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17 September, 2018 10:47:28 AM

The Dengue outbreak

Dengue fever is not uncommon in Bangladesh. Most of the cases remain undiagnosed or misdiagnosed due to lack of awareness and diagnostic facilities, the self-limiting nature of the disease
Mohammed Abul Kalam, PhD
The Dengue outbreak

Up until now, a total of 11 cases of death have been reported due to dengue in the country this season and with a record of 3,374 cases of infection, the tropical viral disease can take turn of an epidemic causing more deaths, health experts warn. A dengue outbreak usually starts in the month of June and continues up to October. Since there are still about two months to go to be naturally free of infection, it is our expectation that the health ministry would take all preventive measures to contain cases of infection (The Independent, September 9, 2018).

Dengue fever is a rapidly spreading viral infection that is endemic in more than 100 tropical and subtropical countries in Africa, the Americas, and the Asia Pacific regions. It is caused by any one of the four serotypes of dengue virus, and infection of one serotype of dengue virus does not provide cross immunity against the other three serotypes. Dengue viruses are spread by female Aedes mosquitoes through blood-feeding on human hosts. Patients suffering from dengue fever experience sudden onset of fever, rashes, muscle aches, joint pain, and leucopenia. A dengue patient usually recovers within 14 days. Nevertheless, some patients develop severe dengue which is a potentially lethal complication characterized by hemorrhagic manifestations, severe plasma leakage, and severe organ impairment. Globally, about 500,000 severe dengue cases with 12,500 deaths have been reported annually.

A disease outbreak happens when a disease occurs in greater numbers than expected in a community or region or during a season. An outbreak may occur in one community or even extend to several countries. It can last from days to years. Sometimes a single case of a contagious disease is considered an outbreak. This may be true if it is an unknown disease, is new to a community, or has been absent from a population for a long time.An epidemic occurs when an infectious disease spreads rapidly to many people.Epidemic refers to an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area. Outbreak carries the same definition of epidemic, but is often used for a more limited geographic area (CDC, USA).

Dengue fever is not uncommon in Bangladesh. Most of the cases remain undiagnosed or misdiagnosed due to lack of awareness and diagnostic facilities, the self-limiting nature of the disease and, most importantly, the prevalence of another arthropod-borne disease in Bangladesh. But the concomitant presence of other arthropod-borne infections with similar courses of illness makes most physicians less aware of this infection. An awareness and clinical knowledge are necessary to diagnose dengue infection properly. An early warning system is an essential tool for pre-epidemic preparedness and effectiveness of dengue control. In recent decades, weather variables such as temperature and rainfall have been widely studied for their potential as early warning tools to fend off climate-sensitive infectious diseases such as Malaria, Dengue, and West Nile Virus.But the national institute - IEDCR is not in a position to provide early warnings or to tackle the Dengue epidemic or any epidemic/endemic/pandemic successfully. Observations make it very clear that the institute wait and pray for outbreaks to conduct seminar, workshops, conferences and other events each and every year during any outbreaks; spend huge amounts of money and come to limelight or in medias! Or like camera, light, action for press briefings!

There are no senior officers at any departments with research backgrounds and like to stay there. The highest authority of the institute as well as the Ministry of Health and Family Welfare is not interested for this recruitment rules. The Ministry issues posting order even for the Chief Scientific Officers (equivalent to the positions of directors of the institute/DGHS) and make senior scientists if they wishes―those has no background of research or on the departmental job descriptions. Some times IEDCR is called ‘dumping station’. It is very surprising to note that how a national research institute could run without a recruitment rules for the last 40 years but the institute spends millions of dollars for its strengthening or capacity building activities without the most potential ingredients – human resource! Career path taken by an employee determines the growth. Career should be planned in a way that it moves forward. Career development provides the framework with skills, goals, awareness, assessment and performance which helps an individual to move in the right direction and achieve the goals one has in one's career.

Generally, dengue epidemiology is influenced by a complex interplay of factors that include rapid urbanization and increase in population density, capacity of healthcare systems, effectiveness of vector control systems, predominant circulating dengue serotypes, herd immunity, and social behavior of the population. Most dengue endemic countries in Asia Pacific have limited resources and/or lack of preparedness to contain dengue epidemic,. Rising international and domestic trade and population movement contribute to the increases in domestic and cross border dengue transmission. As a result, the region is experiencing dengue epidemics with increasing frequency and magnitude. Until a vaccine or drug for dengue is available, vector control operations that eliminate adult mosquitoes and their larvae through breeding-source reduction remain the only effective method to curb dengue transmission. However, vector control can be resource and labor intensive, which poses an economic burden on nations with limited resources.

Numerous studies have revealed the influence of weather variables on the magnitude of dengue distribution through the effects on life cycle development, biting rates, infective and survival rates of vectors and on the incubation period of dengue virus. As temperature increases, Aedes mosquitoes display shorter periods of development in all stages of the life cycle leading to increased population growth; the mosquito feeding rate also increases; and dengue viruses in Aedes adult mosquitoes require shorter incubation periods to migrate to salivary glands. Conversely, high temperatures above 35°C or heavy rainfall possibly lower dengue transmission by reducing the survival rate of Aedes. Heavy rainfall creates abundant outdoor breeding sources for Aedes in the long run, but dry spells in some settings trigger an increase in water storage containers which can serve as breeding habitats.

