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The Roles of Disease in

Wildlife Conservation

Dr.Kedar Karki

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Some Definitions 1. Disease- a disturbance to the normal

function or structure of an animal

2. Pathogen- a disease-spreading agent suchas bacteria, viruses, parasites, and fungi

3. Epizootiology- the study of disease

ecology

4. Reservoirs- the pool of pathogens

harbored in wildlife populations that serves

as a source of infection

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Some Definitions 5. Vectors- organisms that transmit a

disease within and between populations

(usually an insect or another arthropod(ticks)

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Causative Agents Parasites (internal, external)

Toxic chemicals (natural, human-made)

Physiological changes Nutritional

Congenital

Degenerative

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Pathogens Bacteria

Viruses

Rikettsias Parasites

Fungi

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Disease in a wildlife population

is rarely a simple, one-cause,

one-effect situation. Usually it is

the product of profound changes

in the environment

Lars Karstad 1971

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Misperceptions? Disease is a problem of individuals, not

populations

Disease is a natural phenomenon: "Let naturetake its course

Disease is a veterinary matter, outside

the realm of traditional wildlife biology

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Four Reasons to Study Wildlife

Diseases 1. Either domestic or wild animals may serve

as reservoirs or as vectors for pathogens

that ultimately affect each other. In 1920s mule deer in the Stanislaus Nat.

Forest (Calif.) were slaughtered (22,000 shot) when

foot and mouth disease ravaged livestock in

California10% of the deer had the disease

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Why Study Wildlife Diseases? 2. Wildlife populations may be subjected to more diseases

as their habitat shrinks and continues to degrade

Animals on poor nutrition are pre-disposed to contractingdiseases

Danger in having waterfowl or other animals (elk, deer)concentrate in large numbers.

There may be an epizootic (contagious disease) decimate apopulationfowl cholera in waterfowl, lungworm inbighorn sheep)

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Why Study Wildlife Diseases? 3. Endangered species may suffer

disasterous losses from diseases.

1984-insect-borne virus killed 7/39whooping cranes held in captivity

1985-canine distemper almost wiped out

the black-footed ferret

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Why Study Wildlife Diseases?4. Diseases are just part of all issues

facing wildlife managers and it must be dealt

with.

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How Diseases Fit Into the Big

Picture There is almost always low endemic levels of

pathogens in populations- especially bacteria andparasites

All animals have parasites (round, flat worms,liver flukes, lice, fleas, etc)

It is only when the animals are under some kindof stress that these organisms begin to have

significant effects. May pre-dispose them to predation, accidents,

starvation

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Diseases and Habitats

Habitat conditions strongly influence the

course of wildlife diseases Habitat is an important variable influencing

the severity & incidence of diseases.

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Wildlife Disease and

Management/Conservation

Focus on the interaction of wildlife disease

and: Public health Agriculture Conservation of threatened and

endangered species

Recreational use of wildlife

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Wildlife Disease and Public Health:

West Nile Virus

Causes encephalitis Vector-transmitted

First identified in 1999 in North America Infects birds, some mammals, humans

High mortality in corvids (crows, ravens

jays)

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Public health and Wildlife

Disease

Few cases, few deaths

Thousands of cases,thousands of deaths

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Avian Botulism

Caused by a virulent bacterium

Clostridiumbotulinum (Type C) a type of

food poisoning Can cause major die-offs of waterfowl and

shorebirds

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Wildlife Disease and Agriculture:

Bovine Brucellosis Bacterial disease, agent Brucella abortus

Causes abortion, decreased milk production,

retained placenta Infection results in long-term shedding of bacteria .

Transmitted via ingestion of infected material

(placental tissues/fluids, milk,contaminated pasture)

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Wildlife Disease and Agriculture:

Bovine Brucellosis

Endemic in Yellowstones wild ruminants

Concern about spread to domestic cattle

Some surveillance and control measures inplace

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Bovine Brucellosis

2,500 bison in Yellowstone National

Park. Hundreds have been killed in

the hope that they would not spreadthe disease outside the park.

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Sylvatic Plague

The plague of the middle ages

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Sylvatic Plague Epizootiology

High mortality in prairie dog populations

Enzootic/epizootic cycles Destabilizes prairie dog ecosystem for

other prairie dog-dependant species

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Wildlife Disease and Recreation:

Chronic Wasting Disease

A neurological disease that causes

weight loss and abnormal behavior.

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Possible impacts of CWD

Effects on population dynamics and hunting

quotas?

Effects on elk farming? Public health concerns?

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Lead Poisoning

Source primarily from lead shot inshotgun

shells or from bullets Impacts waterfowl and raptors, especially

swans and the California Condor Oncedeposited at the rate of 3,000 tons/yr

Lead shot officially banned in 1991 (steelshot phased into use since 1985)

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Symptoms of lead poisoning:

1. Atrophy of striated muscle

2. Distended gall bladder

3. Anemia4. Fluid accumulation in pericardial sac

5. Atrophy of liver & kidneys

6. Erosion of gizzards grinding surfaces

7. Feeding curtailedemaciation

8. Bile stains in cloacal

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Do Diseases Control Populations?

There is wide disagreement on the role of diseases in

population regulation.

Density-dependence

Epizootics may act in a density-dependent way

(contagious diseases)

Implicated in some cyclic species-red grouse,

showshoe hares (shock disease) Non-cyclic pops-bighorn sheep-lungworms

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Do Diseases Control Populations?

Density-independence

Other diseases appear to act without

regard to population density and may

simply be related to a mix of factors

including weather, food, stress, andincidence of pathogens

ontr ut ons rom e

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ontr ut ons rom eBiologists

Wildlife population dynamics

abundance, distribution, recruitment

Geographical data home ranges, migration routes

Epizootiological surveillance

Disease/agent incidence distribution mortality/morbidity rates,Tissue SampleCollection

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Contributions from Wildlife Biologists

(contd)

Pathological and diagnostic data

Tissue and blood samples, culture swabs, whole organisms, environmental samples

Public education and interface with

wildlife resource users

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Wildlife Disease Resources

and Organizations

Scientific

Wildlife Disease Association Society for Conservation Biology

The Wildlife Society

others

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Wildlife Disease Resources

and Organizations

Governmental

Research Facilities-Veterinary Services

Federal and state wildlife organizations

Regional E.g. SCWDS, cooperative units

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