The Wisconsin Department of Agriculture, Trade and Consumer Protection and the Wisconsin Veterinary Diagnostic Laboratory recently confirmed that a horse in Barron County has tested positive for Eastern equine encephalitis, Wisconsin’s first confirmed EEE case this year. The 22-year-old quarter horse mare had not been vaccinated against EEE, and was euthanized after showing neurological signs and becoming unable to rise.

EEE and West Nile virus are transmitted by mosquitoes that carry these viruses which can affect the nervous system, and may be fatal.

“From an animal welfare perspective, vaccinating horses against EEE and West Nile virus is necessary to prevent the suffering that occurs once the horse contracts the virus,” said Dr. Julie McGwin, DATCP equine program veterinarian. “While the number of cases of EEE and West Nile virus were down last year compared to the previous year, it is heartbreaking for all involved to see any animal suffer through deteriorating health conditions caused by these viruses. We encourage all horse owners to work with their veterinarian to get their horses vaccinated against these diseases.”

In 2018, Wisconsin had a total of two cases of EEE and three cases of West Nile virus reported. In comparison, Wisconsin had a record 24 confirmed cases reported of each virus in 2017. There are currently no reports of West Nile virus cases this year.

The virus is not contagious between horses. While humans may also be infected by WNV and EEE, the viruses do not pass directly between people and horses. Mosquitoes carry the viruses from infected birds and the only route of transmission is from a mosquito bite.

Because the viruses follow mosquito populations, the threat varies depending on the weather but normally starts in mid- to late summer and remains until the first killing frost.

DATCP also confirmed that a horse and a mule on the same premises in Taylor County have tested positive for equine infectious anemia. These are Wisconsin’s first confirmed cases of EIA in almost 15 years. There is no treatment for EIA; therefore to prevent transmitting it, infected animals are humanely euthanized.

“EIA is a devastating disease for horses and their owners. Horses that are not euthanized must be isolated from other horses, which is not usually feasible due to their herd nature, and the lifelong quarantine creates animal welfare issues for the infected horse,” McGwin said. “Horses that survive the initial infection become carriers of the disease and are infectious for life. It’s important for horse owners to work with their veterinarian to have regular testing done for this disease as an infected horse can appear healthy.”

EIA is an infectious and potentially fatal viral infection that affects only equine species, such as horses, ponies, zebras, mules, and donkeys. Symptoms can vary and may include fever and uncontrollable bleeding that can progress to weakness, weight loss, depression, and in some cases death.

Horses can get the disease through blood-feeding flies, such as horseflies and deerflies. The virus can also be transmitted between horses through re-used needles and syringes, blood transfusions, and other contaminated equipment.

To reduce the risk of infection, horse owners should implement fly control measures during fly season, sterilize all needles and syringes used for injections, clean and disinfect equipment shared between animals and isolate any animals with an unknown EIA status until test results are confirmed as negative. There is no evidence that EIA is a public health concern.