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Dengue (disease)

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Dengue and dengue haemorrhagic fever (DHF) are acute febrile diseases, found in the tropics, with a geographical spread similar to malaria. 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 mosquito Aedes aegypti (rarely Aedes albopictus).

Signs and symptoms
The disease is manifested by a sudden onset of fever, with severe headache, joint and muscular pains (myalgias and arthralgias — severe pain gives it the name break-bone fever) 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 a flu or other viral infection. Thus, travelers from tropical areas may inadvertently pass on dengue in their home countries, having not being properly diagnosed at the height of their illness. Patients with dengue can only pass on the infection through mosquitoes or blood products 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 fever (the so-called “biphasic pattern”). Clinically, the platelet count will drop until the patient’s temperature is normal.
Cases of DHF also shows higher fever, haemorrhagic phenomena, thrombocytopenia and haemoconcentration. A small proportion of cases leads to dengue shock syndrome (DSS) which has a high mortality rate.

The diagnosis of dengue is usually made clinically. The classic picture is high fever with no localising source of infection, a petechial rash with thrombocytopenia and relative leukopenia.
Serology and PCR (polymerase chain reaction) studies are available to confirm the diagnosis of dengue if clinically indicated.

The mainstay of treatment is supportive therapy. The patient is encouraged to keep up oral intake, especially of oral fluids. If the patient is unable to maintain oral intake, supplementation with intravenous fluids may be necessary to prevent dehydration and significant hemoconcentration. A platelet transfusion is indicated if the platelet level drops significantly.

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 viral 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. In February 2002 there was a serious outbreak in Rio De Janeiro, affecting around one million people but only killing sixteen.
Significant outbreaks of dengue fever tend to occur every five or six years. There tend 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, as suggested by S.B. Halstead in the 1970s, of enhancement of DHF incidence in secondary infections by serotypes different from the one that caused the primary infection in a process known as antibody-dependent enhancment (ADE). Therefore, people that have passed a primary infection are usually advised to avoid the risk of a second one.
In Singapore, there are about 4000-5000 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 ready vaccine for the dengue flavivirus.
Primary prevention of dengue mainly resides in eliminating or reducing the mosquito vector for dengue. Initiatives to eradicate pools of standing water (such as in flowerpots) have proven useful in controlling mosquito borne diseases.
Personal prevention consists of the use of mosquito nets and repellents.

Potential antiviral approaches
In cell culture experiments Morpholino antisense oligos have shown specific activity against Dengue virus.
Four serotypes of dengue viruses produce dengue fever, dengue hemorrhagic fever, and dengue shock syndrome. They are the most important arbovirus infections of humans, in terms of both morbidity and mortality, constituting one of the most rapidly expanding and re-emerging infectious disease problems in Latin America. In less than 20 years, the region has transformed itself from hypoendemic to hyperendemic, while serotype circulation in most countries has gone from none or single to multiple. Changes in endemicity have coincided with the emergence and increasing incidence of the severer forms of dengue infection. This article reviews the clinical presentations of these diseases. Health care providers who see patients in or returning from areas of Latin America, the Caribbean, and other tropical areas must consider dengue in the differential diagnosis of patients presenting with compatible symptoms, and must be knowledgeable in the current management of this important disease.
The incidence and distribution of dengue virus infection in the tropical regions of Central and South America, as well as the Caribbean, has dramatically increased during the last two decades as a consequence, among other factors, of a wider distribution of Aedes aegypti, higher population density in many large urban areas, lack of effective programmes to contain vector development and deterioration of the urban environment. Some distinctive epidemiological patterns of transmission, such as the occurrence of large epidemics of both dengue fever and dengue haemorrhagic fever separated by long periods of absence of viral circulation among the population, are seen in the area. Concurrent circulation of all four serotypes of the virus is not unusual, favouring the occurrence of more cases of secondary infections, and a higher risk of dengue haemorrhaigc fever and dengue shock syndrome. Unlike other geographic regions, in the Americas older age groups are widely involved. Some clinical manifestations of dengue in adults appear to differ from those habitually described in children and unusual complications, such as acute acalculous cholecystitis and parotitis, have been described. Further clinical information needs to be generated on the impact of dengue virus co-infection with other endemic agents present in the area.

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___________.WEBSCOLAR. Dengue (disease). http://www.webscolar.com/dengue-disease. Fecha de consulta: 5 de marzo de 2019.

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