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