What is Dengue

Dengue fever is a severe mosquito-borne viral virus that has a significant socioeconomic and medical impact on many tropical and subtropical regions around the world. Dengue fever is now considered the most serious arboviral disease since more than half of the world's population lives in places where they are at risk of contracting the disease, and another half lives in dengue-endemic countries. There are four distinct dengue virus serotypes, all of which are descended from the Flavivirus genus and family Flaviviridae (Wilder-Smith et al., 2011).

DENV-1, DENV-2, DENV-3, and DENV-4 are the four serotypes. Infection with any of the 4 viruses leads to lifelong immunity to that particular serotype. Each of the 4 serotypes has been distinctively discovered to be responsible for dengue epidemics and linked to more acute dengue. Dengue virus (DENV) leads to more human mortality and morbidity compared to any other arboviral ailment. According to the latest statistics, about 390 million individuals are every year infected, with 96 million others manifesting with clinically obvious ailments. In its neglected tropical ailments 2013 report, the WHO called for more surveillance on dengue prevention. Of special reference was dengue's volatile epidemic potential as well as the global rise in dengue cases (Pommerville, 2017).

A Global Threat and Burden

Dengue transmission is now present in each World Health Organization (WHO) part of the world and over 125 nations are identified as being dengue endemic (Pommerville, 2017).

Thus, the real force of dengue globally is hard to determine because of factors like insufficient surveillance of disease, misdiagnosis, as well as low reporting levels. At the moment, available data likely grossly underrates the economic, disease and social burden. Global incidence estimates of dengue infections per year ranges between 50-200 million; nevertheless, recent approximates using cartographic techniques suggest this number is nearer to approximately 400 million (Pommerville, 2017). Dengue expansion is anticipated to rise because of such factors as the contemporary dynamics of climate change, travel, globalization, settlement, socio-economics, as well as viral evolution (Pommerville, 2017).

Dengue, particularly, has witnessed a 30-fold growth in incidence over the past half of a century that indicates no sign of reducing. The report calls for not only evaluation but also incorporation of present intervention approaches to attain a 50 percent decrease in dengue mortality as well as 25 percent decrease in dengue morbidity by 2020. DENV's transmission from one individual to another is by Aedes mosquitoes, primarily Aedes aegypti. Infections to human beings can lead to a spectrum of diseases that range from mild, self-limiting febrile sickness to typical dengue fever to shock syndrome and finally death. Nonetheless, it has been noted that most of the infections are mild or indicate no clinical manifestations (Pommerville, 2017).

In 2012, dengue ranked as the most important mosquito borne viral disease in the world.

The disease is now endemic in more than 100 countries in the WHO regions of Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific.

The emergence and spread of all four dengue viruses ("serotypes") across these regions represents a global pandemic threat.

Currently, there exists no commercially available dengue vaccines or antivirals, although improvement on their development is heartening. Therefore, dengue prevention, is at the moment restricted to mosquito control. Moreover, a few well-documented successes show that thorough application of vector control can minimize DENV transmission and ailment. In the 50s and 60s, a local program spanning much of the Caribbean and Central and South America considerably decreased Ae. aegypti populations, leading to striking reductions in human yellow fever and DENV infections, as well as alleged eradication of Ae. aegypti from a large section of the area by the start of 70s. In Singapore, vector control initiatives for dengue control, during the 70s and 80s and in Cuba during the 80s and 90s are likewise identified as public health successes, although, similarly, they too could not be sustained (WHO, 2013).

The incapacity of these nations to effectively sustain their gains is regarded, at least in part, to be the outcome of reduced herd immunity. For instance, less dramatic outcomes, during 2000-2010 in Peru, were viewed by the effective employment of emergency vector control to minimize the impact of DENV infection, that is per capital human infection risk (WHO, 2012). However, there is significant frustration because vector control has not been effective in preventing epidemics and dengue fever's increasing geographic distribution. Even though the idea of vector control is rational, control should be early in an outbreak or deliberately employed during inter-epidemic times to avoid escalation in not only transmission but also effective wide scale application has been hard to accomplish (Holtz, 2017).

From the ongoing argument, success in minimizing the public health burden of dengue will need a multi-faceted strategy that comprises coming up with the fundamental theory of successful dengue control, continuing to review as well as evaluate existing strategies and interventions, in addition to gathering new empirical data that is used for testing underlying ideas and approaches. This can be accomplished via controlled experimental research that are immediately required to evaluate the health effect of dengue vector control on the basis of entomological and epidemiological measures. To tackle this issue, interventions under development are needed. Normally, the gap is usually big for existing strategies and tools, which were made in the time period when epidemiologic evaluations were not done (Holtz, 2017).

Even though greater stress must be put on proactive approaches whose is preventing, diminishing or getting rid of transmission, nonetheless, dengue outbreaks happen and response needs a closer focus on development of strategies and tools that can be quickly deployed and have swift impact. In addition, DENV is a problem that is growing by the day especially in mega-urban centers spanning across regions and countries (Achee et al., 2015).

