like and transparent.
- It is creamy white in colour.
- The anterior end is blunt and the posterior end is pointed.
- Mouth is present at the anterior end and is without any lips.
- The excretory pore occurs at the anteroventral part of the body.
- Mouth leads into pharynx which is muscular anteriorly and glandular posteriorly.
- The digestive and reproductive systems float freely in the body cavity .
- The worm is dimorphic with male and female species. Sexual dimorphism is distinct.
- It is shorter and thinner , measuring 2.5 to 4.0 cm in length and about 0.1 mm in diameter.
- It has three apertures viz., mouth , excretory pore and cloacal aperture.
- The posterior end is curved ventrally with a cloacal aperture. Cloacal aperture is the common opening for digestive and reproductive system.
- A pair of unequal , chitinous pineal spicules or copulatory spicules is present in the cloacal region.
- It is longer and thicker measuring about 8-10 cms in length and 0.2 to 0.3 mm in breadth.
- Its posterior end is straight , rounded and truncated with an anal aperture.
- It is provided with four apertures viz., mouth , excretory pore and vulva at he anterior part and anus at the posterior part .
- Copulatory spicules are absent .
- The larval form of wuchereria is mcrofilaria .
- It is colourless with blunt anterior end and pointed posterior end.
- It measurre about 290 microns in length and 6-7 microns in breadth.
- Body is covered by a loose sheth , which is formed by the stretching of the egg shell. Hence it is sheathed larva.
- the body wall is made up of a single layer of flattened epithelial cells .
- A stylet is present at the anterior end of the larva , where the mouth is formed during further development.
- The larval body also contains
a) A nerve ring – behind the stylet around the neck of oesophagus ,
b) Renette cells – behind the stylet.exretory cells ,
c) Excretory bladder ,
d) Exretory pore ,
e) Visceral cell moss – representing rudimentary alimentary canal ,
f) Four large cells called G-cells – occur in two groups of three in one group and one in one group.
g) Primitive gut anal / cloacl aperture – at the posterior end.
- Microfilaria larvae after entering the blood, they move to the peripheral blood vessels during night 10pm–04am and reside in the deeper blood vessels during day time. This kind of tendency exhibited by microfilaria larva is called nocturnal periodicity.
- The nocturnal periodicityof microfilaria coincides with the prevalence of osquitoes during night time.
- Further development of the larva occurs only on reaching the intermediate host i.e., the female culex mosquito.
- When the mosquito sucks the blood, along the blood, the microfilaria larvae enter the mosquito and accumulate around the anterior end of the stomach.
- Microfilaria larva is the infective stage of Wuchereria to intermediate host i.e., female culex mosquito.
LIFE CYCLE :
Wchereria bancrofti completes its life cycle in two hosts namely man and female culex mosquito.
- Both male and female worms are found coiled together in the lymphatic vessels of men .
- After copulation the female releases the sheathed microfilaria larva into the lymph of man.
- Each sheathed microfilaria larva measures 0.2 – 0.3 mm in length.
- It is surrounded by a loose cuicular sheath which is supposed to be the modified shell .
- They migrate to the blood circulation and reside in the deeper blood vessels during the day time. They move to the peripheral blood circulation during the night between 10 pm – 4 am . this tendency is referred to as nocturnal periodicity.
- when a female Culex mosquito sucks the blood of an infected person, they enter the gut of mosquito.
- They die if they are not transferred to mosquito within 70 days.
- the mid gut of mosquito , the sheath of te larva is dissolved within 2 to 6 hours of infection.
- The ex-sheathed microfilaria larva penetrates the gut wall and reaches the haemocoel of mosquito.
- From there , it reaches the thoracic muscles and transforms into a sausage shaped larva within two days. It is called the first stage microfilaria.
- This undergoes two moultings within 10 to 20 days and transform into a long , infective 3rd stage microfilaria .
- It reaches the labium of the mosquito.
IN MAN AFTER THE INFECTION :
- When the infected mosquito bites a man , the 3rd stage microfilaria larvae enter the blood circulation of man and finally reach the lymphatic vessels
- Here they undergo the 3rd and 4th moultings to produce young fiarial worms. They attain sexual maturityt within 5 to 18 months.
PATHOGENECITY OF WUCHERERIA:
- Pathogenesis of Wuchereria is produced either because of live or dead worms.
- Light infection causes filarial fever which is characterized by headache , mental depression and increase in the body temperature .
- In general , the infection of filarial worm causes inflammatory effect in lymph vessels and lymph glands. Inflammation in the lymph vessels is called lymphangitis ( Gr., angeos – vessels , itis – inflammation) and that of lymph glands is called lymphngitis ( Gr ., adenos – gland , it is – inflammation).
- In case of heavy infection, the accumulation of dead worms blocks the lymph vessels and lymph glands resulting in immense swelling. This condition is called lymphoedema ( Gr., oiedema – a swelling ) . It is noticed in the extremities of limbs , scrotum of males and mammary glands in females.
- Rupture and flow of lymph out of lymph vessels is called lymphorrhage.
- Fibroblasts accumulate in these tissues and form the fibrous tissue. In severe cases , the sweat glands of the skin in the affected regions disintegrate and the skin becomes rough. This terminal condition is referred to as elephantiasis.
- The dilation of lymph vessels is known as lymphangiovarix.
The drugs that act against filariasis are of three types :
- Drugs for adult worms : Mel W
- Drugs for microfilariae: Diethyl carbamazine( Hetrazan)
- For infective larvae and immune adult worms : Para-melaminyl phenyl stibornate ( MSB- 1.5%).
Controlling malaria depends upon the prevention of spread of mosquitoes. It can be achieved by the following methods :
- filling the stagnant water bodies like ditches , pools etc.,
- Closing the overhead water tanks properly.
- Spraying DDT,BHC etc., at the mosquito dwelling places.
- Spraying kerosene and pyrethrum oil over the water bodies , which form a thin layer over the water surface and prevent the diffusion of oxygen cusing hypoxia or anoxia and death of mosquito larvae.
- Biological control includes the release of larvivorous fish like Gambusia , growing insectivorous plants like Utricularia.
- Using msquito nets or mosquito repellants is also of much help in preventing the spread of mosquitoes.