Lyme Disease Research at MARE
Written by Bill Kent
Growing up on horseback in southwestern Virginia, Rebecca Thompson would hear other riders complain that their horses’ personalities had changed for the worse because of Lyme disease. Though none of her horses caught the disease, Thompson became curious about exactly what behavioral changes the disease might cause.
This curiosity led her to study Lyme disease. Now a Ph.D. student at Virginia Tech’s School of Animal Sciences in Blacksburg, she began her research at the Tech’s Middleburg Agricultural Research Extension Center (MARE), a 420-acre living laboratory founded by philanthropist and equine enthusiast Paul Mellon in 1949. At MARE, Thompson met Dr. Robin Foster, a Seattle-based expert on equine behavior.
“Because some of the symptoms of Lyme disease can cause pain, I had to first learn more about how horses indicate they are in pain,” Thompson says. “Dr. Foster flew to Dulles, met me at MARE, and showed me how to assess equines for pain.”
Thompson then examined 131 horses at 20 farms, all in the southwestern part of the state. The examination included bloodwork.
“Approximately half had blood with Lyme antibodies, meaning that the horses were exposed,” she explains. “Unfortunately there is currently no test to determine if horses have an active infection. Fifteen horses were treated by their owners in case an infection was present, and some owners noticed positive changes in their horses’ behavior after treatment.”
A tick-borne infection named for the Connecticut town where it was first identified, the Lyme disease bacterium (also called Borrelia burgdorferi) first appears in humans on the skin as a red, target-like ring where the tick had attached. Within a few days or weeks, the disease may cause skin rashes, swollen joints, headaches, partial paralysis, or chronic fatigue. Common in the northeastern part of the United States, it is most often treated with antibiotics.
Symptoms attributed to Lyme disease in horses include a heightened sensitivity to touch, inflamed joints, stiffness, swollen lymph nodes, as well as depression and irritability.
Dr. Virginia Buechner-Maxwell, a professor of large-animal internal medicine at the Virginia-Maryland College of Veterinary Medicine, sites a 2016 study that showed “there is no doubt infections among human beings are on the rise in the Commonwealth. Similar statewide information has not been published for the Virginia horse population. Because horses are at greater risk for exposure to ticks, it is reasonable to predict that infection in horses is following similar trends.”
Though an antibody titer — a laboratory test that measures the levels of antibodies in a blood sample — can show that a horse has been exposed to the disease, “it is not the same as having an active infection.” Dr. Buechner-Maxwell adds, “Not all horses [that] have elevated titers develop signs of the disease, so it is important to consider other causes of inflamed joints, swollen lymph nodes, depression, and irritability before simply attributing these signs to Lyme disease.”
Thompson’s research stands to “further our understanding of the impact of Lyme disease on the horse population of Virginia,” Buechner-Maxwell concludes. “It is a step toward clarifying the relationship between behavioral change and Lyme disease. Analysis of the information that she is gathering may demonstrate a much-needed statistical probability that horses with reported behavioral changes have been exposed.”
Thompson feels she has enough evidence to show a more specific connection with equine behavior and Lyme infection, and is looking forward to returning to MARE “because I want to find out if there are any environmental ways we can limit infections. Do the chances of infection go up or down if pastures are mowed frequently? Do trees in the pasture increase the chances of infection?”
Thompson expects to publish her findings next year.
Posted on: September 17, 2024