Brucellosis, Q's & A's
Veterinary Services
January 2003
Q. What is brucellosis?
A. It is a contagious, costly disease of animals that also
affects humans. Although brucellosis can attack other animals, its main
threat is to cattle, bison, and swine. The disease is also known as
contagious abortion or Bang's disease. In humans, it's known as undulant
fever because of the severe intermittent fever accompanying human infection
or Malta fever because it was first recognized as a human disease on
the island of Malta.
Q. How serious is brucellosis?
A. Considering the damage done by the infection in animals—decreased
milk production, weight loss in animals, loss of young, infertility,
and lameness—it is a very serious disease of livestock. The rapidity
with which it spreads and the fact that it is transmissible to humans
makes it all the more serious.
Q. What disease agents cause brucellosis?
A. The disease is caused by a group of bacteria known scientifically
as the genus Brucella. Three species of Brucella cause
the most concern: B. abortus, principally affecting cattle,
bison, and cervids; B. suis, principally affecting swine and
reindeer but also cattle and bison; and B. melitensis, principally
affecting goats but not present in the United States. In the Greater
Yellowstone Area, the bacterium of concern is B. abortus. In
cattle and bison, the disease currently localizes in the reproductive
organs and/or the udder. Bacteria are shed in milk or via the aborted
fetus, afterbirth, or other reproductive tract discharges.
Q. What are the signs of brucellosis?
A. There is no effective way to detect infected animals by
their appearance. The most obvious signs in pregnant animals are abortion
or birth of weak calves. Milk production may be reduced from changes
in the normal lactation period caused by abortions and delayed conceptions.
Not all infected cows abort, but those that do usually abort between
the fifth and seventh month of pregnancy. Infected cows usually abort
once, but a percentage will abort during additional pregnancies, and
calves born from later pregnancies may be weak and unhealthy. Even though
their calves may appear healthy, infected cows continue to harbor and
discharge infectious organisms and should be regarded as dangerous sources
of the disease. Other signs of brucellosis include an apparent lowering
of fertility with poor conception rates, retained afterbirths with resulting
uterine infections, and (occasionally) enlarged, arthritic joints.
Q. How is brucellosis spread?
A. Brucellosis is commonly transmitted to susceptible animals
by direct contact with infected animals or with an environment that
has been contaminated with discharges from infected animals. Aborted
fetuses, placental membranes or fluids, and other vaginal discharges
present after an infected animal has aborted or calved are all highly
contaminated with infectious Brucella organisms. Cows may lick those
materials or the genital area of other cows or ingest the disease-causing
organisms with contaminated food or water. Despite occasional exceptions,
the general rule is that brucellosis is carried from one herd to another
by an infected or exposed animal. This mode of transmission occurs when
a herd owner buys replacement cattle or bison that are infected or have
been exposed to infection prior to purchase. The disease may also be
spread when wild animals or animals from an affected herd mingle with
brucellosis-free herds.
Q. What is being done to fight brucellosis?
A. Before 1934, control of brucellosis was limited mainly to
individual herds. Today, there is a Cooperative State–Federal
Brucellosis Eradication Program to eliminate the disease from the country.
Like other animal disease eradication efforts, success of the program
depends on the support and participation of livestock producers. The
program's Uniform Methods and Rules set forth the minimum standards
for States to achieve eradication. States are designated brucellosis
free when none of their cattle or bison are found to be infected for
12 consecutive months under an active surveillance program. As of October
31, 2002, 48 States, plus Puerto Rico and the U.S. Virgin Islands, were
free of brucellosis. Two States (Missouri and Texas) currently have
a herd infection rate of less than 0.1 percent and are considered to
be in Class A status. No States are in Class B (herd infection rate
between 0.11 percent and 1.0 percent) or Class C status (herd infection
rate greater than 1.0 percent).
