Wuchereria is a nematode worm commonly known as filarial worm. It occurs in the lymphatic vessels, muscular tissues and glands of man and causes filariasis. The filarial worm is largely confined to the tropics and sub tropics, occurring in India, Southern China, Japan, Pacific Islands, W. Indies, South America and West and Central Africa. In India, the parasite mainly occurs along the sea coast and banks of large rivers. It has also been reported from Uttar Pradesh, Delhi, Punjab and Rajasthan. The common filarial worm is Wuchereria bancrofti.
MORPHOLOGY :
The worm is long, hair-like, cylindrical or filiform with a slightly swollen anterior end and a pointed posterior end. The body is transparent or creamy white in colour. The female measures about 60-100 mm in length and 0.25 mm in diameter. The tail end is narrow and abruptly pointed. The male measures 2.5 to 4 cm in length and 0.1 mm in thickness. The posterior end of the male is curved and provided with two unequal spinules. The mouth is very simple without any lip. The pharynx is without any bulb. Males and females remain coiled together and it is difficult to separate them.
Larva or Embryo (Microfilaria) :
The eggs develop within the female body and the larva is known as microfilaria, The larva is released into the lymphatic vessels of man. The larva is very active and move in any direction in the circulating It is colourless and transparent. The head is blunt and the tail is rather pointed. It measures about 290 um in length and 6 to 7 um in breadth.
Some of the morphological pecularities of microfilaria are as follows:
1.The larva is enclosed in a hyaline sheath. The sheath is about 359 um in length. Thus, it is much longer than the body of larva, and therefore, the larva can easily move forwards and backwards within the sheath. This sheath is actually the chorionic envelope of the egg.
2.There are granular somatic cells or nuclei present in the central axis of the body from the head to the tail end. The distinguishing feature of microfilaria bancrofti is that at the anterior end, the granules are absent at posterior end.
3. Another distinguishing feature is that the granules are discontinuous or broken at some definite places, such as :
(i) at anus or cloaca — posterior V-spot pr tail spot;
(ii) anterior V spit which represents the rudimentary excretory systern and
(iii) nerve ring, an oblique space.
4. The so-called ‘genital cells” or G - cells are present towards the posterior end. These are G-cell 2, 3 and 4 situated in front of the anal pore, and C-cell 1 is situated further in front.
LIFE CYCLE :
Wuchereria is digenetic, that is, it requires two hosts to complete its life Cycle. The primary or the principal host is the man and the secondary or intermediate host is the mosquito culex, Aedes and Anopheles.
The adult worms both the male and the female occur in the lymphatic system of man. They become matured in about five to eighteen months. The female after fertilization does not lay eggs. The eggs develop within the female body and the larvae known as microfilaria are released by the female into the lymphatic vessels. These larvae then migrate to the peripheral blood stream of man. The microfilaria is colourless and transparent. It is bounded by a delicate membrane or sheath. It measures about 225 - 300 um in length and 10 um in diameter. The microfilariae remain in the capillaries of the lungs, heart, kidney and their arteries during the day time, But they appear in the peripheral blood stream, that is, in the skin capillaries during night between 10 P.M. and 2 A.M. Further development of the larvae take place in the body of the mosquito.
TREATMENT :
The treatment of filarial infection includes use of drugs having filaricidal action or microfilaricidial action. Thus, the drugs are divided into three main groups. These are:
1. Drugs acting on microfilaria Diethylcarbamazine citrate (DEC) is a microfilarial drug. It is a synthetic piperazine derivative. It has no direct lethal action and, therefore, it does not kill microfilariae, but it sensitises microfilariae so that they can be engulfed by phagocytes and removed from circulation. The drug is available as tablets and is administered orally. The drug is given in doses depending on the body weight of the infected person for 2 to 3 weeks. The drug has some side effects like nausea, fever, shortness of breath. But the side effects do not last long. A new drug known as Ivermectin has been found to be very successful in some areas, However, the result of this preliminary observation must be tested further for large scale use of the drug. If successful, this drug will be a new tool for treating filarial infection. It can be used as a single dose and it is likely that the drug may even kill the adult worms along with microfilariae.
2. Drugs acting on adult worms The drug Mel. W is a water soluble form of Mel B (Melarsoprol) which has been originally introduced for the treatment of African trypanosomiasis. It contains trivalent arsenic and is given by intramuscular injection. The drug has been found to kill adult filarial worms. However, further investigations regarding the toxicity of the drug must be done for finding out effectiveness of the drug. 3. Drug acting on infective larvae and immature adult worms The drug para-melaminyl stibonate (MSb) has been found to be effective in killing both the infective larvae and immature adult worms.
PROPHYLAXIS :
Filariasis can be controlled by taking following measures :
1. Vector control (Mosquito control) Mosquitoes can be controlled by various means, such as: i) destroying mosquito larvae by introducing larvivorous fishes in stagnant water-bodies which are the breeding places of mosquitoes. The fishes such as Labistes (guppy) and Gambusia feed voraciously on mosquito larvae. ii) destroying mosquito larvae with the help of bacterial insecticide Bacillus thuringiensis var israelensis BR 14. It kills selectively only mosquito larvae and is ecofriendly. iii) using organs-phosphate and organs-chlorine insecticides for killing mosquitoes. But the chemical insecticides are not ecofriendly and the vector becomes resistant to the insecticides shortly. iv) adopting an integrated control measure for total destruction of vectors. This can be done by employing biological control as well as chemical control.
2. Personal protection (Protection against mosquito bites)
An individual or a family can be protected from mosquito bites if a few simple measures are taken. These are: i) Use of bed-nets Ordinary bed-nets or bed-nets impregnated with insecticides such as premethrin, deltomethrin etc. have been found to be effective. ii) Screening windows with mosquito-netting Fixing mosquito netting in the windows also prevent mosquito biting. iii) Applying mosquito repellent Applying mosquito repellent in the form of paste or liquid chemicals to the exposed part of the body or to the clothes drive away mosquitoes. Neem seed oil, citronella oil etc. are effective.
3. Treatment of carriers The drug hetrazan has been found to be effective in treating carriers of filarial worms.
4. Treatment of persons infected with microfilarae in the blood Along with vector control, treating the infected persons with microfilariae with Diethylcarbamazine citrate (DEC) has been found to be very effective in controlling spread of the disease.
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