U.S. Safe From Tropical Diseases No More: Understanding the recent dengue fever outbreak in Florida

By Alexander Bernstein

A great biological benefit of a nation located in a temperate climate, as is the case with the majority of the United States, is that tropical diseases such as typhoid fever and malaria are typically non-issues. Yet, a recent dengue fever outbreak in Florida seems to indicate that perhaps the changing climate, in tandem with certain additional factors, has ended those days of security against such medical problems.

The structure of a dengue virus (via University of Wisconsin).

On a worldwide basis, some 300 million people are affected by the disease, which, although rarely fatal, accounts for some 25,000 deaths. A mosquito-borne infection  caused by a family of four viral species (DEN-1, DEN-2, DEN-3, and DEN4), dengue yields severe flu-like symptoms with a characteristic combination of very high (>40°C) fever, pain behind the eyes, and general rash. Although there aren’t any specific treatments or vaccines, medical care administered in cases of severe dengue decreases mortality rates from 20% to 1%.

While the past century has seen virtually no locally-acquired cases of dengue in the United States, with any documented infections coming from people crossing the Texas-Mexico border or from immigrants, the recent outbreak in Florida has given researchers serious reason to believe that the virus-carrying mosquitoes have finally gained a foothold on U.S. soil.

Currently, much of the situation is plagued by uncertainty. One phenomenon that is baffling researchers is that while reasonably large populations of dengue-carrying mosquitoes have been found both in Florida and Arizona, only Florida has experienced a chain of confirmed cases of dengue while no documented cases have come from Arizona. Mary Hayden, a researcher at the National Center for Atmospheric Research in Boulder, has so far published the leading theory, in which she suggests that the answer may lie in the length of the virus cycle in the mosquitoes. According to Hayden, Florida’s warm and humid climate appears to allow the infected mosquitoes to live long enough (4-9 days) to transmit the disease to humans. If this theory proves accurate, then it will have serious geographic and climate repercussions as scientists will be able to predict the areas where dengue fever may hit based on the mosquito life expectancy that the area’s climate supports.

With that said, however, Hayden warns that much of her research is still in its infancy as she explains, “We have just finished our first season of collecting mosquitoes but they are still being processed in the lab.” Further, Hayden and colleagues are quick to point out that while cases of patients with dengue fever are documented, little work has been done to track the populations of mosquitoes that carry the virus. Thus, further research is required before the true scope of the situation can be understood and quantitatively evaluated.

With the lack of availability of any true remedies against dengue fever, a better comprehension of why it appears to affect some areas but not others would prove quite the valuable discovery.

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