Information on the following diseases can be found in the Related Disorders section of this report:

• Colorado Tick Fever
• Typhus (Typhoid Fever)
• Yellow Fever
• Other Hemorrhagic Fevers

Dengue Fever is a disorder transmitted by female mosquitoes (Aedes aegypti and Aedes albopictus) carrying dengue virus. The disorder is characterized by a sudden onset of symptoms. There is an incubation period of 5 to 8 days after the mosquito bite occurs. The patient has chills or chilly sensations, a fever, exhaustion, diarrhea, and/or vomiting. Pain behind the eyeballs (postorbital) occurs on moving the head. The head, lower back, legs and joints ache. The patient feels very weak. The temperature rises rapidly, sometimes to as high as 40C or 104F, accompanied by a relatively slow heart beat (bradycardia) and abnormally low blood pressure. The lymph glands in the neck, shoulder, and groin are usually enlarged.

Two or three days after the first fever, a rash of flat or elevated (maculopapular) spots appears, particularly on the face. A second temperature rise follows. The presence of Dengue virus in the blood (viremia) can confirm the diagnosis. The patient subsequently develops immunity against this type of Dengue virus. However, reinfection with a different type of this virus is possible.

Secondary forms of Dengue Fever are Dengue Hemorrhagic Fever, and Dengue Shock Syndrome. These forms of the disorder primarily affect children between 3 and 6 years of age who have been infected a second time with dengue virus, and infants 7 to 8 months of age. These forms of the disorder are characterized by sudden fever, headache, nausea, vomiting, and abdominal pain. Coughing, throat infection and difficulty in breathing also occur. Shock may occur 2 to 6 days after the beginning of the fever, with sudden collapse, cool clammy extremities (the trunk is often warm), a weak pulse, and bluish discoloration of the skin around the mouth (cyanosis). In serious cases, a tendency to bleed excessively occurs, either as purpura or in pinpoint spots (petecchiae). The bleeding may appear in many parts of the body. Blood vessels become dilated and congested, and swelling (edema) may also occur. Gastrointestinal bleeding may lead to vomiting of blood (hematemesis) and passing of dark stools stained with blood pigment (melena).

Dengue Fever is caused by a virus that belongs to a family of viruses known as Flaviviruses. There is no vaccine, so travelers going to parts of the world where it is endemic during Dengue season (July to November) are urged to protect themselves from mosquito bites by wearing protective clothing and mosquito repellant.

Dengue Fever occurs mainly in subtropical or tropical climates including southern Asia, South America (particularly Brazil), and the Caribbean including Puerto Rico and the U.S. Virgin Islands. The virus has also been imported into the United States by tourists from these areas. It is thought that approximately 200 cases of Dengue Fever are unknowingly carried into the United States each year.

The Dengue virus is a B Arbovirus which has 4 distinct serogroups.

Colorado Tick Fever (Mountain Fever; Mountain Tick Fever) is a virus infection transmitted by ticks which is prevalent in the western United States. Fever, headaches, muscle aches, and generalized discomfort characterize the illness, which resolves spontaneously. (For more information on this disorder, choose "Colorado Tick Fever" as your search term in the Rare Disease Database.)

Epidemic Typhus (European Typhus; Classic Typhus; Louse-Born Typhus; Jail Fever) is a severe infectious disorder which begins suddenly and is characterized by prolonged high fever, persistent headache, and a rash of elevated spots on the skin. Epidemic Typhus is caused by Rickettsia prowazekii, an organism that resembles viruses and bacteria. This disorder can be transmitted by lice.

Yellow Fever is an arbovirus infection characterized by sudden onset and variable severity of symptoms. The disorder is characterized by a fever of 102 degrees to 104 F (39 degrees to 40 C), and an abnormally slow heart beat. In a few severe cases, excessive amounts of protein are present in the urine. In these few cases a yellow skin color (jaundice), bleeding and coughing up blood also tend to occur. The virus which causes Yellow Fever is transmitted by the bite of a mosquito. (For more information on this disorder, choose "Yellow Fever" as your search term in the Rare Disease Database.)

Other Hemorrhagic Fevers which are characterized by internal bleeding are caused by a variety of viruses. Some of these fevers that occur in Africa and South America are: Lassa Fever, Machupo Fever (Bolivian Hemorrhagic Fever), Junin Fever (Argentinian Hemorrhagic Fever), Lymphocytic Choriomeningitis, Marburg Virus (Hemorrhagic Fever), and, Ebola Virus (Hemorrhagic Fever). Blood tests may be used to identify the virus.

Diagnosis
Dengue Fever is diagnosed by testing a blood sample for the presence of the Dengue virus or its antibodies, specifically immunoglobulin M (IgM). The body, in order to combat invading microorganisms, toxins, or other foreign substances such as the virus that causes Dengue Fever, produces antibodies, also known as immunoglobulins. However, a different type of the Dengue virus might cause a second infection.

Treatment
Complete bedrest is important. Affected individuals should take measures to avoid additional mosquito bites in order to prevent reinfection. Fluids should be given to compensate for dehydration.

Treatment for Dengue Hemorrhagic Fever depends on the individual's degree of dehydration. Affected individuals should be closely monitored to prevent shock. When skin appears bluish in color, oxygen should be given. Collapse of blood vessels and loss of fluid from the circulation (hemoconcentration) require immediate fluid replacement, preferably with a solution like Ringer's lactate. Plasma or human serum protein (albumin) should also be given if there is no response in the first hour. Fresh blood or blood platelet transfusions may control bleeding. Agitated patients may be given paraldehyde, chloral hydrate, or diazepam.

Scientists have studied the effect of human interferon on Hemorrhagic Dengue Fever. More research is needed before this drug will be available for more general use in treating Dengue Fever. Additionally, scientists are trying to develop a vaccine that may someday prevent this infectious disorder.

A pharmaceutical company known as Genelabs Technologies, Inc., is working on an RNA-binding drug program that has produced several compounds that potentially inhibit viral activity. It is hoped that this might lead to drug treatment options for RNA viruses, including yellow fever, hepatitis C, Japanese encephalitis, and Dengue fever. More research is necessary to develop and test such drugs for safety and long-term effectiveness.

Researchers at OraVax, Inc., plan to create vaccines against several forms of Dengue Fever by modifying a proven Yellow Fever vaccine. Genes from one of several types of Dengue Fever viruses will replace a gene in a Yellow Fever virus. Vaccines from the modified Yellow Fever virus will be tested for safety and efficacy against the Dengue Fever virus.

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