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Dengue fever (IPA: /ˈdɛŋgeɪ/) and dengue hemorrhagic fever (DHF) are acute febrile diseases, found in the tropics and Africa, with a geographical spread similar to malaria. One major difference, however, is that malaria is often eradicated in major cities, whereas dengue is often found in urban areas of developed tropical nations, including Singapore, Taiwan and Brazil. Caused by one of four closely related virus serotypes of the genus Flavivirus, family Flaviviridae, each serotype is sufficiently different that there is no cross-protection and epidemics caused by multiple serotypes (hyperendemicity) can occur. Dengue is transmitted to humans by the Aedes aegypti (rarely Aedes albopictus) mosquito, which feeds during the day.
Additional recommended knowledge
Signs and symptoms
This infectious disease is manifested by a sudden onset of fever, with severe headache, muscle and joint pains (myalgias and arthralgias—severe pain gives it the name break-bone fever or bonecrusher disease) and rashes. The dengue rash is characteristically bright red petechia and usually appears first on the lower limbs and the chest; in some patients, it spreads to cover most of the body. There may also be gastritis with some combination of associated abdominal pain, nausea, vomiting or diarrhea.
Some cases develop much milder symptoms which can, when no rash is present, be misdiagnosed as influenza or other viral infection. Thus travelers from tropical areas may inadvertently pass on dengue in their home countries, having not been properly diagnosed at the height of their illness. Patients with dengue can pass on the infection only through mosquitoes or blood products and only while they are still febrile.
The classic dengue fever lasts about six to seven days, with a smaller peak of fever at the trailing end of the disease (the so-called "biphasic pattern"). Clinically, the platelet count will drop until the patient's temperature is normal.
Cases of DHF also show higher fever, haemorrhagic phenomena, thrombocytopenia, and haemoconcentration. A small proportion of cases lead to dengue shock syndrome (DSS) which has a high mortality rate.
Dengue shock syndrome is defined as dengue haemorrhagic fever plus:
The mainstay of treatment is supportive therapy. Increased oral fluid intake is recommended to prevent dehydration. Supplementation with intravenous fluids may be necessary to prevent dehydration and significant concentration of the blood if the patient is unable to maintain oral intake. A platelet transfusion is indicated in rare cases if the platelet level drops significantly (below 20,000) or if there is significant bleeding.
The presence of melena may indicate internal gastrointestinal bleeding requiring platelet and/or red blood cell transfusion.
It is very important to avoid aspirin and non-steroidal anti-inflammatory drugs; these drugs may aggravate the bleeding tendency associated with some of these infections. Patients should receive instead acetaminophen preparations to deal with these symptoms if dengue is suspected.
Emerging evidence suggests that mycophenolic acid and ribavirin inhibit dengue replication. Initial experiments showed a fivefold increase in defective viral RNA production by cells treated with each drug. In vivo studies, however, have not yet been done.
The first epidemics occurred almost simultaneously in Asia, Africa, and North America in the 1780s. The disease was identified and named in 1779. A global pandemic began in Southeast Asia in the 1950s and by 1975 DHF had become a leading cause of death among children in many countries in that region. Epidemic dengue has become more common since the 1980s. By the late 1990s, dengue was the most important mosquito-borne disease affecting humans after malaria, there being around 40 million cases of dengue fever and several hundred thousand cases of dengue hemorrhagic fever each year. There was a serious outbreak in Rio de Janeiro in February, 2002 affecting around one million people and killing sixteen.
Significant outbreaks of dengue fever tend to occur every five or six years. There tends to remain large numbers of susceptible people in the population despite previous outbreaks because there are four different strains of the dengue virus and because of new susceptible individuals entering the target population, either through childbirth or immigration.
There is significant evidence, originally suggested by S.B. Halstead in the 1970s, that dengue hemorrhagic fever is more likely to occur in patients who have secondary infections by serotypes different from the primary infection. One model to explain this process is known as antibody-dependent enhancement (ADE), which allows for increased uptake and virion replication during a secondary infection with a different strain. Through an immunological phenomenon, known as original antigenic sin, the immune system is not able to adequately respond to the stronger infection, and the secondary infection becomes far more serious. This process is also known as superinfection (Nowak and May 1994; Levin and Pimentel 1981).