Q. What about free-ranging bison herds?
A. The presence of brucellosis in free-ranging bison and elk
in Yellowstone National Park and Grand Teton National Park threatens
the brucellosis status of the surrounding States and the health of their
livestock herds, which are free of the disease. Reintroduction of the
disease into a brucellosis-free State could have a serious economic
impact on domestic livestock markets and potentially threaten export
markets. The U.S. Department of Agriculture's (USDA) Animal and Plant
Health Inspection Service (APHIS) is working cooperatively with other
State and Federal agencies toward containing the spread of brucellosis
from bison to domestic livestock and eliminating the disease from the
Yellowstone and Teton herds while maintaining viable free-roaming bison
herds in the parks.
Q. How do epidemiologists help fight brucellosis?
A. Epidemiologists are specially trained to investigate disease
sources and the means of eliminating
infection in affected herds and areas. Epidemiologists are concerned
with disease in a group or population of animals and evaluate circumstances
connected with the occurrence of disease. These veterinarians help eliminate
brucellosis by identifying factors essential to its control and prevention.
Q. How costly is brucellosis to the livestock industry?
A. The livestock and dairy industries and the American consumer
have realized great financial savings from the success of the Cooperative
State– Federal Brucellosis Eradication Program. Annual losses
from lowered milk production, aborted calves and pigs, and reduced breeding
efficiency have decreased from more than $400 million in 1952 to less
than $1 million today. Studies have shown that, if brucellosis eradication
program efforts were stopped, the costs of producing beef and milk would
increase by an estimated $80 million annually in less than 10 years.
Q. How effective is the Brucellosis Eradication Program?
A. At the beginning of the program, brucellosis was widespread
throughout U.S. livestock, but eradication efforts have had dramatic
results. In 1956, 124,000 affected herds were found by testing in the
United States. By 1992, this number had dropped to 700 herds, and as
of October 31, 2002, no known affected herds remained in the entire
United States. A total of 8 affected herds were found and depopulated
in fiscal year 2002. APHIS expects the Cooperative State– Federal
Program to achieve the goal of nationwide eradication of brucellosis
from domestic cattle and bison in the very near future.
Q. What is the basic approach to eradication?
A. Historically, the basic approach has always been to vaccinate
calves, test cattle for infection, and send infected animals to slaughter.
Identification of market animals for tracing, surveillance to find infected
animals, investigation of affected herds, and vaccination of replacement
calves in high-risk areas are important features of the current program.
Q. How is infection found in cattle?
A. Two primary surveillance procedures are used to locate infection
without having to test each animal in every herd. Milk from dairy herds
is checked two to four times a year by testing a small sample obtained
from creameries or farm milk tank for evidence of brucellosis. Bison
herds and cattle herds that do not produce milk for sale are routinely
tested for brucellosis by blood-testing animals sold from these herds
at livestock markets or at slaughter. In addition, some States require
adult cattle and bison to be subjected to blood tests for brucellosis
upon change of ownership even if sold directly from farm to another.
The cattle and bison remaining in the herds from which such animals
originated are not tested unless evidence of brucellosis is disclosed
among the market animals.
Q. What happens when evidence of disease is found by surveillance
testing?
A. Once an infected herd is located, the infection is contained
by quarantining all infected and exposed cattle and bison and limiting
their movement to slaughter only, until the disease can be eliminated
from the herd. Diagnostic tests are used to find all infected cattle
and bison. Also, Federal and State animal health officials test neighboring
herds and others that may have received animals from the infected herd.
All possible leads to additional infection are traced.
Q. How does the brucellosis milk surveillance test (BMST) surveillance
work?
A. The BMST procedure makes it possible to do surveillance
on whole dairy herds quickly and
economically. Milk or cream from each cow in the herd is pooled, and
a sample is taken for testing. A suspension of stained, killed Brucella
organisms is added to a small quantity of milk. If the milk from one
or more infected animals is present in the sample, a bluish ring forms
at the cream line as the cream rises.
Q. How does market cattle identification (MCI) work?
A. Numbered tags, called backtags, are placed on the shoulders
of adult breeding animals being marketed from beef, dairy, and bison
herds. Blood samples are collected from the animals at livestock markets
or slaughtering plants and tested for brucellosis. If a sample reacts
to a diagnostic test, it is traced by the backtag number to the herd
of origin. The herd owner is contacted by a State or Federal animal
health
official to arrange for testing of his or her herd. Once the animals
have been gathered, all of the eligible
animals in the herd are tested at no cost to the owner.
