Diarrhoea and related diseases are a major threat to the American troops posted in the Middle East, a report by the US-based Walter Reed Army Institute of Research said.

"Diarrhoeal diseases are the number one threat to the US soldiers in Iraq," Dr Malabi Venkatesan, a researcher at the Institute's Department of Enteric Infection said.

"Such diseases pose enormous logistical and manpower problems," she said.

Though she could not give exact figures, Venkatesan said during Operation Desert Storm in 1991, at least 20 per cent of US soldiers developed some kind of diarrhoeal diseases, including dysentery.

Unsanitary living conditions, changes in diet, and hygiene factors make diarrhoea one of the most infectious 'disease threats'.

"Shigellosis or bacillary dysentery is dangerous because as few as 100-1000 virulent bacteria can cause the disease," Venkatesan said.

Researchers at the Institute are now developing new vaccines to help US soldiers ward off bacterial threats.