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 effects the lymphatic system which is a major part of the body's natural defense 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 - the mosquitoes.

Lisa Reimer teaches at the Liverpool School of Tropical Medicine. She formerly served in Papua New Guinea, as part of the team studying the disease. The team involved researchers from Papua New Guinea, Britain, Australia and the United States. 

Doctor Reimer says she was surprised at how effective anti-malaria bed nets covered with insecticide could be at fighting the disease.

"Filariasis is only picked up by mosquitoes late in the evening, so this is the time when people are more likely to be protected by their bed nets. So we found that bed net use actually is a greater barrier against filariasis transmission whereas malaria transmission may still be occurring outside the times when the user is under the net."

Doctors normally use drugs to fight the disease. Ms Reimer says doctors in Papua New Guinea gave the drugs to people of five villages. She says this treatment nearly ended the threat from the worm to humans, but the drugs didn't stop the threat from mosquitoes.

The treated nets block female mosquitoes from securing blood, which is necessary for them to reproduce. The insecticide also cuts the life of the insects in half.

"If we can reduce mosquito-biting rates then we're able to increase the thresholds below which the disease prevalence will move to zero. So by controlling mosquitoes we're making the targets for the mass drug administration more obtainable."

The World Health Organization (WHO) has set a goal of stopping lymphatic filariasis as a public health problem by the year 2020.

The WHO estimates that 1.4 billion people in 73 countries are at risk of the disease. children are often infected, but they do not show signs of the disease until later in life.

And that's the Health Report from VOA Learning English. I'm Bob Doughty.