Dengue fever
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| Dengue virus | |
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| Missing image Dengue.jpg An electron micrograph showing dengue virus Template:Taxobox begin placement virus Template:Taxobox group iv entry | |
| Family: | Flaviviridae |
| Genus: | Flavivirus |
| Species: | Dengue virus |
|} 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).
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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, than can, when no rash is present, be missdiagnosed as a flu or other viriasis. This is the cause of some travelers from tropical areas passing through denge in their home countries without being properly diagnosed.
The classical 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 (DDS) which has a high mortality rate.
Diagnosis
The diagnosis of dengue is usually made clinically. The classical picture is of 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.
Treatment
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.
Epidemiology
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 4-5000 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. The mortality rate for dengue is therefore probably less than 1 in 1000.
Prevention
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.
Potential antiviral approaches
In cell culture experiments Morpholino antisense oligos have shown specific activity against Dengue virus [1] (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15795296) .
Recent outbreak
Recent dengue outbreaks in South East Asia:
- Thailand (May 2005) 7200 infected. Atleast 12 dead. Most recent infection in the world.
- Indonesia (February 2004) claimed almost 200 lives. This number may still grow.
- Malaysia (January 2005), 33,203 cases.
- Singapore ((2004), 9460 cases, (2003), 4788 cases.
Dengue_distr.gif
References
- Theiler, Max and Downs, W. G. 1973. The Anthropod-Borne Viruses of Vertebrates: An Account of The Rockefeller Foundation Virus Program 1951-1970. Yale University Press.
- Downs, Wilbur H., et al. 1965. Virus diseases in the West Indies. Special edition of the Caribbean Medical Journal, Vol. XXVI, Nos. 1-4, 1965
External link
- CNN report on dengue fever (http://edition.cnn.com/2004/WORLD/asiapcf/02/20/indon.dengue/).ar:دنجي
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