In Singapore, there are about 4,000–5,000 reported cases of dengue fever or dengue haemorrhagic fever every year. In the year 2003, there were 6 deaths from dengue shock syndrome. It is believed that the reported cases of dengue are an underrepresentation of all the cases of dengue as it would ignore subclinical cases and cases where the patient did not present for medical treatment. With proper medical treatment, the mortality rate for dengue can therefore be brought down to less than 1 in 1000.
There is no commercially available vaccine for the dengue flavivirus. However, one of the many ongoing vaccine development programs is the Pediatric Dengue Vaccine Initiative which was set up in 2003 with the aim of accelerating the development and introduction of dengue vaccine(s) that are affordable and accessible to poor children in endemic countries. Thai researchers are testing a dengue fever vaccine on 3,000–5,000 human volunteers after having successfully conducted tests on animals and a small group of human volunteers. A number of other vaccine candidates are entering phase I or II testing.
Primary prevention of dengue mainly resides in mosquito control, i.e. eliminating or reducing the mosquito vector for dengue. Public spraying for mosquitoes is the most important aspect of this vector. Application of larvicides such as Abate® to standing water is more effective in the long term control of mosquitoes. Initiatives to eradicate pools of standing water (such as in flowerpots) have proven useful in controlling mosquito-borne diseases. Promising new techniques have been recently reported from Oxford University on rendering the Aedes mosquito pest sterile.
In 1998, scientists from the Queensland Institute of Research in Australia and Vietnam's Ministry of Health had introduced a scheme that encouraged children to place a water bug, a crustacean called Mesocyclops, in water tanks and discarded containers where the mosquito, Aedes aegypti, was known to thrive. It is viewed as being more cost-effective and more environmentally friendly than pesticides, though not as effective, and required the ongoing participation of the community.
Personal prevention consists of the use of mosquito nets, repellents containing NNDB or DEET, covering exposed skin, use of DEET-impregnated bednets, and avoiding endemic areas.
Potential antiviral approaches
The yellow fever vaccine (YF-17D) is a related Flavivirus,[clarify] thus the chimeric replacement of yellow fever vaccine with dengue has been often suggested[clarify] but no full scale studies have been conducted to date.
During the first months of 2007, over 16,000 cases have been reported in Paraguay, of which around 100 have been detected as DHF cases. Ten deaths have also been reported, including a high ranking member of the Ministry of Health. One Department of Health official resigned because he had approved the use of expired batches of insecticide to control the mosquito vectors of dengue. The disease has propagated to Argentina (where it is not considered endemic) by people who recently arrived from Paraguay. In the Brazilian state of Mato Grosso do Sul, which borders on Paraguay, the number of cases in March 2007 is estimated to be more than 45,000. Epidemics in the states of Ceará, Pará, São Paulo, and Rio de Janeiro have taken the Brazilian national tally of cases to over 70,000, with upwards of 20 deaths. Larvae have also been found in Parana state. The proportion of cases registered as DHF is reported to be higher than in previous years.
As of October 2007 there is a serious problem in Monterrey Nuevo Leon Mexico almost reaching epidemic proportions
The origins of the word dengue are not clear, but one theory is that it is derived from the Swahili phrase "Ka-dinga pepo", which describes the disease as being caused by an evil spirit. The Swahili word "dinga" may possibly have its origin in the Spanish word "dengue" (fastidious or careful), describing the gait of a person suffering dengue fever or, alternatively, the Spanish word may derive from the Swahili. It may also be attributed to the phrase meaning "Break bone fever", referencing the fact that pain in the bones is a common symptom.
Outbreaks resembling dengue fever have been reported throughout history. The first definitive case report dates from 1789 and is attributed to Benjamin Rush, who coined the term "breakbone fever" (because of the symptoms of myalgia and arthralgia). The viral etiology and the transmission by mosquitoes were only deciphered in the 20th century. Population movements during World War II spread the disease globally.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Dengue_fever". A list of authors is available in Wikipedia.|