- Lymphatic filariasis is a parasitic infection that can result in an altered lymphatic system and the abnormal enlargement of body parts, causing pain, severe disability and social stigma.
- About 1.23 billion people in 58 countries worldwide are threatened by lymphatic filariasis and require preventive largescale treatment, also known as preventive chemotheraphy, to stop its spread.
- Over 120 million people are 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 single doses of 2 medicines for persons living in areas where the infection is present.
- A basic, recommended package of care can alleviate suffering and prevent further disability among patients.
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 lead to permanent disability. These patients are not only physically disabled, but suffer mental, social and financial losses contributing to stigma and poverty.
Currently, 1.23 billion people in 58 countries are living in areas where lymphatic filariasis is transmitted and are at risk of being infected. Approximately 80% of these people are living in the following 10 countries: Bangladesh, Côte d’Ivoire, Democratic Republic of Congo, India, Indonesia, Myanmar, Nigeria, Nepal, Philippines and the United Republic of Tanzania.
Globally, an estimated 25 million men suffer with genital disease and over 15 million people are afflicted with lymphoedema. 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
- B. timori, which also causes the disease.
Adult worms lodge in the lymphatic system and disrupt the immune 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 the Culex mosquito that is widespread across urban and semi-urban areas; the Anopheles mainly in rural areas, and Aedes, mainly in endemic islands in the Pacific.
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 as well as alter the body’s immune system.
Acute episodes of local inflammation involving skin, lymph nodes and lymphatic vessels often accompany the chronic lymphoedema or elephantiasis. Some of these episodes are caused by the body's immune response to the parasite. However most are the result of bacterial skin infection where normal defences have been partially lost due to underlying lymphatic damage.
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 lead to social stigma, as well as financial hardship from loss of income and increased medical expenses. The socioeconomic burdens of isolation and poverty are immense.
World Health Assembly Resolution 50.29 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 with the aim of eliminating the disease as a public health problem. In 2012, the WHO NTD Roadmap reconfirmed the target date for achieving elimination as 2020.
WHO’s strategy is based on 2 key components:
- stopping transmission 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. Large-scale treatment involves a single dose of 2 medicines given annually to an entire at-risk population in the following way: albendazole (400 mg) together with ivermectin (150–200 mcg/kg) or with diethylcarbamazine citrate (DEC) (6 mg/kg).
These medicines have a limited effect on adult parasites but effectively clear microfilariae from the bloodstream and prevent the spread of parasites to mosquitoes. This recommended large-scale treatment strategy, called preventive chemotherapy, when conducted annually for 4–6 years can interrupt the transmission cycle.
At the start of GPELF, 81 countries were considered endemic for lymphatic filariasis. Further epidemiological data indicated that preventive chemotherapy was not required in 9 countries. From 2000 to 2013, over 5 billion treatments were delivered to a targeted population of about 984 million individuals in 56 countries, considerably reducing transmission in many places. Recent research data show that the transmission of lymphatic filariasis in at-risk populations has dropped by 43% since the start of GPELF. The overall economic benefit of the programme during 2000–2007 is conservatively estimated at US$ 24 billion.
Currently 73 countries are considered endemic and 17 of these have successfully implemented recommended strategies and are under surveillance to demonstrate that elimination has been achieved.
However, preventive chemotherapy has not been delivered to all endemic areas and 28 countries are not on track to achieve elimination targets and stop treatment by 2020.
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 of lymphoedema and acute inflammatory episodes can be improved using 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 improving 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 progression of lymphoedema and debilitating, inflammatory episodes of ADL,
- hydrocele surgery,
- treatment with antifilarial medicines to destroy any remaining worms and microfilariae by preventive chemotherapy or individual treatment.
Mosquito control is another supplemental strategy supported by WHO. It is used to reduce transmission of lymphatic filariasis and other mosquito-borne infections. Measures such as insecticide-treated nets or indoor residual spraying may help protect people from infection. In some settings, vector control in the absence of preventive chemotherapy has eliminated lymphatic filariasis.