Dengue VirusEssential Information

Dengue Virus OriginsThe dengue viruses are members of the Flavivirus family, and are medium sized enveloped viruses. Enveloped viruses are easy to kill on environmental surfaces through disinfection or on hands through use of alcohol hand rubs. However, dengue transmission is not generally believed to occur through these environmental routes. Dengue is transmitted through vector transmission primarily from the bites of infected Aedes aegypti mosquitoes and a small number of cases through the bites of aedes albopictus mosquitoes. Global estimates are that there are 400 million dengue infections each year with 100 million showing clinical symptoms (25%), 500,000 requiring hospitalization, and 2.5% of all hospitalized cases resulting in death.

Dengue viruses were first identified in the 1950s and can cause a more serious form of dengue infection called “severe dengue” (previously called Dengue Hemorrhagic Fever). While dengue infections are not generally fatal, severe dengue can be fatal if not diagnosed and properly treated in a timely manner. Proper diagnosis and management of severe dengue can reduce the mortality to <1%.

Geographic Risk of ExposureDengue infections occur in more than 100 countries (representing ~40% of the world’s population) and are associated with tropical and subtropical climates, being quite common in Southeast Asia, Latin America, the Pacific Islands, and Puerto Rico, but rarely occur in the United States. Travel related cases, where an infected traveler becomes infected in one country and travels back home to another country, do occur, but since person to person transmission is believed not to easily occur, this does not result in people in their home country becoming infected unless the Aedes mosquitoes are also common in their home country. The risk of transmission is highest during seasons when mosquito populations are highest, which is usually when rainfall is optimal for mosquito breeding.

Source/Natural ReservoirAedes mosquitoes are the primary vector for causing infection in people, but it is not clear whether there are additional animal hosts that carry the virus. A mosquito can become infected with dengue virus by biting a person that has dengue virus in their blood. The person does not have to be symptomatic to pass the virus to a mosquito. From the time of biting an infected person, the mosquito becomes capable of transmitting the virus to healthy people in about a week.

DiagnosisAbout 75% of people infected with dengue virus show no symptoms. The incubation period (the time from exposure to symptoms) of dengue virus disease is 3-10 days (4-7 days being most common). Symptoms typically last for 2-10 days (2-7 days being most common). Younger children and people infected with dengue for the first time generally have milder illnesses than older children and adults. Typical dengue infection symptoms include::• High fever lasting 2-7 days• Severe headache• Severe pain behind the eyes• Muscle, joint, and bone pain• Rash• Mild bleeding from the nose or gums or easy bruising

Severe Dengue (also called Dengue Hemorrhagic Fever) occurs in about 0.5% of all dengue infections and includes the symptoms consistent with a dengue infection shown above. However, when the fever stops (3-7 days after first symptoms), new symptoms appear including:

• Persistent vomiting• Severe abdominal pain and/or vomiting of blood• Difficulty breathing• Red spots or patches on the skin• Bleeding from nose or gums• Black, tar colored feces• Drowsiness or irritability• Pale, cold or clammy skin

For 24-48 hours after the new symptoms appear, small blood vessels leak fluid and can cause failure of the circulatory system leading to shock and death if the circulatory system failure is not corrected. A person who has a fever that declines, but then develops any of the symptoms above is at risk of having severe dengue and should seek immediate medical attention.

The symptoms likely to present early in a dengue infection are often seen in patients with any of a number of other conditions. Diagnosis and treatment should only be performed by a trained physician who can rule out other potential diseases. Aspirin and ibuprofen are typically not recommended for people with dengue infections or severe dengue because it can increase the risk of bleeding.

Method of Transmission/ContagiousnessPeople can become infected with dengue virus by being bitten by a mosquito that is infected with the virus. After an incubation period, an infected person will have dengue virus in their blood for about a week. A mosquito can become infected with dengue virus by biting a person that has dengue virus in their blood, which is typically a 5 day period during the middle of the illness when large amounts of dengue virus are present in the infected person’s blood. The person does not have to be symptomatic to pass the virus to a mosquito.

From the time of biting an infected person, the mosquito becomes capable of transmitting the virus to healthy people in about a week (8-12 days). After this incubation period and for the rest of its lifetime, an infected mosquito will infect healthy people it bites. Dengue cannot be transmitted directly from person to person except through direct exposure to blood and body fluids of an infected person, which historically rarely occurs.

Dengue virus is transmitted to people primarily through the bite of an infected Aedes species mosquito. These are the same mosquitoes that spread Zika and Chikungunya viruses. These mosquitoes typically lay eggs in and near standing water in things like buckets, bowls, animal dishes, flower pots and vases, roughly 3 days after feeding on blood (biting people). Once hatched, the larvae mature in as little as 7-8 days and the adult mosquito can live for 3-4 weeks. They are aggressive daytime biters, prefer to bite people, and live indoors and outdoors near people. Aedes mosquitoes have a flight range of <200 m, so they tend to lay eggs close to where adult mosquitoes are found.

As the dengue virus is primarily transmitted through infected mosquitoes, environmental contamination does not appear to play a significant role in the transmission of the virus. Bloodborne transmission is possible through exposure to infected blood, organs, and other tissue and for infants born while the mother is acutely ill.

Use of hard surface disinfectants and hand hygiene, which are important in interrupting routes of infection involving the environment for many other pathogens, do not appear to play much of a role for dengue infections. If environmental surfaces are visibly covered with blood or body fluids, the use of disinfectants, hand hygiene, and barriers may play a role in prevention dengue infection.

Prevention• There are currently no vaccines available to prevent

nor medicines to treat dengue infections, but several promising vaccines are in development and trials. Recovery from one strain (serotype) of dengue is believed to provide life-long immunity to that serotype of dengue, but only partial and temporary protection against the other three serotypes of dengue virus.

The primary method of prevention is to minimize the risk of mosquito bites:

• Reduce breeding areas for mosquitoes by eliminating all standing water in and around houses and yards. Items that collect rainwater such as flower pots, plastic containers, pet water dishes, and auto tires are ideal breeding grounds for mosquitoes. If outdoors containers (pet watering bowls, bird baths, etc.) must contain standing water, they should be cleaned weekly to remove any mosquito eggs and larvae.

• Keep mosquitoes out of a building by using screens on windows and doors, repairing any holes in screens, and using air conditioning when available. Using physical barriers such as screens, closed doors and windows and sleeping under mosquito nets when sleeping outdoors or in a room that is not well screened are key elements of preventing mosquito bites. If traveling to other countries, consider taking a bed net if you will not be staying in an air conditioned hotel.

• Use governmental registered insect repellents containing 20-30% DEET, picaridin, oil of lemon eucalyptus (OLE), or IR3535. Always use as directed. Exposed skin and outside clothing should be sprayed to offer maximum protection. Pregnant and breastfeeding women can use governmental registered insect repellents, including DEET, according to the product label. Most repellents, including DEET, can be used on children aged >2 months.

• Cover exposed skin by wearing light colored, long-sleeved shirts and long pants. Heavier fabrics offer more protection than thin clothing. Use permethrin-treated clothing and gear (such as boots, pants, socks, and tents) when outdoors. Pre-treated clothing and gear is available, or can be sprayed with the appropriate repellents.

• Where mosquitoes are breeding outdoors, the use of governmental approved insecticides should also be considered to reduce the population of mosquitoes, but this should always be supplemented with the use of insect repellants.

References and useful websites

Reference materials on dengue are available from the Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) websites. Many of these resources were used as references for the creation of this brochure.

http://www.who.int/mediacentre/factsheets/fs117/en/#

http://www.cdc.gov/dengue/

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