Lymphatic Filariasis Disease Information

Introduction

In Africa, LF is caused by the parasitic thread-like worm, Wuchereria bancrofti, and is transmitted to humans through the bites of mosquitoes. Unlike onchocerciasis, which is also found in hoofed animals, humans are the only host for this parasite.

Long-term infection with LF can lead to painful and disfiguring chronic enlargement of the arms and legs of people of all ages. It also causes severe swelling in the genitals of males; a condition known as hydrocele. The disease is commonly called “elephantiasis” because of the elephant-like appearance of swollen limbs in those most severely affected.

Infection with LF can cause severe physical and psychological disability. In addition, men with hydroceles often suffer from sexual dysfunction. Like onchocerciasis, LF also has a significant economic impact when productivity is reduced due to the disabilities caused by the disease.

Disease Burden

The World Health Organization (WHO) estimates that worldwide there are:

• 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

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. 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. 

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.