EEE: Mosquito-Borne Disease Season Begins in South Florida, Wellington Warmblood Dead

Mosquitoes carry diseases that can be fatal to both horses and humans. Photo by Debris Field.

Eastern Equine Encephalitis is one of the most widely publicized–and feared–diseases in horses in the United States. It is spread by mosquitoes and each spring we follow its progress north with the heat.

But today’s news from Florida is unusual. Florida is a hot bed of EEE and may have as many as 200 horses a year die from the disease. But they aren’t usually in South Florida, and today’s death announcement was from the most exclusive and horsiest address: Wellington, Florida.

The Palm Beach County Health Department has issued a public health alert for the region. The alert mentions that from late May to early June, Culiseta melanura mosquitoes were discovered in the sentinel mosquito traps monitored by County Mosquito Control and used to determine mosquito counts and species,. This is the mosquito that carries the EEE virus; it is not generally found in South Florida.

Dr. Mary Echols, who oversees arbovirus activities for the Health Department said, “Normally we see EEE in horses that have traveled out of area and infected prior to returning to our county. However, this case was in an unvaccinated horse that had not traveled outside the county the month prior to its illness. Coupled with the mosquito finding it is the first locally acquired case of this virus, this year.”

Mike Short, DVM, Equine Program Manager for the State of Florida Veterinary Office in Tallahassee was in his office late on a Friday afternoon and took time out to answer some questions about this outbreak.

First of all, Dr. Short wanted to be clear that EEE vaccinations are available and promoted throughout the state of Florida. The vaccine is inexpensive, but it needs to be repeated annually. No area of Florida is immune to the danger of EEE.

Since the disease is spread by mosquitoes, it is important to understand that the disease cannot be transmitted from one horse to another. However, if an infected mosquito can bite a horse, it can also bite and infect a human.

Some reports have suggested that the appearance of EEE in South Florida might be related to the recent torrential rains in the region, particularly from Tropical Storm Debby.

Dr. Short agreed that rain can cause an increase in mosquitoes, but that an association with EEE is not consistent. Florida has been in a drought cycle. He referenced the state records for specific years in which cases of EEE in Florida were down, in spite of heavy rains.


What is a typical year’s count of EEE cases in the state of Florida?

Dr. Short said, “We have EEE every year in Florida. An average year claims 74 horses, with a high around 200 cases in some years. But, so far, this year is slow; we have only had nine cases so far. Last year (2011) was quite low, with a total of only six cases for the entire year. Typically, Florida has low counts for five or six years, and then it peaks again. This is probably because the virus is changing.? Some years it is more virulent.

Which months usually have the most infections?

June and July are the peak months in Florida.

Why is the Wellington horse’s death significant?

EEE is not unknown in South Florida. Historically, we did not have cases in the five southern counties. But there were a few cases in 2009 and in 2010 a couple of cases in Palm Beach County.

Why do you think people don’t get their horses vaccinated for EEE?

Horseowners are complacent. They are more worried about a new disease than about EEE, which is a known killer. We find that about 90 percent of horses that contract the disease have not been vaccinated in the past year. Also, the economy is having an effect. Veterinarians tell us that some people are skipping vaccinations to save money.

Are there cultural prejudices against vaccinations, such as in New York with the Amish not vaccinating their horses?

Not really. It’s more economic. Or some people just don’t get around to it. There are a few holistic people who object to vaccinations as being harmful to the horse.

Can you provide any more details on the horse in Wellington that died last week? Was it from another state?

Yes, we have details. The horse that died had not traveled in the past month. It was a three-year-old warmblood gelding and had been in Wellington.

Is EEE the biggest danger to horses in Florida now? Are you following any other horse disease problems?

A. EEE is preventable by vaccination, and it must be given every year. Pigeon fever (Corynebacterium pseduotuberculosis) is potentially a bigger problem, although it is not a fatal disease and it can be cured. It’s also not a virus, it’s a bacterial infection.

I know of one veterinarian who has treated 60 cases; there is more pigeon fever than ever before. This disease was traditionally not seen in Florida very often. There was an outbreak in Walton County and there have been 6 to 10 cases in Ocala. Our office has sent information to the veterinarians. It is true that some horse shows in the Panhandle area have been cancelled. Pigeon fever affects all types of horses and there’s no vaccine.

Horseowners should contact their veterinarians to schedule vaccinations for horses and take all precautions to remove standing water on property where mosquitoes may breed. Also take proper precautions when and if your community plans aerial or roadside spraying operations. Since EEE can also affect humans, insect repellant and/or long sleeves and long pants are important for humans who are outside.

Thanks to Dr. Short for his interview.

To learn more:

Visit the state of Florida’s web page on Eastern Equine Encephalitis (EEE).

Download the state of Florida’s warning about pigeon fever in horses.




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