understand and prevent dengue

Topics: Fever, Dengue fever, Immune system Pages: 16 (1423 words) Published: April 20, 2014


Table of Contents

Understand and Prevent Dengue Fever

Introduction of Dengue Fever
Dengue fever, a very old disease, has reemerged in the past 20 years with an expanded geographic distribution of both the viruses and the mosquito vectors, increased epidemic activity, the development of hyperendemicity (the co circulation of multiple serotypes), and the emergence of dengue hemorrhagic fever in new geographic regions. In 1998 this mosquito-borne disease is the most important tropical infectious disease after malaria, with an estimated 100 million cases of dengue fever, 500,000 cases of dengue hemorrhagic fever, and 25,000 deaths annually. The reasons for this resurgence and emergence of dengue hemorrhagic fever in the waning years of the 20th century are complex and not fully understood, but demographic, societal, and public health infrastructure changes in the past 30 years have contributed greatly. This paper reviews the changing epidemiology of dengue and dengue hemorrhagic fever by geographic region, the natural history and transmission cycles, clinical diagnosis of both dengue fever and dengue hemorrhagic fever, serologic and virologic laboratory diagnoses, pathogenesis, surveillance, prevention, and control. A major challenge for public health officials in all tropical areas of the world is to develop and implement sustainable prevention and control programs that will reverse the trend of emergent dengue hemorrhagic fever. Dengue Virus and the Mosquito Vector

The dengue virus is a single-stranded RNA virus belonging to the Flaviviridae family. The viral genome is approximately 11 kb in length and is surrounded by an icosahedral nucleocapsid covered by a lipid envelope. The mature virion has three structural (core, membrane-associated and envelope) and seven non-structural (NS1, NS2a, NS2b, NS3, NS4a, NS4b and NS5) proteins.

Figure : mosquito vector
The envelope protein is involved in the main biological functions and is responsible for binding and transport into host cells. It is also associated with the induction of neutralizing antibodies and development of protective immune response in the host. The non-structural proteins are expressed as both membrane-associated and secreted forms and have been implicated in the pathogenesis of severe disease. There are four serotypes classified according to their immunological properties – DEN-1, DEN-2, DEN-3 and DEN-4. Infection with one dengue serotype confers lifelong immunity against that serotype but only transient protection against infection by other serotypes. All four serotypes have been associated with outbreaks, having seen DEN-2 as the predominant serotype of primary infection during the outbreak in 2005. Recent data have also demonstrated that the various genotypes within each serotype possess varying epidemic potential. The primary vector for the dengue virus is the A. aegypti mosquito, although the virus may be transmitted by the Aedes albopictus and Aedes polynesiensis as well. Infected humans are the main carriers and amplification host of the dengue virus. Female mosquitoes acquire the virus by biting infected humans in the viraemic phase and become infective after an extrinsic incubation period of 7–14 days. Subsequently, the mosquito may transmit the virus during every feeding. The length of the extrinsic incubation period is dependent on the ambient temperature and the virus involved, both of which affect the replication rate of the virus in the vector. Aedes aegypti is a highly domesticated mosquito that breeds in artificial containers such as water storage tanks, subterranean pits, flowerpot trays and other ornamental containers. The vector is known to prefer to rest indoor, although studies have shown that they may seek oviposition outdoors. Peak biting activity is at dawn and dusk. The multiple feeding behavior of A. aegypti and its preference for human hosts are believed to contribute to the explosive spread of dengue...
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