Lymphatic filariasis is infection of the lymphatic system caused by one of three species of roundworms.
People have a fever, swollen lymph nodes, pain in the limbs and groin, and, if the infection becomes chronic, swelling that can become constant and disfiguring.
The infection is diagnosed when doctors identify the worm larvae (microfilariae) in a sample of blood.
People are usually treated with the drug diethylcarbamazine, which kills the immature larvae in the blood and some of the adult worms.
(See also Overview of Parasitic Infections and Filarial Worm Infections Overview.)
Lymphatic filariasis is a filarial worm infection that is a common cause of permanent disability worldwide. About 51 million people were infected as of 2018, and 40 million have been disfigured by the disease.
In 2000 the World Health Organization launched its Global Program to Eliminate Lymphatic Filariasis. As a result, substantial progress has been made in stopping the spread of infection through large-scale, annual treatment of eligible people in areas where infection is present. In 2020, more than 860 million people lived in areas where enough infection was present to require such annual treatment.
Lymphatic filariasis is caused by
Wuchereria bancrofti: In tropical and subtropical areas of Africa, Asia, the Pacific, and the Americas, including Haiti.
Brugia malayi or Brugia timori: In South and Southeast Asia.
Transmission of lymphatic filariasis
Lymphatic filariasis is transmitted when an infected mosquito bites a person and deposits larvae of the worm in the skin. The larvae travel to the lymphatic system, where they mature. Adult worms may be 1 1/2 to 4 inches (4 to 10 centimeters) long. The adults produce millions of worm larvae (called microfilariae) that circulate in the bloodstream and lymphatic system. The infection is spread when a mosquito bites an infected person, then bites another person.
Symptoms of Lymphatic Filariasis
Lymphatic filariasis symptoms are caused by adult worms. Microfilariae do not cause symptoms and gradually disappear from the bloodstream after people leave the affected area.
Early (acute) infection
Early in the infection, people may have symptoms for 4 to 7 days. They may have a fever, swollen lymph nodes in the armpits and groin, and pain in the limbs and groin. Pus may collect in a leg and drain to the skin's surface, resulting in a scar.
Bacterial infections of the skin and tissues under the skin are more likely because the worms block the lymphatic vessels which makes the immune system less able to defend the skin and adjacent tissues from bacteria.
Often, symptoms resolve, then recur. They are more severe when people are exposed to the infection for the first time.
Chronic infection
After many years of infection, the blocked lymph vessels widen. Most people have no symptoms. But in a few people, the widened lymph vessels cause swelling that gradually becomes permanent (chronic). The legs are affected most often, but the arms, breasts, and genitals may be also. This swelling (called lymphedema) develops because
The adult worms live in the lymphatic system and reduce the flow of lymph fluid from tissues, causing the fluid to back up in lymph vessels.
The worms trigger a response from the immune system that produces inflammation and swelling.
The swelling makes the skin spongy. Pressing on the skin leaves an indentation that does not disappear right away (called pitting). Chronic swelling may make the skin hard and thick (called elephantiasis). In men, the scrotum may swell.
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Bacterial and fungal infections of the skin are common in people with lymphatic filariasis. These infections, along with the inflammation caused by the worms, can cause pain and discomfort. The infections also contribute to the development of elephantiasis of the legs and occasionally arms and sometimes massive swelling in the scrotum.
Some people have mild joint pain and blood in the urine.
Less commonly, the lungs are affected by microfilariae in the blood stream, resulting in a disorder called tropical pulmonary eosinophilia. People may have a low-grade fever, feel short of breath, cough, or wheeze. If the infection persists, scar tissue (fibrosis) may form in the lungs.
Diagnosis of Lymphatic Filariasis
Examination of a blood sample
Blood tests
Doctors diagnose lymphatic filariasis when they identify microfilariae in a sample of blood or biopsy of lymphatic tissue examined under a microscope. When ultrasonography is done, adult worms can be seen moving in the widened lymph vessels.
Blood tests that can rapidly identify signs of infection (such as antibodies to the worm) have been developed. (Antibodies are proteins produced by the immune system to help defend the body against a particular attack, including that by parasites.) However, the value of blood tests is limited because they cannot distinguish between worms that cause lymphatic filariasis and some other worms nor between past and current infection.
Prevention of Lymphatic Filariasis
The best protection against lymphatic filariasis for individuals is to reduce the number of mosquito bites by doing the following:
Using insect repellents on exposed skin
Wearing long-sleeved shirts and long pants
Using netting over beds
In areas where lymphatic filariasis is common, annual mass-treatment programs can help prevent the spread of infection. Treatment programs usually use 2 or 3 anti-worm medications, depending on whether other parasitic worms are present in the area. Mass treatment reduces the number of microfilariae in the blood of infected people and thus prevents the infection's spread by mosquitoes.
Treatment of Lymphatic Filariasis
Diethylcarbamazine
Treatment of long-term effects
Treatment of acute infection
The brief early symptoms usually resolve on their own. Whether treatment prevents or lessens the long-term effects of infection is uncertain.
Treatment of chronic infection
Typically, lymphatic filariasis is treated with diethylcarbamazine. This drug is taken by mouth for 1 or 12 days. It kills microfilariae and some adult worms.
Before treating people with diethylcarbamazine, doctors check them for loiasis and onchocerciasis because diethylcarbamazine can have serious side effects in people with these infections.
Treatment of the effects of chronic infection
The effects of chronic infection are treated.
Chronic swelling requires meticulous skin care. People must be careful not to damage the skin and to thoroughly clean any minor cuts and scrapes. Such care helps prevent bacterial infections. Swelling may be reduced by wrapping elastic bandages around the affected limb or by elevating the limb. If elephantiasis, including swelling in the scrotum, is severe, surgery may be done to improve drainage in the lymphatic system.
Bacterial skin infections are treated with antibiotics given by mouth. The antibiotics may slow or prevent progression to elephantiasis.
For lung-related problems, diethylcarbamazine, taken for 14 to 21 days, is effective. However, the infection recurs in about one fourth of people. For them, treatment must be repeated.
