Lymphatic filariasis, considered globally as a neglected tropical disease (NTD), is a parasitic disease caused by 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 is spread from person to person by mosquitoes.

People with the disease can suffer from lymphedema and elephantiasis and in men, swelling of the scrotum, called hydrocele. Lymphatic filariasis is a leading cause of permanent disability worldwide. Communities frequently shun and reject women and men disfigured by the disease. Affected people frequently are unable to work because of their disability, and this harms their families and their communities.

Lymphatic filariasis (LF) is a neglected tropical disease (NTD) caused by microscopic, thread-like worms. The adult worms only live in the human lymph system, which maintains the body’s fluid balance and fights infections. LF is spread from person to person by mosquitoes. People with LF can suffer severe and even permanent disability. Affected people frequently are unable to work because of their disability, and this harms their families and their communities. LF affects over 120 million people in 72 countries worldwide. You cannot get infected with the worms in the continental United States.

Key Facts

• Lymphatic filariasis (LF) is a parasitic disease caused by three species of microscopic, thread-like worms.
• The disease spreads from person to person by mosquito bites.
• If you live in or travel to an area with lymphatic filariasis, avoiding mosquito bites is the best way to prevent it.
• LF is considered a neglected tropical disease because it causes substantial illness for more than 1 billion people globally.
• Neglected tropical diseases are infectious diseases that cause devastating illness for more than 120 million people.

The Impact of NTDs

Neglected tropical diseases (NTDs) are a group of parasitic and bacterial diseases that cause substantial illness for more than one billion people globally. Affecting the world’s poorest people, NTDs impair physical and cognitive development, contribute to mother and child illness and death, and make it difficult to earn a living.

LF’s Devastation

Lymphatic filariasis is a leading cause of permanent disability worldwide. Communities frequently shun and reject women and men disfigured by the disease. Affected people frequently are unable to work because of their disability, and this harms their families and their communities.

Treatment for LF

Experts believe that lymphatic filariasis can be eliminated globally. The elimination strategy is based on annual treatment of whole communities with combinations of drugs that kill the microscopic worms. Hundreds of millions of people are being treated each year.

The Impact of NTDs

Neglected tropical diseases (NTDs) are a group of parasitic and bacterial diseases that cause substantial illness for more than one billion people globally. Affecting the world’s poorest people, NTDs impair physical and cognitive development, contribute to mother and child illness and death, and make it difficult to earn a living.

Prevention Tips

Avoiding mosquito bites is best. People who live in or travel to an area with lymphatic filariasis should also:

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

There are three different filarial species that can cause lymphatic filariasis in humans. Most of the infections worldwide are caused by Wuchereria bancrofti. In Asia, the disease can also be caused by Brugia malayi and Brugia timori.

The infection spreads from person to person by mosquito bites. The adult worm lives in the human lymph vessels, mates, and produces millions of microscopic worms, also known as microfilariae. Microfilariae circulate in the person’s blood and infect the mosquito when it bites a person who is infected. Microfilariae grow and develop in the mosquito. When the mosquito bites another person, the larval worms pass from the mosquito into the human skin, and travel to the lymph vessels. They grow into adult worms, a process that takes 6 months or more. An adult worm lives for about 5–7 years. The adult worms mate and release millions of microfilariae into the blood. People with microfilariae in their blood can serve as a source of infection to others.

A wide range of mosquitoes can transmit the parasite, depending on the geographic area. In Africa, the most common vector is Anopheles and in the Americas, it is Culex quinquefasciatus. Aedes and Mansonia can transmit the infection in the Pacific and in Asia.

Many 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.

Programs to eliminate lymphatic filariasis are under way in more than 66 countries. These programs are reducing transmission of the filarial parasites and decreasing the risk of infection for people living in or visiting these communities.

Geographic Distribution

In the 50 U.S. states, Charleston, South Carolina, was the last known place with lymphatic filariasis. The infection disappeared early in the 20 century. The U.S. territory of American Samoa remains the only location in the United Sates where one could become infected with lymphatic filariasis.

Africa: Angola, Benin, Burkina-Faso, Cameroon, Central African Republic, Chad, Comoros, Congo (Brazzaville), Côte d’Ivoire, Democratic Republic of the Congo, Equatorial Guinea, Eritrea, Ethiopia, Gabon, Ghana, Guinea, Guinea-Bissau, Kenya, Liberia, Madagascar, Malawi, Mali, Mozambique, Niger, Nigeria, Sao tome and Principe, Senegal, Sierra Leone, South Sudan, Sudan, Tanzania, Togo*, Uganda, Zambia, Zimbabwe

Asia: Bangladesh, Brunei Darussalam, Burma (Myanmar), Cambodia*, India, Indonesia, Laos, Malaysia, Maldives*, Nepal, Philippines, Sri Lanka*, Thailand*, Timor-Leste (East Timor), Vietnam

The Caribbean: Dominican Republic, Haiti

The Middle East: Egypt*, Yemen

The Pacific Islands: American Samoa (a U.S. Territory), Cook Islands*, Federated States of Micronesia, Fiji, French Polynesia, Kiribati, Marshall Islands, New Caledonia, Niue*, Palau, Papua New Guinea, Samoa, Tonga*, Tuvalu, Vanuatu*, Wallis, Futuna

South America: Brazil, Guyana

*Countries that have been validated by the World Health Organization as having eliminated LF as a public health problem.

