Dengue Fever

Dengue fever (DF) and its potentially deadly complication, dengue hemorrhagic fever (DHF), are infectious diseases spread by certain types of viral-transmitting mosquitoes. (Read about "Animal & Insect Borne Diseases") The Centers for Disease Control and Prevention (CDC) estimate 2.5 billion people worldwide live in areas at-risk for epidemics of dengue. It is estimated that there are 50 to 100 million cases of dengue fever (DF) and several hundred thousand cases of dengue hemorrhagic fever each year around the world. Dengue has become the most common arboviral disease of humans, according to CDC. (Read about "Arboviral Encephalitides")

Geographical distribution

Dengue's global distribution is similar to malaria. (Read about "Travel & Health") Tens of millions of cases of DF occur annually in tropical and subtropical countries. The spread of disease has increased since the 1980s and continues to spread.

Although scientists do not fully understand reasons for the continued increase, they have developed some theories. One theory is the combination of uncontrolled urbanization and population growth has led to substandard public health conditions. Inadequate water, sewer and waste management systems provide rich breeding grounds for mosquitoes, according to CDC. Any place there is standing water is a possible breeding ground for the mosquitoes. Dengue fever and DHF are found in urban and semi-urban areas around the world.

The United States is not immune. Though most cases in the U.S. involve people who have contracted the disease outside the country, there have been periodic outbreaks inside the U.S.

Cause and transmission

One of four viruses causes dengue. (Read about "Microorganisms") The strains are named DEN-1 through DEN-4. The four are closely related strains but just because you are infected by one, doesn't mean you can't be infected by another. Infection by one provides lifelong immunity against that virus, but only gives partial protection against subsequent infection by the other three viruses, according to the World Health Organization (WHO).

These viruses are spread by the Aedes mosquito. The main culprits are Aedes aegypti and her sister bug, Aedes albopictus. The Aedes species is usually active and bites its victims in the daytime. (Read about "Insect Bites") A few hours after dawn and a few hours before sunset are the most common times. A mosquito becomes infected by biting an infected human. An infected mosquito transmits the virus by biting another person and transmitting the infection. It is important to realize that Dengue cannot be spread directly from person to person.

Symptoms

The National Institute for Allergy and Infectious Diseases (NIAID) says health experts have known about DF for more than 200 years. The disease used to be nicknamed "break-bone" fever because muscle and joint pain symptoms were so severe they felt similar to bones breaking. Symptoms generally occur within one week of being bitten by an infected mosquito. Symptoms of DF include:

• high fever
• severe headache
• vomiting and nausea
• severe joint and muscle pain
• rash

The rash may appear over most of the body 3 to 4 days after the fever begins, subside after 1 to 2 days and recur a few days later.

CDC says that important risk factors for patient's acquiring DHF include age of the patient and history of previous dengue infection. DHF can cause death. The symptoms include all of the symptoms of classic dengue listed above with marked damage to blood and lymph vessels (Read about "The Lymph System") and bleeding from the nose, gums, or under the skin, causing purplish bruises.

The most severe form of dengue is called dengue shock syndrome. In addition to the previously mentioned symptoms, the victim may suffer from massive bleeding, fluids leaking outside of blood vessels and shock, including a dramatic drop in blood pressure. It is sometimes fatal, especially in children and young adults.

Diagnosis

There are blood tests that can show viral antibodies in the patient's blood. (Read about "Laboratory Testing") CDC says that the blood test should be taken two to three weeks apart. During an epidemic, there may not be time for the wait between blood tests and a healthcare provider is forced to make a diagnosis based on the symptoms they see.

Treatments and complications

A doctor should be consulted if any over-the-counter products are needed to treat symptoms such as fever. Complications such as Reye's syndrome (Read about Reye's syndrome in "The Liver") can occur if aspirin is taken, according to CDC. There is no specific treatment for DF and most people recover within two weeks.

NIAID recommends people with DF:

• get plenty of bed rest
• drink fluids

Prevention and control

Because Aedes mosquitoes usually bite during the day, be sure to take precautions, especially during early morning hours just before and after daybreak and in the late afternoon before dark. Travelers to tropical and subtropical regions are cautioned to take preventive measures to protect against mosquito bites:

• Use a mosquito repellent when outdoors.
• Dress in long-sleeved shirts, long pants, socks and shoes.
• Keep window and door screens repaired.
• Eliminate areas of standing water in flowerpots, containers, birdbaths, discarded tires, etc.

No dengue vaccine is available. Scientists supported by NIAID are trying various approaches but believe that it will be a few years before an effective vaccine is licensed for public use by the Food and Drug Administration.