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Key West Must Continue the Fight Against Dengue

There were no reported dengue cases in Key West during 2011! This welcome breathing spell provides Key West with time to reflect and prepare itself for any dengue in its future.

In 2009 Key West had 23 cases of locally‐acquired dengue. The U. S. Centers for Disease Control studied the blood of 113 Key West residents that allowed CDC to estimate that about 1,000 Key West residents were infected with dengue virus in 2009. Most of these people were likely asymptomatic, had symptoms that were not severe enough to seek medical attention or their infections were not reported by their physicians if they did seek medical help.

In 2010 there were 65 more dengue cases in Key West, 3 times the number of cases in 2009, and hence it is reasonable to estimate that another 3,000 Key West residents could have been infected with the virus. These estimates suggest that about 4,000, or 1 in every 5, Key West residents have been infected with the dengue strain or serotype DENV‐1! Though now immune to further infection with DENV‐1, these people are more at risk for severe dengue should they be infected with one of the other three dengue serotypes.

Why did dengue not occur in Key West in 2011? Three equally likely explanations come to mind. All may have contributed to some extent. 1) Key West mosquito control and the Department of Health successfully reduced populations of the dengue vector mosquito Aedes aegypti and reduced public exposure to Ae. aegypti mosquitoes. 2) Dengue virus did not survive through the Key West dry winter season when there are fewer adult mosquitoes, and/or the virus was not reintroduced into Key West from an infected traveler. 3) The 4,000 previously infected residents, all now immune to DENV‐1 and likely the high risk population of Key West, reduced the number of high risk susceptible people so that the transmission of DENV‐1 could not be sustained.

What does this mean for Key West? Although 4,000 citizens are immune to DENV‐1 there is now the danger that these people will develop severe symptoms should they be infected by any of the other three DENV serotypes. This will result in more severe disease, more people seeking medical help, and the great potential for dengue shock syndrome in some patients, and a greater potential for fatal cases would be expected. You can learn more about dengue and disease severity at http://edis.ifas.ufl.edu/in699 or http://www.cdc.gov/dengue/symptoms/index.html.

Hopefully the absence of DENV‐1 in 2011 was due to the efforts of Key West mosquito control and public health agencies. If true, these efforts must be continued to reduce the impact of another serotype by reducing human exposure to both the vectors and the virus. The anti‐Aedes aegypti campaign should include community‐based participation, with the public actively eliminating all the sites where these mosquitoes breed in and around their homes and businesses. Everyone should be exerting peer pressure on their fellow citizens to actively take precautions to reduce vector abundance throughout Key West. Does one have the right to produce mosquitoes on one's property that endanger the health of one's neighbors? Actions taken now will reduce Ae. aegypti, and prevent or mitigate transmission should it begin again this summer.

I hope I am wrong, but I believe it is unlikely that dengue has vanished from Key West and will never appear again. It is prudent to anticipate another case of dengue in Key West's future that may be a prelude to more cases. In the event of future dengue cases it will be vital for Key West to immediately identify the dengue virus serotype. If it is not DENV‐1 then the previously infected Key West citizens are in peril of severe disease. These will be the people who must understand in clear terms how they must change their behavior to reduce their exposure to Ae. aegypti and DENV. It is imperative that both mosquito control and the public work together to reduce the vector populations and reduce mosquito‐human contact.

Key West's community leaders need to declare war on dengue to continue aggressive mosquito control operations against Ae. aegypti. The public should be active in reducing water containers that support Ae. aegypti around their homes and businesses, using effective mosquito repellent as personal protection against biting mosquitoes and, if needed, curtailing activities that increase exposure to mosquitoes. The appearance of another DENV serotype in Key West might warrant declaration of a medical threat and bring additional anti‐mosquito resources to bear, so that the public is advised to minimize outdoor activities wherever and whenever Ae. aegypti mosquitoes are active. This would, of course, have other consequences on the Key West community and the declaration of such measures would not be taken lightly or cavalierly. However, the public health consequences might warrant such action.

Preventing dengue in Key West is important to the rest of Florida. The incidence of dengue in Key West was 325 cases/100,000 people in 2010. Should this incidence occur in Florida's Southeast Metropolitan Area extending from West Palm Beach to south of Miami, population of about 5 million, more than 15,000 people would have dengue symptoms severe enough to seek medical attention, and another 750,000 people would have less severe symptoms! Key West's anti‐dengue campaign must continue to be vigorous, even in this period without active dengue transmission. Although Key West mosquito control continues to fight Ae. aegypti, I fear that a call by community leaders for public action in the fight in August would be too late.

   Walter J. Tabachnick, Florida Medical Entomology Laboratory
   Professor, Department of Entomology and Nematology
   University of Florida IFAS
   Vero Beach, Florida