Dengue An Epidemiological Approach Biology Essay

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In this world there are many small invisible creatures which affect humans in many ways. These include viruses, bacteria etc. Among these creatures, some have unmercifully claimed the lives of millions. One such organism is dengue virus that has been inflicting mankind since time immemorial. Dengue is creating headlines nowadays in the media. The havoc it is creating is huge. According to WHO (2009), 50 million dengue infections occur annually and approximately 2.5 billion people live in dengue endemic countries. Globally dengue epidemics are known to occur over the consecutive last three centuries in tropical, subtropical and temperate areas (WHO, 2011). Furthermore, Park (2009) proposes that dengue has become one of the leading causes of deaths in Asia. Moreover, Nathan, Drager and Guzman (2009) mention that dengue imposes significant health, economic and social burden on the populations of endemic areas. Furthermore, literature suggests that people are less aware of disease indications leading to delay in medical help. Itrat et al. (2008) also found decreased awareness about dengue among Pakistani people. Considering devastating effects of dengue in many countries as well as in Pakistan, this paper attempts to discuss prevalence, causes, natural history, prevention, management and recommendations with regards to dengue.

Sapir and Schimmer (2005) define dengue as the "most important arthropod-borne viral disease of public health significance" (p.1). From an epidemiological viewpoint, dengue is considered to be most rapidly spreading disease with 30 folds increased incidences in last 50 years (Khan and Hassan, 2011). According to WHO (2002), two-fifths of world population are at risk of dengue and annually 500,000 cases of dengue hemorrhagic fever and mortality rate of 2.5% are reported. During the period from 2000 to 2006, about 545,000 cases were reported in 44 countries (Gomez-Dantes &Willoquet, 2009).

Dengue is now endemic in more than 100 countries in Africa, America, Eastern Mediterranean, Southeast Asia and Western Pacific regions (Burattini et al., 2007). Furthermore, Jahan (2011) asserts that pandemic of dengue began in Southeast Asia after World War II and spread worldwide. Another report estimates 12,000 dengue related deaths in Southeast Asia, 4,000 in Western-Pacific and 2,000 in America in 2002 (WHO, 2004).

Over the last few years, dengue cases in Pakistan have also been increased. Khan and Hassan (2011) indicate that Pakistan has experienced a number of dengue fever outbreaks since 1992 and in 2005. In October 2010, Ministry of Health Government of Pakistan reported a total of 1500 dengue cases including 15 deaths due to complications (Riaz, 2011). According to Idrees & Ashfaq (2012), dengue cases are observed throughout the year in Pakistan with peak incidences in post monsoon period. They added that 2007 and 2011 have been the worst years for Pakistan because of floods increasing dengue incidences. Moreover, Pakistan National Health Department confirms more than 5,050 cases in the year 2010 (Yusuf, 2011). These statistics show that there is high prevalence of dengue cases not only in Pakistan but also worldwide.

All infectious diseases including dengue can be explained on the basis of epidemiological triad that is host, agent and environment. Sajid, Ikram & Ahmed (2012) explain that the agent in this triad is dengue virus (DEN) which is a "small single-stranded encapsulated RNA virus," comprises of four different serotypes (DEN1 to 4) belonging to the genus Flavivirus. Since dengue is an infectious disease and is specifically caused by DEN virus, there is a natural universal susceptibility to infection for all who are exposed to dengue (Gomez-Dantes & Willoquet, 2009). This fulfills the Bradford Hill criteria and Henle-Koch's postulates. The virus itself cannot infect humans through penetration rather it needs a vector Aedes aegypti mosquito to cause disease (Jahan, 2011). Moreover, Nathan et al. (2009) assert that this mosquito is tropical and subtropical specie mainly a daytime feeder occupying human habitation including water containers, non-recyclable products (plastic, metal and glass containers, tires), rainwater reservoirs, poor housing conditions and insufficient water and sewage systems (Jahan, 2011). This vector and its habitat form the environmental component of this triad. In addition, humans are considered to be preferred host of dengue virus. There are certain host factors that predispose a person to infection. According to Dinh et al. (2012), one risk factor is age associated with severity. They assert that children are more likely to experience plasma leakage and severe forms of dengue i.e. dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS) than adults while bleeding and organ dysfunction are more common in adults. Gender is another factor but not so significant. Gender based vulnerability varies among regions. Barney (2008) suggests that women are at higher risk as most women work at homes, increasing contact with house-dwelling and biting by vector increasing transmission risk. Furthermore, dengue is found to be associated with variations in genes PLCE1 and MICB which encode a protein coordinating the immune antiviral response (Dinh et al., 2012). Additionally, low socioeconomic status is also an important factor. Higher rates of dengue are associated with farmers and people with low income and education level (Phuong et al., 2008). Moreover, lack of street drainage and garbage collection trucks after heavy rain facilitates vector spread (Barney, 2008).

This agent-host-environment triad plays a key role in dengue transmission. Shepherd (2012) elaborates that when mosquitoes suck an infected person's blood, they acquire the virus. Studies have shown that infected persons can transmit virus as early as 2 days before symptoms develop. After entering the mosquito, virus requires 8-12 days incubation before transmitting to a non-infected person (Teo, Ng & Lam, 2009). Besides human-vector-human transmission, vertical or intrapartum transmission is also reported increasing fetal mortality risks (Sirinavin et al., 2004). Transmissions through needle stick injury, blood transfusion and organ transplantation in rare cases are also found (Chuang et al., 2008).

