(Survival manual/6. Medical/b) Disease/Dengue fever)
Dengue Fever Overview
Dengue fever is a disease caused by viruses that are transmitted to people by mosquitoes. Dengue fever usually causes fever (high, about 104 F-105 F), skin rash (see Figure 1), and pain (headaches and often severe muscle and joint pains). The disease has also been termed “breakbone” or “dandy fever” because the unusually severe muscle and joint pains can make people assume distorted body positions or exaggerated walking movements in an effort to reduce their pain.
Dengue fever is endemic in tropical and subtropical areas. Dengue fever is estimated by the WHO (World Health Organization) to cause about 50-100 million infections per year worldwide. The CDC considers dengue fever to cause the majority of acute febrile illnesses in travelers returning to the U.S. In 2009, dengue fever was noted to occur in Key West, Florida, in residents who did not travel
outside the U.S. More cases were identified in 2010, which suggests that dengue fever may become endemic in Florida, and possibly south Texas, due to new infections also diagnosed in this area. The first clinical report of dengue fever was in 1789 by B. Rush, although the Chinese may have described the disease associated with “flying insects” as early as 420 AD. Africans described “ka dinga pepo” as cramp-like seizure caused by an evil spirit. The Spanish may have changed “dinga” to dengue since it means fastidious or careful in Spanish, which describes the gait of people trying to reduce the pain of walking.
[Photo above right: Rash on legs due to dengue fever; image reprinted from eMedicine.com, photo courtesy of Duane Gubler, PhD.]
(See also CDC Health Travel Advisory, updated to 8 September 2011: http://wwwnc.cdc.gov/travel/notices/outbreak-notice/dengue-tropical-sub-tropical.htm
Unfortunately, the disease incidence seems to be increasing in Thailand, India, Singapore, Philippines,
Puerto Rico, Mexico, and Cape Verde with new outbreaks in 2009-10. Researchers suggest the surge in dengue fever may be due to several factors:
• Increased urban crowding with more sites for mosquitoes to develop
• International commerce that contains infected mosquitoes, thus introducing the disease to areas previously free of the disease
• Local and world environmental changes that allow mosquitoes to survive the winter months
• International travelers who carry the disease to areas where mosquitoes have not been previously infected.
“…Currently, dengue fever and its complications cause an estimated 50 to 100 million infections, a half-million hospitalizations, and 22,000 deaths annually in more than 100 countries, including parts of South America, Central America, the Caribbean, India, Southeast Asia, and Africa. By 2085, an estimated 5.2 billion people—3 billion additional people worldwide—are projected to be at risk for dengue because of climate change–induced increases in humidity that contribute to increased mosquito presence. Already, the specific types of mosquitoes that can transmit dengue fever have become established in a swath of at least 28 states and the District of Columbia, and across the south and mid-Atlantic regions of the United States and there were 4000 cases of the disease reported to the Centers for Disease Control between 1995 and 2005…”
Dengue Fever Symptoms and Signs
The symptoms and signs for dengue begin about three to 15 days after a mosquito bite transfers a virus (dengue virus serotype 1-4) to a person previously unexposed to the viruses. Fever and painful muscle and joint aches can occur during the first few hours of symptoms when headache, chills, rash, and swollen lymph nodes first appear. Pain behind the eyes is also a common symptom. These symptoms usually last about two to four days and then diminish, only to reappear again with a rash that covers the body and spares the face. The rash also may occur on the palms of the hands and the bottom of the feet, areas frequently spared in many viral and bacterial infections. The symptoms may last about one to two weeks with complete recovery, in most cases, in a few weeks. However, some people can develop more severe symptoms and complications, such as hemorrhagic areas in the skin, gums, and the gastrointestinal tract. This clinical problem is termed dengue hemorrhagic fever (DHF). The majority of DHF is seen in children under 15 years of age, but it can occur in adults. Another clinical variation of dengue fever is termed dengue shock syndrome (DSS); DHF usually precedes DSS. The patients eventually develop severe abdominal pain, heavy bleeding, and blood pressure drops; this syndrome, if not treated quickly, may cause death.
Causes of Dengue Fever
Four closely related viruses cause dengue fever. The viruses are transmitted from Aedes aegypti and Aedes albopictus mosquitoes to humans in a viral cycle that requires both humans and these mosquitoes. There is no human-to-human dengue fever transmission. Once a mosquito is infected, it remains infected for its life span. A human can infect mosquitoes when the human has a high number
of viruses in the blood (right before symptoms develop). The viruses belong to the Flaviviridae family and have an RNA strand as its genetic makeup.
Virologists term them dengue virus types 1-4 (DENV 1-4). All four serotypes are closely related. However, there are enough antigenic differences between them that if a person becomes immune to one serotype, the person can still be infected by the other three serotypes.
Diagnosis of Dengue Fever
Dengue fever is presumptively diagnosed by a medical caregiver by the relatively characteristic sequence of high fever, rash appearance, and other symptoms in a person who has a history of recent travel to dengue endemic areas and recalls mosquito bites while in the endemic area. However, if not all of the symptoms or history is complete, the caregiver is likely to run a number of tests to obtain a
definitive diagnosis. Other diseases may yield similar symptoms (for example, leptospirosis, typhoid fever, yellow fever, scarlet fever, Rocky Mountain spotted fever, meningococcemia, and several others) if the patient has severe symptoms; or if the medical caregiver does not have enough information to make a presumptive diagnosis, the patient is likely to undergo a number of other tests to definitively distinguish dengue fever from other diseases. In general, the more serious the symptoms such as easy bruising, fevers at or above 104 F, hemorrhages or shock syndrome, the more tests are likely to be done.
