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Florida Medical Entomology Laboratory

Florida Medical Entomology Laboratory

Prepare in Advance for Dengue or Chikungunya in Your District

Anyone paying attention to recent events would have to bet that Florida will very likely experience an outbreak of dengue or chikungunya in the near future. The primary mosquito vectors of dengue virus (DENV) and chikungunya virus (CHIKV), Aedes albopictus and Aedes aegypti, are common in many regions of Florida. Aedes aegypti-borne transmission of DENV has already caused focal outbreaks of dengue in Key West, Monroe County in 2009 and 2010, and in Rio, Martin County in 2013. In addition there have been isolated cases of dengue in other counties in south Florida in the past several years caused by infected mosquitoes in Florida. Florida transmission has included 3 of the 4 DENV serotypes. Aedes aegypti-borne CHIKV caused hundreds of cases of chikungunya on several islands in the Caribbean in 2013-2014. Chikungunya is now being transmitted in the western hemisphere for the first time in recorded history. DENV is in Florida and CHIKV is poised to enter the U. S. and the most likely entry is Florida.

What might Florida expect? Both viruses could cause focal outbreaks similar to Key West and Rio, with a high incidence of cases confined to a small focal area, resulting in a low number of total cases. By comparison, other regions of the world have experienced outbreaks with numbers of cases in the thousands, e.g., dengue in Singapore and Thailand, or even in the millions, e.g., chikungunya in India. Hence, 22 and 66 dengue cases in Key West in 2009 and 2010, respectively, and 23 cases in Martin County in 2013 are cause for concern. Were DENV to take hold in the Florida southeast metropolitan area, West Palm Beach to Miami, population 5 million, with a similar incidence as Rio in 2013 of 800/100,000, there might be 45,000 cases! What should Florida mosquito control districts do to prepare for dengue or chikungunya? How can a district prepare for the expected focal outbreak in the community? What might districts do to prepare against more widespread outbreaks?

Florida mosquito control districts must take the possibility of dengue and chikungunya seriously and be ready. Mosquito control must not first initiate an anti-Ae. aegypti or anti-Ae. albopictus campaign after the appearance of the first dengue or chikungunya cases in a county. There is little chance that such a strategy can impact an outbreak that has already started. The message to all Florida mosquito control districts is to start such campaigns now!

Florida mosquito control is ill prepared to control domestic mosquitoes like Ae. albopictus and Ae. aegypti or the pathogens they can transmit. Mosquito control methods, though successful against other mosquitoes, e.g., various species of Culex and other Aedes, will not be successful against domestic mosquitoes developing in containers and living close to humans.

It is important that Florida's mosquito control and public health professionals understand the explosive nature of Ae. albopictus- and Ae. aegypti-borne DENV and CHIKV outbreaks. There are no surveillance methods analogous to Florida's surveillance programs for West Nile virus or St. Louis encephalitis virus. The only indication of dengue in a region of Florida will be the reporting of the first human case. Hence, reporting of cases quickly and involving mosquito control becomes even more critical to a successful intervention. Florida's recent dengue outbreaks unfolded quickly within a few weeks of the appearance of the first case. Likely a Florida epidemic could be similar to the Ae. albopictus CHIKV outbreak in Ravenna, Italy where 205 cases of CHIKV infection occurred between July 4 to Sept 27, 2007 (Rezza et al. 2007. Infection with chikungunya virus in Italy: an outbreak in a temperate region. Lancet 370: 1840-1846). The origin of this outbreak was an infected traveler who returned from India. The case incidence in Ravenna (pop. 158,000) was 131/100,000. The authors concluded "This outbreak of CHIKV disease in a non-tropical area was to some extent unexpected and emphasizes the need for preparedness and response to emerging infectious threats in the era of globalization."

Here I offer advice to all Florida mosquito control districts. Every district should implement the following immediately, before the appearance of a human case. It is critical to act now and not wait for the first case.

