Q: What is dengue fever, and can you get it in the U.S.?

A: Dengue fever is an infectious disease caused by the dengue virus (there are four different "strains") which is transmitted by an Aedes mosquito bite (this mosquito lives in warm climates in the tropics and subtropics). After someone is infected (whether they develop symptoms or not) the virus may persist in their blood for several days to a couple of weeks, so if another Aedes mosquito bites them during that time it can become a carrier of the virus (it does not harm the mosquito) for the days, weeks or even a month of its remaining lifespan, and then spread it to someone else it subsequently bites.

Although dengue is the most common insect transmitted infection (the World Health Organization, WHO, estimates that worldwide there are hundreds of millions of people infected every year, and up to 100 million cases develop some symptoms; almost half the people on the planet are at risk of becoming infected), almost all the several hundred to a thousand cases diagnosed in the U.S. per year are contracted by people who have traveled to other countries. However, there have been rare cases of dengue that are believed to have been contracted in patients in the U.S. (in the warmer states where the Aedes mosquito may be found).

WHO has identified three subtypes of infection from dengue; dengue fever (DF), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). DHF and DSS are sometimes grouped together and termed “severe dengue fever.” DF may be caused by any of the four strains of the virus, and infection with any of the strains of the virus is thought to give the patient lifetime immunity to that specific strain. DHF and DSS are thought to occur in a small percentage of patients who have a history of having been infected with one strain of the virus and then at a later time become infected with a different strain; an "overreaction" of the patient’s immune system is thought to play a role in them developing the more severe symptoms described below.

DF is the mildest form of dengue infection. Fifty to 90 percent of people infected with dengue have minimal or no symptoms. After an incubation period of several days to a couple of weeks, those who do have symptoms may develop muscle, bone and/or joint pain (sometimes very severe, and hence DF is sometimes called break-bone fever), fever (often as high as 104 degree or higher), headache, weakness, nausea and/or vomiting, rash (flat red areas covered with small bumps that may be patchy and may be found on the face, chest, an insides of the arms/legs), sore throat, mild bleeding (for example bleeding of the gums, small red/purple dots on the skin called petechiae, other minor bleeding), swollen glands and/or other symptoms. The symptoms usually resolve on their own in a few days to a week, and are often milder in children under age 15. Less than one percent of DF patients die from their disease.

As noted above, DHF (hemorrhagic meaning bleeding) and DSS may occur in someone who has been infected with one strain of the dengue virus in the past and who is now exposed to a different strain. Untreated patients with DHF have a mortality as high as 20 percent, although with aggressive supportive treatment this may be brought down to 5 percent or lower.

Despite the "hemorrhagic" in the name DHF, it is thought that patients with this condition (and those with DSS) actually develop leakage of the liquid part of the blood and lymphatic fluid (the plasma) from blood vessels (which may be from sites of trauma, in the intestines/other parts of the gastrointestinal system, in the urinary system, or in other body organs). This loss of fluid from the blood vessels may result in shock (inadequate supple of oxygen and nutrition, specifically blood glucose, to the body’s cells; it is our blood, pumped by the heart, that carries these to "feed" the cells/organs of our body).

There are no specific treatments for dengue infections. Symptomatic treatment is indicated as needed for DF patients (such as pain medication, medicines to reduce fever, oral fluids, etc.) whereas DHF and DSS may require hospitalization (possibly in the intensive care unit), intravenous fluid administration, possibly blood transfusions, medications to treat shock (such as medications to help stabilize blood pressure, cause the heart to be stronger, and/or others) and/or other supportive care.

The diagnosis of dengue infection is suspected based on the patient’s symptoms and potential for exposure (for example in a patient who lives or has traveled to someplace tropical/subtropical where the disease is endemic), and is confirmed by specialized blood tests (or in some cases tests on other body fluids or tissues).

The vaccination that has been developed to prevent dengue only seems to prevent severe disease in about 30 percent of those who receive it. Therefore the best way to prevent dengue is to minimize mosquito bites (for example by using insect spray containing DEET, wearing clothing to minimize skin exposure, possibly sleeping under mosquito netting, other techniques). People who may have been at risk for exposure and who develop symptoms possibly consistent with dengue infection should seek immediate medical care.

Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.