Viral Infections and Global Change

Sunit Kumar Singh

• Publisher: Wiley-Blackwell
• Year: 2013
• Print ISBN:
  9781118297872
• Edition: 1
• eBook ISBN:
  9781118297520
• Topic: Biological Sciences
• Subtopic: Microbiology
• Index: Biological Sciences

A timely exploration of the impact of global change on the emergence, reemergence, and control of vector-borne and zoonotic viral infections

From massively destructive "superstorms" to rapidly rising sea levels, the world media is abuzz with talk of the threats to civilization posed by global warming. But one hazard that is rarely discussed is the dramatic rise in the number and magnitude of tropical virus outbreaks among human populations. One need only consider recent developments, such as the spread of chikungunya across southern Europe and dengue in Singapore, Brazil, and the southern United States, to appreciate the seriousness of that threat.

Representing a major addition to the world literature on the subject, Viral Infections and Global Change explores trends of paramount concern globally, regarding the emergence and reemergence of vector-borne and zoonotic viruses. It also provides up-to-date coverage of both the clinical aspects and basic science behind an array of specific emerging and reemerging infections, including everything from West Nile fever and Rift Valley fever to zoonotic hepatitis E and human bunyavirus.

Important topics covered include:

• Epidemiology, molecular pathogenesis, and evolutionary mechanisms
• Host-pathogen interactions in an array of viral infections
• The impact of climate change on historical viral outbreaks
• The roles of socioeconomics, human behavior, and animal and human migrations
• The growing prevalence of drug and pesticide resistance
• The introduction of microbes and vectors through increased transboundary travel
• Spillover transmissions and the emergence of viral outbreaks
• Detecting and responding to threats from bioterrorism and emerging viral infections
• Predictive modeling for emerging viral infections

Viral Infections and Global Change is an indispensable resource for research scientists, epidemiologists, and medical and veterinary students working in ecology, environmental management, climatology, neurovirology, virology, and infectious disease.

I

GENERAL ASPECTS

1

CLIMATE CHANGE AND VECTOR-BORNE VIRAL DISEASES

Ying Zhang

Discipline of Public Health, The University of Adelaide, Adelaide, Australia School of Public Health, China Studies Centre, University of Sydney, Sydney, Australia

Alana Hansen

Discipline of Public Health, The University of Adelaide, Adelaide, Australia

Peng Bi

Discipline of Public Health, The University of Adelaide, Adelaide, Australia

TABLE OF CONTENTS

1.1 Introduction

1.2 Epidemiology of VVD

1.2.1 What are VVD?

1.2.2 Temporal–spatial distribution of VVD around the world

1.2.3 Factors that affect the transmission

1.3 Association between climatic variables and emerging VVD

1.3.1 Dengue fever

1.3.2 Yellow fever

1.3.3 Viral encephalitis: Japanese encephalitis, Murray Valley encephalitis, and West Nile encephalitis

1.3.4 Ross River fever and Barmah Forest fever

1.3.5 Chikungunya fever

1.3.6 Rift Valley fever

1.3.7 Omsk hemorrhagic fever and Crimean–Congo hemorrhagic fever

1.4 Invasion of nonzoonotic vvd to humans

1.5 Implications and recommendations for prevention and control

References

1.1 INTRODUCTION

There is an increasing threat of infectious disease due to globalization and climate change. It is now widely accepted in the scientific community that the Earth’s climate system is changing, which has brought great public health challenges around the world. The impact of climate change on the transmission of infectious diseases, particularly on vector-borne diseases (VVD), has been examined in both developing and developed countries (Lafferty, 2009; Weaver and Reisen, 2010). In particular, emerging and reemerging VVD are expected to increase due to climate change and variability (Zell et al., 2008). For the first time, in the last decades, several VVD, such as West Nile virus infection, chikungunya virus infection, and viral hemorrhagic fevers, have been spreading geographically and recorded in areas outside their original ranges. However, the lack of knowledge and effective, safe vaccines and diagnosis for some VVD makes it challenging to prevent and reduce the burden of ­disease associated with the changing environment.

This chapter aims to present a synthetic view of the health impact of climate change and variability on VVD in order to assist evidence-based decision and policy making for disease prevention and control. We have divided this chapter into three parts. The first part will discuss the epidemiological background of VVD, including the scope; the ­temporal–spatial distribution around the world; a summary of the factors that affect their ­­­transmission, including the causal relationship between climatic factors and VVD; and its prevention and control. The second part will focus on the association between climatic variables and some emerging VVD, such as dengue fever (DF), Rift Valley fever (RVF), viral encephalitis, yellow fever (YF), and others. Implications and recommendations are provided in the third part of this chapter to inform decision and policy making for a range of stakeholders, for example, public health practitioners, doctors, and other health service providers at medical clinics, governments, researcher centers, and local communities.

1.2 EPIDEMIOLOGY OF VVD

1.2.1 What are VVD?

Vector-borne viral diseases are virus infections transmitted via vectors. To clarify the scope of the discussion in this chapter, we adopted epidemiological and biological definitions of vector and virus to select eligible VVD for discussion. Vectors are organisms that transmit infections from one host to another (Last, 2001). Vectors of human disease are typically arthropods (e.g., species of mosquitoes and ticks) that are able to transmit pathogens. A virus is a small infectious agent, consisting of nucleic acid in a protein coat, that can ­replicate only inside the living cells of organisms with a wide diversity of shapes and sizes (Koonin et al., 2006). There are more than 500 “vector-borne viruses” and about 100 of them are of ­veterinary and/or human importance, which can cause major epidemics (Moormann, 2012). Some selected emerging VVD have been listed in Table 1.1. Some other important infectious diseases that are sensitive to climate variations, for example, malaria (not viral) and hemorrhagic fever with renal syndrome (not vector borne), are not included in our discussion.

