American Bison - Buffalo Field Campaign

consistent with conservation programme goals and incorporates
the expert counsel of wildlife veterinarians, epidemiologists,
and other disease specialists. Disease management plans
should be developed in a local context and involve considerable
stakeholder participation.
9.5.1 Prevention
Thorough efforts should be made to prevent the introduction
of exotic diseases into existing and future free-ranging bison
populations. Introduction of novel pathogens into bison
populations could occur by contact with free-ranging wildlife
or through contact with captive wildlife or livestock (herein
referred to as “potential disease sources”). As a general strategy,
managers should strive to maintain population attributes that
reduce the likelihood of disease establishment, or an increase in
disease prevalence should a pathogen be introduced (Table 9.5).
For example, animal density may influence disease transmission
and nutritional status of animals. Habitat conditions (e.g.,
marshy areas for bluetongue or dry conditions for anthrax) and
the presence or absence of predators can influence disease
establishment or prevalence.
A disease risk assessment should be conducted for existing
and future free-ranging bison populations. This risk assessment
should include components of disease surveillance (in both
the potential disease source and the population at risk) to
determine what potential pathogens are involved, contact
potential (to determine risk of disease transmission), potential
consequences of disease transmission, recommended strategies
to mitigate disease risk, and collateral impacts
of these actions. Preventive actions may include
prevention of dispersal between infected and
at risk populations, habitat modification, and
maintaining optimal population density, as well as
understanding the history of pertinent diseases
within the region.
The development of a clinical infectious disease
involves a complex interaction between the
host (bison), the agent (pathogen), and the
environment (habitat). Alterations to any one of
these factors may influence the ability of a disease
to be introduced or established within a given
population. Therefore, a thorough understanding
of the biology of the host, agent, and environment
is necessary to minimise the risk of introducing or
amplifying non-native diseases.
9.5.2 Surveillance
The first step in managing diseases in a population
is to determine if a pathogen is present, and if no
infected animals are detected, the probability that
96 American Bison: Status Survey and Conservation Guidelines 2010
the disease is present, but at an undetectable level. Surveillance
can also be used to determine the prevalence of a disease known
to occur, and to monitor changes in its prevalence over time.
Disease surveillance can be passive or active.
Passive, or opportunistic, surveillance would include disease
testing of animals with clinical signs and/or those that are found
dead or moribund. If a cause of death is not apparent, it may
be prudent and informative to submit the entire carcass, where
possible, for a full diagnostic necropsy to determine cause
of death. Local management staff should be trained in basic
necropsy techniques, and to correctly collect critical samples
when it is not feasible to submit entire carcasses. Diagnostic
evaluation is particularly important if human contact may have
led to transmission of a zoonotic disease to an employee or a
member of the public. If predators are present in the ecosystem,
they may remove or compromise carcasses before they can be
collected for investigation.
Active surveillance would include capturing animals and
testing for diseases, or soliciting samples from hunters of
hunted populations. Often, disease surveillance is performed
by collecting serum from blood samples and testing these for
antibodies to diseases of interest. It is important to remember
that the presence of antibodies does not confirm disease in an
animal, only exposure to the pathogen at some point in the past.
However, one might infer that the pathogen of interest is present
in a population based on positive serological results from
individual animals. Additionally, most diagnostic tests have been
developed for domestic livestock and their applicability in bison
Table 9.5 Potential management techniques appropriate for management objectives to
passively manage, control, or eradicate disease.
Passive Control Eradication
Monitor herd for clinical
signs of disease
Implement movement
restrictions from
populations that are
diseased or of unknown
disease status
Modify habitat to
minimise congestion
All techniques under
passive category
Manipulate population
density to minimise
spread of densitydependent
diseases
Herd level treatment
if feasible (rarely
appropriate in freeranging
populations)
All techniques in passive
and control categories
Test and cull infected
members of the
population where
scientifically founded
and logistically feasible
Combinations of
vaccination, treatment
or test and cull
developed to rapidly
eliminate disease
Vaccination if available Depopulation of host
species followed by repopulation
with diseasefree
animals
Implement temporal/
spatial separation
between infected and
susceptible populations
(wildlife or livestock).
Elimination of bison
from affected areas