Essentials of Disease in Wild Animals

Gary A. Wobeser

• Publisher: Wiley-Blackwell
• Year: 2013
• Print ISBN: 9780813805894
• eBook ISBN: 9781118708873
• Edition: 1
• Topic: Medicine
• Subtopic: Veterinary Medicine

The interrelationship between wild animal, domestic animals and human health is appreciated now more than ever before. This is because of the recognition of the involvement of wild animals in diseases of humans and domestic animals, the impact of disease on wildlife management and conservation biology, recognition of new forms of environmental contamination, and academic interest in disease as an ecological factor.

This is the first introductory level book about disease in wild animals that deals with basic subjects such as the nature of disease, what causes disease, how disease is described and measured, how diseases spread and persist and the effects of disease on individual animals and populations. In contrast to authors of many other veterinary books, Gary A. Wobeser takes a more general approach to health in wild animals, recognizing that disease is one ecological factor among many and that disease can never be considered satisfactorily in isolation. Rather than focus on individual causative agents and their effect on the individual animal, the emphasis is on why disease occurred, and on the complex interactions that occur among disease agents, the environment and host populations.

Written by a leading researcher in wildlife diseases, this book will fill a knowledge gap for those called to work with disease in wild animals who lack experience or training in the general features of disease as they relate to wild animals. Veterinarians, ecologists, wildlife biologists, population biologists and public health workers will find this book invaluable.

1

Introduction

The study of disease in wild animals is a relatively new scientific discipline when compared to the study of disease in humans or domestic animals. During the first half of the twentieth century a small number of scientists began pioneering studies of diseases such as tularemia and plague in wild rodents (McCoy 1911; McCoy and Chapin 1912), avian botulism in waterfowl (Kalmbach and Gunderson 1934), and rinderpest in African antelope (Carmichael 1938) and Elton (1931) reviewed epidemic diseases of wild animals. Formation of an international scientific body, the Wildlife Disease Association, in 1951 marked the beginning of more organized study of disease in wild animals, but most of the people involved in the early years of that organization would have identified themselves as members of some other discipline, such as virology, toxicology, parasitology, ecology, and pathology, who worked with wild animals rather than as wildlife disease specialists. During the past two decades, there has been a huge increase in interest in the subject. Scientists from a wide spectrum of disciplines including conservation biology, wildlife management, veterinary medicine, agriculture, public health, theoretical ecology, toxicology, animal behavior, and human medicine have become interested, on an unprecedented scale, in the particulars of disease in wild animals.

There are several reasons for this sudden increase in interest and involvement. A major factor has been a burgeoning awareness of the involvement of wild animals in infectious diseases of humans. Despite earlier optimism that infectious diseases in humans could be eliminated or controlled, it is now clear that infections have not been vanquished. “Emerging infectious diseases” have become a medical growth industry. New human diseases continue to be discovered and many old foes have returned with a vengeance because of environmental and demographic changes, declines in public health activities, and evolution of resistant organisms. Public health officials and physicians have been forced to deal with wild animals by the discovery that most of the emerging infectious diseases of humans are diseases that are shared with animals (zoonoses), and that wild animals have a central role in many of these conditions (table 1.1). Many other important human diseases in addition to those shown in table 1.1, including severe acute respiratory syndrome (SARS), Ebola disease, and Marburg virus infection, are believed to originate in wildlife, although the specific wild animal has not been identified to date. Many well-established human diseases that continue to cause problems including plague, tularemia, Lassa fever, rabies, and influenza are linked directly to wild animals.

Table 1.1 Emerging Diseases of Humans in Which Wild Animals Are Important

Disease in humans	Causative agent	Wild species involved
Viruses
Hantavirus pulmonary syndrome	Sin Nombre virus and many other New World hantaviruses	Rodents
Hemorrhagic fever with renal syndrome	Puumala virus and other Old World Rodents hantaviruses	Rodents
West Nile fever	West Nile virus	Birds
Hemorrhagic fevers (Argentinean, Bolivian, Brazilian, Venezuelan)	Arenaviruses	Rodents
Australian bat lyssavirus infection	Lyssavirus similar to rabies virus	Bats
Bacteria
Human granulocytic ehrlichiosis	Ehrlichia phagocytophila	Rodents, cottontail rabbits
Monocytic ehrlichiosis	Ehrlichia chaffeensis	White-tailed deer
Lyme disease	Borrelia burgdorferi	Rodents, birds, deer
Cardiopathy, endocarditis	Bartonella spp.	Rodents
Cestodes (tapeworms)
Alveolar echinococcosis	Echinococcus multilocularis	Fox, rodents
Nematodes (roundworms)
Visceral larva migrans	Baylisascaris procyonis	Raccoons

Note: An emerging disease is one whose incidence in humans has increased recently or that threatens to increase in the near future. Included are previously unrecognized infections, new infections as a result of a change in a previously recognized causative agent, infections spreading to new areas or populations, and old infections that are reemerging because of deterioration in control or public health measures.

Veterinarians and agriculturists also have developed a great interest in wild animals, because of the involvement of free-ranging animals in many diseases of domestic animals (table 1.2). Some of the associations between wild animals and diseases of domestic animals have been known for many years, but, in other instances, the role of wild animals in the disease did not become apparent until there was effective control of the disease in domestic animals. As an example, rabies in much of North America was thought of as a disease for which the domestic dog was the principal animal host; however, when rabies in dogs was controlled by vaccination and leash laws, it became obvious that the disease was not going to disappear, because it was still cycling in wild carnivores and bats. As the disease was studied further, it was discovered that there was not one rabies virus, as had been thought, but many strains, each circulating in one principal wild species. Thus, in North America, different strains of rabies virus occur in skunks, foxes, and raccoons as well as several strains in bats.