TABLE 1.1 Summary of Selected Emerging VVD and Their Vectors

Source: Modified from WHO (2012a, b).

1.2.2 Temporal–spatial distribution of VVD around the world

Most VVD are restricted to the tropics and are often seen in temperate regions only as imported diseases, because of the required living environment for certain arthropod vectors like the Anopheles or Aedes mosquitoes. The majority of the mortality and morbidity burden of VVD occurs in Africa, South America, South Asia, and the Pacific Islands (WHO, 2004). However, geographical expanding of VVD has been reported around the world recently. This includes the emergence of West Nile virus in the Americas and Japanese encephalitis (JE) in Australasia, the spread of dengue, and the reemergence of YF virus in South America (Mackenzie and Williams, 2009; Mackenzie et al., 2004).

Due to the development of effective public health preventions and control measures targeted for VVD during the last century, many VVD, particularly mosquito-borne ­diseases, were controlled in many areas. However, over the last 20 years, some VVD, such as DF and West Nile virus infections, have reemerged in some areas, for example, Asia and the Americas (DeCarlo et al., 2011; Phillips, 2008; Rezza, 2012). Potential invasion of ­non-zoonotic VVD (only affect animals, not human beings) is of concern. For example, the world has recently witnessed the emergence and spread of a tick-borne VVD, that is, the outbreak of bluetongue, which currently affects sheep, goats, and cattle (Institute of Medicine of the National Academies, 2008).

1.2.3 Factors that affect the transmission

The epidemiology of VVD is influenced by the probability of contact between the vectors, the human population, and, for many viruses, the amplifying hosts, whether birds (most arboviral encephalitis), monkeys (YF virus), or rodents (hemorrhagic fever), which serve as reservoirs for the viruses. Like other infectious diseases, the transmission of VVD is influenced by social, economic, and environmental factors (Figure 1.1).

It is well established that climate is an important determinant of the spatial and temporal distribution of vectors and viruses (Bezirtzoglou et al., 2011; Slenning, 2010). The interplay of climate, vector, and host significantly influences the transmission of VVD (Sellers, 1980). Climate conditions affect the transmission of VVD mainly in three ways: altering the distribution of vector species and their reproductive cycles; influencing the reproduction of the virus within the vector organism, known as the external incubation period (EIP); and affecting human behaviors and activity that may increase the chance of contact with infected vectors (Zhang et al., 2008).

Figure 1.1. The VVD episystem showing interactions with influencing factors. For color detail, please see color plate section.

1.3 ASSOCIATION BETWEEN CLIMATIC VARIABLES AND EMERGING VVD

Some emerging and reemerging VVD have been selected for discussion in this chapter with a focus on their epidemiology and the association with climatic variability and climate change. These are DF, YF, several types of viral encephalitis, Ross River fever, Barmah Forest virus (BFV) disease, chikungunya fever, RVF, Omsk hemorrhagic fever (OHF), and Crimean–Congo hemorrhagic fever (CCHF). Findings from both historical data analyses and projective modelings indicate an increasing number of cases and expanding epidemic areas with projected climate change scenarios.

1.3.1 Dengue fever

Dengue is the most common arboviral infection in the world (Rezza, 2012). The disease, caused by the four dengue virus serotypes, ranges from asymptomatic infection, ­undifferentiated fever, and DF to severe dengue hemorrhagic fever (DHF) with or without shock. Symptoms may include fever, chills, and joint pain. It can be diagnosed by laboratory testing for virus isolation, viral antigen detection, or specific antibodies (serology). During the last 25 years, there have been increasing reports of dengue infection with unusual ­manifestations (Pancharoen et al., 2002). Great efforts are being made to understand the pathogenesis of this disease in order to develop a safe and effective dengue vaccine.

Dengue is transmitted by several species of mosquitoes within the genus Aedes, ­principally Aedes aegypti. Ae. aegypti has adapted well to urban environmental conditions such as poor housing, overcrowding, and inadequate sanitation, indicating the persistence of this species in regions with lower socioeconomic status, due to the close association ­between Ae. aegypti, humans, and the environment (Jansen and Beebe, 2010). The resilient vector may be a reason for the observed reemerging of dengue around the world (Bangs et al., 2007; Phillips, 2008; Rezza, 2012). Figure 1.2 shows the reemerging of dengue in the Americas following a successful hemispheric eradication campaign during the 1950s and 1960s (CDC).

Figure 1.2. Reemergence of Ae. aegypti and dengue in the Americas. For color detail, please see color plate section. Source: Image from CDC.

The association between climatic variables and DF has been documented worldwide, indicating a positive relationship between notified cases and increasing temperature (Banu et al., 2011; Johansson et al., 2009; Patz et al., 1998; Russell et al., 2009; Vezzani and Carbajo, 2008). Climate change, in particular a warming climate, along with globalization and international traveling, may broaden the transmission range for Ae. aegypti. Accordingly, a slight increase in temperatures could result in epidemics of dengue in the world. But the vector population may develop independently from rai...

Table of contents

• COVER
• TITLE PAGE
• COPYRIGHT PAGE
• DEDICATION
• FOREWORD
• PREFACE
• CONTRIBUTORS
• ABOUT THE EDITOR
• I GENERAL ASPECTS
• II SPECIFIC INFECTIONS
• SUPPLEMENTAL IMAGES
• INDEX