FILARIASIS

Filariasis is caused by several round, coiled and thread-like parasitic worms belonging to the family filaridea. These parasites after getting deposited on skin penetrate on their own or through the opening created by mosquito bites to reach the lymphatic system. The disease is caused by the nematode worm, either Wuchereria bancrofti or Brugia malayi and transmitted by ubiquitous mosquito species Culex quinquefasciatus and Mansonia  annulifera/M.uniformis respectively. The disease manifests often in bizarre swelling of legs, and hydrocele and is the cause of a great deal of social stigma.

Brugian filariasis: Lymphadenitis (swollen and painful lymphnode) occurs episodically, most commonly affecting one inguinal lymph node at a time. The infection lasts for several days and usually heals spontaneously. The frequency of episodes may vary from 1-2 attacks per year to several attacks per month. Sometimes lymphadenitis is followed by a characteristic retrograde lymphangitis. The infection may spread to the surrounding tissues, and occasionally involves the whole thigh or entire limb. The infected lymph node may become an abscess, ulcerate, and heal with  fibrotic scarring. The acute clinical course with its complications may last from several weeks to 3 months. Characteristically, elephantiasis involves the leg below the knee but occasionally it affects the arm below the elbow. Genital lesions or chyluria (milky colour urine) do not occur in brugian filariasis.

Bancroftian filariasis: The lymphatic vessels of the male genitalia are most commonly affected in bancroftian filariasis, producing  episodic funiculitis (inflammation of the spermatic cord), epididymitis and orchitis. Adenolymphangitis of the extremities is less common.  Hydrocele is the most common sign of chronic bancroftian filariasis, followed by lymphoedema, elephantiasis and chyluria. The swelling involves the whole leg, the whole arm, the scrotum, the vulva or the breast. The fluid of hydrocele and chyluric patients may contain microfilariae, even when they are absent from the blood. Chyluria occurs intermittently and is more pronounced after a heavy meal. It is often symptomless, but some patients complain of fatigue and weight loss, resulting from loss of fat and protein.

Lymphatic filariasis (LF)

Lymphatic Filariasis (LF), commonly known as elephantiasis is a disfiguring and disabling disease,  usually acquired in childhood. In the early stages, there are either no symptoms or non-specific symptoms.  Although there are no outward symptoms, the lymphatic system is damaged. This stage can last for several years. Infected persons sustain the transmission of the disease. The long term physical consequences are painful swollen limbs (lymphoedema or elephantiasis). Hydrocele in males is also common in endemic areas.

Due to damaged lymphatic system, patients with lymphoedema have frequent attacks of infection causing high fever and severe pain. Patients may be bed-ridden for several days and normal  routine activities become difficult.  Such attacks not only cause acute physical suffering but also directly impede the earning capacity of the individual.  Lymphatic filariasis is estimated to be one of the leading causes of disability worldwide.  Elimination of the disease is an important tool for poverty alleviation and economic development.

Filaria vectors

Culex quinquefasciatus transmits filariasis in India.  Culex breeds in polluted water. Common breeding sites are wet pit latrines, septic tanks, barrow pits, cess pools, drains, disused wells, paddy fields, etc.

Transmission of Lymphatic Filariasis

The adult produces millions of very small immature larvae known as microfilariae, which circulate in the peripheral blood with marked nocturnal periodicity. The worms usually live and produce microfilariae for 5-8 years.

Adult Filarial Worms (Macrofilariae)   inhabiting  lymphatic system of man

Lymphatic filariasis is transmitted through mosquito bites.

In India, 99.4% of the cases are caused by the species - Wuchereria bancrofti whereas Brugia malayi is responsible for 0.6% of the problem.

In the adult stage, filarial worms live in the vessels of the lymphatic system. Lymphatic system is the network of lymph nodes and lymph vessels that maintains the fluid balance between the tissues and the blood which is an essential element of the body’s immune defense system.

