Winning the battle against schistosomiasis

Health officials in Cambodia are making inroads in their battle against schistosomiasis, a chronic and debilitating disease commonly known as snail fever.

In northeastern Cambodia, more than 80,000 people living along the 5,000km-long Mekong River are at risk of schistosomiasis, according to the National Center for Parasitology, Entomology and Malaria Control (CNM).

"We've seen a very [big] drop from the last decade," Muth Sinuon, a parasitic worms specialist at the government body, said. She places current prevalence rates at less than 5 percent - a steep fall from the mid-1990s.

"Back around 1995, we saw that between 30 and 70 percent of people in Kratie and Stung Treng were infected," she said. The chronic disease is endemic in the two poor, remote provinces in northeastern Cambodia.

Schistosomiasis is known as snail fever because the parasite lives in freshwater snails. According to the UN World Health Organization (WHO), people become infected when larval forms of the parasite - released by freshwater snails - penetrate their skin during contact with infested water.

In Cambodia, residents go fishing in rivers when water levels are low during the dry season, from February to May, and contract the disease from infested water.

The disease spreads through bathing, washing laundry and fetching water, Muth said.

Left untreated, the worm is perilous even though mortality is low. Schistosomiasis can cause bloody faeces and urine, a bloated belly, intestine damage, liver disease and bladder cancer, say health experts.

In terms of its social and economic impacts, snail fever is second only to malaria as the most devastating parasitic disease in tropical countries, according to the Carter Center, a non-profit charity based at Emory University in Atlanta, Georgia.

Risk to children

Because of their hygiene and play habits in the water, children are particularly at risk.

"These parasites cause growth retardation in children, short- and long-term memory problems, difficulty with reasoning and reading comprehension," said Taing Tek Hong, a US-based Cambodian gastroenterologist, who travels regularly to Cambodia.

Heavily infected people are at risk of malnutrition.

Parasite's lifecycle

Photo: Courtesy of CNM
Abdominal bloating is a common outcome

When human urine or faeces containing the parasite's eggs enter the water, the eggs hatch and release larvae, which search for river snails that live in the fissures of partially submerged rocks.

They enter the snail and multiply, then look for a new host in the water. They break through human skin and infiltrate the blood, move to the liver, and grow into worms.

From there, the worms travel through the blood, laying thousands of eggs in the intestine or bladder.


Since 2002, the Cambodian government has overseen a vast deworming programme. In 2004, the country was the first to reach the WHO's goal of covering three-quarters of school-aged children, or three million people.

Once a year in Kratie and Stung Treng, authorities treat schistosomiasis patients with Praziquantel, a drug that is usually effective with a single dose.

The campaign has led to a drastic fall in cases, said Duong Socheat, head of the CNM.

Even so, more needs to be done to improve sanitation and education, he said.

Many people still defecate into rivers because they have limited access to toilets. Fewer than 16 percent of rural Cambodians have access to adequate sanitation, says the UN Children's Fund (UNICEF).

According to WHO, around the world, 700 million people may be at risk of schistosomiasis. More than 207 million people are infected worldwide, the majority in Africa. Most live in poor communities without access to safe drinking water and adequate sanitation.

Control of schistosomiasis is based on drug treatment, snail control, improved sanitation and health education, the world health body says.