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Florida Medical Entomology Laboratory

Florida Medical Entomology Laboratory

Can Key West Meet the Challenge of a Dengue Epidemic?

What can Key West do to avoid a catastrophic dengue epidemic in the next few years? There is no doubt that Key West is at serious risk from a future outbreak of dengue in view of Key West's recent past experiences with dengue. Key West had 22 dengue cases in 2009 and in 2010 there were 66 cases. Both outbreaks were due to dengue virus serotype 1 (DENV-1) being transmitted by Key West's Aedes aegypti mosquitoes. A study conducted by the U.S. Centers for Disease Control and Florida's Health Department showed that approximately 1,000 Key West citizens were likely infected with DENV-1 during the 2009 outbreak (Radke et al. 2011. Dengue outbreak in Key West, Florida, USA, 2009. Emerging Infectious Diseases Considering there were 3 times the number of cases in 2010, it is likely that an additional 3,000 Key West residents were infected with DENV-1 (Tabachnick WJ. 2012. BuzzWords 12(1): 3-5). With a population of only 20,000 the 2010 incidence of dengue cases of 330/100,000 in Key West represented one of the highest incidences of dengue in the world. The risk for having symptoms of dengue in 2010 were greater in Key West than in the city of Singapore where there were thousands of cases (Tabachnick WJ. 2011. BuzzWords 11(1): 11-14).

There were no dengue cases in Key West in 2011 and 2012. The disappearance of DENV-1 from Key West might be attributed to 1) successful mosquito control having reduced Ae. aegypti populations, 2) failure of dengue to re-enter Key West from elsewhere, 3) not enough susceptible humans in Key West to support epidemic transmission of DENV-1 (Tabachnick WJ. 2011. BuzzWords 11(1) 11-14), and/or 4) lack of detection of infected individuals. It is important to note that due to the 2009 and 2010 DENV-1 outbreaks, approximately 4,000 Key West residents are likely immune to further infection with DENV-1. Further it is reasonable to assume that these are the very people that are most prone to mosquito-borne DENV transmission due to their life styles and behaviors. They have already demonstrated by their previous infection with DENV-1 they were indeed exposed to Ae. aegypti.

What is the risk from a future outbreak? Let's assume that the number of now immune Key West residents have reduced Key West's risk from DENV-1. What might one expect should other DENV serotypes (DENV-2, 3 or 4) enter Key West? Individuals previously infected with one DENV serotype, though immune to further infection with the same serotype, are at risk for more severe disease should they be infected with a different serotype (Pang et al. 2007. Of cascades and perfect storms: the immunopathogenesis of dengue hemorrhagic fever-dengue shock syndrome (DHF/DSS). Immunology and Cell Biology 85, 43–45. doi:10.1038/sj.icb.7100008). The reason for this is a process called dengue immune enhancement. It is most alarming that one in five Key West citizens are at risk for severe dengue from another DENV serotype.

A second infection with a different DENV serotype will result in more severe symptoms, a greater number of cases, and the appearance of dengue hemorrhagic fever with some deaths. It would not be surprising for an epidemic of, for example, DENV-2 to result in hundreds of reported cases and several deaths in Key West. There is no doubt that such an event would be a catastrophe for Key West's population, its health infrastructure and its overall economy.

What should Key West do? The first appearance of a different serotype of DENV in Key West, the appearance of the very first case, should be noted immediately and this appearance must initiate immediate effective actions to protect everyone. The first step is to be certain that anyone suspected of having dengue is identified immediately and the serotype of DENV recorded. If the serotype is identified as DENV-2, 3 or 4 what actions might be taken? The consequences of the entry of another DENV serotype into Key West are so dire it requires an aggressive community response. The Key West Department of Health should immediately declare that a "Medical Threat" exists in Key West. Such a declaration carries with it the ability for greater mosquito control efforts accompanied by very serious public service announcements to warn the public of the threat.

The declaration of a Medical Threat is an essential step. More must be done to make it clear to the public that the situation is extremely serious. Every citizen must take personal precautions to reduce their exposure to mosquitoes. Mosquito repellents such as DEET-based products should be made freely available with instructions posted prominently throughout Key West on their use. Community leaders should widely publicize through prominently displayed posters throughout Key West that everyone must protect themselves and their families from mosquito exposure. A widespread display of informative posters in Key West has been recommended previously (Tabachnick WJ. 2010. BuzzWords 10(4): 13-15). Under a Medical Threat the Monroe County Health Department must use whatever means available to ensure businesses close their windows and doors to prevent free entry and egress of mosquitoes and feeding on their customers, and to curtail outdoor activities such as outdoor dining. Public safety must take priority.

