Humans aren't the only species of mammals that can contract West Nile virus. Horses also share the distinction. In fact, both humans and horses have much the same symptoms once infected and both species have the same risks in severe cases.

Dr. David Guitar, DVM, has had horse patients “go down” with West Nile virus.

“If they go down, they're not going to get back up,” he said and at that point, he added, “We try to get the owner to let us put it to sleep.”

The virus is harbored by birds and carried by mosquitoes, and in the “dryer months with higher temperatures,” Guitar said, “it is difficult to control the mosquitoes. For some reason the heat and dryness of late summer makes the disease a little more fatal.”

There is a West Nile Virus vaccine that “does a good job protecting horses,” however Guitar said that the recommendations are for one shot a year. He's actually treated horses with mild cases of West Nile Virus who have been vaccinated, and so, Guitar recommends two shots each year, six months apart.

A horse of any age can get the virus, but it gets it after being bitten by a mosquito. That means, Guitar said, one horse in a lot with others may get the virus, while the others won't necessarily be affected at all – unless they are also bitten by a mosquito carrier of the virus.

The first symptoms will show seven to 14 days after being bitten by the mosquito, and a horse's symptoms of West Nile virus are very much like a human's.

“The horse will have a headache, fever, change in mood, become hard to handle – almost mean or violent,” Guitar said. “How do you know if a horse has a headache? “In the treatment, you assume the horse has a headache and you try to relieve the pain and discomfort.”

A horse that isn't vaccinated that gets West Nile virus is very difficult to save because the virus gets in the brain, Guitar said.

“It takes about one to three weeks from the first show of symptoms until the point you know it can't be saved,” Guitar said. “It may go really fast, and the horse will get progressively worse every day. It will go down and won't have the faculties to get back up.”

According to a Texas Department of State Health Services website, the intensity of West Nile Virus activity in Texas fluctuates from year to year and depends on a variety of factors including the weather, the numbers of birds and mosquitoes that maintain and spread the virus. The season can last up until the first hard freeze of the year.

While according to the TDSHS website, humans can successfully use “an approved insect repellent every time you go outside,” Guitar said repellents are not really an option for horses.

But other warning precautions such as regularly draining standing water, and ridding the property of known mosquito nesting places such as old tires, buckets and similar receptacles where water can collect and stagnate are helpful.

“In this heat, horses need plenty of water to drink, of course,” Guitar said, “but the water needs to be clean and clear. It's the stagnant water where the mosquitoes breed.”