An experimental drug developed by scientists in China appears to be effective in killing roundworms, a parasite that lurks in the intestines and which affects nearly two billion people in tropical countries.

There is currently one effective drug, albendazole, but its widespread and repeated use -- owing to high re-infection rates -- has led to some signs of resistance. Albendazole is marketed by GlaxoSmithKline.

In a paper published in PLoS Neglected Tropical Diseases, scientists in China and co-workers in the United States discussed a new drug, tribendimidine, which was developed by the Chinese National Institute of Parasitic Diseases and approved for use in people by the China State Food and Drug Administration in 2004.

Roundworms are particularly harmful to children and pregnant women. Their microscopic eggs or larvae are found in the soil and enter the human body through the mouth or minute cracks on the skin.

Apart from causing malnutrition and developmental problems in children, the parasite can cause blindness if it enters the eye. Repeated infections can also bring about swelling of the organs and the central nervous system.

Roundworms do not only affect people in developing areas, but throughout the world, including the United States, although these infections are more common in warm, tropical climates than in cooler, temperate areas.

Some of the risk factors include poor sanitation and hygiene, a weakened immune system, malnutrition and contact with animal feces. Children typically get infected eating dirt or clay.

Recent clinical trials in China and Africa found tribendimidine to be effective against some roundworm parasites, particularly hookworms, they said.

Scientists recommended that tribendimidine be used in places where roundworms have developed resistance to albendazole.

Tribendimidine could also be combined with albendazole to increase the effectiveness of killing parasitic roundworms, since both drugs have different biological killing mechanisms, they said in a statement.