Credit Healthmap Dengue
While mosquito activity is greatly suppressed across most of North America during the winter months, the same cannot be said for the tropics, where mosquitoes – and the diseases they carry – can thrive pretty much year round.
In 2010 Puerto Rico saw its worst Dengue outbreak in years, with the number of new infections at one point reaching nearly a 1,000 a week (see red line in chart below).
This epidemic ended in December of 2010, but before it was quashed it had infected more than 21,000 people, killing 31 (see MMWR: Dengue Epidemic In Puerto Rico).
The following year (2011) was an average or slightly below average year for Dengue in Puerto Rico, but by the middle of last summer (see Dengue Above Epidemic Threshold In Puerto Rico) dengue numbers began to rise in Puerto Rico.
In October of 2012 Health Secretary Lorenzo Gonzalez of the Puerto Rico Health Department once again declared a Dengue epidemic on the island (PDF Link – in Spanish), stating that at least six people have died, two of them being children (see Puerto Rico Declares Dengue Epidemic).
While mosquitoes exist year-round in Puerto Rico, the end of the rainy season (which normally runs April-Nov) usually signals a drop in their numbers.
The number of Dengue cases reported over the past several months has dropped since the epidemic declaration in October, although they remain well above the epidemic threshold.
The good news is that, while more than 3,500 cases have been reported since the first of the year, no fatalities have been recorded in 2013.
There are 4 different serotypes of the Dengue Fever virus (Puerto Rico is reporting types DENV1 & DENV4), so a person can become infected several times over their lifetime. Usually, the first infection with a dengue virus results in the milder form of the illness, while more serious illness can occur with subsequent infections.
With roughly 4 million residents and another 4 million annual visitors to Puerto Rico – 3,541 infections over the first two months of the year – while concerning - is still a small fraction of the exposed population.
One of the worries is that visitors may carry Dengue back home with them, and `seed’ local mosquito populations with the virus.
Cases of dengue in returning U.S. travelers have increased steadily during the past 20 years (8). Dengue is now the leading cause of acute febrile illness in U.S. travelers returning from the Caribbean, South America, and Asia (9).
Many of these travelers are still viremic upon return to the United States and potentially capable of introducing dengue virus into a community with competent mosquito vectors.
In truth, it may take many such introductions of Dengue or Malaria to an area before the right combination of weather, insect vectors, and ongoing transmission occur to enable it to get a foothold in a community.
Florida’s latest Arbovirus Surveillance report lists 19 cases of Imported Dengue thus far in 2013, with 7 of those originating from Puerto Rico:
Imported Dengue: Nineteen cases of dengue with onset in 2013 have been reported in individuals with travel history to a dengue endemic country in the two weeks prior to onset. Countries of origin were: The Caribbean, Columbia (2), Dominican Republic (2), Haiti, Indonesia, Jamaica (3), Philippines, Puerto Rico (7), and Saint Martin. Counties reporting cases were: Brevard, Broward, Clay, Lee, Miami-Dade (6), Orange (5), Osceola, and Palm Beach (3). Three of the cases were reported in non-Florida residents.
So far, no locally acquired Dengue has been reported in Florida this year.
The odds of contracting Dengue, or other mosquito transmitted diseases, are actually pretty low.
But they are certainly not zero.
With no vaccine, it makes sense to take reasonable precautions whenever you are around mosquitoes (and not just in Dengue endemic areas). Those who travel to, or live in areas where mosquitoes are present are reminded that to follow the `5 D’s’:
- Dengue is a mosquito-borne viral infection.
- The infection causes flu-like illness, and occasionally develops into a potentially lethal complication called severe dengue.
- The global incidence of dengue has grown dramatically in recent decades.
- About half of the world's population is now at risk.
- Dengue is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas.
- Severe dengue is a leading cause of serious illness and death among children in some Asian and Latin American countries.
- There is no specific treatment for dengue/ severe dengue, but early detection and access to proper medical care lowers fatality rates below 1%.
- Dengue prevention and control solely depends on effective vector control measures.