Filariasis (fih-luh-RYE-uh-sis) is a tropical disease caused by tiny worms.
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 (voo-ker-E-re-ah ban-CROFT-e). There are also different types of filariasis itself, including cutaneous * or skin-related, body cavity, and lymphatic * * .
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 seven 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.
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, in the early 2000s, the number of cases of filariasis continued to rise. It was estimated that more than 120 million people worldwide had the lymphatic form of illness, and approximately 40 million of them were disabled or disfigured by the disease. Although contracting filariasis is not a risk in the United States, some immigrants may have it, and people who travel to other countries can contract the disease as well. Missionaries and Peace Corps volunteers especially are considered to be at risk.
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.
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 can also 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.
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:
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 in which the disease is common, a serious social stigma * often accompanies it, meaning that people in these countries look down on individuals who have symptoms of the disease.
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 do the following:
See also Elephantiasis • Parasitic Diseases: Overview • Roundworm Infection
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U.S. Agency for International Development, NTD (Neglected Tropical Diseases) Program. http://www.neglecteddiseases.gov/target_diseases/lymphatic_filariasis/ (accessed December 7, 2015).
Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30333. Toll-free: 800-311-3435. Website: http://www.cdc.gov (accessed December 7, 2015).
Global Alliance to Eliminate Lymphatic Filariasis. Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, United Kingdom. Telephone: 44-0-151-705-3145. Website: http://www.filariasis.org (accessed December 7, 2015).
World Health Organization. Avenue Appia 20, CH-1211 Geneva 27, Switzerland. Telephone: 41-22-791-2111. Website: http://www.who.int (accessed December 7, 2015).
* 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 organ isms, such as viruses or bacteria.
* cutaneous (kyoo-TAY-nee-us) related to or affecting the skin.
* 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 nodes (LIMF) are small, bean-shaped masses of tissue containing immune system cells that fight harmful microorganisms. Lymph nodes may swell during infections.
* elephantiasis (eh-luh-fan-TIE-uhsis) is the significant enlargement and thickening of body tissues caused by an infestation of parasites known as filaria.
* larvae (LAR-vee) are the immature forms of an insect or worm that hatches from an egg.
* testicles (TES-tih-kulz) are the paired male reproductive glands that produce sperm.
* chronic (KRAH-nik) lasting a long time or recurring frequently.
* scrotum (SKRO-tum) is the pouch on a male body that contains the testicles.
* intravenous (in-tra-VEE-nus), or IV, 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.