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Lymphatic filariasis

Fact sheet
Updated October 2017


Key facts

  • Lymphatic filariasis impairs the lymphatic system and can lead to the abnormal enlargement of body parts, causing pain, severe disability and social stigma.
  • 856 million people in 52 countries worldwide remain threatened by lymphatic filariasis and require preventive chemotherapy to stop the spread of this parasitic infection.
  • In 2000 over 120 million people were infected, with about 40 million disfigured and incapacitated by the disease.
  • Lymphatic filariasis can be eliminated by stopping the spread of infection through preventive chemotherapy with safe medicine combinations, repeated annually for at least 5 years. 6.7 billion treatments have been delivered to stop the spread of infection since 2000.
  • 499 million people no longer require preventive chemotherapy due to successful implementation of WHO strategies.
  • A basic, recommended package of care can alleviate suffering and prevent further disability among persons living with disease caused by lymphatic filariasis.

The disease

Lymphatic filariasis, commonly known as elephantiasis, is a neglected tropical disease. Infection occurs when filarial parasites are transmitted to humans through mosquitoes. Infection is usually acquired in childhood causing hidden damage to the lymphatic system.

The painful and profoundly disfiguring visible manifestations of the disease, lymphoedema, elephantiasis and scrotal swelling occur later in life and can lead to permanent disability. These patients are not only physically disabled, but suffer mental, social and financial losses contributing to stigma and poverty.

Currently, 856 million people in 52 countries are living in areas that require preventive chemotherapy to stop the spread of infection.

The global baseline estimate of persons affected by lymphatic filariasis was 25 million men with hydrocele and over 15 million people with lymphoedema. At least 36 million persons remain with these chronic disease manifestations. Eliminating lymphatic filariasis can prevent unnecessary suffering and contribute to the reduction of poverty.

Cause and transmission

Lymphatic filariasis is caused by infection with parasites classified as nematodes (roundworms) of the family Filariodidea. There are 3 types of these thread-like filarial worms:

  • Wuchereria bancrofti, which is responsible for 90% of the cases
  • Brugia malayi, which causes most of the remainder of the cases
  • Brugia timori, which also causes the disease.

Adult worms lodge in the lymphatic vessels and disrupt the normal function of the lymphatic system. The worms can live for an average of 6–8 years and, during their life time, produce millions of microfilariae (immature larvae) that circulate in the blood.

Mosquitoes are infected with microfilariae by ingesting blood when biting an infected host. Microfilariae mature into infective larvae within the mosquito. When infected mosquitoes bite people, mature parasite larvae are deposited on the skin from where they can enter the body. The larvae then migrate to the lymphatic vessels where they develop into adult worms, thus continuing a cycle of transmission.

Lymphatic filariasis is transmitted by different types of mosquitoes for example by the Culex mosquito, widespread across urban and semi-urban areas, Anopheles, mainly found in rural areas, and Aedes, mainly in endemic islands in the Pacific.

Symptoms

Lymphatic filariasis infection involves asymptomatic, acute, and chronic conditions. The majority of infections are asymptomatic, showing no external signs of infection. These asymptomatic infections still cause damage to the lymphatic system and the kidneys, and alter the body's immune system.

When lymphatic filariasis develops into chronic conditions it leads to lymphoedema (tissue swelling) or elephantiasis (skin/tissue thickening) of limbs and hydrocele (scrotal swelling). Involvement of breasts and genital organs is common. Such body deformities often lead to social stigma and sub-optimal mental health, loss of income-earning opportunities and increased medical expenses for patients and their caretakers. The socioeconomic burdens of isolation and poverty are immense.

Acute episodes of local inflammation involving skin, lymph nodes and lymphatic vessels often accompany chronic lymphoedema or elephantiasis. Some of these episodes are caused by the body's immune response to the parasite. Most are the result of secondary bacterial skin infection where normal defences have been partially lost due to underlying lymphatic damage. These acute attacks are debilitating, may last for weeks and are the primary cause of lost wages among persons suffering with lymphatic filariasis.

