Many pathogens are being spread among wildlife by global warming, and some could have dire consequences for humans as well, the researchers told participants at the World Conservation Congress in Barcelona.
"Climate change conjures up images of rising sea levels and stranded polar bears," said Steven Sanderson, president of New York-based Conservation Society.
"But perhaps the greatest threat will come from emerging infectious diseases as a result of changing temperatures and rainfall levels."
Outbreaks, for example, of Ebola and its close cousin the Marburg virus -- lethal to gorillas, chimpanzee and humans -- have been closely linked to unusual patterns in rainfall and dry seasons.
There is no known cure for either disease, which cause painful internal hemorrhaging and high fevers.
Increasingly frequent algae blooms known as "red tides", triggered by higher sea surface temperatures, create toxins that have killed massive numbers of fish, caused sea mammal to flounder, and increased mortality among penguins and sea birds.
They can also provoke serious illness and death in humans that consume contaminated shellfish.
Some diseases spread further afield by shifting climate patterns do not harm the animals that host them but are dangerous to people, including lyme disease, transmitted by ticks bloated with deer blood, or mosquito-borne sicknesses such as malaria and yellow fever.
Other bacteria and viruses, however, affect only animals -- at least for now.
"We are seeing novel, emerging threats in the form of disease coming out of nowhere and having devastating impacts on animal populations," said Michael Hoffman, a scientist at the International Union for the Conservation of Nature (IUCN) and co-author of a comprehensive study of the survival status of mammals, published this week in the journal Science.
The survey found that one in four mammals are threatened with extinction, and half are in decline.
"Disease has always had a role to play in affecting populations, but now we are seeing diseases that are highly pathogenic," he told AFP.
Amphibians, in particular, have suffered more species loss more than any other animal group, due to a fungus called chytridiomycosis.
The disease has already wiped out hundreds of frog, toad and salamander species, and is spreading across the globe, in part due to climate change but also through the international trade -- much of it illegal -- in wildlife.
Scientists are scrambling to find a cure that will work in the wild even as more species disappear.
The Tasmanian devil, a carnivorous marsupial found only on the Australian island for which it is named, has declined by 60 percent in only 10 years, ravaged by a terrible face cancer that spreads through contact.
Listed as "endangered" on the IUCN's "Red List" -- an inventory of the survival status of more than 44,000 animals and plants -- its prospects as a species "are extremely bleak," said Simon Stuart, in charge of biodiversity assessment for the IUCN.
Monitoring the health status of wildlife can serve as an "early warning system" for humans, said William Karesh, director of global health programs at the Conservation Society.
"Any disturbance in the environment shows up in wildlife because they don't adapt very quickly or easily," he said.