Frequently Asked Questions (FAQs)


What is lymphatic filariasis?

Lymphatic filariasis is a parasitic disease caused by three species of  microscopic, thread-like worms. The adult worms only live in the human lymph system. The lymph system maintains the body’s fluid balance and fights infections.

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.

How is lymphatic filariasis 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.

Who is at risk for infection?

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.

What are the signs and symptoms of lymphatic filariasis?

Most infected people are asymptomatic and will never develop clinical symptoms, despite the fact that the parasite damages the lymph system. A small percentage of persons will develop lymphedema or, in men, a swelling of the scrotum called hydrocele . Lymphedema is caused by improper functioning of the lymph system that results in fluid collection and swelling. This mostly affects the legs, but can also occur in the arms, breasts, and genitalia. Most people develop these clinical manifestations years after being infected.

The swelling and the decreased function of the lymph system make it difficult for the body to fight germs and infections. Affected persons will have more bacterial infections in  the skin and lymph system. This causes hardening and thickening of the skin, which is called elephantiasis. Many of these bacterial infections can be prevented with appropriate skin hygiene and care for wounds.

Men can develop hydrocele or swelling of the scrotum due to infection with one of the species of parasites that causes LF, specifically W. bancrofti.

Filarial infection can also cause tropical pulmonary eosinophilia syndrome. Eosinophilia is a higher than normal level of disease-fighting white blood cells, called eosinophils. This syndrome is typically found in infected persons in Asia. Clinical manifestations of tropical pulmonary eosinophilia syndrome include cough, shortness of breath, and wheezing. The eosinophilia is often accompanied by high levels of Immunoglobulin E ( IgE) and antifilarial antibodies.

How is lymphatic filariasis diagnosed?

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.

How can I prevent infection?

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.

What is the treatment for lymphatic filariasis?

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.

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Page last reviewed: September 17, 2020