Giving antiparasitic drugs just once a year might be enough to halt the spread of the tropical parasite that causes the deforming disease elephantiasis. The dramatic results, reported in the 5 December issue of The New England Journal of Medicine, suggest that a global campaign under way to eradicate the parasite could very well succeed.
Throughout the tropics, filaria worms cause big problems. They damage the lymphatic systems of tens of millions, causing painful and grotesquely swollen limbs and genitals in some people. Infection takes place years before symptoms appear, when mosquitoes transmit thousands of filaria larvae into the blood. Some of the larvae penetrate lymph nodes and vessels, where they can grow into threadlike worms that churn out up to 12,000 larvae a day. Mosquitoes that feed on an infected person continue the cycle.
No good treatments exist for advanced elephantiasis, but health workers learned in the 1980s that a single annual dose of the antiparasitic drug diethylcarbamazine slashed blood levels of larvae. In 1997, the World Health Organization launched a global campaign to eradicate the disease. As health workers were gearing up, tropical disease researcher James Kazura of Case Western Reserve University School of Medicine in Cleveland, Moses Bockarie of Papua New Guinea Institute of Medical Research in Goroka, and their colleagues began giving annual doses of diethylcarbamazine and another antiparasitic drug, ivermectin, to residents of 14 remote villages in the Papua New Guinea highlands.
The mass treatment strategy worked like a charm. After 4 years, the percentage of people infected with larvae had plummeted from 47% to 1% in moderately afflicted villages, and from 77% to 5% in heavily afflicted villages. Local mosquitoes also became less contagious: Biting mosquitoes had up to 97% fewer larvae. The percentage of infected 5-year-old children fell eightfold to 5%. And most surprisingly, the annual drug treatment, which was designed to prevent new infections, even reversed elephantiasis in many patients.
"The study was terrific," says tropical disease researcher Eric Ottesen of Rollins School of Public Health at Emory University in Atlanta. It represents the first "proof of principle," he says, that giving annual drug treatments to all members of communities could lower infection levels enough to make the disease peter out for good.
Papua New Guinea Institute of Medical Research
Background on lymphatic filariasis from the Global Alliance to End Lymphatic Filariasis
Background on lymphatic filariasis from the World Health Organization