Florida EEE cases up sharply with mosquitoes on rise

Florida EEE cases up sharply with mosquitoes on rise

75-plus horses affected in northern counties; risk of WNV also heightened
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Sep 01, 2008

GAINESVILLE, FLA. — It's a big year for mosquitoes in Florida, and one result is a much higher incidence of Eastern equine encephalitis (EEE).

"We want to get the word out that EEE is a serious problem here this year, so anyone bringing horses down from the North should make sure the animals are vaccinated," Maureen Long, DVM, MS, PhD, Dipl. ACVIM, assistant professor of equine and large-animal medicine at the University of Florida's College of Veterinary Medicine, tells DVM Newsmagazine.

About 75 horses, mostly in north and north-central Florida counties, which have the state's highest equine populations, were infected with EEE by the middle of August, Long says, adding that "we're only at the beginning of the peak season for EEE. We haven't seen numbers like that at this point in the season for a long time."

While most horses are vaccinated against EEE, younger horses that haven't had time to build up sufficient immunity from vaccines are most at risk, she explains.

Emu farms, which raise the large birds for meat and for pets, also present a risk. "They're very pathogenic for EEE," Long says. The birds shed the virus, putting producers at risk while butchering, and veterinarians while examining the pet birds.

There can be spillover risk to dogs and other animals, too. "Any mosquito-borne virus can be seen in many animals; mosquitoes may seek a blood meal from anything that walks. When you start seeing it (virus) in species in which you don't normally see it, that's a strong indication of a serious problem. So the warning is out there that it's time to adjust behaviors as necessary to deal with it," Long says.

In addition to the nearly 75 equine cases of EEE, three emus, one alpaca and one dog have been infected, but so far no human cases have been reported.

Populations of mosquitoes that breed in salt marshes near Florida's ocean and Gulf shores, where most people live, are surging in concentrations not seen in more than a decade, entomologists say, and they're tough to control because of built-up resistance to several pesticides and the fact that water levels in the marshes are low.

Because salt-marsh mosquitoes don't lay their eggs in free-standing water, many counties, including Brevard County on the eastern coast around Cape Canaveral, have built mosquito impoundments, or earthen dikes, around marshes and mangrove swamps to flood out the pests, but this year water levels in them are much lower because of insufficient rain, allowing the mosquitoes to lay their eggs in moist soil above the water mark.

The same is true on the state's Gulf coast.

"This is indeed one of our worst years for salt-marsh mosquitoes," James Burgess, entomologist with the Lee County Mosquito Control District near Fort Myers, tells DVM Newsmagazine. "I don't believe we've seen them in these numbers in the last four or five years, following some good years when there was enough rain to flood them out."