Q. Which animals are eligible for MCI testing?
A. At slaughter, all cattle and bison 2 years of age or older
are tested, except steers and spayed heifers. At market, all beef cattle
and bison over 24 months of age and all dairy cattle over 20 months
of age are tested except steers and spayed heifers. Pregnant or postparturient
heifers are also eligible for testing regardless of their age. Herd
tests must include all cattle and bison over 6 months of age except
steers and spayed heifers.
Q. Why is identification of market cattle important?
A. The key to the MCI program is proper identification of all
animals so they can be traced to their herds of origin. Most livestock
markets identify cattle and bison with numbered USDA-approved backtags.
Backtags, as well as eartags and other identification devices, are collected
and sent to the diagnostic laboratory along with the matching blood
samples to aid in identifying ownership of test-positive animals.
Q. What are the advantages of MCI?
A. MCI provides a means of determining the brucellosis status
of animals marketed from a large area and eliminates the need to round
up cattle and bison in all herds for routine testing. MCI, along with
other preliminary testing procedures, is effective in locating infection
so control measures can be taken to contain the disease and eliminate
it.
Q. What is the brucellosis card test?
A. It is a rapid, sensitive, and reliable procedure for diagnosing
brucellosis infection. It employs disposable materials contained in
compact kits. Brucella antigen is added to the blood serum on a white
card. Results of the test are read 4 minutes after the blood serum and
antigen are mixed.
Q. Are there any other tests for brucellosis?
A. There are a number of supplemental tests based on various
characteristics of antibodies found in the blood and milk of infected
animals. These tests are especially useful in identifying infected animals
in problem herds and herds in which chronic brucellosis infection exists
and from which infection is difficult to eliminate. Another diagnostic
method involves culturing Brucella organisms from infected tissues,
milk, or other body fluids, from aborted calves or fetal fluids and
membranes.
Q. What animals are eligible for testing?
A. With certain exceptions, herd tests must include all cattle
and bison over 6 months of age except steers and spayed heifers.
Q. What is the incubation period of brucellosis?
A. An incubation period is the interval of time between exposure
to an infectious dose of organism and the first appearance of disease
signs. The incubation period of brucellosis in cattle, bison, and other
animals is quite variable ranging from about 2 weeks to 1 year and even
longer in certain instances. When
abortion is the first sign observed, the minimum incubation period is
about 30 days. Some animals abort before developing a positive reaction
to the diagnostic test. Other infected animals may never abort.
Generally, infected animals that do not abort develop a positive reaction
to the diagnostic test within 30 to 60 days after infection, although
some may not develop a positive reaction for several months to over
a year.
Q. Can brucellosis in animals be cured?
A. No. Repeated attempts to develop a cure for brucellosis
in animals have failed. Occasionally,
animals may recover after a period of time. More commonly, however,
only the signs disappear and the animals remain diseased. Such animals
are dangerous sources of infection for other animals with which they
associate.
Q. Can brucellosis be prevented?
A. The disease may be avoided through good sanitation and management
practices, as well as
vaccination. Replacement animals should be tested when purchased and
retested after a 30- to 60-day isolation period during which they are
kept separate from the remainder of the herd. These practices will allow
detection of animals that were in the incubation period of the disease
when acquired.
Q. What about vaccination?
A. For cattle and bison in heavily infected areas or replacement
animals added to such herds, officials recommend vaccinating heifers
with an approved Brucella vaccine. Brucella Strain RB51 is the vaccine
used in the United States. The vaccine is a live product and must be
administered only by an accredited veterinarian or State or Federal
animal health official. For best results, female calves should be vaccinated
when they are 4 to 6 months old. At the time of vaccination, a tattoo
is applied in the ear; that tattoo identifies the animal as an "official
vaccinate." The tattoo identifies the year in which vaccination
took place.
