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What is lymphatic filariasis?
Lymphatic filariasis (LF) is a parasitic disease caused by thread-like worms ('filariae') that live in the human lymphatic system.

How common is the disease?
LF is one of the leading causes of permanent and long-term disability in the world. WHO estimates there are a billion people at risk in about 80 countries. Over 120 million have already been affected by it, and over 40 million of these are seriously incapacitated and disfigured by the disease. One third of the people infected with the disease live in India, one third are in Africa and the rest are in South Asia, the Western Pacific and parts of Central and South America.

What causes lymphatic filariasis?
The thread-like, parasitic filarial worms Wuchereria bancrofti and Brugia malayi that cause LF live almost exclusively in humans. These worms lodge in the lymphatic system, the network of nodes and vessels that maintain the delicate fluid balance between the tissues and blood and are an essential component for the body's immune defence system. Each adult worm lives for an estimated six years in the lymphatic system, and female worms release millions of microfilariae (immature worms) that circulate in the blood.

How is the disease transmitted?
LF is transmitted from person to person by mosquitoes. The mosquitoes bite infected humans and pick up the microfilariae from the blood. The microfilariae then develop inside the mosquito into the infective larval stage in a process that usually takes seven to 21 days. The larvae then migrate to the mosquitoes' mouth, ready to enter the bloodstream of the next unsuspecting individual the mosquito bites. The larvae migrate from the site of the bite to the lymphatic system, thus completing the life cycle.

What are the signs and symptoms?
The adult worms damage the lymphatic system, causing fluid to collect and cause swelling in the arms, legs, breasts and genitals. This is called lymphoedema. Acute episodes of local inflammation involving skin, lymph nodes and lymphatic vessels often precede or accompany lymphoedema. Some of these are caused by the body's immune response to the parasite, but most are the result of bacterial infection of skin where normal defences have been partially lost due to underlying lymphatic damage. Such infections cause a grotesque hardening and thickening of the skin, known as elephantiasis.

In endemic communities, 10-to-50 per cent of men suffer from genital damage, especially hydrocoele (fluid-filled balloon-like enlargement of the sacs around the testes) and elephantiasis of the penis and scrotum. Elephantiasis of the entire leg, the entire arm, the vulva, or the breast - swelling up to several times their normal size - can affect up to 10 per cent of men and women in these communities.

Who is most at risk?
LF is prevalent in remote rural areas and in neglected peri-urban and urban areas, and so is primarily a disease of the poor. Inadequate sanitation, standing water, crowding, lack of screens on houses and bed nets all contribute to the transmission of the disease. The infection is generally acquired early in childhood, but the worst symptoms of the chronic disease do not generally appear until adulthood, affecting men more than women.

In endemic areas, LF symptoms tend to develop more often and sooner in refugees or newcomers than in local populations continually exposed to infection. In newcomers, lymphoedema may develop within six months and elephantiasis as quickly as a year after arrival.

What is the social and economic impact of lymphatic filariasis?
LF occurs primarily in poor communities, and exacerbates poverty by physically incapacitating people and thus preventing them from having a normal working life. The fight against LF is also a fight against poverty.

LF exerts a heavy social burden, particularly since chronic complications are considered shameful and are often hidden. For men, the genital damage is a severe handicap leading to physical limitations, poor self-image and social stigmatisation. Persons affected by lymphoedema are sometimes considered undesirable, and are severely stigmatised. Marriage, usually an essential source of security, is often impossible for men and women with chronic complications.

Is lymphatic filariasis a new disease?
LF has been a scourge of civilisation for thousands of years, being first depicted on the ancient murals of Egypt and in the ancient medical texts of China, India, Japan and Persia. Elephantiasis and hydrocoele were first associated with parasitic filarial worms and their mosquito vectors in the late 19th century by French, English and Australian physicians working with patients from Cuba, Brazil, China and India.

Why has lymphatic filariasis been chosen for elimination?
In 1993, an independent International Task Force for Disease Eradication identified LF as one of only six eliminable infectious diseases. LF was selected because of recent, dramatic advances in treatment methods, both for controlling transmission and for managing the disease, along with remarkable improvement in techniques for diagnosing filarial infections.

In 1997, the World Health Assembly adopted Resolution WHA50.29 calling for the elimination of LF as a public health problem worldwide.

How will lymphatic filariasis be eliminated?
The principal strategy for interrupting transmission of infection is to identify areas in which LF is endemic and then implement community-wide programmes to treat the entire at-risk population. The goal of such treatment is to break the cycle of transmission between mosquitoes and humans thus protecting future generations from the disease.

The programme will be based on once-yearly administration of single doses of two drugs: albendazole plus either diethylcarbamazine (DEC) or Mectizan® (ivermectin, donated by Merck and Co., Inc.). This yearly treatment must reach entire at-risk communities for at least five years..

What will be done for individuals already suffering from lymphatic filariasis?
The supplementary programme, co-ordinated by WHO and the Ministries of Health, will teach individuals with clinical signs of LF effective hygiene measures that can be easily carried out at home. These include regular washing with soap and water and regular exercising of the limbs. Such measures are dramatically effective in preventing painful and debilitating episodes of acute inflammation and can even reverse much of the damage already sustained.

For men with hydrocoele, surgery is the treatment of choice. Guidelines have been developed and disseminated on good, practical surgical procedures to treat hydrocoele and other forms of LF-related genital disease in men.

Who is behind the programme?
Initiated by the World Health Organization and GlaxoSmithKline, the programme to eliminate LF has now become a global alliance between international organisations in the public and private sectors, academia and non-governmental organisations.

What does the programme do for endemic countries?
The programme will support the Ministries of Health in countries where LF is endemic and work in synergy with other disease control or elimination programmes. Collaboration will also be pursued with other ministries such as the Ministry of Education and the Ministry of Agriculture, as well as non-government development organisations (NGDOs) working in the endemic countries.

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