Researchers suggest climate warming will allow diseases to thrive

Friday, June 21st 2002, 12:00 am
By: News On 6

WASHINGTON (AP) _ A warming climate will allow disease-causing pathogens to thrive in places where they once could not live, posing a new risk for species as diverse as butterflies and humans, oysters and lions, a study suggests.

In research published Friday in the journal Science, researchers say that bacteria, bugs, parasites, viruses and fungi that have been restricted by seasonal temperatures may be able to invade new territories and find new victims as the climate warms and winters grow milder.

``Climate change is disrupting natural ecosystems in a way that is making life better for infectious diseases,'' said Andrew Dobson, a Princeton University researcher and a co-author of the study. ``The accumulation of evidence has us extremely worried. We share diseases with some of these species. The risk for humans is going up.''

Climate changes already are thought to have contributed to an epidemic of avian malaria that wiped out thousands of birds in Hawaii; the spread of an insect-borne pathogen that causes distemper in African lions; and the bleaching of coral reefs attacked by diseases that thrive in warming seas.

Humans are also at direct and dramatic risk from such insect-borne diseases as malaria, dengue and yellow fever, the researchers said.

``In all the discussions about climate change, this has really been kind of left out,'' said Drew Harvell, a Cornell University marine ecologist and lead author of the study. ``Just a one- or two-degree change in temperature can lead to disease outbreaks.''

Richard S. Ostfeld, a co-author of the study, said, ``We're alarmed because in reviewing the research on a variety of different organisms we are seeing strikingly similar patterns of increases in disease spread or incidence with climate warming.'' Ostfeld is an environmental researcher at the Institute of Ecosystem Studies in Millbrook, N.Y.

In the study, the authors analyzed how warming temperatures already are letting insects and microbes invade areas where they once were killed by severe seasonal chills. They said mosquitoes are moving up mountainsides, spreading disease among animals formerly protected by temperature. They also found some pathogens reproduce more often in warmer temperatures, so there are more germs around to cause infection.

Among the possible effects they found:

_Epidemics of Rift Valley fever, a deadly mosquito-borne disease, rage through northeastern Africa during years of unusual warmth. If the climate becomes permanently warmer and wetter, as some predict, Rift Valley fever epidemics will become frequent.

_Malaria and yellow fever may become more common as milder winters permit the seasonal survival of more mosquitoes, which carry these diseases. A warmer climate also could enable them to move into areas where the cold once kept them out.

_In Hawaii, a warming climate has chased the chill from some mountains, letting mosquitoes thrive at higher elevations. The bugs have carried with them a type of avian malaria, and the disease has attacked native birds that had no immunity to the disease.

``Today there are almost no native birds (in Hawaii) below 4,500 feet,'' Dobson said.

_Coral reefs in many parts of the world are becoming bleached and dying, killed by pathogens that thrive in the warming seas.

``Previously many of the waters were slightly below the optimal temperatures for these pathogens,'' said Ostfeld. ``Now the temperatures are right on target. There is a strong link between the warming climate and diseases of corals.''

_Germs that attack oysters are thriving in the warming waters. Ostfeld said oyster beds as far north as Maine are now being affected by pathogens once barred by a colder sea.

_An outbreak of distemper killed many lions in Tanzania last year. The scientists linked that to a climate change that enables flies that carry distemper to invade parts of East Africa.

_A parasite that kills monarch butterflies can survive only at warm temperatures, which protected the colorful insect in its northernmost habitats. A warming climate has allowed the parasite to spread. Ostfeld said where the monarch is rare ``it may disappear, and where it is common, it may become less abundant.''

Not all scientists agree that climate warming poses the risk seen by the study's authors.

Sherwood B. Idso, head of the Center for the Study of Carbon Dioxide and Global Change, said the Science paper was based largely on speculation and presented ``no concrete examples that these things will happen in the real world.''

Dobson, however, said coral bleaching ``is a strong existing example'' of disease spread caused by climate warming. He said malaria and cholera infections are expanding in Africa, and these have been linked to warming.