 From VOA Learning English, this is the Health Report. Scientists are working on ways to stop a disease that threatens one-fifth of the world's population. Over 120 million people are infected with lymphatic filariasis, also known as elephantiasis. The disease is found mainly in Southeast Asia and Africa. It affects the lymphatic system, which is a major part of the body's natural defenses for fighting disease. Elephantiasis can cause swelling or enlargement of skin and tissue. The cause is a tiny worm that enters and lives in lymphatic tubes for six to eight years. Scientists say they have been able to demonstrate that the most common cause of elephantiasis can be stopped. They are urging those at risk to sleep under nets treated with chemicals that kill a common insect. Lisa Reimer teaches at the Liverpool School of Tropical Medicine. She formerly served in Papua New Guinea as part of a team studying the disease. The team involved researchers from Papua New Guinea, Britain, Australia, and the United States. Dr. Reimer says she was surprised at how effective anti-malaria bed nets covered with insecticide could be at fighting the disease. Doctors normally use drugs to fight the disease. Lisa Reimer says doctors in Papua New Guinea gave the drugs to people in five villages. She says this treatment nearly ended the threat from the worm to humans. But the drugs did not stop the threat from mosquitoes. The treated nets block female mosquitoes from securing blood, which they need to reproduce. The World Health Organization has set a goal of stopping lymphatic filariasis as a public health problem by the year 2020. For VOA Learning English, I'm Alex Villareal.