The world faces the prospect of "an explosive spread in infectious diseases that are already claiming new victims in industrialised countries", the World Wide Fund for Nature has warned.

The problem is global warming, which is bringing "a combination of rapid warming of the globe and extreme weather events", it says.

Previously unaffected regions are now susceptible, with children and the elderly among the prime victims.

WWF climate policy officer, Dr Ute Collier, says: "Reducing the carbon pollution that causes climate change deserves the same kind of priority that governments are devoting to preventing proliferation of chemical and biological weapons."

Hurricane Mitch: A taste of what is in store

WWF says Hurricane Mitch, which has wrought such appalling destruction in central America, "is a forewarning of further chaos to come as the world warms up".

The report says there is scientific agreement that the world has warmed by 0.6C this century. The seven warmest years in a century-and-a-half of record-keeping have all occurred in the past decade.

If governments do nothing to slow emissions of the gases causing global warming, the report says, a temperature increase of between 1C and 3.5C is predicted over the next century.

Economic risks

WWF is most worried about malaria, cholera, and dengue fever - a flu-like illness which can be fatal and for which there is no vaccine.

National economies could be threatened. A cholera outbreak in Peru in 1991 cost the country more than $1bn in lost seafood exports and tourism.

WWF says the dengue fever threat to the Caribbean could put its $12bn tourist industry in jeopardy.

Both dengue fever and malaria are affecting new populations as warmer conditions allow mosquitoes to survive over a wider area, and at higher altitudes.

The report's author, Dr Paul Epstein, of Harvard Medical School in the USA, says: "Warmer winters and nights are altering the distribution of mosquito-borne diseases, while extreme weather events such as floods and droughts are spawning large 'clusters' of infectious disease outbreaks."

A natural predator, itself at risk

Malaria kills up to two million people a year, and more than two billion are thought to be at risk. It has been found as far north as New York and Michigan.

The report says the problem will be worsened as global warming upsets the population balance of natural predators.

Owls, snakes, birds and bats, which keep insect and rodent numbers in check, are likely to be affected as the earth warms up.

Threat to food supplies

And the report says that health conditions in poor countries depend very much on the success of the harvest.

Floods, which promote the growth of fungi, and droughts, which encourage whiteflies, locusts and rodents, are both expected to become more frequent and more severe.

"Half of the world's agricultural production, worth $250bn, is currently lost to pests and weeds," says WWF.

"This figure could increase with warmer and more unpredictable weather."

It says the governments at the Buenos Aires climate conference must take the threat seriously. WWF wants Western industrialised countries to cut their greenhouse emissions permanently by 2000.