Chapter 8
Wildlife Diseases
CBS580: Veterinary Clinical
Epidemiology
FW720: Epidemiology of Wildlife
Diseases
Essentials of Disease in Wild
Animals (2006)
Gary Wobeser DVM, PhD
Overview


History of disease as part of wildlife
management
Disease issues
What is disease
 Why does it happen (or not)
 Why do we care

Why study it
 Why manage it


Cases
White nose syndrome in bats
Historically…


Not historically considered important to manage
Four phases of development as a component of
wildlife management
Awareness: “regrettable but unmanageable”
 Concern: little knowledge, no skills
 Control: epidemics only
 Prevention: We can only hope…

“The role of disease in
wild-life conservation has
probably been radically
underestimated.”
- Aldo Leopold
Tasmanian Devil facial tumor disease
What is Disease?
Disease

“any impairment that interferes with or modifies
the performance of normal functions, including
responses to environmental factors such as
nutrition, toxicants, and climate; infectious
agents; inherent or congenital defects; or
combinations of these factors” (Wobeser 1981)
Disease

Disease is measured in terms of impairment (not
death)

Disease factors are intrinsic or extrinsic

Disease may result from one or a combo of
factors

Disease may affect many different functions
Continuum of Disease
Costs of Disease

Currency for evaluating costs of disease
ENERGY
 “any physiological dysfunction is likely to have
energetic consequences.” (Wobeser)

Energy

Energy
in
Energy
out
Energy in:
Amount and quality of food
 Feeding activity
 Efficiency of digestion (nutrient extraction)


Energy out:
Respiration (body maintenance, activity, thermoreg)
 Production (growth, reproduction, defense response)
 Storage

Bottom Line

Disease is expensive
Increased spending, decreased income
 Less resources for growth, reproduction, predator
avoidance

Why does disease happen?
To pathogenic microparasites, we and
other mammals are little more than soft,
thin-walled flasks of culture media.
- B. Levin & R. Antia
Ecology of Disease
(Epidemiologic Triad)
Agent
Host
Environment
Factors that play into disease
expression

Agent
Concurrent
infection
Dose
Hardiness
Infectivity
Pathogenicity
Route of exposure
Toxicity
Virulence


Host
Age
Behavior
Concurrent illness
Genetics
Immunity
Innate resistance
Reproductive status
Stressors
Intrinsic vs. Extrinsic

Environment
Inter-group movement
Food availability
Nutrition
Water
Social hierarchy issues
Density
Weather/climatic
conditions
Agent
Host
Environment
Disease
Agent
Host
Environment
Relative
Health
Agent
Environment
Host
Infectious Disease

Microparasites






Macroparasites



Viral – Canine Parvovirus, WNV
Bacterial - Brucellosis
Rickettsias – Lyme disease
Fungal – White Nose Syndrome of Bats
Certain algae – Avian Vacuolar Myelinopathy
Helminths (worms) – Parelaphostrongylus
Arthropods - Ticks
Protozoa - Trichomonas
Definitions

Pathogen


Infection


Presence of agent having the ability to cause disease
Infectious


Any disease producing agent (generally infectious)
Agent capable of causing disease
Contagious

Agent capable of being transmitted
Noninfectious

Noninfectious Transmissible


Toxic



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Natural – Botulism
Natural with anthropogenic change in availability
Anthropogenic – Nitrogenous wastes
Physical Agents


Prions – Chronic Wasting Disease
Weather, Trauma
Nutritional - Starvation
Genetic
Metabolic/Degenerative

Diabetes, Joint disease
More Definitions

Vector


Carrier


an insect or other organism that transmits a pathogen
an individual harboring specific pathogenic organisms who,
though often immune to the agent harbored, may transmit
the disease to others.
Reservoir

the long-term host of the pathogen of an infectious disease,
ability to replicate in the host
Disease Transmission
Portal of entry/Point of exit




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Blood
Urine
Milk
Fetus or egg
Postmortem decomposition
of carcass
Consumption of body by
predator/scavenger
Respiratory tract secretion

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
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Saliva
Ocular discharge
Gastrointestinal excretions
Skin
Genital secretions
Disease Transmission

Direct


Vertical


Immediate transfer from infected to susceptible
Transferred from parent to offspring
Horizontal

