What is lymphatic filariasis? Facts about it and other neglected tropical diseases
By David M. Brown,
Which can cause elephantiasis
Cause: The disease is caused by a parasite transmitted by mosquito bites. The parasite larva develops into an adult worm inside the body. The worms block lymphatic vessels, which are veinlike structures that help recirculate fluid outside of cells.
Symptoms: When lymphatic vessels are blocked, fluid accumulates in tissues, especially in the legs and scrotum. Early, mild swelling resolves with treatment but not after years of infection. Sufferers can also have recurrent attacks in which the swollen limb becomes painful and inflamed.
Scope: More than 1.3 billion people in 72 countries and territories are at risk of infection.
Efforts at control: Mass drug administration is the key strategy. The goal is to eliminate the microscopic form of the parasite from the bloodstream so that it cannot grow into a worm and cannot be further transmitted by mosquitoes. Single doses of two drugs administered together — albendazole and diethylcarbamazine (DEC), or in some places albendazole and ivermectin — protect a person from developing severe infection for a year and over many years eliminates transmission of the parasite. Children are generally treated twice a year.
Lymphatic filariasis is just one in a group known as neglected tropical diseases. The other most-prevalent diseases in this group:
Also known as river blindness, this infection is most prevalent in Africa, where it is transmitted by black flies that breed in moving water. Larvae develop into mature worms that cause severe skin rashes and itching, and in some cases blindness. About 37 million people are at risk for the disease. Mass drug administration with the drug ivermectin, combined with insecticide treatment of black fly breeding sites, has reduced the incidence by nearly 75 percent in recent years.
The parasite that causes schistosomiasis (also known as bilharzias) grows in freshwater snails. The infectious form of the organism is released into water and burrows through the skin of people in contact with the water. In the body they develop into worms that migrate to various organs and cause abdominal pain, fever, anemia, and liver and bladder damage. About 200 million people worldwide are infected. Control measures include annual doses of the drug praziquantel and public education. A vaccine against the disease is in development.
This bacterial infection is passed from eye to hand to eye. Chronic inflammation causes the eyelid to turn inward, where the eyelashes can scratch and scar the cornea. About 84 million people are infected worldwide, with 8 million blind. Control measures include treatment with the drug azithromycin, promotion of face washing, and surgery for sight-threatening cases.
SOIL-TRANSMITTED HELMINTH INFECTIONS
These are caused by three kinds of intestinal worm: whipworm, hookworm and roundworm. Infection occurs when the worms’ eggs or larvae are ingested or soil contaminated with feces contacts open skin. The worms eventually inhabit the intestinal tract, causing many symptoms, including anemia and malnutrition that can stunt the growth and mental development of children. More than 1 billion people are infected by one or more of the worms, which can be killed with annual doses of various drugs, including albendazole, one of the medicines used against lymphatic filariasis.
Sources: World Health Organization; U.S. Agency for International Development’s Neglected Tropical Diseases Program; the Global Network
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