- Brucellosis and
Threat From Bison
What About Other Wildlife?
Vaccine for Bison and Elk
Brucellosis Research Efforts
Brucellosis Be Eradicated From Yellowstone Wildlife?
Brucellosis has caused devastating losses to farmers in the United
States over the last century. It has cost the Federal Government,
the States, and the livestock industry billions of dollars in direct
losses and the cost of efforts to eliminate the disease. Brucellosis
causes abortions, infertility, and lowered milk production in cattle
and bison and is transmissible to humans as undulant fever. In
people, the disease causes severe flu like symptoms that can last
for months or years. Treatment in humans is not always successful.
Moreover, treatment is not successful in animals.
The U.S. Department of Agriculture's (USDA) Animal and Plant Health
Inspection Service (APHIS) has been working cooperatively with the
livestock industries and State animal health authorities to eradicate
brucellosis from the United States. As of March 1, 2002, 48 States
have achieved brucellosis-free status with no known infection.
The only known focus of Brucella abortus infection left
in the nation is in bison and elk in the Greater Yellowstone Area
(GYA). With respect to this area, APHIS is cooperating with State
and Federal agencies to implement a bison management plan, in order
to provide for a free ranging bison herd and to prevent exposure
of cattle to potentially infected wildlife.
There has been concern about the presence of brucellosis in the
Yellowstone National Park (YNP) bison herd since the inception of
the Cooperative State-Federal Brucellosis Eradication Program in
1934. Until the last few years, the number of infected cattle and
bison herds in the Nation was so large that efforts were focused
in other private and public park herds. In addition, YNP officials
felt they could effectively manage the disease risks with a border
control program. Until 1988, the number of bison leaving YNP was
limited. The few bison that did migrate were either hazed back into
the park or shot at the border by Park Service, State of Montana
personnel, or licensed hunters.
During the winter of 1996-97, with the herd population at record
levels, the limited forage in YNP was covered with record levels
of ice and snow. As a result, larger numbers of bison moved to areas
outside the park looking for food; 1,079 bison that exited the Park
were shot or sent to slaughter. An additional 1,300 or more bison
starved to death inside the park. The involved Federal agencies-APHIS,
USDA's Forest Service, and the Interior Department's National Park
Service-then proposed a series of contingency measures to address
the problems caused by that year's severe winter weather in YNP.
The short-term objective was to limit as much as possible additional
killing of bison during the balance of the winter season, while
also preventing transmission of brucellosis to livestock outside
The long-term objective was to develop a long-range plan for management
of the Yellowstone bison herd to prevent the transmission of brucellosis
from bison to cattle and maintain a viable bison herd.
While USDA is charged with eradicating brucellosis from the United
States, it also remains committed to maintaining a viable and free-roaming
bison herd in YNP. The goals of the eventual elimination of brucellosis
from the GYA and maintaining a free-roaming bison herd have been
jointly agreed to in a Memorandum of Understanding between the U.S.
Department of Interior, the States of Montana, Idaho, and Wyoming,
and USDA. Eliminating brucellosis and managing a free-roaming bison
herd at YNP are not incompatible goals, and achieving them will
require a cooperative effort by all involved agencies. The Record
of Decision for Final Environmental Impact Statement and Bison Management
Plan for the State of Montana and Yellowstone National Park was
signed December 20, 2000. The goal of the bison management plan
is to maintain a wild, free ranging bison population while minimizing
the risk of transmitting brucellosis from bison to domestic cattle
on public and private lands in Montana adjacent to YNP. This plan
is a bison management plan, not a brucellosis elimination plan.
More than 50 percent of the bison in YNP test positive for brucellosis.
A positive test indicates that animals have been exposed and are
most likely infected. The concern is that when these bison leave
YNP, they may transmit brucellosis to cattle in the surrounding
States. All three States surrounding YNP are officially free of
In 1990, researchers at Texas A&M demonstrated that bison infected
with Brucella abortus could spread the disease to cattle
through contact. Although this was proven under controlled conditions,
it is difficult to document transmission of a disease in the wild.
In order to document this, a researcher would need to be present
when the transmission occurred and collect samples for tissue culturing.
In addition, the animals would have to have been previously tested
before the transmission had occurred to verify that the event was
caused by the bacterial transmission at the observed time. Therefore,
it was necessary to conduct this research under controlled conditions.
Even though transmission in the wild is difficult to document,
results of epidemiological investigations point to domestic bison
as the likely source of the disease in infected cattle herds found
in Wyoming and North Dakota. In addition, wild elk or bison in the
GYA have been identified as the most probable source of infection
for five additional cattle herds. Infected elk were the most probable
source of brucellosis infection (fistulous withers) in horses in
Wyoming. Most recently, elk were the source of infection of a cattle
herd in Idaho.