A weather-based dengue early warning system could benefit vector surveillance and control in several ways. First, an early warning system enhances efforts of dengue control to reduce the size of an outbreak which in turn decreases disease transmission, averts possible mortality, and lowers healthcare burden and operating costs incurred during an outbreak. Second, the use of publicly available weather variables removes the necessity for financial investment in weather-based predictive methods and further allows vector control units to focus their operations on high risk period; thus, maximizing limited vector control resources. Third, local authorities require a maximum 3 months to curb a localized dengue outbreak. Finally, high precision and sensitivity of a forecast will minimize the use of resources and prevents unnecessary vector control operations triggered by false alarms. Vector control can be resource and capital intensive; hence, high operating costs and unnecessary psychosocial stress in the population subsequent to false alarms could possibly hamper the decision to adopt a dengue early warning. Thresholds for true or false positive rates could vary according to scale of operational complexity and its consequences. I recommend an economic study on cost-effectiveness analysis to identify thresholds of true and false positive rates of forecast to serve as yardstick for decision making as well as to evaluate the long term benefits of an early warning against operating costs.

Nevertheless, a dengue forecasting model faces the challenge of long term sustainability of forecast precision since it assumes that a historic distribution pattern will be repeated in the future; while dengue epidemiology is influenced by a combination of factors which are dynamic and possibly evolving over time. Implementation of a new vector control policy could exert direct impact on the size of the vector population and dengue incidence rate in the locality. These changes are likely to influence the trend and epidemic cycle in the long run. Though changes of dengue distribution in the long term are inevitable due to the dynamics of disease transmission and changes of relevant policy, forecast errors can be minimized by making appropriate adjustment of the model through anticipating (1) changes in risk factors and (2) changes in related fields that will eventually influence the disease transmission. Therefore, current knowledge of factors influencing dengue distribution patterns can be used to re-calibrate the model in the future to maintain long term forecast precision.

Moving towards syndromic surveillance:Syndromic surveillance might help determine the size, spread, and tempo of an outbreak after it is detected, or provide reassurance that a large-scale outbreak is not occurring, particularly in times of enhanced surveillance (e.g., during a high-profile event). Finally, syndromic surveillance is beginning to be used to monitor disease trends, which is increasingly possible as longitudinal data are obtained and syndrome definitions refined.

The fundamental objective of syndromic surveillance is to identify illness clusters early, before diagnoses are confirmed and reported to public health agencies, and to mobilize a rapid response, thereby reducing morbidity and mortality. Epidemic curves for persons with earliest symptom onset and those with severe illness can be depicted graphically. The time between symptom onset for an increasing number of cases caused by deliberate release of a biologic agent and subsequent patient visits to a health-care facility resulting in a definitive diagnosis is represented. Syndromic surveillance aims to identify a threshold number of early symptomatic cases, allowing detection of an outbreak days earlier than would conventional reporting of confirmed cases. The ability of syndromic surveillance to detect outbreaks earlier than conventional surveillance methods depends on such factors as the size of the outbreak, the population dispersion of those affected, the data sources and syndrome definitions used, the criteria for investigating threshold alerts, and the health-care provider's ability to detect and report unusual cases. A framework for evaluating public health surveillance systems for early detection of outbreaks should be useful for comparing syndromic surveillance across jurisdictions and for evaluating system performance.

And on a broader policy level, defining the role of academic and research partners in bridging any potential analytic gaps, defining the role and scope of a national syndromic data repository, and developing policy for integrating laboratory testing and laboratory information systems with syndromic surveillance are on the horizon.

Finally, communities and their religious and political leaders must join the battle against dengue fever in Bangladesh.The public health response to dengue should extend beyond a "one size fits all" approach such as a reliance on insecticide fogging— a change of paradigm in vector management seems essential.

Dengue is now the most rapidly spreading mosquito-borne viral disease in the world. In the absence of an effective drug or vaccine, health authorities rely on controlling the vectors to reduce disease transmission. WHO’s updated guidelines for dengue management, published in December 2009. These include advocacy and social mobilisation; targeted strategies based on thorough understanding of mosquito ecology and attitudes of residents to water containers; and coordination between health and other sectors. Integrated vector management and partnership among stakeholders [local inhabitants in cities, towns and villages] are required. The current control systems have to be re-organised from a paternalistic approach — 'we do everything for you' — to a participatory approach defining the different roles for the different actors.Universal reliance on reducing the source of the Aedes aegypti mosquito is not working in most at-risk societies and dengue fever remains prevalent.

A top priority, regardless of methods used in control programs, is political commitment. Although participation of those affected is crucial, there has never been a successful program without enlightened, adequately funded, and well-organised leadership.

The writer is Former Head, Department of Medical Sociology, Institute of Epidemiology, Disease Control & Research (IEDCR),  

Dhaka, Bangladesh



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Editor : M. Shamsur Rahman
Published by the Editor on behalf of Independent Publications Limited at Media Printers, 446/H, Tejgaon I/A, Dhaka-1215.
Editorial, News & Commercial Offices : Beximco Media Complex, 149-150 Tejgaon I/A, Dhaka-1208, Bangladesh. GPO Box No. 934, Dhaka-1000.

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