Table 1.2 Diseases of Domestic Animals in Which Wild Animals Are a Source of Infection

Disease	Domestic animal(s)	Wild animal(s)
Viral
Hendra virus infection^1	Horse	Fruit bats
Nipah virus infection	Pig	Fruit bats
Louping ill	Sheep	Red grouse, mountain hare
Malignant catarrhal fever	Cattle	Wildebeest
Foot-and-mouth disease	Cattle, sheep, pigs	African buffalo
Classical swine fever	Pigs	Wild boar
Newcastle disease	Poultry	Cormorants, other birds
Avian influenza	Poultry	Wild waterbirds
Bacterial
Bovine tuberculosis	Cattle, deer	Badger, brushtail possum, white-tailed deer, elk, bison
Brucellosis	Cattle	Bison, elk
Anaplasmosis	Cattle, sheep and goats	Wild ruminants
Leptospirosis	Cattle, pigs, dogs	Different forms of Leptospira occur in a number of wild hosts
Protozoa and helminths
Theileriosis	Cattle	African buffalo, eland
Cytauxzoonosis	Domestic cat	Bobcat
Hydatid disease (Echinococcus granulosus)^1	Horse, sheep	Fox, dingo, macropods
Liver fluke (Fascioloides magna)	Cattle, sheep	White-tailed deer, elk
Meningeal worm (Parelaphostrongylus tenuis)	Llama, sheep, goat	White-tailed deer

¹May also affect humans.

Some diseases that have been eliminated from domestic animals continue to occur in wildlife. For instance, cattle in most of North America are free of brucellosis caused by Brucella abortus but remnant pockets of infection in bison and elk in a few locations are considered to be a risk to national eradication programs.

Similarly, the occurrence of Newcastle disease in double-crested cormorants is considered a risk to North American poultry from which the disease has been eliminated (Kuiken 1999). The persistence of disease in wild animals has stymied efforts to eradicate some diseases of domestic livestock. The best documented of these is bovine tuberculosis caused by Mycobacterium bovis. Efforts to eradicate this disease in domestic cattle have stalled in England and Ireland because of tuberculosis in badgers, in New Zealand because of the disease in brushtail possums, and in parts of the United States and Canada because of infection in wild deer and elk. New disease problems involving wild animals continue to be discovered, for example, paratuberculosis, a disease of domestic ruminants caused by Mycobacterium paratuberculosis, is now known to occur in a wide variety of nonruminant wild animals that may pose a risk to domestic livestock (Beard et al. 2001; Daniels et al. 2003).

Conservation biologists have become increasingly concerned about disease because of recognition that disease may play an important role in the survival of threatened or endangered species (Daszak et al. 2000; Cleaveland et al. 2001). Disease may limit captive breeding and release programs, and have devastating effects on small populations. Examples include the impact of avian malaria and poxvirus on indigenous Hawaiian birds (Atkinson et al. 1995), the near eradication of the black-footed ferret by canine distemper (Williams et al. 1988), the possible role of chytrid fungi and iridoviruses in declining amphibian populations worldwide, avian vacuolar myelinopathy in bald eagles and other species (Fischer et al. 2003), and rabies and canine distemper in Ethiopian wolves (Laurenson et al. 1998).

Wildlife managers have been forced to become more involved with disease for several reasons. There has been considerable pressure to manage wild species as part of control programs for diseases that may spread to humans and livestock, such as rabies, Echinococcus multilocularis infection, bovine tuberculosis, and West Nile virus infection. Currently, there is considerable public concern and pressure for action in North America to deal with the expanding known geographic distribution of chronic wasting disease in deer and elk. Managers also have become concerned about the effects of disease on wild species per se. Recent examples of diseaserelated phenomena that appear to have had a serious effect on wild animals include a precipitous population crash of vultures in Pakistan caused by poisoning with an antiinflammatory medication used widely in cattle (Oaks et al. 2004); population declines of house finches as a result of eye infections caused by the bacterium Mycoplasma gallisepticum (Dhondt et al. 1998); massive die-offs of seals caused by morbillivirus infection (Kennedy 2001); loss of lions in the Serengeti to canine distemper (Roelke-Parker et al. 1996); extirpation of the Allegheny wood rat in part of its range by a raccoon parasite (Logiudice 2003); and the spread of bovine tuberculosis in African buffalo, other ungulates, and carnivores in Kruger National Park (Caron et al. 2003). Wildlife managers also have become more aware that their actions can contribute to disease problems ranging from simple things such as muscle injury (capture myopathy) as a result of capture and handling animals to the introduction of new diseases as a result of translocating diseased animals.

Toxicologists have been interested in wild animals for many years and effective control measures have been developed for some diseases such as those caus...

Table of contents

• Cover
• Contents
• Title Page
• Copyright
• Dedication
• Preface
• Acknowledgments
• 1 Introduction
• 2 What Is Disease?
• 3 What Causes Disease?
• 4 How Disease Is Detected, Described, and Measured
• 5 Damage, Pathogenicity, and Virulence
• 6 Defense, Resistance, and Repair
• 7 Environmental Interactions
• 8 Transmission and Perpetuation of Infectious Disease
• 9 Noninfectious Disease: Nutrients and Toxicants
• 10 Effects of Disease on the Individual Animal
• 11 Effects of Disease on Populations of Wild Animals
• 12 Disease Shared with Humans and Domestic Animals
• 13 Disease Management
• 14 Roundup
• Appendix: Scientific Names of Animals
• Glossary
• Bibliography
• Index