WHO updates fact sheet on Lymphatic Filariasis (8 March 2017)

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 that 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.

Key Messages:

Currently, 947 million people in 54 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.

Causes 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.

filariasis-life-cycle

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.

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.

Prevention

Elimination of lymphatic filariasis is possible by stopping the spread of the infection through preventive chemotherapy.

The WHO recommended preventive chemotherapy strategy for Lymphatic Filariasis 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.

Morbidity Management

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.

The Global Programme to Eliminate Lymphatic Filariasis (GPELF) by 2020, advocates 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 disease 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.

Useful Links:

Link to the updated fact sheet:

http://www.who.int/mediacentre/factsheets/fs102/en/

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

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

Link to WHO Progress Report and Strategic Plan to Eliminate Lymphatic Filariasis (English) [PDF]:

http://apps.who.int/iris/bitstream/10665/44473/1/9789241500722_eng.pdf

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