The Florida Commissioner of Agriculture and Consumer Services said today that the mosquito-borne disease has affected 158 horses in 42 counties this year.
There were 25 cases among horses in 2002.
Very few of the horses are usually vaccinated and many usually die. State veterinarians say horses should be vaccinated two to three times a year.
Eastern equine encephalitis is a viral disease that attacks the central nervous system of people and horses. It is spread by mosquitoes, which transmit the disease from infected birds.
Although transmission to people is rare, it can kill up to half of those who catch it.