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Deadly by the Dozen: 12 Diseases Climate Change May Worsen

The Wildlife Conservation Society has identified some of the illnesses that global warming may exacerbate
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©WILLIAM KARESH

Bird flu, cholera, Ebola, plague and tuberculosis are just a few of the diseases likely to spread and get worse as a result of climate change, according to a report released yesterday by the Wildlife Conservation Society (WCS). To prevent such ailments from becoming as destructive as the "black death" (which wiped out a third of Europe's population in the 14th century) or the flu pandemic of 1918 (which killed an estimated 20 million to 40 million people worldwide, including between 500,000 and 675,000 people in the U.S.), WCS suggests monitoring wildlife to detect signs of these pathogens before a major outbreak.

"We will see a shift in the geographic distribution of diseases, with certain areas having reduced prevalence and other areas increasing," says veterinarian William Karesh, WCS's vice president of global health programs. "We are calling for increased attention and action in developing global monitoring networks to look at a wide variety of infectious diseases in a wide variety of wildlife since they are such sensitive indicators of the health of the systems in which they live."

The deadly dozen include:

Bird flu: H5N1 infections are becoming the rule rather then the exception in farmed poultry worldwide, and even wild birds are showing signs of infection more often. It has forced the culling of millions of ducks, chickens and geese globally—and has killed more than 240 people—resulting in at least $100 billion in economic losses.

Babesiosis: This malarialike disease carried by ticks is endemic in the tropics, but has cropped up everywhere from Italy to Long Island, N.Y. It is rare in humans at present and seldom deadly (treatable with antibiotics) but may become more problematic as the globe warms, providing more welcoming environments.

Cholera
: This bacterium thrives in warmer waters and causes diarrhea so severe that it can kill within a week. Without improved sanitation, rising global temperatures will increase deadly outbreaks.

Ebola: This virus is lethal to humans and other primates, and has no cure. In addition, it is unclear where the disease, which causes fever, vomiting and internal or external bleeding, comes from—though scientists suspect fruit bats. What is clear is that outbreaks tend to follow unusual downpours or droughts in central Africa—a likely result of climate change.

Parasites: Many spread easily between humans, livestock and wildlife. Higher average temperatures and more rainfall will help many parasites, such as the tiny worms known as Baylisascaris procyonis that are spread by raccoons, to thrive in the wild before finding a host.

Lyme disease
: This bacterium-caused disease will spread as climate changes extend the ranges of the ticks that carry it.

Plague
: Changes in temperature and rainfall will affect rodent populations globally as well as the infected fleas they carry.

"Red tides"
: Poisonous algal blooms in coastal waters may increase as a result of warming temperatures or changes in littoral sea life.

Rift Valley fever
: A newly emergent virus, carried by mosquitoes that causes fever and weakness, has spread quickly through Africa and the Middle East, killing people, along with camels, cattle, goats and sheep.

Sleeping sickness
: Global warming will change the distribution of the tsetse fly that carries the disease, now infecting more than 300,000 people yearly in Africa. Victims become lethargic and may suffer severe swelling of the lymph nodes.

Tuberculosis
: Both the human and livestock varieties of TB are likely to increase, particularly the latter as droughts bring livestock and wildlife into closer proximity at watering holes.

Yellow fever: Mosquitoes spread this disease, which causes fever and jaundicelike symptoms, between wildlife and humans, and will likely spread into new areas as the climate changes.

To counter outbreaks, monitoring efforts for yellow fever in South American monkeys have already helped target health interventions and vaccinations.

And the Global Avian Influenza Network for Surveillance (GAINS)—an international effort to monitor bird flu in wild and domestic birds—has helped map how the disease spreads, and helped prevent a major outbreak in humans.

Karesh and his colleagues argue that this bird flu network should be transformed into a broader effort that surveys all wildlife diseases. "The GAINS mapping and database systems can be easily adapted to any disease in any species," Karesh says. "In fact, the database is blind to which species or disease is entered into the system."

That might give advance warning of impending public health risks, such as encroaching Lyme disease or an outbreak of Ebola hemorrhagic fever. As it stands, those risks are increasing as a result of human encroachment on remaining wild landscapes, mining and logging, and rapid global transport such as jet travel that promote the speedy spread of disease as does global trade in both livestock and wildlife.

"Most microbes and macroparasites have preferred temperatures and moisture levels for viability," Karesh notes. "Climate change affects both hosts and vectors and thus disrupts the balance that developed over thousands of years."

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