Veterinarians say horses are as susceptible to West Nile, the same virus that has claimed 29 people in Texas -- although it’s unclear how many animals have died in this latest outbreak of 2012.
Dr. Jake Wells, of the Cibolo Valley Animal Clinic, says veterinarians now ask horse owners regularly if their animals have already received the shot, and highly recommend that they get it.
It’s two initial injections, then a booster ever year thereafter.
While dogs and cats don’t appear to be vulnerable, chickens and horses are.
"It's just the way horses are susceptible to encephalitis," Wells said. "Probably other animals are, too, but not to the degree horses are."
Most horses who are exposed to West Nile that have not been inoculated will appear to be unaffected.
But those with weakened immune systems will show symptoms of tremor in two to four weeks. Without treatment, they’ll collapse on their hind end, often described as a "dog-sit" position.
Veterinarians say that is usually when the virus is terminal.
“The key is to get to them early and you have to treat them very, very aggressively and it's very expensive,” he warned.
He says when the first outbreak occurred, about half of the horses who contracted the virus died.
The vaccine costs about $25 to $30.
In Bexar County, the drought may have helped to keep the numbers down of infected mosquitoes, but autumn usually brings wetter weather so the risk may increase over the next few months.
The Texas Department of Health Services is tracking West Nile Virus in all animals and posts daily updates.