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Infectious Disease

Dengue fever: Why it’s becoming more common in the U.S. and what Americans should know

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The Aedes aegypti mosquito, shown here, is one type of mosquito capable of infecting people with dengue fever. (REUTERS/James Gathany/CDC/Handout via Reuters)

Last week, health officials announced that a New York man had contracted dengue fever – an infectious disease found predominantly in tropical climates – from a local mosquito, raising questions about the prevalence of the disease in the United States.

Based on data from the Centers for Disease Control and Prevention (CDC), numerous cases of dengue have cropped up in the United States and its territories throughout 2013, with 20 cases of dengue occurring in Florida, three cases in Texas and 7,221 occurring in Puerto Rico.

Dr. Kay Tomashek, the epidemiology section chief for the CDC’s dengue branch in San Juan, Puerto Rico, said that the disease – while still relatively rare – has become more prevalent throughout the entire Western Hemisphere over the past few decades.

“In the Western Hemisphere, dengue has increasingly become a public health problem,” Tomashek said. “There’s a paper from 2012 showing that in the last three decades, there’s been an exponential increase in dengue cases and dengue severity. We’re seeing more countries having problems with dengue and more frequent and more severe outbreaks.”

A traveler’s disease

The dengue virus is most commonly introduced into the U.S. population by returning travelers who contract the disease abroad, according to Tomashek. In fact, dengue has become the leading cause of illness among travelers returning with acute fevers.

And as people increasingly chose to travel to remote locations, cases of travelers bringing the disease back to the United States have increased.

“If you were to travel to Puerto Rico and get bitten by a mosquito there…and return home and you live in Southern Florida, you could then transmit that virus in your blood to a mosquito if you had one in your house and it bit you,” Tomashek said. “Then, within another week (that mosquito) could transmit the virus to all the people in your household.”

Other factors contributing to climbing rates of dengue fever throughout the world include increasing rates of pesticide resistance among the two types of mosquitos responsible for transmitting dengue – the Aedes aegypti and Asian tiger mosquitos – and a lack of good methods by which to control the disease.

“We haven’t been effective at reducing the population or spread of Aedes aegypti,” Tomashek said. “… We are all in search of a more effective, more sustainable vector control method. We don’t have one now, and no country does.”

What happens when an outbreak occurs in the United States?

During dengue outbreaks in the United States, cases are often managed at the state level, though the CDC is sometimes called in to provide additional assistance. Because there are no primary prevention methods for the disease, the CDC focuses on educating health care providers and locals about the warning signs and risks of dengue.

“When a human does get dengue, we would like to reduce morbidity and (the) chance they would die,” Tomashek said. “What we stress in outbreak response is that the population and physicians and clinicians, nurses seeing dengue patients are able to clinically identify patients and offer them the correct anticipatory guidance so that they don’t come in too late, when they really need to be urgently seeking care.”

Dengue is a febrile illness, meaning it involves a fever that typically lasts a week or less. In the early stages of the disease, victims will feel aches and pains and may experience minor bleeding, such as when brushing teeth. This can be accompanied by increased bruising, and sometimes a rash on the upper face and chest. As the fever breaks, people may also develop small bruises on their lower legs and feet.  

People infected with dengue should focus on hydrating, and patients can take Tylenol to alleviate some of their symptoms.  However, they should avoid non-steroidal anti-inflammatories or Aspirin, due to an increased risk for bleeding, according to Tomashek.

Most people successfully recover from dengue after a week or so, but a small percentage of those infected experience a much more serious, deadly phase of the disease that doesn’t begin until after the initial fever breaks.

“With dengue, when a fever goes away, sometimes in a small proportion of individuals – less than 10 percent, most times less than 5 percent – develop a more severe form of the disease: dengue hemorrhagic fever and dengue shock syndrome,” Tomashek said.

Dengue hemorrhagic fever is characterized by increased bleeding and a worsening of the general symptoms occurring during the febrile phase of the disease - and can ultimately lead to the more severe dengue shock syndrome.  If patients develop persistent vomiting, severe abdominal pain or weakness after their fever breaks, they need to see a health care provider or visit the emergency room (ER) immediately, according to Tomashek. These are signs that a person is experiencing plasma leakage syndrome – which occurs when the small blood vessels in the body open up and plasma from the blood is released into the abdomen and plural cavity, where the lungs reside.

“It becomes an emergency, something where they want to go in and should be seen and treated as in-patients in the hospital,” Tomashek said. “If they remain in shock at home, or for long periods of time in the ER, they can develop severe hemorrhage from the (gastrointestinal) system, rectal bleeding and vomiting blood. And then there are certain individuals who don’t seek care or are not recognized as having dengue or being in shock, they succumb to the disease, they may die.”

During an outbreak, most of the CDC’s efforts are focused on alerting people to the symptoms of dengue and educating the population about when they should seek emergency care..

Overall, people living in New York or other places where cases of dengue have occurred shouldn’t be too worried about an outbreak. But for people traveling to tropical destinations over the holidays, they should be aware of the risk of contracting the disease and carrying it back to the U.S.

“Right now, its winter in New York, so the biggest concern New Yorkers should have is when they go on holiday, they’re more at risk of getting dengue travelling to the tropics than in their own back yard,” Tomashek said. “They should really do a little research about where they are traveling and take precautions.”

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