Lymphatic Filariasis

Lymphatic filariasis is an infectious parasitic disease caused by microscopic, thread-like worms (mostly Wuchereria bancrofti, Brugia malayi, Loa loa, and Onchocerca volvulus). The adult worms only live in the human lymph system, the latter been primarily involved in the maintenance of the body’s fluid balance and to fights infections. The disease affects over 120 million people in 80 countries throughout the tropics and sub-tropics of Asia, Africa, the Western Pacific, and parts of the Caribbean and South America, Malaysia, Indonesia, and some nearby pacific Islands, as well as scattered areas of India, Bangladesh, Vietnam, and China.

The mortality rate in filariasis is quite reduced, but it inflicts great socioeconomic loss on affected individuals. The WHO has identified lymphatic filariasis as the second leading cause (after leprosy) of permanent and long-term disability in the world. It causes severe morbidity in a fashion believed to be due to the host reaction to microfilariae or to developing adult worms in different areas of the body particularly in the lymphatics. Elephantiasis follows the lodgment of the parasite in the lymphatic system and it affects mainly the lower extremities although W. bancrofti can affect the legs, arms, vulva, breasts, while Brugia timori rarely affects the genitals.

The two species of worms most often associated with this disease are Wuchereria bancrofti (Bancroftian filariasis) and Brugia malayi (Malayian filariasis). The larval form of the parasite transmits the disease to humans by the bite of a mosquito and so prevention is ultimately by avoiding mosquito bites by sleeping under a mosquito net, wearing long sleeves and trousers, and the use of mosquito repellent on exposed skin at all times. The vectors breed only in swiftly moving water; hence endemic areas are confined to such locales.

The worms are tissue-dwelling nematodes (roundworms) whose microfilaria larvae are transmitted by several species of mosquitos or flies; Anopheline mosquitos for Wuchereria bancrofti, and Mansonia or Anopheline mosquitos for Brugia malayi. Although malaria is called to mind whenever mosquito is mentioned, elephantiasis (a disease resulting from infestation with tissue parasite and caused by mosquito) is the first disease to be associated with mosquito bites.

SYMPTOMS

Symptoms are s primarily a response to adult worms that cause inflammation. Chronic inflammation may progress to hardening of the lymphatic vessels (fibrosis) and obstruction of the lymph flow. This is mostly discernible as elephantiasis-thickening of the skin and underlying tissues due to chronic lymphedema. Often times, the condition may be asymptomatic but in the early stages of the infection, the patient characteristically complains of episodic bouts of fever, chills, headache, paroxysmal dry cough, wheezing, dyspnoea, anorexia, malaise, weight loss, and skin lesions. Lymphadenopathy mostly in the inguinal region, inguinal pain, testicular pain, skin exfoliation, limb or genital swelling, and inflammatory granulomas occasioned by splenic destruction may also be present. These symptoms mostly characterize adenolymphangitis (ADL), an acute manifestations in lymphatic filariasis.

Symptoms usually begin after six months of infection with localized inflammation in genitalia or extremities. Lymphadenitis and lymphangitis begin at a single site and spread regionally within hours. Within the first day, lymphedema may start to accumulate and may last for weeks after mild symptoms resolve. There are usually filarial abscesses in the groin or axillae, hydrocele, orchitis, and epididymitis are also common especially in males. In chronic disease, there might be gradual and irreversible obstruction of the lymph and serous fluid, this leading to chronic elephantiasis of the lower extremities, testes, and to a lesser extent, arms, breasts, labia, and penis. Obstruction between intestinal lymphatics and thoracic duct may lead to the rupture of renal lymphatics into renal tubules and this could cause chyluria (urine mixed with triglycerides and lymph).

DIAGNOSIS

Because the lifecycle of microfilaria varies according to species and area in which the disease is contracted; and the microfilaria showing diurnal periodicity, peripheral blood of infected persons may or may not have the worms, particularly if proper timing is not done. Detection is primarily in blood and hydrocele fluid, and is routinely done using Giemsa-stained thick blood film. Polymerase chain reaction, enzyme linked immunosorbent assay, complement fixation test, and immunufluorescent antibody test can also be employed to test for the availability of W. bancrofti and B. malayi in blood and sputum. Ultrasound of the scrotum detects adult worms, nodules, or lymphatic dilatation in 80% of affected men, while laboratory investigations may confirm moderate eosinophilia, elevation of serum concentrations of IgE and IgG formed against the worms.

TREATMENT

Ivermectin sometimes combined with albendazole is a treatment of choice in lymphatic filariasis. Asymptomatic microfilaremia can be treated on an outpatient basis while inpatient care may be required initially for those with ADL and chronic filariasis. These patients may need antihistamines, corticosteroids, pain relief, and intravenous antibiotics for secondary infections. Complete eradication of filariasis is possible as studies have shown that transmission of the infection can be broken when a single dose of combined oral medicines is maintained. And so, the basic strategy for eliminating transmission of lymphatic filariasis is by distribution of medicines that kill the microfilariae and stop transmission of the parasite by mosquitoes in endemic communities. A typical example of such medicine is diethylcarbamazine (DEC). Prevention of worsening (chronic) lymphedema is by carefully washing the swollen area; elevating and exercising the limb; and application of compression bandages on the swollen arm or leg to move the fluid and improve the lymph flow.