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MMWR: Travel Associated Dengue Surveillance 2006-2008

 

 

# 4659

 

 

 

Four weeks ago the CDC’s  MMWR released a report on the re-emergence of locally acquired Dengue Fever in Key West, Florida after an absence of 70 years. 

 

A bit ironically, the first case was detected – not in Key West – but in New York state by a doctor who saw a woman returning from a Florida vacation.

 

You can find that report here.

 

While these cases were acquired locally, the virus was probably reintroduced to the area by an infected traveler or visitor who was bitten by a mosquito, and that mosquito went on to bite others.

 

Like many other viral infections (influenza, West Nile, etc), not everyone who is infected experiences symptoms. And with Dengue, it is often the second or third infection (there are 4 sub-types) that proves the most serious.

 

The MMWR described the South Florida’s vulnerability this way:

 

The environmental and social conditions for dengue transmission have long been present in south Florida: the potential for introduction of virus from returning travelers and visitors, the abundant presence of a competent mosquito vector, a largely nonimmune population, and sufficient opportunity for mosquitoes to bite humans.

 

 

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As a former resident of the Florida Keys (Conch Republic to us natives), I can attest to the part about the `abundant presence of a competent mosquito vector’.  We lived slathered in DEET and enclosed the cockpit of our boat with mosquito netting for sitting out on deck at night.

 

While 28 cases of Dengue have been confirmed thus far in Key West since last September, a seroprevalence study conducted last fall suggests that far more may have been exposed.

 

Again from last month’s MMWR.

 

A serosurvey was conducted by FDOH and CDC, using randomly selected households, during September 23--27, 2009. Of 240 participants tested, 13 (5.4%) had evidence of recent dengue infection.

 

The population of Key West runs about 25,000.   But that’s just part of the story. 

 

More than 2 million visitors come to Key West each year. And like the tourist from New York, the concern is some of them might find themselves taking more home with them than just a sunburn and a souvenir Florida Tee-shirt.

 

Yesterday the MMWR came out with a new report on Travel Associated Dengue in the United States between 2006 and 2008. 

 

This surveillance pre-dates the Key West outbreak, and as the study reports, `Clinically recognized cases of travel-associated dengue likely underestimate the risk for importation because many dengue infections are asymptomatic or mildly symptomatic’.

 

The link (read the whole thing) and a small excerpt, then a few more comments on my part.

 

Travel-Associated Dengue Surveillance --- United States, 2006--2008

(EXCERPT)

During 2006--2008, CDCDB received a total of 529 specimens from 524 patients in 41 states and DC for dengue testing (153 in 2006, 272 in 2007, and 104 in 2008).

 

Of the 529 specimens, 136 (26%) resulted in a diagnosis of dengue. Among those 136 specimens, 106 (78%) had elevated antidengue IgM antibodies (probable recent dengue infection), and 30 (22%) had a dengue virus identified in serum by either reverse transcription--polymerase chain reaction (RT-PCR) or viral isolation (confirmed acute dengue infection).

 

Serotype specific data were available for those 30 cases, of which 14 were DENV-1, seven were DENV-2, six were DENV-3, and three were DENV-4. Results for 162 (31%) specimens were classified as indeterminate because blood samples were not collected within specified timeframes.

 

Among the 215 patients (41% of all specimens received) whose laboratory results were negative (RT-PCR or IgM negative, or no virus isolated), 38 (18%) had evidence of past flavivirus infection. In addition, the amount of serum provided for 16 (3%) of the patients was insufficient for testing, and in one sample the infecting virus could not be identified.

 

 

In order to spread, Dengue requires the right mosquito vector.  And the two species best suited to transmit the virus are the Aedes aegypti and Aedes albopictus mosquitoes, which also can spread such diseases as West Nile, Malaria, Yellow Fever, and Chikungunya.

 

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Map showing the distribution of dengue fever (red) and the distribution of the Aedes aegypti mosquito (cyan)  in the world, as of 2006. Agricultural Research Service of the US Department of Agriculture.

 

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Map showing the native habitat (blue) and recent spread (green) of the Aedes albopictus mosquito.

 

According to a recent report, as many as 28 states in the US have at least one of the these mosquito vectors.

 

A few earlier blogs on Dengue, Chik, West Nile and mosquito vectors includes:

 

From the `Nature Bats Last’ Dept
The Threat Of Vector Borne Diseases
Clipping Dengue’s Wings
It's A Smaller World After All

 

For more information on Dengue Fever, and ideas on how to prevent its spread, you may wish to visit the CDC’s comprehensive Dengue Page.

 

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