**Variables that May Affect the Transmission of Dengue – A Case Study for Health Management in Asia**

Muhiuddin Haider and Jamie Turner

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/59983

### **1. Introduction**

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Dengue, an emergent viral infection, has increased exponentially since the 1960s [1]. In spite of the alarming escalation of cases reported, the WHO still believes the disease is significantly underreported [2]. The effects of climate change are expected to dramatically increase the global incidence and geographic locations of dengue. According to the WHO, the number of countries reporting dengue cases has increased from nine countries before 1960 to more than 64 countries in 2007 [2]. Dengue cases continue to climb despite numerous interventions globally to halt the progression. Climate change allows the primary dengue vectors to thrive in more geographical locations; increased population, urbanization and deforestation have also provided favorable conditions for vectors. In areas with poor or nonexistent infrastructure, sanitation, and unreliable water supplies, water storage systems provide ideal breeding grounds for mosquitos. These issues are compounded by intercontinental commerce, specifi‐ cally the transport of tires, which harbor rainwater and mosquito larvae, allowing introduction of non-native mosquitos to other countries.

No cure currently exists for dengue and vaccine development has been fraught with difficul‐ ties. Dengue should be categorized as one of the most imperative global health issues in need of effective solutions. Drastic changes need to occur in public health approaches and health management policies for dengue. Without serious and immediate attention to the escalation of dengue the global burden of disease will significantly intensify.

### **2. Background**

Dengue is believed to be an ancient disease, one with unclear origins. Early Chinese medical records first describe a dengue-like outbreak as early as 400 AD, and later historical docu‐

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mentation in Asia, Africa, and North America made record of a dengue-like epidemic in the seventeenth century. Dengue has often been referred to as "break bone fever"; it was given this name due to the onset of high fever accompanied by agonizing bone and joint pain. The word "Dengue" was first recorded in the nineteenth century derived from the Spanish word meaning "fastidious" possibly to describe the way infected individuals carefully walked while experiencing horrendous bone pain [3].

Dengue is an infection passed from person to person by vector transmission. The predominant vectors for dengue are *Aedes aegypti* and *Aedes albopictus*. The vectors become infected after the female mosquito takes a blood meal from an infected human. Once the mosquito has been infected the virus incubates inside the mosquito host for approximately 8-10 days [4]. Upon completion of the incubation period the infected mosquito is capable of transmitting dengue to any human that it feeds on, for the remainder of its life. Four primary serotypes of dengue exist, DEN-1, DEN-2, DEN-3, DEN-4. Recently the Center for Infectious Disease and Research Policy reported a fifth serotype [5].

The most severe manifestations of the disease are dengue shock syndrome, and dengue hemorrhagic fever. Infection with one serotype does not impart complete or lasting immunity to other serotypes of dengue. Following recuperation from dengue infection, of a specific serotype, an individual has immunity from that serotype however immunity to other serotypes transitory and incomplete leaving individuals at a significantly increased risk of infection with a more severe serotype of dengue [2]. Unlike other vector-transmitted diseases, concurrent dengue infections increase an individual's susceptibility to a more life threatening serotype of dengue. Some cases of dengue are asymptomatic, however the classic symptoms include malaise, severe muscle and joint pain all accompanied with a high fever. The only treatment option currently administered for dengue infection is fluid replacement and rest. More severe cases of dengue cause capillaries in the body to leak blood plasma. This can progress to internal hemorrhaging, organ failure, and death [2].

According to estimates from the Centers for Disease Control and Prevention (CDC) three billion people globally are at risk of contracting dengue [4]. Although accurate assessments of dengue are difficult to ascertain, one undeniable observation is that Asia bears an unequal burden of dengue cases, with an approximate seventy percent of cases arising in Asian countries [6]. Findings from a recent study reveal that dengue is universal throughout tropical regions. Researchers estimate that there are 390 million dengue infections annually, all around the globe [6]. This is more than triple the WHO's most recent estimates of 100 million infections each year [2]. Another 16 million infections are attributed to Africa's burden of disease, which rivals that of the Americas and is significantly larger than previously predicted [6]. It is assumed that these numbers still underestimate the true incidence of dengue. Several factors likely add to the underreporting of dengue. Many tropical regions have various other diseases with symptomatically similar illnesses, which people may not seek treatment for or, if treatment is sought, misdiagnosis can occur. There are also potential economic impacts of reporting dengue for both individuals and countries as a whole.

http://www.who.int/entity/csr/disease/dengue/dengue2008.jpg

**Figure 1.** World Health Organization

mentation in Asia, Africa, and North America made record of a dengue-like epidemic in the seventeenth century. Dengue has often been referred to as "break bone fever"; it was given this name due to the onset of high fever accompanied by agonizing bone and joint pain. The word "Dengue" was first recorded in the nineteenth century derived from the Spanish word meaning "fastidious" possibly to describe the way infected individuals carefully walked while