Once the virus is transmitted, it follows certain stages termed as natural history of disease. It starts with susceptibility stage including certain risk factors which predispose people to dengue as mentioned earlier. Next is subclinical stage. According to Nathan et al. (2009), mostly dengue infections are asymptomatic and its incubation period is 4-10 days in humans. Pathogenesis of dengue in this stage is associated with the host immune response activated by dengue virus (Stephenson, 2005). When the virus enters human body, it binds to WBCs and replicates. WBCs respond through innate immune system by producing signaling proteins (interferons and cytokines). Interferon stimulates antibodies and T-cells production. Major viral replication cites are monocyte-macrophage lineage cells but other tissues such as liver, bone marrow, brain, pancreas and heart are also infected in severe dengue resulting in organ dysfunction due to leakage from blood vessels resulting in hypovolemia and hypo-perfusion. Bone marrow dysfunction leads to thrombocytopenia increasing bleeding tendencies.

The third stage is clinical disease comprising of febrile and critical phases (Nathan et al., 2009). Febrile phase lasts for 2-7 days and is characterized by sudden high grade fever along with facial flushing, erythema, generalized malaise, leukopenia and enlarged liver. Whereas in critical phase drop in temperature, increase in capillary permeability and hematocrit levels and hemorrhagic manifestations occur due to vasoactive mediators (Jahan, 2011). The last stage is recovery, disability or death. If clients survive 24-48 hours critical phase, a gradual extravascular fluid reabsorption occurs in 48-72 hours and general well-being improves with haemodynamic stability. With proper management dengue can be cured but if not managed properly, can lead to DHF/DSS.

The burden of all diseases can be reduced through prevention. Likewise, dengue can also be prevented by taking some measures. Among all levels of preventions, primordial comes first. It includes awareness on mass level through media and campaigns (Queensland Dengue Management Plan, 2011). Primary prevention depends on vector control or interruption of human-vector contact. Preventive measures can be done for vector control through controlled sanitation, appropriate piped water supply, elimination of stagnant water, spraying and fumigation limiting mosquito breeding points (BMJ Evidence centre, 2012). Gomez-Dantes & Willoquet (2009) suggest insecticides as unuseful because mosquitoes breed again within two weeks even with its multiple applications. Moreover, applying door screens, casement blinds and domestic water bud vase covers, covering bare skin areas, using mosquito nets and loops at high risk areas and sealing of windows are also effective (Itrat et al., 2008). Thus, increasing awareness programs are significant as they have a wide public health impact (Rothman, 2010). In this regard, community and public health nurses play a vital role.

Many infected individuals remain asymptomatic causing dengue to be endemic. Therefore, early detection and treatment are very important which constitute secondary prevention. Investigations including CBC, LFTs and Anti dengue antibodies can be carried out (Sajid, Ikram & Ahmed, 2012). When dengue is diagnosed, primary management is to ensure adequate fluid intake consisting of oral rehydration fluid, coconut water, fruit juices and soup rather than plain water. Furthermore, symptomatic treatment is done with antibiotics and antipyretics. Moreover, complications are prevented throughfurther investigations. Doctor should be consulted if fever does not settle, intolerance to fluid, severe abdominal pain, increase bleeding and anuria for more than 6 hours. Blood investigation results should be reviewed as early as possible as a delay can rapidly lead to DHF/DSS (Health Ministry Srilanka, 2010).

Studies suggest primary care providers are more disease focused and show little concern on public health perspectives therefore, they need to be involved in dengue control and prevention (Ang, Rohani & Look, 2010). Following recommendations and strategies can be implemented. Firstly, the vector needs to be controlled. All the favorable breeding places require pest control operators for regular monitoring. It also helped Singapore to control dengue where they made pest control operators at all construction sites, schools and houses (Teng, 2001). On the contrary, it might be impractical in Pakistan because of high costs so it is recommended that government should identify dengue sensitive areas and educate the people for primary prevention. Moreover, specific vector control laws can be made to limit disease transmission. Boo (2001) mentioned about the Control Vectors and Pesticides (CVPA) legislation made by Singapore Government, according to which no one is allowed to create conditions favorable for the vectors. Secondly, effective disease and vector surveillance systems can be established based on reliable laboratory and health information (WHO, 2011). Since dengue is endemic in Pakistan, so constant monitoring can be helpful to prevent sudden outbreaks. Moreover, it is also suggested that people in the community should be educated about dengue control and prevention through awareness programs and provision of informative pamphlets at their doorsteps. This might be difficult in Pakistan because of security issues thus media can play a key role in educating people through health related programs. Education will decrease dengue incidences and severity. In the 2011 outbreak, Punjab Government opened a hotline called Punjab Health Line Project for Dengue to facilitate awareness of signs and symptoms, provide help and ultimately identify susceptible areas. Such work is appreciable but a consistency needs to be maintained. In addition, people can also be involved in prevention and control interventions. This will build community partnerships thus making the programs more effective and sustainable by promoting self-reliance and a sense of control over their own health (WHO, 2011). Moreover, consistent environmental strategies such as improving water supply and storage systems, managing solid waste and frequent street cleansing in the country can reduce dengue transmission and spread. (McCall, Lloyd and Nathan, 2009). For this, community and public health nurses require to identify environmental factors through proper assessment (Gomez-Dantes & Willoquet, 2009). Lastly, research areas can be improved. A tetravalent vaccine is currently being developed and may be available in the future (WHO, 2012). Likewise, researches can be done and methods can be devised to identify and treat dengue on a very primary level.

In conclusion, dengue cases are found globally and are a cause of social and economic burden. It is a communicable disease caused by DEN virus via mosquitoes. However, implementation of comprehensive, effective and integrated preventive strategies will reduce incidences of dengue among populations globally. Early detection is possible through profound awareness facilitating diagnosis and treatment. Supplementary researches are vital as currently the treatment of dengue is only symptomatic. Since dengue is epidemic, so effective partnerships at national, regional and global levels can lead to sustainable prevention and dengue eradication.