Introduction | Lifecycle | Distribution/Map | Treatment | Loiasis

• More than 1 billion people at risk for infection, one third live in Africa
  
• More than 120 million people infected, 40 million live in Africa
  
• 44 million people with symptoms^1,2 

Lymphatic filariasis (LF) can lead to painful and disfiguring chronic enlargement of the arms, legs and genitals in people of all ages and in both sexes, and of the breasts in women. This disease is often called “elephantiasis” because of the physical appearance of the swollen limbs in those most severely affected.^3,2

The acute and chronic manifestations of the disease can cause severe physical and psychological disability in affected people. In addition, men with hydroceles and women with lymphedema of the breasts or genitals may suffer severe sexual dysfunction. LF can also have a significant economic impact in endemic communities since some of the disabilities may lead to reduced productivity.^3,2

In Africa, LF is caused by the parasitic thread-like worm, Wuchereria bancrofti, and is transmitted to humans through the bites of mosquitoes. Humans are the definitive host for this parasite; there is no animal reservoir.^2,4

Diagnosis

Definitive diagnosis of LF is through identification of the microfilariae in blood samples taken at night. A newer immunodiagnostic test, based on the detection of antigens of W. bancrofti, is highly specific and sensitive.³ An added benefit of this test is that blood samples do not have to be taken at night.

Clinical Manifestations

In the first year of infection, a person may experience few to mild symptoms. However, with repeated infections over several years, a person may develop outward manifestations of the disease. Through a variety of mechanisms, the adult worms in the lymphatic system alter the structure and functioning of the lymphatic vessels, resulting in one or more of the following conditions:

Adenolymphangitis: inflamed lymphatic vessels that can stand out as palpable, painful chords that can prevent movement of the limbs.

Lymphedema: abnormal accumulation of lymph fluid in the tissues, causing swelling of a limb or other parts of the body which are then more susceptible to repeated bacterial infections.

Elephantiasis: disabling and disfiguring chronic lymphedema of the limbs, breasts or genitals, accompanied by marked thickening of the skin.

Hydrocele: fluid-filled balloon-like enlargement of the sacs around the testes which, if left untreated, can destroy the testicles.^3,4

Using Mectizan to Combat Lymphatic Filariasis

In 1998 Mectizan™ was approved for treatment of proven or suspected microfilaremia caused by W. bancrofti. WHO currently recommends that when lymphatic filariasis co-exists with onchocerciasis, treatment should be on an annual basis with Mectizan in combination with albendazole (donated by GlaxoSmithKline).

A single annual dose of Mectizan alone has been found to effectively decrease the number of W. bancrofti microfilariae in the blood by 90% for one full year.

A single annual dose of Mectizan, co-administered with albendazole, has been found to effectively reduce microfilaremia by 99% for one full year.  Researchers believe that such reductions in microfilaremia over time may interrupt transmission of the parasite and possibly eliminate the disease.

LF has been reported from 80 countries/territories in Africa, Asia, the Western Pacific, and parts of the Americas. It is hoped that epidemiologic mapping of the extent and distribution of disease in all 80 countries will be completed by 2005.

In Africa, 40 countries are believed to be endemic. The extent of overlap between LF and onchocerciasis within these African countries is currently unknown. It is expected that a total of 28 African countries and Yemen, in which onchocerciasis and LF are co-endemic, will ultimately establish national programmes to eliminate LF based on co-administration of Mectizan and albendazole.

References

1. World Health Organization. Lymphatic filariasis. Wkly Epidemiol Rec 2001;76(20): 149-154.
2. Ottesen EA, Duke BOL, Karam M, Behbehani K. Strategies and tools for the control/elimination of lymphatic filariasis. Bulletin of the World Health Organization 1997;75(6): 491-503.
3. World Health Organization. Lymphatic filariasis: reasons for hope. Geneva: World Health Organization; 1997. Document No.: WHO/CTD/FIL/97.4 Rev.1.
4. World Health Organization. Lymphatic Filariasis: the disease and its control, fifth report of the WHO Expert Committee on Filariasis. Geneva: World Health Organization; 1992. Technical Report Series No.: 821.