Falling ill from climate change

Sheep with swollen, bright blue tongues: it is a surreal sight only recently spotted in Germany.

Aptly dubbed Bluetongue, the deadly disease causing the coloration was previously well known in veterinary medicine as a virus specific to Africa, says Heribert Hofer, the director of the Leibniz Institute for Zoo and Wildlife Research and a professor at Free University of Berlin. It particularly occurs in sheep, cattle and goats.

Yet over the past 10 years, several cases have been reported throughout Western Europe due to an increase of the warm and wet temperatures where the disease thrives. To date, it’s killed more than 1.5 million sheep in Europe.

"Climate change makes it easier for the pathogen to spread beyond its normal places," says Hofer. "In places where it exists already, it might become more severe."

Bluetongue is one of a number of climate-affected diseases impacting the health of animals. Scientists such as Hofer say they will become more prevalent due to rising temperatures.

Animal diseases are a "canary in a coalmine", or an early-warning indicator of a greater problem at hand, says Matthew Bylis, head of Liverpool University’s Climate and Infectious Diseases of Animals (LUCINDA) group. Two-thirds of human diseases originate in animals, about half of which are farm animals.

Bluetongue is transmitted by Cullicoides immitus, a tiny biting midge, similar to the way that malaria is spread by mosquitoes.

Changing the rules of the game for pests

Pests such as the biting midges, mosquitoes and flies used to be fenced into a specific geographic range or habitat type by climatic factors. Many of them thrive the warmer it gets, but then can no longer persist at higher altitudes. That’s quickly changing, though, says Richard S. Ostfeld, a senior scientist at the Cary Institute of Ecosystem Studies in Millbrook, New York.

"The concern is that, as there are places on the planet where conditions are currently too cold for the vectors to occur," says Ostfeld. "As the climate warms, the vectors will spread into those new areas and there will be a net increase in their geographic ranges."

Warming temperatures are giving these insects a competitive advantage, according to a 2011 article by Harvard University health researchers Samuel S. Myers and Aaron Bernstein. It is not only speeding up the rates of reproduction, development, survival and biting of blood-feeding pests, but is also shortening the parasite development time inside these disease-transmitters.

"Even though the actual change in temperature has not been very large, from our perspective, from the perspective of an insect, a pathogen in an insect is quite substantial because they’re so much more sensitive to climate," says Baylis. "All insects are affected by temperature and rainfall."

Take Rift Valley Fever, a virus transmitted by mosquitoes that has recently spread throughout Africa and the Middle East due to rainfall increases of up to three times their average annual rate. It has caused mass fatalities in camels, cattle, goats and sheep, and impacted the livelihoods of the farmers that depend on them.

Climate change also prompts behavioral changes of animals that make them more susceptible to disease, says Baylis. For example, during periods of drought animals will cluster together more at waterholes. The close proximity will allow diseases to spread more – and the animals, often in worse physical condition, will be unable to resist them.

Yet it’s not just warming, but climate fluctuations as a whole, which are sparking the spread of disease. There are a number of species of fungi, a couple of which serve as wildlife pathogens, which bode better under colder conditions.

Take the so-called Bd, a recently identified chytrid fungus deadly to European salamanders and newts, as well as frogs and toads worldwide. The lethal skin disease threatens more than 200 amphibian species around the world.

"Bd has been shown to not spread as rapidly or proliferate as rapidly under warm conditions," says Ostfeld, pointing out that higher temperatures are also known to reduce the ability of some amphibians to fight off infection. "So the fungus is actually assisted by cooler conditions."

Like most species, these amphibians evolve to adapt to changes in their environment -- but sometimes the change is too fast for them to keep up with. Thus, animal populations and their geographic ranges will shrink due to disease.

Impacting biodiversity

Infectious diseases in animals will have a more profound impact on biodiversity than has previously been realized, says Hofer.

"We recognize that infectious disease pathogens are a major force shaping not only the ecology of natural ecosystems, but also the evolution of species, their ability to handle challenges, and the development of new species," he says.

Combating these issues requires massive investment, training, and development of vaccines, says Ostfeld.

Species do move, and they can shift their positions in response to changing conditions, he adds. Yet the rate of climate change "is so fast right now", that in many cases neither evolutionary change nor behavioral change is sufficient to keep up.

"Whatever we can do to slow things down," says Ostfeld, "we’re going to give untold numbers of species a fighting chance to adapt rather than disappear."