Recent discussions on social media have raised concerns regarding the identification of Jamestown Canyon virus (JCV) in a Pennsylvania horse. What do we know about this virus, and what is there to be discovered?

What We Know About Jamestown Canyon Virus in Horses

Jamestown Canyon virus is a mosquito-borne virus that primarily affects humans. Researchers first identified this virus in Colorado in 1961. It is spread by mosquitoes that pick up the virus when feeding on infected animals, especially deer; mosquitoes then transmit the virus to other animals, including humans. Most animals and people exposed to JCV do not appear sick, although there have been rare cases of severe neurologic (brain and spinal cord) disease associated with JCV in people.

Jamestown Canyon Virus Infection in Horses

Jamestown Canyon virus is not a new virus and should not be a cause for alarm for horse owners.

In seroprevalence studies researchers look for antibodies against a particular pathogen (a disease-causing organism such as a virus or bacterium); in North America they have revealed horses have likely been exposed to JCV for decades, with studies as far back as the 1970s showing a subset of horses has been exposed. There are very rare reports of the virus causing illness in horses. The only known published report of JCV infection in a horse involved blisters affecting the coronary band and mouth of a Colorado horse in 1997.

More recently, scientists identified the virus in spinal fluid samples from a horse seen at the University of Pennsylvania’s New Bolton Center, in Kennett Square, in late October 2024. The patient was euthanized due to significant neurologic disease and, after extensive testing efforts over several months, clinicians identified JCV in that horse’s samples.

This is the first case we are aware of where this virus was identified in a horse with neurologic disease. Given what we know about exposure of horses to the virus and how rarely we see disease associated with JCV in horses, this is unlikely to be a significant cause of disease in horses. However, in response to this novel detection, researchers at Penn Vet are working with other University of Pennsylvania researchers to better understand how JCV affects horses. If you are interested in donating to support this research, please visit this link.

What Can Owners Do To Protect Their Horses?

To protect yourself and your horse from JCV, do what you can to reduce mosquito populations near your barns by eliminating standing water and take steps to prevent mosquito bites. For more information about JCV in people, mosquito-bite prevention, and Pennsylvania surveillance for mosquito-borne disease, please see the Pennsylvania Dept of Health JCV Fact Sheet and the Pennsylvania Department of Environmental Protection’s mosquito map.