One of the most largest challenges in enhancing mosquito control for prevention of DENV is scaling up from the effective small-scale experimental trials to wide-scale public health application. In addition, there has been an ever rising agreement that eradicating DENV as a public health problem can only be attained by incorporating vector control by use of vaccines. Making vector interventions a priority on the basis of their likelihood of disease prevention will enable determination of how to combine the best options by use of DENV vaccines (Holtz, 2017).

Policy on a Global Level

The goal of the global strategy is to reduce the burden of dengue by:

Reducing dengue mortality by at least 50% by 2020

Reducing dengue morbidity by at least 25% by 2020

Estimating the true burden of the disease by 2015.

The target audiences of the strategy are leaders in national control programmes, research and funding organizations and other stakeholders involved in dengue prevention and control.

Dengue fever is classified as an infectious disease in the Infectious Disease Act (2008). According to the Ministry of Environment and Water Resources' Public Health Policy (2015), controlling the vector population to protect public health is important, and the goal is to maintain a low incidence of vector-borne and food-borne diseases, by:

Encouraging the community to help protect public health

Finding better ways to monitor and control vector-borne diseases

Control of vectors and pesticides act

Concerns the destruction of vectors (mosquitoes) and control of vector-borne diseases by:

Prohibiting the creation of conditions suitable for the breeding/harbouring of vectors

Requiring any person suspected of being infected with a vector-borne disease to undergo investigations and treatment

Fumigation of public areas

Licensing of pest control companies

Penalties for breaking these laws

Singapore has a good surveillance system with dengue being a legally notifiable disease, with worldwide probably the most reliable data on dengue incidence over decades (Struchiner, Rocklöv, Wilder-Smith, & Massad, 2015). Larval source reduction and control are the most effective methods to deal with the Aedes vector (Ooi, Goh, & Gubler, 2006), and Singapore has been using this along with WHO-recommended control methods such as public health education, community participation, and geographical clinical surveillance systems.

Existing Strategies

This is being achieved by implementing:

The mozzie wipeout campaign- which entails public education/outreach campaign, Posters placed around housing areas, Flyers distributed door-to-door, Exhibits and road shows," Dengue prevention volunteers" - ordinary citizens who help spread the dengue prevention message.

Dengue community alert system-Banners are put up around housing areas to alert residents about the dengue situation in their neighborhood. This allows residents to be more vigilant about not keeping stagnant water in or around their homes and take precautionary measures such as using repellent and wearing long sleeves.

Wolbachia-Aedes Mosquito Suppression Strategy - "Project Wolbachia"-Male Aedes mosquitoes infected with the Wolbachia bacterium are released into the wild around areas with dengue clusters/ known population of aedes mosquitoes. Only female mosquitoes feed on blood, male mosquitoes feed on plant nectar.When the Wolbachia-Aedes males mate with non-Wolbachia females, their resulting eggs do not hatch.This thus reduces the naturally occurring Aedes mosquito population, and thus the number of dengue-carrying female Aedes mosquitoes.

Critique of Evidence

Actively check for and get rid of stagnant water by practising the 5-step Mozzie Wipeout

According to WHO Recommendations for Occupational Health and Safety Following Disasters, pools of standing or slow-flowing water provides a breeding ground for mosquitoes that can transmit infection. Campaign was developed in Singapore to control vectors and pesticides. Control of Vectors and Pesticides Act - NEA enforces the law against recalcitrant persons who continually breed mosquitoes or do not remove potential mosquito breeding habitats in their premises despite having being told to do so ("Singapore Statutes Online - 59 - Control of Vectors and Pesticides Act", 2017). Through a 'carpet combing' exercise over 6 weekends in HDB blocks and surrounding areas,1,000 mosquito breeding habitats were found and destroyed with an additional 8,400 potential breeding sites removed.

This had contributed to the reduction of the mosquito population which in turn led to a drop in dengue cases in the subsequent months.

Based on an open data which was released on January 2016, it gives the public more specific, actionable information on how to protect themselves from mosquito bites in dengue clusters, and where a high level of vigilance is required in order to combat mosquito breeding. Thus dengue alert colour codes have been designed. For instance a yellow color code indicates that there are less than 10 cases reported in one's neighborhood, a red color code indicates that there are 10 or more cases reported in a neighborhood while a green color code indicates that there has been an improved surveillance and efforts of vigilance are bearing fruit.

Global Policy Example

In the 21st century Brazil became the country of the world with the most reported cases of dengue fever, occupying first place in the international ranking for total cases of the disease, with more than three million cases reported from 2000 to 2005. The National Plan for Dengue Control (PNCD) was developed in 2002. The main objective is to reduce Ae. aegypti infestation and thereby reduce the incidence of dengue and its lethal hemorrhagic manifestations.

The policy of Dengue involving vertically integrated programs not only activities to eliminate Ae. aegypti but also environmental sanitation, epidemiological and health surveillance, laboratory support, and health information and education measures, among others.