Should other efforts be promoted in the chance that these could prevent an epidemic? How can Key West reduce its Ae. aegypti populations? Can Key West simply allow the unrestrained production of Ae. aegypti by businesses and homeowners? There is no doubt that Key West mosquito control would spray for mosquitoes and identify and destroy many water containers where Ae. aegypti is produced. This is a very difficult task. We know that mosquito control was unable to do this single-handedly during the 2009 and 2010 epidemics partly because there was little community involvement and responsibility to assisting this effort. The employment of the genetically-altered Ae. aegypti males being considered for use in Key West would be likely helpful. What else could help? Key West is facing a potentially catastrophic epidemic.

I urge Key West to consider that all homes and businesses with containers capable of producing Ae. aegypti be subject to a fine to compel property owners to destroy Ae. aegypti habitats. This should be demanded by the community as a whole to protect everyone in Key West. For example, consider notices throughout Key West that beginning on some specified date all Key West properties identified having larval containers capable of producing Ae. aegypti will be issued notice giving the owners five (5) days to remove the containers. After five days of the issuance date those owners who do not comply will be fined $100, and then $100 per day thereafter until the property owner does comply. The citizens of Key West need to band together in block or community groups to compel their neighbors to comply.

There is precedence for this in Florida though the programs that are suggested must be instituted with local community authority and approval. Florida Statutes Chapter 388.291 (3) does state "Property owners in a developed residential area shall maintain their property in a manner that does not create or maintain any standing freshwater condition capable of breeding mosquitoes or other arthropods in significant numbers so as to constitute a public health, welfare, or nuisance problem…… If such a condition is found to exist, the local arthropod control agency shall serve notice on the property owner to treat, remove, or abate the condition. Such notice is prima facie evidence of maintaining a nuisance, and upon failure of the property owner to treat, remove, or abate the condition, the local arthropod control agency or any affected citizen may proceed pursuant to s. 60.05 to enjoin the nuisance and may recover costs and attorney's fees if they prevail in the action."

Figure 1 shows a yard that would result in a fine of $100 five days after initial notice to the owner. Is this unreasonable? Consider that this yard has the potential to produce enough Ae. aegypti to cause serious illness throughout an entire neighborhood. Does a homeowner have the right to do this? Can the neighbors and the community not take action to protect their families?


Figure 1. How many potential Ae. aegypti producing containers can you find? Does such a homeowner have the right to endanger the health and safety of a community? Are responsible officials in public health and mosquito control obligated to do something to prevent such a situation? Is cleaning such a property the responsibility of public health and mosquito control professionals? Are they able to essentially be trash removal for all of Key West? Photo credit: Dr. J. R. Rey  wtDengueKW1

Summary of a Proposed Key West Plan to Combat Dengue:

  1. Institute a program that fines owners of properties with containers capable of producing Ae. aegypti.
  2. Identify the appearance of DENV-2, 3 or 4 immediately.
  3. Declare a "medical threat" upon the first appearance of DENV-2, 3 or 4 in Key West. Institute public service announcements, such as displaying posters, about the need for precautions against mosquitoes, including repellent use, precautions for businesses and homes.
  4. Distribute mosquito repellents throughout Key West through schools, businesses etc. with instructions for use.
  5. Reduce mosquito exposure through closing windows and doors in businesses and homes; reduce exposure to children in schools.

This is serious business. The recommended measures are commensurate with the seriousness of the risk. Some will argue that the recommendations can have dire consequences on Key West's economy. It is almost certain that failure to aggressively combat dengue will result in many sick people and some who may die as a result. Such an event will surely damage Key West's economy due to the impact on its health infrastructure trying to care for the sick. It will also lead to a loss in visitors to the area due to a loss in confidence in Key West's ability to protect the public health. Key West has ample warning of what to expect. This is the time for the community to demand that actions are initiated to reduce the chance of a dengue epidemic.

Walter J. Tabachnick, Ph.D. - Retired
Florida Medical Entomology Laboratory
Department of Entomology and Nematology
University of Florida
Vero Beach, FL