Dengue is an infection passed from person to person by vector transmission. The predominant vectors for dengue are *Aedes aegypti* and *Aedes albopictus*. The vectors become infected after the female mosquito takes a blood meal from an infected human. Once the mosquito has been infected the virus incubates inside the mosquito host for approximately 8-10 days [4]. Upon completion of the incubation period the infected mosquito is capable of transmitting dengue to any human that it feeds on, for the remainder of its life. Four primary serotypes of dengue exist, DEN-1, DEN-2, DEN-3, DEN-4. Recently the Center for Infectious Disease and Research

The most severe manifestations of the disease are dengue shock syndrome, and dengue hemorrhagic fever. Infection with one serotype does not impart complete or lasting immunity to other serotypes of dengue. Following recuperation from dengue infection, of a specific serotype, an individual has immunity from that serotype however immunity to other serotypes transitory and incomplete leaving individuals at a significantly increased risk of infection with a more severe serotype of dengue [2]. Unlike other vector-transmitted diseases, concurrent dengue infections increase an individual's susceptibility to a more life threatening serotype of dengue. Some cases of dengue are asymptomatic, however the classic symptoms include malaise, severe muscle and joint pain all accompanied with a high fever. The only treatment option currently administered for dengue infection is fluid replacement and rest. More severe cases of dengue cause capillaries in the body to leak blood plasma. This can progress to internal

According to estimates from the Centers for Disease Control and Prevention (CDC) three billion people globally are at risk of contracting dengue [4]. Although accurate assessments of dengue are difficult to ascertain, one undeniable observation is that Asia bears an unequal burden of dengue cases, with an approximate seventy percent of cases arising in Asian countries [6]. Findings from a recent study reveal that dengue is universal throughout tropical regions. Researchers estimate that there are 390 million dengue infections annually, all around the globe [6]. This is more than triple the WHO's most recent estimates of 100 million infections each year [2]. Another 16 million infections are attributed to Africa's burden of disease, which rivals that of the Americas and is significantly larger than previously predicted [6]. It is assumed that these numbers still underestimate the true incidence of dengue. Several factors likely add to the underreporting of dengue. Many tropical regions have various other diseases with symptomatically similar illnesses, which people may not seek treatment for or, if treatment is sought, misdiagnosis can occur. There are also potential economic impacts of

experiencing horrendous bone pain [3].

78 Topics in Public Health

Policy reported a fifth serotype [5].

hemorrhaging, organ failure, and death [2].

reporting dengue for both individuals and countries as a whole.

Climate and population growth are important factors for predicting the current risk of dengue around the world. With population explosion, globalization, and constant urbanization, dramatic shifts in the distribution of the disease are anticipated. The virus may be introduced to areas that previously were not at risk, and those, that are currently affected, may experience enormous increases in the number of cases. Endemic transmission in Africa and the Americas, recent outbreaks in Portugal, and the ever-increasing incidence in Asia are proof of the challenges that plague an effective dengue control and the issues surrounding vector control [6]. This is a pivotal moment in the fields of global health and health management systems. Efforts to combat dengue appear stuck. However, recent vaccine developments appear to be more effective at delivering a more feasible vaccine Strategies for tackling dengue need to be rethought in order to maximize the value and cost-effectiveness of health management systems, by indicating where resources can be targeted to achieve maximum and sustainable impact.

Humans have known for a long time that climatic conditions affect epidemic diseases. Today there is a worldwide increase in many infectious diseases and this reflects the combined impacts of rapid demographic changes, as well as social and environmental changes in human living conditions. Important determinants of vector-transmitted disease include: vector survival, reproduction, and the vector's biting habits. Vectors can survive and reproduce within a range of optimal climatic conditions, which include factors such as temperature, rainfall, proximity to large bodies of water, amount of daylight and elevation. There is a large body of evidence demonstrating associations between climatic conditions and infectious diseases. Dengue is of great public health concern and may be very sensitive to long term climate change. Dengue varies seasonally in highly endemic areas. Excessive rainfall and high humidity are major contributing factors to enhancing mosquito breeding sites and thus overall mosquito populations. Mathematical modeling methods have been used to demonstrate the relationship between climatic variables and biological parameters such as breeding, survival, and biting rates. Landscape modeling is also used because climate also influences habitats. Combining climate bases models with spatial analytical methods to study the effects of both climatic and environmental factors are beginning to be used to predict how climate induce changes would affect mosquito populations.

http://www.who.int/entity/csr/disease/dengue/dehngueemergence.jpg

**Figure 2.** World Health Organization

### **3. Burden of Disease**

The burden of disease due to dengue started in Asia after the commencement of World War II [7]. Major factors contributing to the post war dengue proliferation include: worldwide rapid population expansion, urbanization, and globalization of markets. These factors coupled with new modes of human transportation could have facilitated the dissemination of both people and disease [7].

In order to initiate successful health management policies and programs it is important to understand the economic impact of dengue on Southeast Asia. Several articles have been published about this topic as well as assessments from the WHO. The overwhelming consensus
