American Bison - Buffalo Field Campaign

one) followed by its widespread dispersal and ecological
establishment. Wild bison were abundant and widely distributed
at the time of European colonisation. Once infected with anthrax
they may have played an important early role in the ecological
establishment and widespread dispersal of A.Br.WNA. The broad
diversity of anthrax lineages represented in the industrialised
south-eastern region of the continent (Van Ert et al. 2007) is
suggestive of the accumulation of additional sub-group types
over time. A likely mechanism is importation of contaminated
animal products into mills and tanneries on the eastern seaboard
and New England which process imported hair, wool, and hides.
The World Health Organisation (WHO 2008) commented on
the role of tanneries as a point source of anthrax outbreaks.
Contaminated products come from animals that died of anthrax.
Wastewater effluent from plants can contaminate downstream
sediments and pastures with anthrax spores, providing a
source of local outbreaks in livestock and further proliferation
of novel introduced variants of the pathogen. Marketing of
inadequately sterilised bone meals and fertilisers, rendered from
contaminated materials, can result in long distance redistribution
and introducing “industrial” strains to livestock remote from the
original source (Hugh-Jones and Hussaini 1975).
Under certain environmental conditions, concentrations of
endospores have caused periodic outbreaks among wood bison
in the Slave River Lowlands (SRL), Mackenzie Bison Sanctuary
(MBS), and Wood Buffalo National Park (WBNP) (Dragon and
Elkin 2001; Gates et al. 2001b; Pybus 2000). Between 1962 and
1971, anthrax and the associated depopulation and vaccination
programmes employed to control the disease, accounted for
over 2,800 wood bison deaths (Dragon and Elkin 2001). Further
outbreaks occurred in the MBS in 1993, in the SRL in 1978, 2000
and 2006, and in WBNP in 1978, 1991, 2000, and 2001 (Gates
et al. 1995; Nishi et al. 2002c). Four factors that are associated
rather consistently with these epizootics are high ambient
temperatures, intense mating activity, high densities of insects,
and high densities of bison as they congregate and compete for
diminishing water and food supplies (APHIS, USDA 2006). Based
on these four factors, two hypotheses have been proposed to
explain outbreaks of anthrax in bison in northern Canada: (1)
“the modified host resistance hypothesis” (Gainer and Saunders
1989) and (2) “the wallow concentrator hypothesis” (Dragon et
al., 1999). These two hypotheses are not mutually exclusive.
A recent outbreak was reported in a commercial herd in
south-western Montana that killed over 300 bison pasturing
on a large foothills landscape beneath the Gallatin Mountain
Range (Ronnow 2008). Despite mass deaths of bison during
anthrax outbreaks, the sporadic nature of outbreaks and
predominance of male deaths suggest that the disease plays a
minor role in long-term population dynamics unless operating
in conjunction with other limiting factors (Joly and Messier
2001b; Shaw and Meagher 2000). Anthrax is not treatable in
free-ranging wildlife, but captive bison can be vaccinated or
treated with antibiotics (Gates et al. 1995; Gates et al. 2001b).
Carcass scavenging facilitates environmental contamination
with anthrax spores (Dragon et al. 2005); therefore timely
carcass treatment and disposal during an active outbreak in
free-ranging bison is considered an important preventative
strategy for reducing the potential for future outbreaks (Hugh-
Jones and de Vos 2002; Nishi et al. 2002a). Anthrax is a public
health concern and humans are susceptible, however, exposure
from naturally occurring outbreaks requires close contact with
animal carcasses or hides. In addition, humans have rarely been
exposed to anthrax through the purchase of curios purchased by
tourists (Whitford 1979).
5.1.3 Bluetongue
Bluetongue (BLU) is an insect-borne viral hemorrhagic disease
affecting many ungulates in the lower latitudes of North America.
The BLU virus is a member of the genus Oribivirus of the family
Reoviridae. Worldwide there are 24 known BLU serotypes,
but only six are active in domestic and wild ruminants from
North America (Pearson et al. 1992). Bluetongue viruses are
closely related to the viruses in the epizootic hemorrhagic
disease and BLU is known to infect a wide variety of wild and
domestic ruminants (Howerth et al. 2001). Bison are susceptible
to BLU, and the virus has been isolated under field, captive,
and experimental conditions (Dulac et al. 1988). The arthropod
vectors of the bluetongue virus are various species of Culicoides
midges (Gibbs and Greiner 1989; Howerth et al. 2001). Clinical
symptoms include fever, stomatitis, oral ulcerations, lameness,
and occasionally, reproductive failure (Howerth et al. 2001).
There are subacute, acute, and even chronic expressions of the
disease in many wild ungulates and domestic livestock. BLU
typically occurs in the late summer and early fall depending
upon the seasonal patterns of vector activity (Howerth et al.
2001). Factors influencing the frequency and intensity of disease
outbreaks are innate herd immunity, virulence factors associated
with viruses, and vector competency and activity. BLU occurs in
livestock over much of the U.S. and its distribution parallels that
of domestic livestock. Its distribution is more limited in Canada
where it once was a regulated disease until rules were relaxed
in July 2006 (CFIA website). There is considerable difference in
the epidemiology of the disease between northern and southern
portions of North America depending on the consistency of
vector activity. In the southern areas, vector activity is more
common and animal populations exhibit a higher prevalence
of seroreactivity and antibody protection. BLU has not been
widely reported in bison herds in North America. Serologic
surveys of several Department of Interior bison herds in the
U.S. have not found seroreactors for bluetongue virus (T. Roffe
personal communication; Taylor et al. 1997). The U.S. Fish and
Wildlife Service (USFWS) has opportunistically examined bison
American Bison: Status Survey and Conservation Guidelines 2010 29