Filariasis (fih-luh-RYE-uh-sis) is a tropical disease caused by tiny worms.
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What Is Filariasis?
Filariasis is caused by different species of microscopic parasitic * roundworms that are passed to people through the bites of insects, most commonly mosquitoes. Several strains * of these worms, known as filariae (fih-LAIR-e-e), can infect humans, including Wuchereria bancrofti (vooker-E-re-ah ban-CROFT-e). There are also different types of filariasis itself, including cutaneous (kyoo-TAY-nee-us) or skin-related, body cavity, and lymphatic * infections. In the cutaneous disease, the worms live in the layers of the skin; in body cavity filariasis, they inhabit certain body openings and surrounding tissue; and in the lymphatic form of infection, they invade the vessels of the lymphatic system and the lymph nodes * .
Lymphatic filariasis, which can progress to a condition called elephantiasis * , is the most serious form of the disease. It begins when an infected female mosquito injects worm larvae * into a person's blood while feeding. The larvae travel to the lymphatic vessels, where they grow into adult worms. As adults, the worms can survive and reproduce for up to 7 years. The gradual buildup of worms in the vessels hinders the lymphatic system's ability to fight infection, and causes lymph fluid to collect—typically in the arms, legs, breasts, and male genitals—leading to swelling and disfigurement.
How Common Is the Infection?
Filariasis is most common in tropical and subtropical regions, including parts of Africa, the western Pacific, Asia (especially India), and Central and South America. In these areas, the number of cases of filariasis continues to rise. It is estimated that more than 120 million people worldwide have the lymphatic form of illness today, and approximately 40 million of them have been disabled or disfigured by the disease. Although contracting filariasis is not a risk in the United States, some recent immigrants may have it, and people who have traveled to other countries can contract the disease as well. Missionaries and Peace Corps volunteers are considered to be most at risk.
* parasitic (pair-uh-SIH-tik) refers to organisms such as protozoa (one-celled animals), worms, or insects that can invade and live on or inside human beings and may cause illness. An animal or plant harboring a parasite is called its host.
* strains are various subtypes of organisms, such as viruses or bacteria.
* lymphatic (lim-FAH-tik) means relating to the system of vessels and other structures that carry lymph, a colorless fluid, throughout the body's tissues; the lymphatic system plays an important role in protecting the body from infections.
* lymph (LIMF) nodes are small, bean-shaped masses of tissue that contain immune system cells that fight harmful microorganisms. Lymph nodes may swell during infections.
* elephantiasis (eh-luh-fan-TIE-uh-sis) is the significant enlargement and thickening of body tissues caused by an infestation of parasites known as filaria.
Is Filariasis Contagious?
The disease does not spread from direct person-to-person contact. Instead, it is transmitted by the bite of a mosquito. When one of these insects bites someone who is infected, it takes in the parasites along with its meal of blood. The mosquito then can pass those parasites on to the next person it bites. Usually, someone must be bitten many times, typically over a long period, to develop symptoms of filariasis.
What Are the Signs and Symptoms
of the Disease?
The lymphatic form of filariasis usually produces fever, swollen or painful lymph nodes in the neck and groin, pain in the testicles * , and swelling in the limbs or genitals. Males and the male urinary and genital systems are particularly likely to be affected. In elephantiasis, a severe form of chronic * lymphatic filariasis, the blocked flow of lymph causes one or both legs to swell significantly. Over time, the skin on the leg also can change, taking on a rough texture so that it resembles the skin of an elephant. Although elephantiasis is unusual, up to half of all men with lymphatic filariasis may show serious symptoms, such as swelling of the scrotum * . In some cases people may have no obvious symptoms, but they still may have serious damage to the kidneys and lymphatic system.
Making the Diagnosis
Knowing that the person lives in or has spent time in a country where filariasis poses a risk can help a doctor diagnose the disease. The doctor may also take skin and blood samples from the patient to look for signs of the parasite.
What Is the Treatment for Filariasis?
Ideally, treatment begins as soon as possible after the patient becomes infected. Prompt treatment may not be possible, however, because the disease can be difficult to detect in its early stages. When the diagnosis is made, treatment may include:
- medication to kill the young worms in the bloodstream and stop the parasite's life cycle (although the medicine cannot kill adult worms)
- exercising and moving swollen limbs to improve lymph flow
- bed rest and compression bandages to treat swelling
- medications to lessen swelling and discomfort
- hospitalization and intravenous * (IV) antibiotics for secondary infections that might appear because the damaged lymphatic system is less able to assist in defending the body against infectious agents
- surgical treatment for deformities, such as enlarged limbs and scrotum, sometimes with several procedures and skin grafts * to correct cases of disfigurement
* larvae (LAR-vee) are the immature forms of an insect or worm that hatch from an egg.
* testicles (TES-tih-kuls) are the paired male reproductive glands that produce sperm.
* chronic (KRAH-nik) means continuing for a long period of time.
* scrotum is the sac of skin that contains the testicles.
* intravenous (in-tra-VEE-nus) means within or through a vein. For example, medications, fluid, or other substances can be given through a needle or soft tube inserted through the skin's surface directly into a vein.
* grafts are tissue or organ transplants.
* stigma is a mark of shame.
How Long Does the Disease Last and
What Are the Complications?
Filariasis can last a lifetime, and without treatment it can worsen. The disease can lead to permanent disfigurement and damage to the lymphatic system and kidneys, secondary infections, hardening and thickening of the skin, and sexual and psychological problems. In countries where the disease is common, a serious social stigma * often accompanies it.
Can Filariasis Be Prevented?
There is no vaccine to prevent filariasis, but controlling the populations of blood-sucking insects, especially mosquitoes, can limit the spread of the disease. In some areas where filariasis is common, people are treated yearly with preventive medicine to kill any immature worms in their blood. To protect themselves, people can also:
- Stay inside as much as possible from dusk to dawn, when mosquitoes are most active.
- Sleep under mosquito netting.
- Place screens in all windows.
- Use insecticides around living areas.
- Apply insect repellent to exposed skin.
U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton
Road, Atlanta, GA 30333. The CDC provides a fact sheet and other
information on filariasis at its website.
World Health Organization (WEHO), Avenue Appia 20, 1211 Geneva 27,
Switzerland. The WHO tracks disease outbreaks around the world and
offers information about filariasis at its website.