In 2009 when test results on the ailing New York woman who had vacationed in Key West came back positive for the dengue virus, it was the first reported case in Florida since 1934.
Dana Focks, Ph.D., a research professor in the department of environmental and global health who develops mathematical models for vector-borne disease, is examining the cause of the outbreak. With 22 cases in 2009 and 61 cases in 2010, dengue in Key West is certainly not at epidemic proportions, but because of the large number of tourists who visit the island, it’s important to understand the best ways to prevent the virus’ spread.
“There are almost 2 million cruise ship visitors who get off their ships and walk around Old Town in Key West,” said Focks, a member of UF’s Emerging Pathogens Institute. “A lot of those ships have ports of calls in dengue endemic areas before they arrive in Key West.”
Dengue causes flu-like symptoms — fever, headache and muscle and joint pain. The World Health Organization estimates there are 50 to 100 million infections each year. About 500,000 people with the virus will develop potentially lethal dengue hemorrhagic fever, which causes about 22,000 deaths, mostly in children.
Dengue passes from person to person by way of the mosquito Aedes aegypti, an insect found in mostly urban, subtropical areas. Except for the Texas-Mexico border, the only location in the United States where Aedes aegypti exists in epidemically significant levels is in the Florida Keys.
When Focks evaluated data collected by the Florida Mosquito Control District he discovered an inconsistency in the mosquito population that may be traced to Key West’s historic homes.
“Aedes aegypti breeds in domestically stored water and bromeliads,” Focks said. “In Key West they do a good job controlling mosquitoes in containers above ground they can see, but when you look at how many adult mosquitoes they have compared to the number of immatures — the larvae and the pupae — there’s a disconnect. What we’ve concluded is that they’ve got a lot of breeding in underground water storage cisterns.”
It was common for early Key West residents to build cisterns under their houses to collect rainwater, but throughout the years as homes change hands and access holes to the cisterns are covered up, some current homeowners may not even know the cisterns exist, Focks said.
“I’m hopeful that if they control the cisterns and some septic tanks, Key West will have mosquito populations too low to support dengue,” he said.
The El Niño climate pattern also plays a major role in worldwide mosquito populations and disease, Focks said.
“Higher temperatures speed up the mosquito’s incubation period for dengue,” Focks said. “When you raise the temperature a few degrees you might double the number of potentially infectious mosquitoes. Also, higher temperatures make them lay eggs faster so they lay their eggs and they’re back on the street looking to bite someone to get more protein to make more eggs.”
Focks has developed an early warning system for dengue that uses National Oceanic and Atmospheric Administration (NOAA) satellite data of sea temperatures to predict the risk of dengue up to four months into the future for countries with endemic dengue, like Indonesia.
“An early warning system helps them manage the disease,” Focks said. “If they have a head’s up that they’re going to have dengue they can put messages out in the schools and send home fliers with the kids to tell their parents to pay special attention to keeping their water storage containers clean and free of mosquitoes.”