Todayโs path rounds are on ๐๐ช๐ฎ๐ข๐ง๐ ๐๐ง๐๐๐ฉ๐ก๐๐ฅ๐ข๐ญ๐ข๐ฌ ๐ฏ๐ข๐ซ๐ฎ๐ฌ๐๐ฌ!
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
The ๐๐ช๐ฎ๐ข๐ง๐ ๐๐ง๐๐๐ฉ๐ก๐๐ฅ๐ข๐ญ๐ข๐ฌ ๐ฏ๐ข๐ซ๐ฎ๐ฌ๐๐ฌ are all viruses of the Togoviridae family, and they all cause inflammation in the brain. There are three viruses we think of in this group, Eastern equine encephalitis virus (EEE), Western equine encephalitis virus (WEE) and Venezuelan equine encephalitis virus (VEE).
๐๐ก๐๐ญโ๐ฌ ๐ญ๐ก๐ ๐๐ข๐๐๐๐ซ๐๐ง๐๐ ๐๐๐ญ๐ฐ๐๐๐ง ๐ญ๐ก๐๐ฆ?
Basically the difference is where the viruses mainly exist. EEE is primarily found in the Atlantic states and provinces, and extends down into South America. WEEV is primarily found in the Western states and provinces. VEE is found in Venezuela, Colombia and Peru.
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
As the name might suggest, these diseases are primarily seen in horses. However, humans are also able to get this disease, with a few cases reported every year.
๐๐จ๐ฐ ๐๐จ ๐๐ง๐ข๐ฆ๐๐ฅ๐ฌ ๐ ๐๐ญ ๐ข๐ง๐๐๐๐ญ๐๐?
Birds and rodents are the actual โhostsโ of this virus, and horses and humans acquire the disease via mosquito bites. Horses are considered to be a dead end host of this disease, meaning that a mosquito biting an infected horse is very unlikely to transfer the disease to another horse.
Once a horse acquires the virus from a mosquito, the virus replicates in blood vessels and lymph nodes, producing a ๐ฏ๐ข๐ซ๐๐ฆ๐ข๐ (large amounts of virus in the bloodstream). Eventually, the virus is able to enter the brain via the bloodstream. In the brain, the virus causes ๐ง๐๐ฎ๐ซ๐จ๐ง๐๐ฅ ๐ง๐๐๐ซ๐จ๐ฌ๐ข๐ฌ (death of neurons) and inflammation surrounding blood vessels.
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
By the time the brain is infected with the viruses, the horses will display ๐ง๐๐ฎ๐ซ๐จ๐ฅ๐จ๐ ๐ข๐ ๐ฌ๐ข๐ ๐ง๐ฌ like paralysis, restlessness, blindness, strange posturing and walking in circles. The diseases are often fatal after 2-4 days in severely affected animals, if the horse is not euthanized.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
While the horse is still alive, the best test is taking a sample of ๐๐๐ซ๐๐๐ซ๐จ๐ฌ๐ฉ๐ข๐ง๐๐ฅ ๐๐ฅ๐ฎ๐ข๐ (the fluid found around the spinal cord and brain) to look at the cells present. The veterinarian can also do a ๐ฌ๐๐ซ๐จ๐ฅ๐จ๐ ๐ฒ (immune response) test to see if the animal has antibodies against the virus.
At necropsy, there are no specific signs that can be seen, however occasionally you can see hemorrhage in the brain and spinal cord. Microscopically, you can see infiltrates of ๐ง๐๐ฎ๐ญ๐ซ๐จ๐ฉ๐ก๐ข๐ฅ๐ฌ (a main clean up cell of the body) around the blood vessels, as well as neuron death.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐? ๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ฉ๐ซ๐๐ฏ๐๐ง๐ญ๐๐?
Unfortunately, there is no specific treatment for these diseases. Often they get supportive care like fluids and pain control. Horses that do recover often have lingering neurologic signs and may never recover full function.
Prevention is the most important thing you can do, and thankfully we have very effective vaccines for all three viruses. It is recommended that all horses get a vaccine once a year prior to mosquito season.
๐๐ก๐จ๐ญ๐จ๐ฌ
1-2) Examples of hemorrhage in the spinal cord and brain.
3-5) Examples of what can be see under the microscope with these diseases.
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Maxie, G. Jubb, Kennedy and Palmerโs Pathology of Domestic Animals, Volume 1. Sixth Edition.
Photos 1-5 courtesy of Noahโs Arkive.