WHO response

World Health Assembly resolution WHA50.29 encourages Member States to eliminate lymphatic filariasis as a public health problem. In response, WHO launched its Global Programme to Eliminate Lymphatic Filariasis (GPELF) in 2000. In 2012, the WHO neglected tropical diseases roadmap reconfirmed the target date for achieving elimination by 2020.

WHO’s strategy is based on 2 key components:

  • stopping the spread of infection through large-scale annual treatment of all eligible people in an area or region where infection is present; and
  • alleviating the suffering caused by lymphatic filariasis through increased morbidity management and disability prevention activities.

Large-scale treatment (preventive chemotherapy)

Elimination of lymphatic filariasis is possible by stopping the spread of the infection through preventive chemotherapy. The WHO recommended preventive chemotherapy strategy for LF elimination is mass drug administration (MDA). MDA involves a combined dose of 2 medicines given annually to an entire at-risk population in the following way: albendazole (400 mg) together with either ivermectin (150-200 mcg/kg) or with diethylcarbamazine citrate (DEC) (6 mg/kg).

These medicines have a limited effect on adult parasites but effectively reduce the density of microfilariae in the bloodstream and prevent the spread of parasites to mosquitoes. MDA can interrupt the transmission cycle when conducted annually for 4–6 years with effective coverage of the total population at risk. Salt fortified with DEC has also been used in a few settings to interrupt the transmission cycle.

At the start of GPELF, 81 countries were considered endemic for lymphatic filariasis. Further epidemiological data reviewed since, indicate that preventive chemotherapy was not required in 10 countries. From 2000 to 2015, 6.7 billion treatments were delivered to more than 850 million people at least once in 66 countries, considerably reducing transmission in many places.. The population requiring MDA has declined by 36% (499 million) where infection prevalence has been reduced below elimination thresholds. The overall economic benefit of the programme during 2000-2007 is conservatively estimated at US$ 24 billion. Now with14 years of MDA, at least US$ 100.5 billion of economic loss will be avoided over the lifetime of cohorts who have benefited from treatment.

Ten countries (Cambodia, The Cook Islands, Maldives, Marshall Islands, Niue, Sri Lanka, Thailand, Togo, Tongaand Vanuatu) were acknowledged as achieving elimination of LF as a public health problem. Eleven additional countries have successfully implemented recommended strategies, stopped large-scale treatment and are under surveillance to demonstrate that elimination has been achieved. Preventive chemotherapy is still required in 52 countries but has not been delivered to all endemic areas as of the end of 2016. Enhanced strategies are now required to create any chance of meeting the global target but more importantly to get these national programmes on the path to elimination.

Morbidity management

Morbidity management and disability prevention are vital for improving public health and should be fully integrated into the health system to ensure sustainability. Surgery can alleviate most cases of hydrocele. Clinical severity and progression of the disease, including acute inflammatory episodes, can be reduced and prevented with simple measures of hygiene, skin care, exercise, and elevation of affected limbs. People with lymphoedema must have access to continuing care throughout their lives, both to manage the disease and to prevent progression to more advanced stages.

The GPELF aims to provide access to a minimum package of care for every person with associated chronic manifestations of lymphatic filariasis in all areas where the disease is present, thus alleviating suffering and promoting improvement in their quality of life.

Success in 2020 will be achieved if patients have access to the following minimum package of care:

  • treatment for episodes of adenolymphangitis (ADL);
  • guidance in applying simple measures to manage lymphoedema and hydrocele to prevent disease progression and debilitating, inflammatory episodes of ADL;
  • surgery for hydrocele;
  • treatment of infected persons with antifilarial medicines.

Vector control

Mosquito control is a supplemental strategy supported by WHO. It is used to reduce transmission of lymphatic filariasis and other mosquito-borne infections. Depending on the parasite-vector species, measures such as insecticide-treated nets, indoor residual spraying or personal protection measures may help protect people from infection. The use of insecticide-treated nets in areas where Anopheles is the primary vector for filariasis enhances the impact on transmission during and after MDA. Vector control has in select settings contributed to the elimination of lymphatic filariasis in the absence of large-scale preventive chemotherapy.