In general, most clinicians will order a complete blood test (CBC), with a metabolic panel, along with coagulation studies in most patients with high fever and any bleeding problems.
Dengue Fever Treatment
Fortunately, this viral disease is usually self-limited and usually adequate hydration and pain control will help the person through the infection. However, for dengue fever, a caution is given by most clinicians in home treatment. Nonsteroidal anti-inflammatory agents (for example, aspirin (Bayer, Ecotrin), ibuprofen (Motrin), and other NSAIDs) should be avoided because of the tendency of the dengue viruses to cause hemorrhages. The NSAIDs may add to the hemorrhage symptoms. Other medications such as acetaminophen (Tylenol), codeine, or other agents that are not NSAIDs may be used.
Self-Care at Home
Home care for dengue fever is simply supportive care. Good oral hydration, pain control with Tylenol (or other non-NSAIDs) is usually adequate treatment for most people. However, there is no role for home care in patients with dengue hemorrhagic fever or for dengue shock syndrome; depending on the patient’s condition, many clinicians consider these conditions to be medical emergencies.
Dengue Fever Risk Factors
The risk factors for dengue fever are as follows:
• traveling to or living in endemic or outbreak areas, especially if no mosquito control is attempted by
the people or government;
• mosquito bites;
• a repeated infection with another serovar of dengue virus with antibodies in the serum active against the first infecting serovar;
• and not taking precautions to avoid mosquito bites.
Dengue Fever Complications
The complications of dengue fever are usually associated with the more severe forms of dengue fever, hemorrhagic and shock syndrome. The most serious complications, although infrequent, are as follows:
• bleeding (hemorrhage);
• low platelets;
• low blood pressure (hypotension);
• liver damage;
• neurological damage (seizures, encephalitis);
• and death.
Dengue Fever Prognosis
For the large majority of people infected with dengue fever viruses, the prognosis is excellent, although they are likely to feel very ill during the first one or two weeks of the acute illness and weak for about one month. Patients with underlying illness or immune depression have a fair to good prognosis because they are more likely to get complications. Also, people who have been infected by one dengue viral serovar are still able to be infected by the remaining three serovars; a second infection increases the possibility that complications will develop so patients with second-time dengue fever have a less optimal prognosis. Patients who develop DHF or DSS have a range of outcomes from good to poor, depending on their underlying medical problems and how quickly supportive measures are given. For example, DHF and DSS have about 50% fatality rate if untreated but about a 3% rate if treated with supportive measures.
Overall, the fatality rate is about 1% of all dengue fever infections. While this rate may seem low, worldwide it means that about 500,000 to 1 million people die each year from dengue fever. This is a concern since the worldwide case numbers and outbreaks are increasing.
Dengue Fever Prevention
Dengue fever can be prevented by stopping mosquitoes from biting because they are the vectors the dengue viruses require for transfer to humans. The CDC (2010) has supplied these general rules to prevent transfer of viruses and other pathogens by mosquitoes and other biting vectors:
• Avoid outbreaks: To the extent possible, travelers should avoid known foci of epidemic disease transmission. The CDC Travelers’ Health web page provides alerts and information on regional disease transmission patterns and outbreak alerts (http://www.cdc.gov/travel).
• Be aware of peak exposure times and places: Exposure to arthropod bites may be reduced if travelers
modify their patterns of activity or behavior. Although mosquitoes may bite at any time of day, peak biting activity for vectors of some diseases (for example, dengue, chikungunya) is during daylight hours. Vectors of other diseases (for example, malaria) are most active in twilight periods (for example, dawn and dusk) or in the evening after dark. Avoiding the outdoors or focusing preventive actions during peak hours may reduce risk. Place also matters; ticks are often found in grasses and other vegetated areas.
Local health officials or guides may be able to point out areas with greater arthropod activity.
• Wear appropriate clothing: Travelers can minimize areas of exposed skin by wearing long-sleeved shirts, long pants, boots, and hats. Tucking in shirts and wearing socks and closed shoes instead of sandals may reduce risk. Repellents or insecticides such as permethrin (Elimite) can be applied to clothing and gear for added protection; this measure is discussed in detail below.
• Check for ticks: Travelers should be advised to inspect themselves and their clothing for ticks during outdoor activity and at the end of the day. Prompt removal of attached ticks can prevent some infections.
• Bed nets: When accommodations are not adequately screened or air conditioned, bed nets are essential to provide protection and to reduce discomfort caused by biting insects. If bed nets do not reach the floor, they should be tucked under mattresses. Bed nets are most effective when they are treated with an insecticide or repellent such as permethrin. Pretreated, long-lasting bed nets can be purchased prior to traveling, or nets can be treated after purchase. The permethrin will be effective for several months if the bed net is not washed. (Long-lasting pretreated nets may be effective for much longer.)
• Insecticides: Aerosol insecticides, vaporizing mats, and mosquito coils can help to clear rooms or areas of mosquitoes; however, some products available internationally may contain pesticides that are not registered in the United States. Insecticides should always be used with caution, avoiding direct inhalation of spray or smoke.
• Optimum protection can be provided by applying repellents.
The CDC recommends insect repellent should contain up to 50% DEET (N,N-diethyl-m-toluamide) which is the most effective mosquito repellent for adults and children over 2 months of age.
There are no vaccines currently available commercially for dengue virus serovars.