American Bison - Buffalo Field Campaign

long as 156 days post-infection. Some animals recover and
remain persistently infected (Schultheiss et al. 1998). Clinical
signs in bison include hemorrhagic cystitis, colitis, conjunctivitis,
ocular discharge, nasal discharge, excess salivation, anorexia,
diarrhoea, melaena, haematuria, multifocal ulceration of the
oral mucosa, fever, circling, ataxia, behaviours suggestive of
blindness, lameness, and difficult urination (Liggitt et al. 1980;
Ruth et al. 1977; Schultheiss et al. 1998). Lymphadenomegaly
and corneal opacity occur in fewer than half the cases
(Schultheiss et al. 2001). Direct contact between bison and
domestic sheep is considered the most likely source of infection.
Hence, bison should not be grazed in the same pastures or
adjacent to pastures with sheep. Although most infections occur
when bison are in close association with domestic sheep, MCF
was reported in bison herds that were five kilometres (three
miles) from a lamb feedlot (Schultheiss et al. 2001). Dr. T. Roffe
has conducted serologic surveys of two U.S. Department of
the Interior bison herds not associated with domestic sheep
and has found no sero-reactors for MCF (T. Roffe, personal
communication). There is no vaccine or effective treatment for
MCF and the best way to control this disease is to minimise
contact with reservoir hosts. There is no evidence that isolates of
MCF are infectious to humans (Heuschele and Seal 1992).
5.2 Episodes of Reportable Diseases in
Plains Bison
Based on this survey, two plains bison conservation herds in
North America have significant chronic disease issues: YNP
herd and the Jackson herd in GTNP/NER. These herds, which
account for 4,700 bison (as of winter 2008), or 24% of the entire
North American plains bison conservation population, harbour
brucellosis.
5.2.1 Yellowstone National Park
Brucellosis was first detected in the YNP bison population
in 1917 (Mohler 1917). The origin of brucellosis in the park is
unclear, but was probably the result of transmission from cattle
(Meagher and Mayer 1994). Opportunistic and systematic
serological surveys in the area revealed sero-prevalence varying
between 20% and 70%, while bacterial cultures indicated
an infection prevalence of approximately 10% (Dobson and
Meagher 1996; Meagher and Mayer 1994). Although the true
prevalence of the disease is unknown, the YNP bison population
is considered to be chronically infected with brucellosis (Cheville
et al. 1998). More recent research on the epidemiology of
brucellosis in Yellowstone bison found that 46% of the sero-
reactor animals were culture positive (Roffe et al. 1999b). Recent
demographic analysis indicates that brucellosis has a significant
reproductive effect, that the growth rate of the population could
increase by 29% in the absence of brucellosis (Fuller et al. 2007),
and that brucellosis is not a threat to the long-term viability of
the YNP bison (Mayer and Meagher 1995; USDOI and USDA
2000). Fuller et al. (2007) conducted a detailed analysis of the
demographics of the Yellowstone population from 1900-2000
and found evidence of density dependent changes in population
growth as numbers approached 3,000 animals. This population
appears robust and has grown at times to exceed 4,000,
although it was reduced to fewer than 3,000 several times during
the past decade under the current herd management regime (R.
Wallen, personal communication).
Herd management is affected by the presence of brucellosis
primarily because of the potential risk the disease poses to the
livestock industry (Keiter 1997). Bison leaving the park could
potentially transmit the disease to domestic cattle grazing
on adjacent National Forest and private lands in Montana,
Wyoming or Idaho (USDOI and USDA 2000). Bison leave the
park in the winter on the north and west boundaries within
Montana; movement to the east and south is rare because of
topographical barriers (R. Wallen, personal communication).
Transmission of brucellosis from bison to cattle has been
demonstrated in captive studies; however, there are no
confirmed cases of transmission in the wild (Bienen 2002;
Cheville et al. 1998; Shaw and Meagher 2000). Nevertheless,
the potential exists, and this has created a contentious bison
management issue in the area.
Relying on the Animal Industry Act of 1884, the U.S Department
of Agriculture began preventing and controlling the spread of
contagious livestock diseases in the U.S. In 1947, federal and
state officials began working closely with the livestock industry
to eradicate brucellosis (Keiter 1997; NPS USDOI 2000). Each
state represented in the GYA is a co-operator in the National
Brucellosis Program and has authority to implement control
programmes for brucellosis infected or exposed animals
within their respective boundaries. Due to the transmission of
brucellosis to cattle, presumably by elk, Montana, Wyoming, and
Idaho have each periodically lost their brucellosis-free status
as certified by APHIS. Transmission of brucellosis to cattle in
Montana, Wyoming or Idaho indirectly affects all producers in
these states. If their APHIS status is downgraded, other states
may refuse to accept cattle from producers in the GYA (Cheville
et al. 1998).
Resolution of this issue requires the involvement of, and
cooperation among, agencies in several jurisdictions: The
National Park Service (NPS), the U.S. Forest Service (USFS),
APHIS, and the State of Montana Department of Livestock
(MDOL) and Montana Department of Fish, Wildlife, and Parks
(MFWP). After many years of media and legal controversy over
bison management, the agencies acknowledged the need to
cooperatively develop a long-term bison management plan
(Plumb and Aune 2002). In 1990, they commenced the process
American Bison: Status Survey and Conservation Guidelines 2010 33