Any form of transference
from animal to animal that is
not vertical
Disease Transmission

Indirect
Airborne
 Vehicle/Fomite
 Vector

Mechanical
 Biological

Definitions

Epidemic (epizootic)


(of a disease) affecting many persons at the same
time, and spreading from person to person in a
locality where the disease is not permanently
prevalent.
NCSU

Endemic (enzootic)

(of diseases) prevailing among or afflicting animals in
a particular locality

Epidemic

Endemic
SIR Disease model


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Compartmental models in epidemiology
S – Susceptible
I – Infectious
R – Recovered
β (α) – infection rate; – removal rate
Solver
S
α
I
γ
R
Exposure and Resistance


Determines outcome of interaction of host and agent ( , )
Amount vs. defenses



More attacking invaders
More persistent the attack
Simultaneous attacks by different invaders




DISEASE
Higher fortress walls
Numerous and well armed defenders
More rapidly the defenders respond

HEALTH
Means of avoiding disease

Resistance
All body’s defenses against infection
 Innate (inflammation) vs. Acquired (immunity)


Immunity

Resistance associated with cells, hormones, chemical
messengers, antibodies
Active – acquired through previous exposure
 Passive – transfer of antibodies from outside the animal


Maternal antibodies
Means of avoiding disease

Behavior
Avoidance
 Grooming/preening
 Nest “fumigation”
 Mate selection


Physical Barriers

Epithelial surfaces – skin, lining of alimentary,
respiratory and urogenital tracts
Why study disease?
Habitat
Quantity
Population
Dynamics
Food Quality
Disease
Habitat
Quality
Food Quantity
Food
Habits
Reproduction

Presence and influence of reservoirs/vectors


Wildlife/Domestic/Human interface
Issues of population density

Density dependent diseases

Endangered species losses

Exists in relation to all other
issues facing wildlife managers

Public interest/involvement
(Epidemiology/Epizootiology)

Epidemiology (dictionary.com)



Epizootiology/Epizoology (dictionary.com)


the branch of medicine dealing with the incidence and
prevalence of disease in large populations and with detection
of the source and cause of epidemics of infectious disease.
"the study of what is upon the people" - Greek origin
The science dealing with the character, ecology, and causes of
diseases in animals, especially epizootic diseases.
The 5 W’s (and one H)

Who, What, When, Where, Why, How
Why Attempt Management of
Disease?

Managers may want to intervene in a case where:

1. Wild animals are involved in a disease of humans
(Zoonosis - Any disease of animals communicable to humans)

2. Wild animals are involved in a disease affecting
domestic animals

3. Disease is having a deleterious effect on one or
more wild species
Objectives of Disease Mgmt


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1. Prevention
2. Control
3. Eradication
Managing Disease
You can attempt management through:

Manipulation of Disease Agent

Manipulation of Environment

Manipulation of Animal
Managing Disease
You can attempt management by:

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Testing
Vaccination
Culling
Vector control
Restriction of Movement

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Quarantine
Fencing
Habitat restructuring
Medical intervention
Biological Control
Measurements of Success

Disease surveillance

IMPORTANT (but expensive and difficult)

Has rarely been done

Must define goals


elimination or low prevalence
Need for flexibility

Adaptive management?
Detecting Disease

Disease in wildlife may be difficult to detect at
any level



Difficult to find diseased or dead due to habitat,
predation
Acute disease often results in death with no
clinical signs
Chronic disease may be inconspicuous due to
ability to compensate
Personal Protection
(or how to protect yourself from disease in the field)

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
Know what diseases occur in the species and
habitat
Use protective clothing
Never let an animal bite or scratch you
Avoid animals acting abnormally

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
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Treat all animals found dead with respect and
rubber gloves
Avoid direct contact with abnormal skin
Avoid contact with feces, especially carnivores
Treat all rodents with respect
Think about the next person down the line
Seek medical advice
The factors of disease in wild populations are
influenced by human activities…
Agent
HUMANS
Host
Environment
Resources
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Wildlife Disease Association Homepage
National Wildlife Health Center
Southeastern Cooperative Wildlife Disease
Survey
Wildlife Disease Information Node
“Field Manual of Wildlife Diseases in the
Southeastern United State. 3rd Edition” William
R. Davidson (2008)