Florida: Fewer Mosquitoes, Fewer EEE Cases

Fifteen cases of Eastern equine encephalitis (EEE) have been detected in Florida this year, prompting veterinarians to conclude that drought has been keeping mosquito numbers down. Typically, the state logs an average of 65 cases by the end of summer.

"This is certainly much lower than our average number," said Mike Short, DVM, equine programs manager for Florida's Division of Animal Industry. "I have looked back at records for the last approximately 18 years…this (decrease) is at least in part due to the significant lack of rainfall. It's been really dry here. In fact, our drought index is pretty high throughout most of the state."

The past two years have been marked by hurricane activity associated with heavy rainfall, creating standing water that served as breeding grounds for mosquitoes. High numbers of EEE cases in those years likely was caused by the bumper crops of mosquitoes that emerged after the storms.

According to Short, areas of Florida are still 20 inches below normal annual rainfall this year, even though there has been some rain in recent weeks. Another contributing factor to fewer EEE cases is the cyclic tendency of the disease, which historically peaks every five to eight years in Florida. After logging more than 150 cases each year for the past two years, the state could be experiencing a natural waning of the disease.

Eastern equine encephalitis is a reportable disease in Florida, so veterinarians must submit samples from suspect cases for testing. The reporting form requires information on the horse's EEE vaccination history, if it is known.

"There are a lot of times the veterinarians aren't sure about the vaccine status, and I think a lot of times the vaccination history is vague," Short said. Only one of the 15 cases this year was confirmed as current on its EEE vaccination. The vaccination status for most of the 15 horses was unknown.

Short recommended that owners contact their veterinarians and have their horses vaccinated for EEE at least twice a year.

The EEE cases this year were reported in 11 counties: Alachua, Columbia, Duval, Glades, Jefferson, Lake, Levy, Madison, Marion, Polk, and Santa Rosa. Nine of the affected horses died or were euthanized, five survived, and the status of one horse is unknown. In addition to the equine cases, an EEE case was confirmed in a sick hawk from Volusia County. 

"Anytime we get a different wildlife species (with EEE)…they can act as rough sentinels for the disease, as do horses and chickens," Short said. "This helps public health officials decide where the risk for the disease is, and whether they should spray for mosquitoes or put out public service announcements."

There have not been any confirmed cases of West Nile virus in Florida this year.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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