Lymphatic filariasis

Alternate names

Filariasis; Elephantiasis; Wuchereria Bancrofti infection; Filarial elephantiasis; Malayi tropical eosinphilia; Wuchereriasis; Bancroftian filariasis; Elephantitis

Definition

Lymphatic filariasis is a parasitic disease caused by microscopic, thread-like worms that only live in the human lymph system, which maintains the body's fluid balance and fights infections. Lymphatic filariasis, considered globally as a neglected tropical disease (NTD).

Cause

The causative agents of lymphatic filariasis (LF) include the mosquito-borne filarial nematodes Wuchereria bancrofti, Brugia malayi, B. timori An estimated 90% of LF cases are caused by W. bancrofti (Bancroftian filariasis).

Epidemiology

Lymphatic filariasis affects over 120 million people in 72 countries throughout the tropics and sub-tropics of Asia, Africa, the Western Pacific, and parts of the Caribbean and South America. You cannot get infected with the worms in the United States.

Spread

• The disease spreads from person to person by mosquito bites.
• When a mosquito bites a person who has lymphatic filariasis, microscopic worms circulating in the person’s blood enter and infect the mosquito.
• When the infected mosquito bites another person, the microscopic worms pass from the mosquito through the skin, and travel to the lymph vessels.
• In the lymph vessels they grow into adults.
• An adult worm lives for about 5–7 years.
• The adult worms mate and release millions of microscopic worms, called microfilariae, into the blood.
• People with the worms in their blood can give the infection to others through mosquitoes.

Risk factors

• Repeated mosquito bites over several months to years are needed to get lymphatic filariasis.
• People living for a long time in tropical or sub-tropical areas where the disease is common are at the greatest risk for infection.
• Short-term tourists have a very low risk.
• An infection will show up on a blood test.

Signs and symptoms

Most infected people are asymptomatic and never develop clinical symptoms. A small percentage of people develop lymphedema, which may affect the legs, arms, breasts, and genitalia; bacterial infections that cause hardening and thickening of the skin, called elephantiasis; hydrocele (swelling of the scrotum) in men; and pulmonary tropical eosinophilia syndrome.

Clinical presentation

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms

• Lymphadenopathy(Swollen lymph nodes)
• Predominantly lower limb lymphedema

30%-79% of people have these symptoms

• Circulating immune complexes
• Fatigue(Tired)
• Hypereosinophilia
• Hyperkeratosis
• Hyperpigmentation of the skin(Patchy darkened skin)
• Lymphadenitis(Inflammation of the lymph nodes)
• Pain

5%-29% of people have these symptoms

• Abnormal lung morphology(Abnormality of lung structure)
• Cough(Coughing)
• Fever
• Hydrocele testis
• Lymphangiectasis
• Opportunistic bacterial infection
• Orchitis(Inflammation of testicles)
• Restrictive ventilatory defect(Stiff lung or chest wall causing decreased lung volume)
• Vaginal hydrocele
• Wheezing

1%-4% of people have these symptoms

• Ankle swelling
• Epididymitis
• Glomerulonephritis
• Hematuria(Blood in urine)
• Knee osteoarthritis
• Nephrotic syndrome
• No social interaction
• Proteinuria(High urine protein levels)
• Urethral obstruction

Diagnosis

• The standard method for diagnosing active infection is the examination of blood under the microscope to identify the microscopic worms, called microfilariae.
• This is not always feasible because in most parts of the world, microfilariae are nocturnally periodic, which means that they only circulate in the blood at night.
• For this reason, the blood collection has to be done at night to coincide with the appearance of the microfilariae in the blood.
• Serologic techniques provide an alternative to microscopic detection of microfilariae for the diagnosis of lymphatic filariasis.
• Because lymphedema may develop many years after infection, lab tests are often negative with these patients.

Treatment

• People infected with adult worms can take a yearly dose of medicine, called diethylcarbamazine (DEC), that kills the microscopic worms circulating in the blood.
• While this drug does not kill all of the adult worms, it does prevent infected people from giving the disease to someone else.
• People with lymphedema and elephantiasis are not likely to benefit from DEC treatment because most people with lymphedema are not actively infected with the filarial parasite.
• Physicians can obtain DEC from CDC after lab results confirm infection.
• People with lymphedema and hydrocele can benefit from lymphedema management, and in the case of hydrocele surgical repair.
• Even after the adult worms die, lymphedema can develop.
• You can ask your physician for a referral to see a lymphedema therapist for specialized care.

Prevent the lymphedema from getting worse by following several basic principles:

• Carefully wash and dry the swollen area with soap and water every day.
• Elevate the swollen arm or leg during the day and at night to move the fluid.
• Perform exercises to move the fluid and improve lymph flow.
• Disinfect any wounds. Use antibacterial or antifungal cream if necessary.
• Wear shoes adapted to the size of the foot to protect the feet from injury.
• Men with hydrocele can undergo surgery to reduce the size of the scrotum.

Prevention

Avoiding mosquito bites is the best form of prevention. The mosquitoes that carry the microscopic worms usually bite between the hours of dusk and dawn . If you live in or travel to an area with lymphatic filariasis:

• Sleep under a mosquito net.
• Wear long sleeves and trousers.
• Use mosquito repellent on exposed skin between dusk and dawn.

NIH genetic and rare disease info

• NIH info on Lymphatic filariasis

Lymphatic filariasis is a rare disease.

Lymphatic filariasis Resources
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