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DENGUE FEVER

Definition
Dengue fever is a disease — ranging from a mild to severe — caused by four related viruses spread by a particular species of mosquito. Mild dengue fever causes high fever, rash, and muscle and joint pain. More severe forms of the disease — dengue hemorrhagic fever and dengue shock syndrome — can additionally cause severe bleeding, a sudden drop in blood pressure (shock) and death.

No specific treatment for dengue fever exists, and most people recover. But if you have a severe form of the disease, you need hospital care.

Fifty million to 100 million cases of dengue infection occur worldwide each year. Most cases of dengue fever occur in urban areas of tropical and subtropical regions. A few cases have been reported in the United States — particularly in Texas, along the border with Mexico, and in Hawaii.
Symptoms
Signs and symptoms of dengue fever usually begin four to seven days after you've been bitten by a mosquito carrying a dengue virus. These signs and symptoms can vary, depending on the form of the disease. More severe forms of the disease usually begin the same way as the mild form (dengue fever), then become worse after several days.

Dengue fever signs and symptoms typically include:

* High fever, up to 105 F
* A rash over most of your body, which may subside after a couple of days and then reappear
* Severe headache, backache or both
* Pain behind your eyes
* Severe joint and muscle pain
* Nausea and vomiting


Dengue fever rarely causes death, and symptoms usually get better after five to seven days.

Dengue hemorrhagic fever — a more severe form of the disease — can also cause:

* Significant damage to your blood and lymph vessels
* A decrease in the number blood cells that help your blood clot (platelets)
* Bleeding from the nose, mouth and under the skin, creating the appearance of bruising
* Death


Dengue shock syndrome — the most severe form of the disease — may also cause:

* Blood vessel fluid (plasma) leakage
* Heavy bleeding
* A sudden drop in blood pressure (shock)
* Death


These signs and symptoms usually appear between the third and seventh day of illness, after fever has improved. They may be preceded by severe abdominal pain, frequent vomiting and disorientation. Two percent to 5 percent of those with a severe form of the disease die. Modern supportive hospital care decreases this risk.
Recovery from dengue fever may include a long period of listlessness, fatigue and even depression.

Causes
Dengue fever is caused by any one of four dengue viruses spread by the Aedes aegypti mosquito. These mosquitoes thrive in and near human habitations where they breed in even the cleanest water.

Mosquitoes transmit the virus back and forth between humans. When a mosquito bites a person infected with a dengue virus, the virus enters the mosquito's bloodstream. It then circulates before settling in the salivary glands. When the infected mosquito then bites another person, the virus enters that person's bloodstream, where it may cause the serious illness.

You can become infected with dengue fever more than once. This happens when you're exposed to a different one of the four dengue viruses than one to which you were previously exposed. Infection a second time is typically what causes the more severe form of the disease — dengue hemorrhagic fever.
Risk factors

If you live or travel in tropical areas
Living in or traveling to an area where dengue fever viruses are present puts you at risk of the disease. These areas include many tropical and subtropical areas around the world, for example:

* Central and South America
* Southeast Asia
* The Caribbean
* Africa
* India
* The Middle East
* The South and Central Pacific


Particularly high-risk areas include tropical Asia, Central and South America and the Caribbean. Dengue virus transmission may occur year-round, although the risk is highest during a recognized dengue fever outbreak.

If you've had dengue fever before
If you've had dengue fever before, you can get it again if you become infected with another one of the four dengue viruses. Having antibodies to a virus in your blood from a previous infection usually helps protect you. But in the case of dengue fever, it actually increases your risk of severe disease — dengue hemorrhagic fever — if you're infected again. So previous infection with a dengue fever virus increases your risk of a more severe form of the disease. This most often occurs in children.

If you're young, white or female
If you are younger than age 12, female or white, you are also at greater risk of the severe form of the disease — dengue hemorrhagic fever.

When to seek medical advice
If you have any signs or symptoms of dengue fever, see your doctor, and explain that you've recently traveled to a region in which the disease is known to occur.

Tests and diagnosis
Diagnosing dengue fever can be difficult. That's because its signs and symptoms can be easily confused with those of other diseases, such as malaria, leptospirosis and typhoid fever. Still, diagnosis of dengue fever is typically done by evaluating your signs and symptoms along with your medical and travel history. To diagnose your condition, your doctor will likely ask about these. In addition, your blood may be tested for evidence of a dengue virus.

Medical history
Your doctor will likely ask about your medical and travel history and any exposure to mosquitoes. Be sure to describe international trips in detail, including the countries you visited and the dates, as well as any contact you may have had with mosquitoes.

Blood tests
Laboratory tests, usually using a sample of your blood, are needed to confirm a diagnosis of dengue fever. If you have dengue fever, your blood may reveal the virus itself. If not, blood tests known as hemagglutination inhibition (HI) assay, enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase-polymerase chain reaction (RT-PCR) also can detect antigens, antibodies or nucleic acids specific to the viruses. These tests may take several days.

Complications
Most people with dengue fever recover within five to 14 days. Some, particularly adults, may feel listless, tired and even depressed for several weeks to months after being infected.

If severe, dengue fever can lead to dengue hemorrhagic fever and dengue shock syndrome, which can cause heavy bleeding, shock and — in about 2 percent to 5 percent of those with these conditions — death. Those who survive may experience liver, blood vessel and brain damage, as well as seizures.

Treatments and drugs
No specific treatment for dengue fever exists.

If you have a mild form of the disease, your doctor will recommend making sure to drink enough fluids to avoid dehydration from vomiting and high fever. You can also take acetaminophen (Tylenol, others) for pain and fever. Avoid aspirin or other nonsteroidal anti-inflammatory drugs, such as ibuprofen (Advil, Motrin, others) and naproxen sodium (Aleve). These can increase the risk of bleeding complications.

If you have a more severe form of the disease, treatment consists of supportive care in a hospital. Such care includes intravenous fluids and electrolyte replacement, maintaining adequate blood pressure and replacing blood loss.
If you have any form of dengue fever, you may also be kept away from mosquitoes, to avoid transmitting the disease to others.

Prevention
No dengue fever vaccine exists. If you are living or traveling in an area where dengue fever is known to be, the best way to avoid dengue fever is to avoid being bitten by mosquitoes that carry the disease.

To reduce your exposure to mosquitoes:

* Avoid unnecessary outdoor activity when mosquitoes are most prevalent, such as at dawn, dusk and early evening.
* Wear long-sleeved shirts, long pants, socks and shoes when you go into mosquito-infested areas.
* Stay in air-conditioned or well-screened housing. Patch screens if necessary, especially where there will be night-time exposure.
* Use bed netting if available.
* Apply permethrin-containing mosquito repellent to your clothing, shoes, and camping gear and bed netting. You can also buy clothing made with permethrin already in it. Use repellent with a 10 percent to 30 percent concentration of DEET to your skin. Choose the concentration based on the hours of protection you need — a 10 percent concentration of DEET is effective for about two hours, whereas higher concentrations last longer. Keep in mind that chemical repellants can be toxic, and use only the amount needed for the time you'll be outdoors. Don't use DEET on the hands of young children or on infants under 2 months of age. Instead, cover your infant's stroller or playpen with mosquito netting when outside. According to the Centers for Disease Control and Prevention, oil of lemon eucalyptus, a more natural product, offers the same protection as DEET when used in similar concentrations.