Survivors face disease threat
Emergency relief head warns of risks
Residents displaced by a tsunami sit in a relief camp in a temple in Varichikudi, India.
CNN's Allan Chernoff demonstrates water purification kits.
Witnesses describe the devastation of the tsunamis.
Thousands have drowned and thousands are missing in India.
(CNN) -- As the death toll from the Indian Ocean tsunamis soars past 80,000, relief workers warn of even greater tragedy ahead if disease breaks out on a wide scale.
The threat of typhoid, malaria, cholera, dysentery and waterborne disease is particularly acute in the worst-hit areas of Sri Lanka, India and Indonesia, where a combination of surging seawater, hot and humid weather, and decomposing bodies means many water supplies are contaminated.
Medical workers must focus above all else on ensuring those affected by the tsunami have access to clean water, said Gerald Martone, of the International Rescue Committee, a non-governmental organization that provides assistance to refugees around the world.
Contaminated water, which can carry more than 50 diseases, "is the leading killer of populations affected by disasters," Martone told CNN.
Martone's comments have been echoed by David Nabarro, head of crisis operations for the World Health Organization (WHO), who said clean water was the "absolute priority."
He told CNN Wednesday that the next three weeks would be the critical period, particularly for people already weakened by the tragedy.
He said children and old people were most at risk.
Nabarro said malaria and dengue fever, both carried by mosquitoes, could dramatically increase in an environment transformed by pools of stagnant water.
United Nations emergency relief head Jan Egeland called the devastation unprecedented and said the risk of disease still confronts the hundreds of thousands of people injured and made homeless by Sunday's catastrophic events.
Egeland said the cost of the disaster would run into "many billions of dollars."
The tsunamis were triggered by a magnitude 9.0 earthquake that struck off the west coast of the Indonesian island of Sumatra Sunday morning. It was the most powerful quake in 40 years. (Explainer: Tsunami and earthquake facts)
The waves hit the coasts of Indonesia, Malaysia, Thailand, Sri Lanka, India, Bangladesh, Myanmar, the Maldives and as far away as east Africa, destroying fishing villages and tourist resorts and sweeping thousands of people into the sea.
Oxfam Hong Kong director Chong Chan Yau told CNN Tuesday that survivors needed clean water, food, medicine, shelter and sanitation as a priority.
He said children were the most vulnerable group and warned that the next few months represented a crucial period for long-term survival.
CNN's Hugh Riminton in Colombo said Sri Lanka officials were expressing grave concern about disease. He said they were still at the "assessment stage" of the relief effort, working out where best to stockpile reserves of water and medicine for imminent distribution.
"The next 36 hours is critical," he said.
Other relief agencies are warning of a "second wave" of fatalities from injuries and disease over the next week.
According to the IRC's Martone, the first job of medical workers will be to locate water sources and protect them from contamination.
"You wall them off with cement aprons, protective fencing, drainage," he said.
The next task is to teach people how to add chlorine to ensure it is potable, how to protect the water source and how to treat people who get sick with a water-borne disease.
"Cholera is one I fear the most," Martone said, citing the severely dehydrating form of diarrhea that can kill within two hours if a person is not rehydrated appropriately.
Treatment is simple with a rehydration solution made of salt, juices and water.
Malaria too is a risk, he said, because the tsunami has left pools of standing water -- ideal breeding grounds for the mosquitoes that carry the disease.
Sri Lanka's Prime Minister Mahinda Rajapakse said the full extent of the tragedy on the island would not be known for another two days.
A similar situation applies in Indonesia's Aceh province, where the death toll has climbed to 27,174.
CNN's Atika Shubert said some of the worst-hit areas in Aceh were remote and difficult to reach. With most of the infrastructure destroyed, there was a very serious concern about the situation there, she said.
The Catholic Relief Services agency said its workers in Indonesia feared that in some areas diseases like cholera and dysentery may spread rapidly because there was not enough dry ground to bury corpses.
Hundreds of international relief workers have begun arriving in affected regions such as the Thai resort island of Phuket, and the southeast coast of Sri Lanka. Rescue agencies are flying in water purification equipment and stocks of bottled water.
Two Australian Defense Force C-130 Hercules aircraft left Australia Monday night for Indonesia, carrying medical supplies, water and a team of health specialists, and two more C-130s were due to depart Tuesday.
CNN's weather anchor Mari Ramos said Tuesday the forecast for Sri Lanka and southern India was for hot weather, with more rain and thunderstorms on the way.
Dr. Ian Wilderspin, Bangkok-based regional disaster coordinator of the International Federation of Red Cross (IFRC), told CNN it was likely some of the biggest health challenges would not emerge immediately.
Egeland, the U.N. undersecretary-general for humanitarian affairs and emergency relief, has called for a major international response -- and went so far as to call the U.S. government and others "stingy" on foreign aid in general.
"If, actually, the foreign assistance of many countries now is 0.1 or 0.2 percent of the gross national income, I think that is stingy, really," he said. "I don't think that is very generous.
"We need rich countries, rich individuals, even only those of us who are reasonably affluent to respond generously," Egeland said.
"Here we are facing people who have lost everything. Hundreds of thousands of people have lost everything. Millions of people are now living in the worst possible hazards of having polluted drinking water, no sanitation, no health services," he said, adding that the conditions are sure to lead to disease.
UNICEF Executive Director Carol Bellamy told CNN that the agency is doing "everything possible," focusing on getting blankets, medicine and water purification tablets sent to the affected areas.
"Getting clean water to people is crucial," she said, and predicted widespread disease if that is not done.
But the relief task was not easy, she said, because transportation and communications in many of the affected areas were difficult even in the best of times.