Dengue virus a growing health problem
Dengue Virus laboratory, NUST Center of Virology & Immunology (NCVI), National University of Sciences & Technology (NUST), H-12, Islamabad, Pakistan
Dengue virus (DEN) is a member of family flaviridae. DEN is an arbovirus which means it spreads through an insect vector. Its principal vector is aedes aegypti, a day time biting mosquito. These mosquitoes breed in plastic containers, tyres and small pools of clean water outside homes (1, 2). DEN infections are becoming a global health issue. There are estimated 50100 million illnesses annually, including 250'000 500'000 cases of dengue hemorrhagic and 24'000 deaths. 2.5 billion of the world's population are estimated to be at risk living in tropical areas (3). Pakistan is one of the country that experience dengue outbreaks each year due to early rains and unchecked urbanization. Mosquitoes close contact with the humans increases the chances of the mosquitoes bites with subsequent infection. Once the mosquito bites it transfer the virus to humans. Now the virus reside inside the body and starts replication within the tissues of the human like spleen, kidneys, liver and lungs. Beside other cells dengue also infects immune cells like dendritic cells (DCs), monocytes, macrophages, lymphocytes (4). There are four dengue serotypes DEN-1, DEN-2, DEN-3 and DEN-4. All the four serotypes are antigenically different from each other. Immunity against one serotype can elicit immunity against that specific serotype but not other. A subsequent secondary infection with a different serotype causes severe diseased condition that leads to Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS) with association of plasma leakage (5, 6). DEN is a RNA genome virus of approximately 11kb comprising of three structural (CAPSID, MEMBRANE and ENVELOPE) and seven non structural genes (NS1, NS2a, NS2b, NS3, NS4a, NS4b and NS5) (7). Envelope gene is the main antigenic gene associated with antibodies production. There is no specific treatment, medicine available against dengue infection. Different laboratories across the globe are engaged in development of a protective vaccine against dengue. Vaccines that have been tested for dengue are killed, subunit, live attenuated, DNA and viral vectors based vaccines. But there is no effective marketed vaccine against dengue.
Dengue and Pakistan
Pakistan stands amongst the list of the dengue virus infected countries. According to available reports in 1994 dengue virus outbreak occurred in Pakistan. Most of the reported cases of dengue infections are from Punjab and Sindh regions. DEN infection morbidity rate is high than mortality in Pakistan. DEN serotype 2 and 3 are the most prevalent serotypes in Pakistan (8). In 1994 there were 15 patients reported with dengue infection (9). In 2006, Pakistan suffered its worst outbreak of dengue, resulting in 52 deaths. In 2007, 22 people died of the illness and in 2008 just five. Between October 2006 and January 2008, there were 3,242 laboratory-confirmed cases of dengue. In Sindh Province since January 2009, there have been 224 suspected cases reported of which 135 were confirmed. So far in 2009, four people have died of dengue (10).
There is no vaccine and drug available for dengue till now. The only strategy to control this disease is to prevent its spread through mosquitoes. Personal protection is necessary to avoid contact with the vector. Mosquitoes nets and mosquitoes repellent should be used. Larvicidal chemicals should be sprayed on the mosquitoes breeding reservoirs like tanks, containers, tyres and sinks. More research should be promoted to develop an effective vaccine against dengue. Vaccine should be formulated such that it can elicit immune system against all the four serotypes.
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