Info on Dengue Fever

Dengue fever and dengue hemorrhagic fever (DHF) are acute febrile diseases, found in the tropics and Africa, and caused by four closely related virus serotypes of the genus Flavivirus, family Flaviviridae. The geographical spread is similar to malaria, but unlike malaria, dengue is often found in urban areas of developed tropical nations, including Singapore, Taiwan, Indonesia, India and Brazil.

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.

dengue06

World-wide dengue distribution, 2006. Red: Epidemic dengue. Blue: Aedes aegypti. source: wikipedia

During the first months of 2007, over 16,000 cases have been reported in Paraguay and in the end of the year, more than 100.000, of which around 300 or 400 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.

On March 20, 2008, the secretary of health of the state of Rio de Janeiro, Sérgio Côrtes, announced that 23,555 cases of dengue, including 30 deaths, had been recorded in the state in less than three months. Côrtes said, “I am treating this as an epidemic because the number of cases is extremely high.” Federal Minister of Health José Gomes Temporão also announced that he was forming a panel to respond to the situation. Cesar Maia, mayor of the city of Rio de Janeiro, denied that there was serious cause for concern, saying that the incidence of cases was in fact declining from a peak at the beginning of February.  By April 3, 2008, the number of cases reported rose to 55,000

Significant outbreaks of dengue fever tend to occur every five or six years. The cyclicity in numbers of dengue cases is thought to be the result of seasonal cycles interacting with a short-lived cross-immunity for all four strains, in people who have had dengue (Wearing and Rohani 2006). When the cross-immunity wears off, the population is then more susceptible to transmission whenever the next seasonal peak occurs. Thus in the longer term of several 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.

For more on this see these links:

Dengue Fever Fact Sheet [CDC]

Dengue Info

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~ by redspyda on April 7, 2008.

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