Dengue Fever Case Study

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CHAPTER ONE

INTRODUCTION

1.1 Background of the study

Dengue is an arbovirus disease complex which includes dengue fever (DF) and dengue hemorrhagic fever (DHF) and its subsequent dengue shock syndrome (DSS). It is caused by four serotypes of dengue virus. A dengue virus infection may be asymptomatic or it may lead to undifferentiated viral fever syndrome, dengue fever, fever hemorrhagic fever or dengue shock syndrome. (World Health Organization 2003)
The disease is often, though not exclusively, closely associated with poor environmental sanitation, inferior housing and inadequate water supplies. Communities where such conditions prevail must be told what step they should take to prevent and control DHF. The diagnosis and management of
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There are four serotypes of the dengue virus namely DEN-l, DEN-2, DEN-3 and DEN-4. Dengue viruses are transmitted to humans through the bite of an infected Aedes mosquito (which normally attacks at dawn and at dusk) The Aedes aegypti are mainly found in urban areas and while the Aedes Albopictus is usually found in the rural and sub-urban areas. The dengue virus is transmitted via the bite of the Aedes mosquito, in particular the A.aegypti and A.albopictus. Infection with any one of the serotype confers lifelong immunity to that virus serotype.
Although all four serotypes are antigenically similar, they are different enough to elicit cross-protection for only a few months after infection by any one of them. The four serotypes of the dengue virus may all circulate concurrently in the same season but in different geographical regions. One serotype may predominate over other serotypes depending on the susceptibility or immunity of the population Dengue virus is now believed to be the most common arthropod-borne disease in the world. Dengue is mainly found in the tropics because the mosquitoes require a warm
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The principal vector mosquito for the dengue virus is the A.aegypti. According to WHO (1997) A.aegypti is the most important epidemic vector for dengue diseases, but other species such as A.albopictus, A.polynesiensis, and several species of the A.scutellaris complex, and A.(Finlaya) niveus (WHO, 1999) have also been incriminated as secondary vectors. All except Ae.aegypti have their own restricted geographical distribution and, they have been identified as a host for the dengue virus, although the most efficient epidemic vector for dengue is still the A. aegypti. A study by Varma (1989), noted that the A.aegypti and A.albopictus are the principal vectors Of the dengue virus in rural and urban areas in Malaysia, but not in the deep jungle. He also said that the Aedes niveus, which feeds on human and monkeys, is believed to be the vector of the wild life cycle in Malaysia. A aegypti is one of the most efficient mosquito vectors for the arboviruses because It is highly anthro-pophilic and thrives in close proximity to humans and often live indoors.

2.2.6 Dengue Host

Humans are the main urban reservoir of the dengue virus. Transmission of the dengue virus from infected humans to the feeding mosquito is determined by the magnitude and duration of the viraemia in the human hosts; persons With high viraemia provide a higher infectious dose of the virus to the feeding mosquito, normally leading to a

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