LIFE CYCLE OF FILARIA PARASITE

Man is the definitive host i.e. where the mature adult male and female  parasites  mate and produce microfilariae whereas the mosquito is the intermediate host. The adult parasites are usually found in the lymphatic system of man. They give birth to as many as 50,000 microfilariae per day, which find their way into blood circulation. The life span of microfilaria is not exactly known which preferably may survive up to a couple of months.

The parasite cycle in the mosquito begins when the microfilariae are picked up by the vector mosquitoes during their feeding on the infected person (microfilaria carrier). The microfilaria in mosquito develops into three stages and under optimum conditions of temperature and humidity; the duration of the cycle in the mosquito (extrinsic incubation period) is about 10-14 days. When the infective mosquito feeds on other human host, the infective larvae are deposited at the   site of mosquito bite from where the infective larvae get into lymphatic system. In the human host, the infective larvae develop into adult male and female worms. The adult worms survive for about 5-8 years or sometimes as long as 15 years or more.

Magnitude of disease 

Filariasis has been a major public health problem in India next only to malaria.  The disease was recorded in India as early as 6^th century B.C. by the famous Indian physician, Susruta in his book ‘Susruta Samhita’. In 7^th century A.D., Madhavakara described signs and symptoms of the disease in his treatise ‘Madhava Nidhana’ which hold good even today.  In 1709, Clarke called elephantoid legs in Cochin as ‘Malabar legs’.

The discovery of microfilariae (mf) in the peripheral blood was made first by Lewis in 1872 in Calcutta (Kolkata).

Indigenous cases have been reported from about 250 districts in 20 states/Union Territories.

The North-Western States/UTs namely Jammu & Kashmir, Himachal Pradesh, Punjab, Haryana, Chandigarh, Rajasthan, Delhi and Uttaranchal and North-Eastern States namely Sikkim, Arunachal  Pradesh, Nagaland, Meghalaya, Mizoram, Manipur and Tripura are known to be free from indigenously acquired filarial infection.

Cases of filariasis have been recorded from Andhra Pradesh, Assam, Bihar, Chhattisgarh, Goa, Jharkhand, Karnataka, Gujarat, Kerala, Madhya Pradesh, Maharashtra, Orissa, Tamil Nadu, Uttar Pradesh, West Bengal, Pondicherry, Andaman & Nicobar Islands, Daman & Diu, Dadra & Nagar Haveli and Lakshadweep.

National Filaria Control Programme (NFCP)

After pilot project in Orissa from 1949 to 1954, the National Filaria Control Programme (NFCP) was launched in the country in 1955 with the objective of delimiting the problem, to undertake control measures in endemic areas and to train personnel to manage the programme. The main control measures were mass DEC administration, antilarval measures in urban areas and indoor residual spray in rural areas. The NFCP set-up and population protected are given in the table below:

Population protected under NFCP and the set-up as on 01-03-2002

Strategy

• Recurrent anti-larval measures at weekly intervals.
• Environmental methods including source reduction by filling ditches, pits, low lying areas, deweeding, desilting, etc.
• Biological control of mosquito breeding through larvivorous fish.
• Anti-parasitic measures through ‘detection’ and ‘treatment’ of microfilaria carriers and disease person with DEC by Filaria Clinics in towns covered under the programme.

Revised Strategy

Annual Mass Drug Administration  with single dose of DEC was taken up as a pilot project covering 41 million population in 1996-97 and extended to 77 million population by 2002. During 2004 about 400 million population were brought under MDA. This strategy is to be continued for 5 years or more to the population excluding children below two years, pregnant women and seriously ill persons in affected areas to interrupt transmission of disease.

National goal

The National Health Policy 2002 aims at Elimination of Lymphatic Filariasis by 2015.

STRATEGY FOR Elimination of lymphatic filariasis

The strategy for achieving the goal of elimination is by Annual Mass Drug Administration of DEC for 5 years or more to the population excluding children below two years, pregnant women and seriously ill persons in affected areas to interrupt transmission of disease.

Home based management of cases who already have the disease and hydrocelectomy operations in identified CHCs and hospitals.

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National Vector Borne Disease Control Programme, 22, Shamnath Marg, Delhi - 110054.