In the May 2012 issue, we reported that 87 percent of readers in our "Gallop Poll" had observed changes in climate trends where they lived. Read more about how those climate changes could affect your horse.
Climate change: The heating of the inner atmosphere, oceans, and land surfaces of the earth. The warming is associated with more intense extreme weather events and the altered timing, intensity, and distribution of precipitation.
—Paul R. Epstein, "Climate Change and Public Health: Emerging Infectious Diseases," Harvard Medical School Center for Health and the Global Environment
You've been hearing about weird weather for a while: A historic drought in Texas... followed by regional flooding. Killer tornadoes in Alabama and elsewhere. A rare hurricane on the upper East Coast. Balmy weather in New Hampshire...in January. What gives?
Theories abound. But regardless of cause, changing weather patterns seem to be the new norm. Such weather-pattern changes may cause more than the typical weather-related problems, which can range from inconvenience to destruction. (Last year alone, the U.S. suffered a record-smashing 14 separate billion-dollar weather disasters.) They also may be affecting the spread of infectious disease (and more).
I've witnessed that firsthand in Texas, where I live. (See, "Outbreak!," This Horse Life, page 10.) That led me to contact three experts in equine infectious disease: Dr. Craig Carter, of University of Kentucky, and Dr. Noah Cohen and Dr. Tracy Norman, of Texas A&M University. (See, "The Experts," page 2.) I asked them how climate change might affect our horses' health. Here's what they had to say. Then read on to see how you can help protect your horses.
Dr. Craig Carter: 'A scary thing to watch'
Climate-change scenarios project a shift in the spread of infectious disease, due to warming and associated weather extremes, such as flooding and droughts. "It's a scary thing to watch," says Dr. Carter. "My wife is a master gardener, so she keeps me up to date on plant zones. In the '80s, Kentucky was a Zone 6. Today, the state is mostly a Zone 7, which indicates it's warming. (Such zones, with 1 being the coldest, and 13 the warmest, are the U.S. Department of Agriculture's indicator of whether a plant or tree will survive the winters in a given region.)
"Insect vectors (carriers of disease) are in concert with that trend," he continues. "For instance, West Nile virus, which is transmitted by mosquitoes, appeared in Canada for the first time in 2002. Mosquitoes, ticks, flies, and other insects are moving northward as it warms. It's not just horses (and people) at risk; crops are being affected, as are trees, due to beetle infestations. Climate change affects all forms of life."
It doesn't appear that the warming trend will end anytime soon.
"Ice caps are melting. I read one study done down on the Equator estimating that 2,000 plant and animal species are moving north at a rate of a mile per year," Dr. Carter says. "We need to be ready, such as with vaccine development, better drugs, preventive measures—that all takes increased research dollars."
Pigeon fever, which typically causes deep-muscle abscesses, is an example of an equine infectious disease on the move.
"Drought increased the biting-fly population in areas like Texas, Louisiana, and Colorado," says Dr. Carter. "Flies can mechanically transmit Corynebacterium pseudotuberculosis, the cause of pigeon fever." (More about that later.)
Leptospirosis is also on the move.
"We're currently doing a study on equine leptospirosis at the University of Kentucky," Dr. Carter says. "Interestingly, the horse is the only domestic animal that gets infected by lepto that doesn't have a vaccine. Somehow it's considered a ‘Kentucky' problem. But our research team is seeing high blood titers (indicating exposure to the bacteria) all over the country."
Leptospires are one cause of equine recurrent uveitis, an eye inflammation that eventually can cause blindness; lepto also can cause abortion in broodmares. "It's a multi-species disease," explains Dr. Carter. "Horses, cattle, dogs, and other animals pick it up from rodent urine in grass, contaminated hay, and other things in the environment. The Leptospira bacteria bore through the mucous membranes and infect the animal." Outbreaks seem to follow wet years.
"Last year, Kentucky had the highest rainfall on record. We had 67" of rain; normal is about 40"," says Dr. Carter. "That's resulting in a high prevalence of lepto this year. In 2006, another very wet year, we had 41 abortions confirmed in our lab alone, but that was only the tip of the iceberg. Yes, we predict 2012 will be another big lepto/abortion year."
The economic impact on Kentucky farms alone is huge.
"In 2006, we attempted to trace back all the lepto abortions confirmed in our lab. We were only able to get good data from 20 of the affected farms. The value of the foals lost on those farms was $3.5 million. We can't estimate the economic damage and suffering related to the uveitis syndrome. Again, that's just the tip of the iceberg.
"We need more funding for research to better understand the epidemiology of this disease," he states. "But we're not going to give up until we have a vaccine for the horse."
Dr. Carter says a recent graduate-student study at the University of Kentucky demonstrated that infected horses may be a risk factor for humans.
"Leptospirosis affects the kidneys in humans and can be fatal," he says. "It's a worldwide issue—it's one of the most prevalent zoonotic (spreads to humans) diseases seen around the world."
Unusual weather makes disease a moving target for veterinarians.
"Take equine herpes virus, a neurological disease that can be fatal, and one that's highly contagious," Dr. Carter continues. "It tends to follow cold-weather stress, which causes a horse's immune system to be suppressed. EPM (equine protozoal myeloencephalitis), another neurological disease, has also been associated with cold stress. When a cold snap hits areas where horses aren't used to it, they get stressed until they acclimate. They can come down with just about anything."