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Lymphatic Filariasis

By Richard D. Pearson, MD, Emeritus Professor of Medicine, University of Virginia School of Medicine

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.

Lymphatic filariasis is a filarial worm infection that is a common cause of permanent disability worldwide. About 120 million people are infected, and 40 million have been disfigured by the disease. 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

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 worm makes the lymphatic system less able to defend the body against infections.

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 lymph vessels widen. Most people have no symptoms. But in a few people, swelling 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.

Bacterial and fungal infections of the skin are common in people with chronic lymphatic filariasis. These infections contribute to the development of elephantiasis.

Some people have mild joint pain and blood in the urine.

Less commonly, the lungs are affected, 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

  • Examination of a blood sample

  • Blood tests

Doctors diagnose lymphatic filariasis when they identify microfilariae in a sample of blood 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

The best protection against lymphatic filariasis is to reduce the number of mosquito bites by doing the following:

  • Using insect repellents on exposed skin

  • Wearing clothing that has been saturated with the insecticide permethrin

  • Wearing long-sleeved shirts and long pants

  • Using netting over beds

In areas where lymphatic filariasis is common, diethylcarbamazine can help prevent infection. These drugs reduce the number of microfilariae in the blood of infected people and thus prevent the infection's spread. In some areas, diethylcarbamazine has been added to table salt.

Treatment

  • 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.

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  • ELIMITE, NIX