Climate change could threaten dogs with diseases pushing into new parts of the USA
Though diseases in dogs are not tracked as intensively as those in humans, veterinary epidemiologists and biologists said Rocky Mountain spotted fever, a bacterial disease that can cause fever, joint pain and vomiting, is moving into California and Texas. Heartworm disease, which can damage the cardiovascular system and clog the heart, is spreading beyond its traditional home in the South and Southeast. Lyme disease, which can cause joint swelling and lameness, affects dogs as far north as Canada.
"The veterinarians need to know what's local. But what's out there is changing so fast, how are you going to keep up?" said Janet Foley, a professor of epidemiology at the School of Veterinary Medicine of University of California, Davis.
Many of these diseases also affect humans. But dogs are especially at risk because they spend a lot of time outdoors and in vegetation.
Warren Hess, assistant director of the American Veterinary Medical Association, said the spread of heartworm disease is increasing because of the changes in how frequently dogs are moved across the country.
"With the increased social pressure to restrict the sale of dogs in pet stores, this has resulted in a dramatic increase in the movement of dogs from pet shelters to fill the demand," he said.
Natural disasters also play a part. "The biggest spread in heartworm disease in the United States certainly followed the 2005 national distribution of dogs due to Hurricane Katrina," said Hess, whose responsibilities include disaster preparedness.
He said that although climate change is happening, and will continue to happen, "it is important that we properly frame the discussions and use all available science as we further the discussion."
Linking the expansion or shift of ticks that carry diseases, infection rates and dog populations is not an easy task. There are no mandated reporting requirements as there are for some human diseases. Data on tick and mosquito distribution is piecemeal in many areas. Tests for some of the diseases that appear to be on the move didn't exist 10 years ago, so it's difficult to judge their historic range.
Even so, many scientists see patterns and links that point them toward climate change.
"There's no smoking gun, and there will never be a smoking gun. We're trying to connect two things that operate at very different scales both in time and space," said Ram Raghavan, a professor of spatial epidemiology at the College of Veterinary Medicine at Kansas State University in Manhattan, Kansas.
He's documented significant changes to the tick populations in the Midwest - in infestation intensity, the areas and when ticks are active. His team's surveillance in western parts of Kansas and Oklahoma found Lone Star ticks that didn't use to live there. These ticks can carry ehrlichiosis, a disease that in dogs can cause bruising of the gums, bleeding from the nose and lameness.
"There is this belief that these ticks do not exist in these areas, but increasingly over the last five years, we're constantly finding them. So I'm pretty sure they've expanded" their habitat, he said. "Tick-borne diseases have really gone up. We go out into the field, and we see and find ticks more easily than we used to do in the past."
To get to the bottom of it will require data that doesn't exist. Raghavan has written several grant proposals to the U.S. National Institutes of Health for funding to do long-term studies, broad testing and analysis.
"Regardless of who caused climate change, climate has changed. Let's take the emotion out of the debate and get some answers," he said.
Temperatures in the contiguous USA are on average 1.5 degrees warmer than they were the century before, according to the U.S. National Oceanic and Atmospheric Administration. Rainfall and humidity levels have changed in some areas. All of these factors affect where insects that can carry disease thrive.
Veterinarians and biologists who study diseases spread by insects observed that it's not just where but when the diseases strike that's changing. The times of year when dogs are at risk are changing in some areas where summers are becoming too hot to support the insects or the diseases they carry. That doesn't stop the spread.
"Diseases like Lyme disease that used to be transmitted in the peak summer months could now be peaking in the spring and fall because it's too hot in the summer. So you get a longer transmission window," said Andrew Dobson, a professor of ecology and evolutionary biology at Princeton University in New Jersey.