  1. Engage local health departments to be certain there will be surveillance and rapid communication of identified dengue or chikungunya cases, especially to mosquito control.
  2. Identify those areas in the district with Ae. albopictus and/or Ae. aegypti.
  3. Identify the high priority areas with the greatest numbers of these two species.
  4. Identify potential hot spots for transmission that need to be targeted for control now.
  5. Identify locations with the greatest number of larval habitats for the two vectors and target these locations for control now.
  6. Institute a public campaign to reduce Ae. albopictus and Ae. aegypti larval habitats in the community.
  7. Initiate a campaign that elicits public demand for local government to enforce ordinances prohibiting citizens from allowing Ae. albopictus and Ae. aegypti larval habitats on their property.
  8. Provide a document to the supervising authority over mosquito control that strongly advises that authority on the danger of dengue and chikungunya, and that it is the mosquito control districts' expert advice that local government must be informed of the requirement for government policies that will result in reducing habitat for mosquito larvae in the community.
  9. Work with local government and public health authorities to develop and implement policies, ordinances, actions that will result in compelling anyone who maintains Ae. aegypti or Ae. albopictus larval habitats to destroy these habitats.
  10. Initiate a mosquito control, public health and law enforcement campaign to reduce Ae. albopictus and Ae. aegypti larval habitats and monitor reductions in house indices.
  11. Prepare a plan for aggressive anti-Ae. albopictus and anti-Ae. aegypti mosquito control with consideration to using all means available to reduce transmission in the event of a widespread outbreak. Consider the following methods:
    1. Adulticiding by ground (truck mounted sprayers)
    2. Spraying individual houses and businesses as needed using hand held sprayers
    3. Reducing larval habitats on specific locations through house-to-house inspections
    4. Enlisting local government to enforce ordinances against productive larval habitats for Ae. albopictus and Ae. aegypti
    5. Providing mosquito repellents to citizens
    6. Campaigning with public service announcements of the danger and precautions against mosquitoes and mosquito larval habitats
    7. Reduce adult vectors, reduce transmission with consideration for using novel methods, if shown to be safe and effective, in addition to pesticides, source reduction and personal protection, i.e.,
      1. Replace the transmitting Ae. albopictus and Ae. aegypti with nontransmitting Ae. albopictus and Ae. aegypti
      2. Reduce adult vectors using GMO's to reduce populations, reduce transmission

Preparing for dengue or chikungunya.
I strongly advise every mosquito control district in Florida to seriously consider each of the above steps. If one thinks this is not something to be concerned about, I suggest that individuals just ask colleagues in the Florida Keys Mosquito Control District and at Martin County Mosquito Control. Failure to prepare, failure to advise those with authority over mosquito control of the danger and the need for implementing government ordinances and policies to enforce public participation in anti-mosquito efforts, is simply avoiding mosquito controls' professional responsibility. Responsible mosquito control professionals must provide correct information to government to enable elected officials to make sound policy. Our elected officials therefore must be advised about the need for ordinances that will reduce dengue and chikungunya and it is their decision to follow such advice or not. Florida mosquito control professionals have had ample warning. It will be professionally irresponsible if an outbreak occurs in a district that has not considered and taken some of the suggested steps above.

Preparing for dengue or chikungunya

Every Florida mosquito control district must be prepared. I can think of no current higher priority for Florida than to have better information from research on more effective methods to control dengue or chikungunya in Florida. I hope that those with responsibility to provide support for mosquito research in Florida recognize this critical need.

Mosquito control is not very good at controlling mosquito-borne DENV or CHIKV. We are not good at identifying the most productive habitats for Ae. albopictus and Ae. aegypti. With better information we might be able to target the worst areas with maximum benefit in reducing transmission. Where is the research to provide this information? Better tools are needed against container mosquitoes that include novel reagents, pesticides and/or non-pesticide biocontrol to control adults and larvae. Where is the research to provide this? We need messages to the public that will elicit effective government and public pressure that results in the active participation of residents in larval habitat reduction in homes and businesses. Where is the research that will provide the required successful messages?

Florida has a dengue or chikungunya epidemic in its future. Where an epidemic might occur is anyone's guess, however, South Florida seems most at risk based on recent history. The safe bet is for Florida's mosquito control organizations to prepare now and prepare the citizens they serve for whatever is in store for their county. Failure to do what is needed now is unacceptable and, if an epidemic occurs in a county, mosquito control will have to defend any failure on their part to take appropriate advanced steps to protect the public health and wellbeing. Florida's mosquito control organizations have the responsibility of alerting and engaging government leaders in their counties, and the public at large, about the danger of DENV and CHIKV now, in advance, to prepare their constituents for what will be required should the county experience an outbreak.

Florida has been amply warned.

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