New York at Low Risk for Dengue

I was able to interview Dr. Roxanne Connelly, who is Associate Professor and Extension State Specialist of Medical Entomology at the University of Florida on July 16. She provided insight into the current outbreak of dengue fever in the Key West area, and the ways that it might spread, including into New York.

Many tropical illnesses are carried from person to person by mosquitoes. The Aedes aegypti is the variety carrying dengue fever in South Florida. Dr. Connelly describe this type of mosquito as living very close to people. It hides in closets and under tables, dark places with little air movement.

Party Central
Duval Street in Key West is described by Dr. Connelly as "party central". Doors and windows are open all the time and unscreened. Mosquitoes seeking shelter from the sun and heat can enter any of the bars and restaurants, hiding under tables, chairs and benches, and humans come to them. The most common area for A. aegypti to bite is the lower leg. This area is the focus of most of the cases.

There have been 28 cases of dengue fever traced to Key West in 2009 and 2010. In mid-July 2010 additional cases were reported in the Miami area and farther north in Florida. Connelly told me that many of these cases will be found to have been acquired abroad, and pointed to two in particular. One case of dengue was caught in Puerto Rico where the disease is endemic. Another was caught in Haiti. The Centers for Disease Control (CDC) warn about the potential for exposure in both Haiti and Puerto Rico.

The CDC has estimated, based upon blood samples obtained from a representative set of individuals in Key West, that as many as 1,000 local residents may have contracted dengue fever. Dr. Connelly also pointed out that when the Key West outbreak began, in the late summer of 2009, the primary health concern for physicians and patients was swine flu. She suggests that a number of dengue cases were simply regarded as the flu, since the symptoms are virtually identical in mild and moderate cases.

A. aegypti does not winter over very far north in the United States. A relative, Aedes albopictus, the Asian Tiger mosquito, is found much farther north and has been caught, during the summer, in New York City. In an e-mail, Dr. Laura Harrington, Associate Professor, Department of Entomology at Cornell University, described this mosquito:

"This is a more temperate species originally introduced in used tires from Asia in the mid 1980s. Although this species has not been able to overwinter in Western New York State yet (it may with climate change in the coming years), we have collected it in the summer time in New York, especially in the New York metropolitan area.

I am currently on sabbatical at the Arthropod Borne Diseases Laboratory in Colorado, and am looking at the vector competence of New Jersey strains of Ae. albopictus for Chikungunya virus. Invasion into New York State will likely be by this New Jersey strain which does have the ability to overwinter in New Jersey. In addition, we are working on predictive risk models for the New York and Northeast to understand what the risks are for introduction of Chikungunya (and other viruses) in the area and how quickly it would spread. We are also interested in identifying the most effective intervention, monitoring and education methods.

The Asian tiger is also a competent vector of all four Dengue viruses as well as a long list of other viral pathogens that impact human health, so if you are concerned about Dengue, this species would be the culprit."

Dr. Connelly pointed out that the Key West lifestyle, with the open windows and doors in a semi-tropical climate, enables the spread of dengue fever by A. aegypti. New York and New York City have a greatly different climate and lifestyle making the spread of dengue into the area unlikely.

She does warn that nothing is impossible. A more likely scenario for for a New York outbreak of dengue or any other mosquito borne virus is one where a traveler brings the illness home, and is bitten enough by local mosquitoes to create a local outbreak. That person might not know they are infected yet could still be the source of an outbreak. She pointed to the last malaria outbreaks in Florida as examples of such a scenario.