All About Lymphatic 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. 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.

Brugian 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.

Bancroftian 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.

Lymphatic filariasis (LF)

Photo 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

C.quinquefasciatus is the vector of W.bancrofti in the mainland. C.quinquefasciatus breeds in association with human habitations and is the domestic pest mosquitoes, preferring polluted waters, such as sewage and sullage water collections including cess pools, cess pits, drains and septic tanks. In the absence of such type of water collections, they can breed in comparatively clean water collections also.

The eggs are laid in rafts containing 150-40 eggs each depending on quality and quantity of blood meal taken. At the optimum temperature of 250C to 300C, the eggs hatch within 24 to 48 hours. The youngest stage is the first instar larva which moults to subsequent instars each within 24-48 hours at optimum temperature. There are four instars in the larval stages, and all the instars are voracious eaters, taking anything and everything of microscopic size into the buccal cavity by instant vibration of its feeding brushes. They are mainly bottom feeders but may feed from the surface also.

The IV instar at the end of its stage gives rise to a comma shaped pupa, which lasts upto 24-48 hours at optimal condition. Pupae do not feed but are very active, respiring through its pair of breathing trumpets. The pupa emerges into an adult mosquito, through a longitudinal slit formed between the two trumpets. The entire cycle from egg to emergence of adult is completed in 10-14 days.

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.

The persons having circulating microfilariae are outwardly healthy but transmit the infection to others through mosquitoes.

The persons with chronic filarial swellings suffer severely from the disease but no longer transmit the infection.

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.


Photo 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 (extensive 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 6th century B.C. by the famous Indian physician, Susruta in his book Susruta Samhita. In 7th 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 256 districts in 21 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, Telangana, Uttar Pradesh, West Bengal, Pondicherry, Andaman & Nicobar Islands, Daman & Diu, Dadra & Nagar Haveli and Lakshadweep.


Endemic district 256
(in 21 States/UTs)
Population: 650 Million

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 man the programme. The main control measures were mass DEC administration, antilarval measures in urban areas and indoor residual spray in rural areas.

NFCP 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.

Elimination of Lymphatic Filariasis (ELF)

In 1997, The World Health Assembly adopted resolution, WHA 50.29, for Elimination of Lymphatic Filariasis as a global public health problem by 2020.In 2002, National Health Policy set a goal for ELF in India by 2015, further it was extended to 2017. In 2004, ELF was launched covering 202 endemic districts in 20 States/UTs. Subsequently it is scaled up to cover all the 256 endemic districts (21 States/UTs) targeting a population of about 650 million..

The twin pillars of LF elimination strategy include:

  • children below 2 years? Transmission control- To prevent occurrence of new infection by annual MDA with DEC + Albendazole for 5 years or more to population at risk except children below 2 yrs, pregnant women & seriously ill persons.

  • Disability prevention and morbidity management for those who already have the disease:
    • Home based management –limb hygiene for lymhoedema
    • Hospital based management – surgical correction for hydrocele

    List of state-wise LF endemic districts

    LF Updated Status - January, 2018
    • States/UTs endemic for lymphatic Filariasis- 21
    • Districts endemic for lymphatic Filariasis -256
    • Five states (Assam, Tamil Nadu, Goa, Puducherrey, Daman & Diu) stopped MDA after achieving elimination status and observing post MDA surveillance activities.
    • Districts cleared 1st TAS and stopped MDA- 97
    • Districts cleared 1st and 2nd TAS - 27
    • Districts proposed for 1st TAS - 16
    • Districts proposed for MDA- 143

    Morbidity Management and Disability Alleviation
    • Morbidity Management is another pillar of strategy for ELF and states/UTs were advised on up-scaling home based morbidity management of Lymphoedema cases and Hydrocele operations. The process involved updating the line-listing of Lymphoedema & Hydrocele cases in the districts. Training and education materials detailing these strategies were provided to public health facilities at state and district levels and to 79 medical colleges in endemic areas. Motivate for surgical intervention to hydrocele cases. As per data shared by states till 2017, total numbers of Hydrocele and Lymphoedema cases are 3.9 Lakhs and 8.8 Lakhs respectively.
    • Since 2004, the states/UTs have reported 1.42 Lakhs hydrocele operations. Different states have initiated management of Lymphodema cases through demonstrating home based foot hygiene method to patients at local levels.



    Use of Albendazole 400 mg tablets as co-administration for lymphatic filarisis programme -DCGI Letter