Z o o n o s e s !
Bison and elk are the remaining reservoirs of brucellosis in the United States.
RB51, the new vaccine that protects bison from the disease, will be evaluated
for protection of elk (shown above).
|Zoonosesanimal diseases that
are naturally communicable to humanshave inflicted health problems on
millions of people worldwide. But the power of three devastating zoonotic
diseasesbrucellosis, leptospirosis, and tuberculosis (TB)may
someday be broken up by new knowledge of how they are transmitted from wildlife
to domestic animals to humans. Agricultural
Research Service researchers at the National Animal Disease Center (NADC)
in Ames, Iowa, are gaining this knowledge.
White-tailed deer in northeast Michigan have recently been identified as a
wildlife reservoir of TB, which is caused by Mycobacterium bovis. The
bison is a natural host for brucellosis. Leptospirosis, also called Weil's
Disease, is transmitted to humans mainly through direct contact with infected
animals, but it can also sicken humans via contaminated soil or water.
"Elk, deer, and bison threaten U.S. brucellosis and tuberculosis
eradication efforts by presenting the opportunity for reinfection,"
according to ARS veterinarian Carole A. Bolin, leader of bacterial disease
As USDA's chief scientific research agency, ARS assists and advises other USDA
agencies working with zoonotic diseasesthe Animal and Plant Health
Inspection Service (APHIS) and the Food Safety and Inspection Service
(FSIS)and other federal agencies like the Centers for Disease Control and
Prevention (CDC) in Atlanta, Georgia.
Microbiologist Diana Whipple (left) and
animal caretaker Katy Lies offer treats to a white-tailed deer being used to
study tuberculosis in its wild counterparts.
Milk is pasteurized to safeguard humans from becoming infected with M.
bovis. The incidence of TB in cattle has declined steadily since 1917 when
the state-federal eradication program was begun. In 1992, however, there was a
resurgence of the disease. In addition, tuberculosis in captive deer and elk
was recognized as a growing problem.
The presence of TB in wild white-tailed deer in Michigan poses a serious threat
to the program to eradicate the disease from domestic livestock. ARS scientists
have been conducting research on TB in white-tailed deer to determine how to
control and one day eliminate it.
Veterinarian Carole Bolin prepares to inject a cow with the new vaccine for
| ARS microbiologist Diana Whipple and
ARS veterinarian Mitchell V. Palmer developed a method to experimentally infect
white-tailed deer with M. bovis. This method has been used to study the
transmission of TB from experimentally infected deer to noninfected deer in
research pens at NADC.
Their work has provided the first animal model to study TB transmission in
white-tailed deer. "White-tailed deer experimentally infected with M.
bovis developed lesions similar to those found in naturally infected
deer," says Whipple.
In other studies, Whipple says NADC researchers have identified a possible
route of transmission of M. bovis from experimentally infected deer to
other animals. "We found M. bovis in deer saliva and nasal and
tonsil secretions. Therefore a cow or another deer might become infected with
M. bovis by eating feed contaminated with these secretions," says
DNA fingerprints show that both wild and captive deer in Michigan are infected
with the identical strain of M. bovis recovered from coyotes, raccoons,
a bear, and cattle.
From Michigan deer to a public body of water in Springfield, Illinois, and in
remote areas of Nicaragua, ARS researchers have tracked another bacterial
disease that plagues animals and humans. Leptospirosis is caused by
spiral-shaped bacteria called spirochetes (SPY-row-keets). Infected domestic
animals and wildlife harbor these bacteria, more than 200 of which can cause
To complicate matters, some animal species can be a host to several different
bacterial strains, although usually animals are infected with only one type at
a time. Humans can contract the disease, which is treatable with antibiotics,
from urine if traces come in contact with the membranes around their eyes and
An international expert on zoonotic diseases, Carole Bolin traced the cause of
a human outbreak of leptospirosis in Nicaragua to dogs. (See "Cracking the
Hard Cases," Agricultural Research, June 1996, p. 4.)
In June 1998, Bolin was called by the CDC to help investigate the cause of a
feverish illness in more than 100 U.S. athletes who became ill after swimming
in Lake Springfield. The illness resembled leptospirosis. NADC researchers
tested water samples from the lake and isolates of bacteria from the patients.
They also surveyed the livestock and wildlife residing near Lake Springfield.
Laboratory tests confirmed the presence of pathogenic leptospires in the lake;
however, the scientists were not able to identify the specific animal source.
In cattle, leptospirosis causes abortions, stillbirths, and reproductive
inefficiency. The NADC researchers have studied this disease since 1987. Their
studies show that previous commercial vaccines for cattle have not adequately
protected them against some types of leptospirosis.
However, "a new vaccine, developed by BioCore in Omaha, Nebraska, gives
100 percent protection to cattle. Use of the vaccine blocks bacterial
colonization in the urinary and reproductive tracts of the cattle," says
Bolin. She and her research team are gathering data to support licensing of the
This is not the first time NADC researchers have supported and tested new
vaccines to protect cattle against zoonotic diseases. ARS veterinarian Steven
C. Olsen continues to explore the use of Brucella abortus strain RB51 in
"Brucellosis in bison is very similar to brucellosis in cattle," says
Olsen. He and the research team of Mark G. Stevens, Mitchell V. Palmer, Shirley
M. Halling, Betsy J. Bricker, and Norman F. Cheville extensively tested RB51
for cattle. Because of their efforts, RB51 was approved by the USDA as the
official vaccine to protect U.S. cattle against brucellosis, which costs U.S.
beef and dairy producers nearly $30 million annually. This was the first time
in over 50 years that a new vaccine was approved for brucellosis in cattle.
RB51 replaced strain 19, a vaccine that is essentially no longer used.
Preliminary data suggest that the RB51 vaccine also protects bison against
brucellosis. A larger study of bison heifer calvesnow under
wayshould provide more conclusive data on the efficacy of the RB51
vaccine for calves. The animals were vaccinated as calves and have been growing
up. Once they get pregnant, the bison will be challenged with a virulent strain
of B. abortus to evaluate whether the RB51 vaccine protects them against
abortion or infection. This study, begun in 1996, will not be concluded until
the spring of 2000.
To lay the groundwork for commercial use of RB51 in bison, Olsen collaborated
with scientists from the Wyoming Game and Fish Department and APHIS to evaluate
the potential effect of the vaccine on several nontarget species. RB51 did not
cause visible signs of disease in birds, rodents, or other wild species. What
we know about using RB51 in bison calves is that the young animals don't shed
the vaccine strain; it persists longer in their lymph nodes than it does in
"By next spring, we may have enough data to obtain a conditional approval
for using RB51 in bison calves," says Olsen. Since 1996, commercial use of
RB51 has been only in calvesboth bison and cattle. The results of
inoculating bison calves with RB51 should pave the way for considering its use
in a program to control bison brucellosis in Yellowstone National Park. This
decision will be made by the National Park Service.By
Linda McGraw, Agricultural
Research Service Information Staff.
This research is part of Animal Health, an ARS National Program (#103)
described on the World Wide Web at
All of the researchers mentioned in this article are at the USDA-ARS
National Animal Disease Center,
Bacterial Diseases of Livestock Research Unit, 2300 N. Dayton Rd., Ames, IA
50010; phone (515) 663-7325, fax (515) 663-7458, e-mail
"Z o o n o s e s !" was published in the
February 2000 issue of
Agricultural Research magazine.