WHO updates fact sheet on Lymphatic Filariasis

The World Health Organization (WHO) has recently updated its fact sheet on lymphatic filariasis.

Background Information:

Lymphatic filariasis, commonly known as elephantiasis, is a neglected tropical disease.

It 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 approximately 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.

Key Messages:

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.

The global baseline estimate of people affected by lymphatic filariasis was 25 million men with hydrocele and over 15 million people with lymphoedema.  At least 36 million people remain with these chronic disease manifestations.

Clinical Features

Lymphatic filariasis infection involves

  1. asymptomatic,
  2. acute, and
  3. chronic conditions.

The majority of infections are asymptomatic, showing no external signs of infection while contributing to transmission of the parasite. 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 people suffering with lymphatic filariasis.

Elimination of Lymphatic Filariasis

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. More than 6.7 billion treatments have been delivered to stop the spread of infection since 2000.

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 provision of the recommended basic package of care.

Preventive chemotherapy

The WHO recommended preventive chemotherapy strategy for lymphatic filariasis elimination is mass drug administration (MDA).  MDA involves administering an annual dose of medicines to the entire at-risk population. The medicines used 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.

The MDA regimen recommended depends on the co-endemicity of lymphatic filariasis with other filarial diseases. WHO recommends the following MDA regimens:

  • albendazole (400 mg) alone twice per year for areas co-endemic with loiasis
  • ivermectin (200 mcg/kg) with albendazole (400 mg) in countries with onchocerciasis
  • diethylcarbamazine citrate (DEC) (6 mg/kg) and albendazole (400 mg) in countries without onchocerciasis

Recent evidence indicates that the combination of all three medicines can safely clear almost all microfilariae from the blood of infected people within a few weeks, as opposed to years using the routine two-medicine combination.

WHO now recommends the following MDA regimen in countries without onchocerciasis:

  • ivermectin (200 mcg/kg) together with diethylcarbamazine citrate (DEC) (6 mg/kg) and albendazole (400 mg) in certain settings

499 million people no longer require preventive chemotherapy due to successful implementation of WHO strategies.

The overall economic benefit of the programme during 2000-2007 is conservatively estimated at US$ 24 billion. Treatments until 2015 are estimated to have averted at least US$ 100.5 billion of economic loss expected to have occurred over the lifetime of cohorts who have benefited from treatment.

Fourteen countries (Cambodia, The Cook Islands, Egypt, Maldives, Marshall Islands, Niue, Palau, Sri Lanka, Thailand, Togo, Tonga, Vanuatu, Viet Nam and Wallis and Fortuna) are now acknowledged as achieving elimination of lymphatic filariasis as a public health problem.

Seven additional countries have successfully implemented recommended strategies, stopped large-scale treatment and are under surveillance to demonstrate that elimination has been achieved.

Morbidity Management and Disability Limitation

Morbidity management and disability prevention are vital for improving public health and are essential services that should be provided by the health care 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,
  • exercises, 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.

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 to prevent progression of disease and debilitating, inflammatory episodes of ADL;
  • surgery for hydrocele;
  • treatment of infected people with antifilarial medicines

Vector Control

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.

Useful Links:

Link to the updated WHO fact sheet:

http://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis

Link to WHO’s Global Plan to Eliminate Lymphatic Filariasis (GPELF) Progress Report 2000-2009; and Strategic Plan 2010-2020 (English) [PDF]:

http://apps.who.int/iris/bitstream/handle/10665/44473/9789241500722_eng.pdf?sequence=1

Link to GPELF Progress Report 2015 (English) [PDF]:

http://apps.who.int/iris/bitstream/handle/10665/250245/WER9139.pdf?sequence=1

Link to WHO Guideline: Alternative MDA Regimens to Eliminate Lymphatic Filariasis (2017) (English) [PDF]:

http://www.who.int/lymphatic_filariasis/resources/9789241550161/en/

Link to video on Lymphatic Filariasis Elimination Program:

 

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