Vector Control

Mechanical control: removing potential breeding sites for mosquitoes and covering water tanks in order to prevent oviposition by Aedes aegypti female mosquitoes.

Chemical control: using chemical compounds called insecticides, which can affect the larval or adult stages of mosquitoes.

Biological control: is designed to eliminate mostly mosquito larvae using biological agents.

Use Bacillus thuringiensis israelensis (Bti), a bacterium that, when ingested by mosquito larvae, synthesizes lethal endotoxins

Use of larvivorous fish in intra-domestic pots for mosquito control has proven to be an intelligent solution→ culture difference

The strategy Vaccines to Vaccination (v2V) was formed in 2009 to enable DENV vaccines delivery after regulatory approval. Following results publication from a phase 2b clinical dengue vaccine trial in Thailand, showing differing degrees of vaccine efficiency, there was reconfiguration of the program into the Partnership for Dengue Control (PDC)-an independent and multi-sponsored initiative (Runge-Ranzinger et al., 2016). Program re-direction was in line with the rising agreement amongst the dengue prevention community that there exists no one particular intervention will be sufficient in controlling DENV (Runge-Ranzinger et al., 2016). This is because of heterogeneities in viral pathogen, mosquito vector, as well as human host factors that contribute to transmission complexity. Therefore, it was established that, for the biggest possibility of continued dengue prevention, the PDC mission must be to encourage not only development but also implementation of the numerous integrated, innovative, as well as synergistic interventions (Holtz, 2017).

The anticipation of PDC is that whenever a successful DENV vaccine is available commercially, the public health community will go on depending on vector control since the two approaches complement and improve each other (Holtz, 2017). A dengue vaccine may be utilized in artificially elevating herd immunity coupled vector control aimed at reducing the infection force. Theory as well as outcomes from field research including other vector-borne pathogens aid the impact of concurrently focusing on the pathogen and vector. Reduction of global malaria load has been implemented utilizing anti-Plasmodium in combination with bed nets that are insecticide-treated (Holtz, 2017).

For instance, Lymphatic filariasis (LF) is more efficiently and rapidly managed when there is a combination of anti-parasite drugs and vector control compared to when drugs alone are utilized. Just like in the case of lymphatic filariasis and malaria, guidance for the best integrative interventions against an intricate, multi-strain pathogen having intricate transmission dynamics such as DENV will highly profit from theoretical, preliminary evaluation with simulation and mathematical models (Runge-Ranzinger et al., 2016).

Employment of several approaches for the prevention of vector-borne ailments is based on the Integrated Vector Management (IVM) program of WHO for mosquito vectors control, comprising those that are responsible for the transmission of mosquito vectors, involving those that are responsible for transmitting DENV. One component of IVM is making of decisions under the guidance of operational research and epidemiological and entomological evaluation and surveillance (Holtz, 2017).

The anticipation is that as availability of field data increases, for DENV vector interventions, so, too, will the capability of refining guiding principles for maximizing and implementation impact. Such evidence will act as the basis for evaluation, challenging conventional changes and paradigms in the standards for vector control and/ or vaccines control (Runge-Ranzinger et al., 2016). The PDC, as first step, launched a research to evaluate high-tech, dengue vector control. Objectives were to review critically various strategies and tools, identify those strategies with the highest possibility for positive public health influence, recognize core missing information needed for guiding effective management of vector, in addition to proposing productive techniques for filing up knowledge gaps as well as advancing the prevention of dengue (Holtz, 2017).

Reflections fell into 3 major classes: present up to date (current) interventions, secondly mosquito ecology coupled with modeling and thirdly new strategies and tools (methods being developed). Assessment, for present interventions, comprised the targeted life stage together with evidence showing the extent to which the intervention affects mosquito populations and subsequent DENV transmission (Runge-Ranzinger et al., 2016).

Conclusion

In conclusion, dengue is now prevalent in over 125 countries worldwide. There exists multifactorial reasons for the currently witnessed and envisaged expansion. They might comprise virus evolution, climate change and societal factors including rapid urbanization, growth of population and development, coupled with socioeconomic factors like global trade and travel. Currently, there exists no vaccination or antiviral therapy for dengue, leaving only fast detection and symptomatic treatment by use of fluid resuscitation important fir severe cases management. Consequently, due to constrained therapeutic approaches, successful vector control techniques are important and are thus encouraged worldwide by the WHO via the strategic IVM technique. This approach, for dengue, targets the Aedes genus of mosquito in scenarios where high instances of human-vector contact take place. Surveillance together with reporting is vital for successful dengue control, and more correct quantification of the influence of dengue internationally will enable enhanced financial, political and study prioritization and informed decision making together with improved modeling (Nading, 2014).

The recognized economic, social as well as disease burden of dengue globally is disturbing and it is clear that the broader effect of this sickness is grossly underrated. A global multi-sectoral response, like WHO's 2012-2020 Dengue Prevention and Control Global Strategy, is now important in reducing the important influence this ailment projects worldwide.

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