A wide range of mosquitoes can transmit the parasite, depending on the geographic area. In Africa, the most common vector is Anopheles and in the Americas, it is Culex quinquefasciatus. Aedes and Mansonia can transmit the infection in the Pacific and in Asia.

Although the parasite damages the lymph system , most infected people have no symptoms and will never develop clinical symptoms. These people do not know they have lymphatic filariasis unless tested. A small percentage of persons will develop lymphedema. This is caused by fluid collection because of improper functioning of the lymph system resulting in swelling. This mostly affects the legs, but can also occur in the arms, breasts, and genitalia. Most people develop these symptoms 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. These people 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 as well as skin and wound care .

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

Filarial infection can also cause tropical pulmonary eosinophilia syndrome, although this syndrome is typically found in persons living with the disease in Asia. Eosinophilia is the presence of higher than normal disease-fighting white blood cells in the body. Symptoms 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.

The standard method for diagnosing active infection is the identification of microfilariae in a blood smear by microscopic examination. The microfilariae that cause lymphatic filariasis circulate in the blood at night (called nocturnal periodicity). Blood collection should be done at night to coincide with the appearance of the microfilariae, and a thick smear should be made and stained with Giemsa or hematoxylin and eosin. For increased sensitivity, concentration techniques can be used.

Serologic techniques provide an alternative to microscopic detection of microfilariae for the diagnosis of lymphatic filariasis. Patients with active filarial infection typically have elevated levels of antifilarial IgG4 in the blood and these can be detected using routine assays.

Because lymphedema may develop many years after infection, lab tests are most likely to be negative with these patients.

Patients currently infected with the parasite

Diethylcarbamazine (DEC) is the drug of choice in the United States. The drug kills the microfilariae and some of the adult worms. DEC has been used world-wide for more than 50 years. Because this infection is rare in the U.S., the drug is no longer approved by the Food and Drug Administration (FDA) and cannot be sold in the U.S. Physicians can obtain the medication from CDC after confirmed positive lab results. CDC gives the physicians the choice between 1 or 12-day treatment of DEC (6 mg/kg/day). One day treatment is generally as effective as the 12-day regimen. DEC is generally well tolerated. Side effects are in general limited and depend on the number of microfilariae in the blood. The most common side effects are dizziness, nausea, fever, headache, or pain in muscles or joints.

DEC should not be administered to patients who may also have onchocerciasis as DEC can worsen onchocercal eye disease. In patients with loiasis, DEC can cause serious adverse reactions, including encephalopathy and death. The risk and severity of the adverse reactions are related to Loa loa microfilarial density.

In settings where onchoceriasis is present, Ivermectin is the drug of choice to treat LF.

Some studies have shown adult worm killing with treatment with doxycycline (200mg/day for 4–6 weeks).

Patients with clinical symptoms

People with lymphedema and elephantiasis are unlikely to benefit from DEC treatment because most people with lymphedema are not actively infected with the filarial parasite.

To prevent lymphedema from getting worse, patients should ask their physician for a referral to a lymphedema therapist so they can be informed about some basic principles of care such as hygiene, elevation, exercises,skin and wound care, and wearing appropriate shoes.

Patients with hydrocele may have evidence of active infection, but typically do not improve clinically following treatment with DEC. The treatment for hydrocele is surgery.

There is some evidence that suggests that a course of the antibiotic doxycycline may prevent lymphedema from getting worse.

The best way to prevent lymphatic filariasis is to avoid mosquito bites. The mosquitoes that carry the microscopic worms usually bite between the hours of dusk and dawn . If you live in an area with lymphatic filariasis:

• At night
  • Sleep in an air-conditioned room or
  • Sleep under a mosquito net
• Between dusk and dawn
  • Wear long sleeves and trousers and
  • Use mosquito repellent on exposed skin.

Another approach to prevention includes giving entire communities medicine that kills the microscopic worms — and controlling mosquitoes. Annual mass treatment reduces the level of microfilariae in the blood and thus, diminishes transmission of infection. This is the basis of the Global Programme to Eliminate Lymphatic Filariasis.

Experts consider that lymphatic filariasis, a neglected tropical disease (NTD), can be eliminated globally and a global campaign to eliminate lymphatic filariasis as a public health problem is under way. The elimination strategy is based on annual treatment of whole communities with combinations of drugs that kill the microfilariae. As a result of the generous contributions of these drugs by the companies that make them, hundreds of millions of people are being treated each year . Since these drugs also reduce levels of infection with intestinal worms, benefits of treatment extend beyond lymphatic filariasis. Successful campaigns to eliminate lymphatic filariasis have taken place in China and other countries.

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.