American Bison - Buffalo Field Campaign

near a recent outbreak of BLU in deer and found no evidence
of exposure (T. Roffe personal communication). As with many
vector-born diseases, climate change is a potential factor
affecting the distribution of vectors and therefore the occurrence
of BLU (Gibb 1992). There is no effective treatment and, under
natural conditions, the disease is not considered a significant
threat to human health. There has been one human infection
documented in a laboratory worker (WHO website).
5.1.4 Bovine spongiform encephalopathy
Bovine spongiform encephalopathy (BSE), or “mad cow
disease” as it is commonly known, is one of a suite of distinct
transmissible spongiform encephalopathies (TSE) identified
during the past 50 years. TSEs are apparently caused by rogue,
misfolded protein agents called prions (PrPSC) that are devoid
of nucleic acids (Prusiner 1982). No other TSE in man or animal
has received more worldwide attention than BSE (Hadlow 1999).
It was first identified in 1986 in England and has since had far
reaching economic, political, and public health implications. BSE
is a neurologic disease characterised by spongiform change
in gray matter neurophil, neuronal degeneration, astrocytosis,
and accumulation of misfolded PrPSC (Williams et al. 2001).
Clinically the disease is progressive, displaying gradual
neurologic impairment over months or years and is usually fatal.
The disease causes progressive weight loss, low-level tremors,
behavioural changes, ataxia, and postural abnormalities.
Substantial evidence exists for genetic variation in susceptibility
among and within species (Williams et al. 2001). Cases of
BSE were identified in 10 species of Bovidae and Felidae
at a zoological collection in the British Isles (Kirkwood and
Cunningham 1994). At least one of these cases included bison.
Worldwide, other species susceptible to BSE include cheetah,
macaques and lemurs (Williams et al. 2001). The recent BSE
epidemic in Europe was linked to oral ingestion of contaminated
feed (containing ruminant derived protein), however, there is
some evidence for low-level lateral transmission. There are no
known treatments or preventions for BSE. The human form
called new variant Creutzfeldt-Jakob disease has been linked
to consumption of BSE contaminated foods. Due to the risk
of human exposure to BSE, this disease is highly regulated
worldwide. Recent cases of BSE have been reported in Canada
and the U.S. but are extremely rare in the livestock industry.
Canada reported a case in 1993 that was imported from England
and the first domestic case was detected in 2003. The U.S.
reported its first case of BSE in 2003. Since then, protein by-
products were banned in livestock feed, national surveillance
was implemented in both countries, and several regulations
were promulgated to restrict imports and exports across the
U.S.-Canada boundary. Although bison are considered to be
susceptible, there has not been a case of BSE reported in
American bison.
30 American Bison: Status Survey and Conservation Guidelines 2010
5.1.5 Bovine brucellosis
Bovine brucellosis, also known as Bang’s disease, is caused
by infection with the bacterium Brucella abortus (Tessaro 1989;
Tessaro 1992). The primary hosts for bovine brucellosis are
cattle, bison, and other bovid species (Tessaro 1992), however,
other wild ungulates such as elk (Cervus elaphus) are also
susceptible and seem to play a role in interspecies transmission
in the Greater Yellowstone Area (GYA) (Davis 1990; Rhyan et al.
1997; Thorne et al. 1978). Evidence suggests that brucellosis
was introduced to North America from Europe during the
1500s (Meagher and Mayer 1994; Aguirre and Starkey 1994).
The disease is primarily transmitted through oral contact
with aborted foetuses, contaminated placentas, and uterine
discharges (Reynolds et al. 1982; Tessaro 1989). The impacts
of brucellosis on female bison include abortion, inflammation of
the uterus, and retained placenta (Tessaro 1989). Greater than
90% of infected female bison abort during the first pregnancy;
however, naturally acquired immunity reduces this abortion rate
to 20% after the second pregnancy, and to nearly zero after the
third pregnancy (Davis et al. 1990; Davis et al. 1991). Male bison
experience inflammation of the seminal vessels, testicles, and
epididymis, and, in advanced cases, sterility (Tessaro 1992).
Both sexes are susceptible to bursitis and arthritis caused by
concentrations of the bacterial organism in the joints, resulting
in lameness, and possibly increased vulnerability to predation
(Tessaro 1989; Tessaro 1992).
Serology is used to detect exposure to B. abortus by identifying
the presence of antibodies in the blood. Sero-prevalence is the
percentage of animals in a herd that carry antibodies (Cheville
et al. 1998). A sero-positive result, indicating the presence
of antibodies, does not imply current infection, and may
overestimate the true level of brucellosis infection (Cheville et
al. 1998; Dobson and Meagher 1996) because the organism
must be cultured from tissue samples to diagnose an animal
as infected. However, a disparity between serology results
and level of infection could also be attributed to false negative
culture results related to the difficulties in isolating bacteria from
chronically infected animals (Cheville et al. 1998).
There is currently no highly effective vaccine for preventing
bovine brucellosis (Cheville et al. 1998; Davis 1993). Strain 19
(S19) was a commonly used vaccine administered to cattle
from the 1930s until 1996 (Cheville et al. 1998). It was only 67%
effective in preventing infection and abortion in cattle (Cheville
et al. 1998). S19 was found to induce a high frequency of
abortions in pregnant bison (Davis et al. 1991). Other studies
failed to demonstrate efficacy of S19 as a bison calfhood
vaccine (Templeton et al. 1998). A newer vaccine, strain RB51, is
now preferred over S19 because it does not induce antibodies
that can interfere with brucellosis serology tests for disease
exposure (Cheville et al. 1998; Roffe et al. 1999a). RB51 protects