07 August 2010

DENGUE FEVER: AN INCREASING WORLDWIDE THREAT

Dengue fever is by far the most common and significant mosquito-borne viral infection, affecting 100 million people yearly. It is transmitted by the bite of an Aedes mosquito. The most prevalent areas of occurrence are Latin America and the Caribbean, and Southeast and South Central Asia. It is a frequent cause of hospitalization in endemic areas, particularly in among small infants. It is also the second most common infectious cause of hospitalization in travelers returning from the tropics. Although most cases reported in the US are in returning travelers, the disease is endemic in Puerto Rico, Samoa and Guam. Recently, locally acquired cases have been reported in Florida and South Texas.

Often acute dengue causes few or no symptoms. The usual clinical presentation is the onset of fever after an incubation period of 3-7 days, severe retro-orbital headache and severe muscle and joint pains (hence the term breakbone fever). A maculopapular rash often appears as the fever subsides.

There are four dengue serotypes. Infection with any of these produces a life-long immunity to that serotype, but no protection against infection with the other three serotypes. In fact, subsequent infection with another serotype often produces the more severe dengue hemorrhagic fever, DHF, and dengue shock syndrome, (DSS), which require intensive care management and have a high mortality rate, over 20,00 deaths each year.

Clinicians and scientists have long puzzled over the increasing severity of dengue in patients who have recurrent disease. Recent research has demonstrated that prior infection with another dengue strain actually increases the virulence of a new serotype by a process known as antibody dependent enhancement. The virus becomes not only more infective, but causes an inflammatory over-response, and produces the capillary leakage, the hemorrhage, and the shock of severe dengue. This phenomenon also explains the tendency of small infants to develop DHF and DSS. After they are born to dengue immune mothers, passively acquired antibodies gradually wane, and the infants enter a period of increased risk for severe disease by the mechanism described above.

There is currently no specific treatment for any type of dengue, and no vaccine is available. Development of an effective vaccine will be complex, in view of the risk of actually increasing the risk of severe complications. At present our best advice is to protect against day-biting mosquitos in endemic areas, and to be aware of the possibility of dengue and its severe complications in endemic regions.

References:

1. Schmidt, A. C. Response to Dengue Fever----the Good, the Bad, and the Ugly?

NEJM 2010: 363; 484-487.

2. CDC Commentaries: Dengue Fever. www.cdc.gov/dengue

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