The return of dengue fever to Florida for the first time since 1934 is "unusual but not unexpected," state health officials said Tuesday. They acknowledged they can only speculate why it's happening.
So far in 2010, Florida has seen 28 locally acquired cases in Key West and one in Broward, plus 67 cases in the rest of the state acquired in foreign countries. Key West also had 25 cases in 2009, Florida's first in decades.
"We used to have dengue fever years ago, but it went away when we got better housing and better mosquito control," Dr. Carina Blackmore, expert in mosquito-borne illnesses for the Florida Department of Health, said in a Tuesday press conference.
"We know which mosquito (Aedes aegypti) transmits dengue fever. Those mosquitoes have been here all along, so we've known it could be transmitted. We've been watching for it for years.
"Because of human behavior, we've stayed indoors in the air conditioning, so mosquitoes didn't have access to us. So it was hard for dengue to be sustained in Florida."
Blackmore countered stories that dengue fever might have come via aid workers visiting Haiti, where dengue fever is prevalent. DNA testing has shown that the Key West cases came from Mexico, she said.
The Broward dengue fever case apparently had a different source because it was from the Type 3 strain of dengue, while the Key West cases are from the Type 1 strain. Samples from the Broward case are being sent to the dengue lab in Puerto Rico run by the U.S. Centers for Disease Control and Prevention, but she said it could take weeks to identify its origin.
Protecting against the Aedes aegypti is different from protecting against other mosquito species, Blackmore said. Most mosquitoes fly at dusk and dawn, so people should wear long sleeves and pants and use repellent at those times.
"The dengue mosquito is a day-flyer," she said, so people should use precautions all day long.
Also unlike other mosquitoes, which can feed on humans and animals alike, the Aedes aegypti feeds almost exclusively on humans, she said. So it flies around front and back doors, breeding in bird baths and water-filled pet dishes. It even tries to get inside the house, where it can breed in vases and even in water-filled bottle caps.
Spraying doorways with pesticides from home improvement stores can help, mosquito control officials have said, although such sprays contain lower concentrations of bug-killing ingredients than the sprays used by county trucks.