The bison and elk populations in the GYA are the only wildlife
populations in the United States known to be infected with B.
abortus. Due to the behavior of bison
and elk, there is more risk of disease transmission from individual
bison than from elk. Bison are more gregarious than elk and tend
to congregate together more than elk during calving time, which
is when disease transmission is most likely. There is a greater
chance of spreading the disease to herd mates through direct
contact with birthing fluids and contaminated soil and vegetation
during calving than at other seasons.
On the other hand, under natural conditions, elk prefer to calve
in seclusion, meticulously cleaning up the area by consuming the
placental tissues and fluids to avoid attracting predators. They
prefer to keep the calf separate from other animals for the first
few days before returning to the herd, a behavior pattern that
also reduces the chance for disease transmission.
However, under unnatural conditions, such as at artificial elk
feedgrounds, elk are more concentrated and less likely to calve
in seclusion. Infected elk also may abort during the time they
are congregated in the feedgrounds. Under these conditions, the
risk of disease spread from elk is increased. APHIS has assisted
the State of Wyoming with funding to vaccinate elk on elk feedgrounds
to reduce the prevalence of the disease and to fund habitat improvement
efforts to keep the elk dispersed over a larger area and away
from cattle and feedgrounds. Eliminating brucellosis in elk remains
a high priority with APHIS.
Other species of wildlife are more resistant but can become transiently
infected with the brucella organism.
Predators and scavengers, such as coyotes, crows, vultures, and
bears, are rarely infected and are not at high risk for shedding
the bacteria. However, predators can serve as mechanical vectors
by dragging infected tissues, placentas, and fetuses away from abortion
Strain RB51 vaccine is a brucellosis vaccine
conditionally approved for cattle in 1996 that does not interfere
with blood test results. Tests of the RB51 vaccine in bison look
promising. Preliminary studies indicate that RB51 is safe and effective
in bison calves. In order for RB51 to be conditionally licensed
in bison, it must pass additional safety and efficacy trials.
Researchers are testing this vaccine on bison calves, male bison,
and pregnant bison to determine its safety and effectiveness.
Strain 19, the traditional brucellosis vaccine is about 65 percent
effective in preventing infection in cattle and bison under field
exposure. (Sixty-five percent is considered effective for a brucella
vaccine.) The primary difficulty with Strain 19 vaccine is that
it can cause an animal to produce antibodies to brucellosis blood
tests and, therefore, produce false-positive results when tested.
The RB51 vaccine does not cause animals to produce antibodies
that can be detected with standard tests and, therefore, eliminates
APHIS has committed in excess of $3 million toward research on
the brucellosis problem in the GYA.
APHIS continues to support brucellosis research at universities
and is also working with USDA's Agricultural Research Service to
further study RB51 vaccine, and to develop alternative brucellosis
vaccines that would be more effective in wild bison and elk herds.
Current vaccines are about 65 percent effective. It is unlikely
that new vaccines would protect 100 percent of vaccinated animals.
However, new vaccines may provide additional protection for the
animals and help reduce the incidence of the disease within the
herds. APHIS is also involved in studying the brucellosis disease
agent-how it is transmitted and shed by infected animals into the
Research efforts are also underway to develop a safe and effective
vaccine delivery system so that bison can be vaccinated remotely,
as opposed to only hand injection. In addition, APHIS has a veterinarian
with wildlife management training and experience stationed in
Montana, to function as a liaison among involved government agencies.
APHIS is confident that, as more activity is generated on this
issue, this liaison position will become increasingly important
in ensuring that all involved parties are informed and that APHIS'
involvement is coordinated.
Yes. APHIS officials are confident, based on experience in other
public and private bison and elk herds and on other successful disease
eradication programs, that use of a combination of disease-eradication
and herd-management measures will lead to the successful elimination
of brucellosis from bison and elk in the Yellowstone ecosystem.
APHIS is interested in protecting the bison and neighboring livestock
from diseases introduced into the herds from outside sources. APHIS
intends to work with the cooperating agencies to develop a plan
to eliminate brucellosis from the GYA while ensuring a wild, free-roaming,
and viable bison herd in Yellowstone. Similar eradication efforts
have been successful in other parks, including Wind Cave National
Park and Custer State Park in South Dakota and Wichita Mountain
Wildlife Refuge in Oklahoma.
For more information concerning the brucellosis problem in Yellowstone
bison, contact APHIS Legislative and Public Affairs at (202) 720-2511,
Forest Service Public Affairs at (202) 205-1760, or the National
Park Service Office of Public Affairs at (202) 482-6843.
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