People queue up for water in Port Blair on Thursday. (AFP)

Bangkok, Dec. 30 (Reuters): Preventing outbreaks of diseases across tsunami-hit Asia is a race against time, but contrary to popular belief, thousands of rotting corpses do not pose the main threat, health officials said today.

Sewage-contaminated water is the main risk factor in the spread of deadly diseases like cholera, malaria and dengue fever and aid organisations are scrambling to get clean drinking water to the affected areas.

?There is no risk of epidemics because of dead bodies,? said Harsaran Pandey, World Health Organisation?s regional spokesperson in New Delhi.

Most agents carrying diseases do not survive long in the human body after death and the source of acute infections is more likely to be tsunami survivors who may already be carrying diseases, the WHO said.

The giant walls of water which crashed ashore on December 26 destroyed safe water supplies for hundreds of villages and polluted what was left with sewage. It is this contaminated water which poses the greatest threat, the WHO said.

The international health organisation has said the tsunami death toll, now feared to be 120,000, could double if epidemics broke out in the affected countries.

?I could say many, many, many people could die if we are not able to reach people in a timely manner with safe water for the prevention of death from water-borne diseases,? said Pandey.

?Diseases are spread by contaminated water, drinking water and water used to clean food,? she added.

The first symptom of contaminated water consumption is diarrhoea and doctors in Sri Lanka and elsewhere are already reporting cases of diarrhoea and vomiting.

?If a person gets dehydrated from diarrhoea then that is when it gets serious and a person can die,? the spokesperson said.

If deadly diseases are present, people will start showing symptoms within a few more days, Pandey pointed out.

The WHO and other international aid bodies are shipping tonnes of water purification tablets to Indonesia, Sri Lanka and Maldives while foreign navies are sending ships with desalination units to produce drinking water.

However, while rotting corpses pose little threat to survivors, relief workers handling them face a risk of contracting tuberculosis, hepatitis, HIV as well as gastro-intestinal infections such as diarrhoea, salmonellosis, typhoid fevers and cholera.

Wide tracts of coastal land in Indonesia, Thailand, India and Sri Lanka have been flooded by the tsunami and this may lead to an increase in mosquito-borne diseases such as malaria and dengue fever, which are endemic in southeast Asia.

The WHO said flooding may initially flush out mosquito breeding grounds; but once the waters recede in six to eight weeks, people risk outbreaks of malaria.

The UN children?s organisation, UNICEF, has said a third of tsunami victims may be children and they are the most vulnerable to infections such as pneumonia and measles.

?You would worry in the next stage for the children,? said Pandey.