DENGUE FEVER 
Dengue (DF) and dengue hemorrhagic fever (DHF) are caused by one of four closely related, but antigenically distinct, virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4), of the genus Flavivirus. Infection with one of these serotypes provides immunity to only that serotype for life, so persons living in a dengue-endemic area can have more than one dengue infection during their lifetime. DF and DHF are primarily diseases of tropical and sub tropical areas, and the four different dengue serotypes are maintained in a cycle that involves humans and the Aedes mosquito. However, Aedes aegypti, a domestic, day-biting mosquito that prefers to feed on humans, is the most common Aedes species. Infections produce a spectrum of clinical illness ranging from a nonspecific viral syndrome to severe and fatal hemorrhagic disease. Important risk factors for DHF include the strain of the infecting virus, as well as the age, and especially the prior dengue infection history of the patient.
The first reported epidemics of DF occurred in 1779-1780 in Asia, Africa, and North America. The near simultaneous occurrence of outbreaks on three continents indicates that these viruses and their mosquito vector have had a worldwide distribution in the tropics for more than 200 years. During most of this time, DF was considered a mild, nonfatal disease of visitors to the tropics. Generally, there were long intervals (10-40 years) between major epidemics, mainly because the introduction of a new serotype in a susceptible population occurred only if viruses and their mosquito vector could survive the slow transport between population centers by sailing vessels.
History of Dengue
A pandemic of dengue began in Southeast Asia after World War II and has spread around the globe since then. Epidemics caused by multiple serotypes (hyperendemicity) are more frequent, the geographic distribution of dengue viruses and their mosquito vectors has expanded, and DHF has emerged in the Pacific region and the Americas. In Southeast Asia, epidemic DHF first appeared in the 1950s, but by 1975 it had become a frequent cause of hospitalization and death among children in many countries in that region.
What are the signs and symptoms of dengue?
After being bitten by a mosquito carrying the virus, the incubation period ranges from three to 15 (usually five to eight) days before the signs and symptoms of dengue appear. Dengue starts with chills, headache, pain upon moving the eyes, and low backache. Painful aching in the legs and joints occurs during the first hours of illness. The temperature rises quickly as high as 104° F (40° C), with relative low heart rate (bradycardia) and low blood pressure (hypotension). The eyes become reddened. A flushing or pale pink rash comes over the face and then disappears. The glands (lymph nodes) in the neck and groin are often swollen.
Fever and other signs of dengue last for two to four days, followed by rapid drop in temperature (defervescence) with profuse sweating. This precedes a period with normal temperature and a sense of well-being that lasts about a day. A second rapid rise in temperature follows. A characteristic rash appears along with the fever and spreads from the extremities to cover the entire body except the face. The palms and soles may be bright red and swollen.
How is dengue fever treated?
Because dengue is caused by a virus, there is no specific medicine or antibiotic to treat it. For typical dengue, the treatment is purely concerned with relief of the symptoms (symptomatic). Rest and fluid intake for adequate hydration is important. Aspirin and nonsteroidal anti-inflammatory drugs should be avoided. Acetaminophen (Tylenol) and codeine may be given for severe headache and for the joint and muscle pain (myalgia).
What is the outcome with typical dengue?
Typical dengue does not result in death. It is fatal in less than 1% of cases. The acute phase of the illness with fever and myalgias lasts about one to two weeks. Convalescence is accompanied by a feeling of weakness (asthenia), and full recovery often takes several weeks.
What is dengue hemorrhagic fever?
Dengue hemorrhagic fever (DHF) is a specific syndrome that tends to affect children under 10. It causes abdominal pain, hemorrhage (bleeding), and circulatory collapse (shock). DHF is also called Philippine, Thai, or Southeast Asian hemorrhagic fever and dengue shock syndrome.
DHF starts abruptly with high continuous fever and headache. There are respiratory and intestinal symptoms with sore throat, cough, nausea, vomiting, and abdominal pain. Shock occurs two to six days after the start of symptoms with sudden collapse, cool, clammy extremities (the trunk is often warm), weak pulse, and blueness around the mouth (circumoral cyanosis).
In DHF, there is bleeding with easy bruising, blood spots in the skin (petechiae), spitting up blood (hematemesis), blood in the stool (melena), bleeding gums, and nosebleeds (epistaxis). Pneumonia is common, and inflammation of the heart (myocarditis) may be present.
Patients with DHF must be monitored closely for the first few days since shock may occur or recur precipitously. Cyanotic (bluish) patients are given oxygen. Vascular collapse (shock) requires immediate fluid replacement. Blood transfusions may be needed to control bleeding.
The mortality, or death rate, with DHF is significant. It ranges from 6%-30%. Most deaths occur in children. Infants under a year of age are especially at risk of dying from DHF.
How can dengue fever be prevented?
The transmission of the virus to mosquitoes must be interrupted to prevent the illness. To this end, patients are kept under mosquito netting until the second bout of fever is over and they are no longer contagious.
The prevention of dengue requires control or eradication of the mosquitoes carrying the virus that causes dengue. In nations plagued by dengue fever, people are urged to empty stagnant water from old tires, trash cans, and flower pots. Governmental initiatives to decrease mosquitoes also help to keep the disease in check but have been poorly effective.
Wear long pants and long sleeves. For personal protection, use mosquito repellant sprays that contain DEET when visiting places where dengue is endemic. Limiting exposure to mosquitoes by avoiding standing water and staying indoors two hours after sunrise and before sunset will help. The Aedes aegypti mosquito is a daytime biter with peak periods of biting around sunrise and sunset. It may bite at any time of the day and is often hidden inside homes or other dwellings, especially in urban areas.
There is currently no vaccine available for dengue fever. There is a vaccine undergoing clinical trials, but it is too early to tell if it will be safe or effective.
