A spike in deadly infectious diseases in wildlife and people may be the "most immediate consequence" of global warming, according to a new report released today.
Dubbed the "deadly dozen," sicknesses such as Lyme disease, yellow fever, plague, and avian influenza, or bird flu, may skyrocket as global shifts in temperature and precipitation transform ecosystems.
Babesia, cholera, Ebola, intestinal and external parasites, red tides, Rift Valley fever, sleeping sickness and tuberculosis round out the list. (Read descriptions.)
An "early warning system" based on an international wildlife-monitoring network may be the only effective defense, said William Karesh, a report co-author and vice president of Global Health Programs at the New York-based Wildlife Conservation Society.
Observing wildlife could yield crucial signals of potential outbreaks.
"Without the presence of wildlife, we would be clueless about what's going on in the environment," Karesh told a briefing at the International Union for Conservation of Nature (IUCN) World Conservation Congress in Barcelona.
"Why wait until people are sick and dying?"
Out of Sync
Of 14,000 known infectious organisms, 600 are shared between animals and humans.
The deadly dozen were chosen by the conservation society's health experts as some of the most ominous health threats.
"The reason we want to draw attention to [microbes] is they're difficult to see, they have devastating effects, and we also don't think about them until it's too late," Karesh said.
Since microbes and wildlife have evolved together over time, animal species have developed adaptations to cope with the organisms. So disease spikes usually point to something "out of sync with nature," Karesh said.
Climate change has already thrown ecosystems off balance, experts say.
For example, bird flu—which can "jump" to humans, as it did to cause the Spanish flu of 1918—may be worsened by drought. Wild birds that carry the disease have been seen drinking alongside domesticated birds at scarce water sources.
(Related: "'Bird Flu' Similar to Deadly 1918 Flu, Gene Study Finds" [October 5, 2005].)
Such behavior has created a "loss of natural boundaries [that] natural hosts have evolved," said Kristine Smith, assistant director of Global Health Programs for the society.
Jeff McNeely, IUCN's chief scientist, said that the "ecology of climate change is receiving inadequate attention.
"To me, the most important part of climate change is that it's changing the distribution of ecosystems, and diseases tend to be specific to ecosystems," McNeely told National Geographic News.
On-the-ground monitoring has already been shown to work, said the Wildlife Conservation Society's Karesh.
In Brazil forest communities that spot primates sick with yellow fever report back to their health agencies, which in turn start vaccinating for the mosquito-borne illness.
In the Republic of the Congo a group of local hunters has been trained to pinpoint symptoms of Ebola hemorrhagic fever in animals. The strategy has led to three years without a single human case in that region, said Karesh.
The Global Avian Influenza Network for Surveillance also draws on indigenous knowledge through a system of people in 34 countries, who monitor wild bird populations for signs of sickness.
Of course, other unnatural forces are contributing to the spread of disease, experts added.
For instance, the illegal wildlife trade, especially robust in Asia, is bringing people and animals into closer quarters, said the Wildlife Conservation Society's Smith.
The 2002 outbreak of severe acute respiratory syndrome (SARS) was traced to civets. The cat-size mammal, prized for its meat, had ended up in wildlife markets in China, she said.