Q. How does the vaccine work?
A. B. abortus vaccine produces a response that increases
the animal's resistance to the disease. However, vaccination is not
100 percent effective in preventing brucellosis; it typically protects
about 80 percent of the vaccinated cattle from becoming infected by
an average exposure to Brucella.
Q. Previously, Strain 19 was the only approved Brucella vaccine.
What is the difference between Strain 19 and RB51?
A. USDA recently licensed a new Brucella vaccine, called Strain
RB51, for use in cattle. Strain RB51 is as efficacious as Strain 19
vaccine but virtually eliminates adverse postvaccination reactions in
cattle, such as abortions and localized inflammation at the vaccine
injection site. Most importantly, unlike Strain 19, Strain RB51 does
not stimulate the same type of antibodies that can be confused on standard
diagnostic tests with those antibodies produced by actual infection.
Q. Is Strain RB51 vaccine approved for use in bison?
A. B. abortus Strain RB51 has been approved for use
in bison in an official USDA program.
Q. Where or when is vaccination in calves most important?
A. Owners whose herds are located in areas of relatively heavy
infection or who ship replacement
cattle or bison to, or receive animals from, such areas should carry
out a vigorous calfhood vaccination
program. Every cattle or bison owner, regardless of location, should
discuss the advantages and
disadvantages of vaccination with his or her veterinarian. Some States
do not allow cattle and bison to be imported for breeding if they have
been officially vaccinated and they are beyond the age at which they
should have been vaccinated.
Q. Where is vaccination less important?
A. In many areas of the country, low herd infection rates coupled
with improvement in the detection of early infection through BMST, MCI,
and other surveillance systems have lessened the need to continue calfhood
vaccination. Vaccination should be reduced in such areas, provided that
adequate regulatory measures are in effect to prevent reintroduction
of the disease.
Q. How does brucellosis affect humans?
A. People infected with the brucellosis organism usually develop
symptoms similar to a severe influenza, but this disease, called undulant
fever, persists for several weeks or months and may get progressively
worse. Farmers, ranchers, veterinarians, and packing plant workers are
infected most frequently because they come into direct contact with
infected animals. The initial symptoms are fatigue and headaches, followed
by high fever, chills, drenching sweats, joint pains, backache, and
loss of weight and appetite. Undulant fever does not often kill its
victims, but the disease is too serious to be dealt with lightly. For
additional information on brucellosis in humans, visit the Centers for
Disease Control and Prevention Web site at www.cdc.gov.
Q. What are the main sources of human infection?
A. In years past, prior to pasteurization, raw milk was considered
the prime source of brucellosis in humans. Today, most humans contract
the disease by coming into direct contact with aborted fetuses, afterbirth,
and uterine discharges of diseased animals or with infected carcasses
at slaughter. However, one 1994 study suggests that human brucellosis
in California is most likely to be a food-borne illness (unpasteurized
milk or cheese products) acquired in Mexico or from Mexican products
consumed in California. Rarely, if ever, does a human contract the disease
from another human.
Q. How common is human brucellosis in this country?
A. Fortunately, the combination of pasteurization of milk and
progress in the eradication of the disease in livestock has resulted
in substantially fewer human cases than in the past. Ninety-eight cases
of human brucellosis were reported in 1997, a fraction of the 6,400
cases reported in 1947. Currently, about 80-100 cases of human brucellosis
are reported annually. Many of those are people who have traveled internationally
and ingested unpasteurized dairy products.
Q. Can people get brucellosis by eating meat?
A. There is no danger from eating cooked meat products because
the disease-causing bacteria are not normally found in muscle tissue
and they are killed by normal cooking temperatures. The disease may
be transmitted to humans when slaughtering infected animals or when
processing contaminated organs from freshly killed animals.
Q. How can people be protected from brucellosis?
A. Ranchers, farmers, or animal managers should clean and disinfect
calving areas and other places likely to become contaminated with infective
material. All individuals should wear sturdy rubber or plastic gloves
when assisting calving or aborting animals, and scrub well with soap
and water afterward. Precautions against drinking raw milk or eating
unpasteurized milk byproducts are also important. Ultimately, the best
prevention is to eliminate brucellosis from all animals in the area.
Q. Where can I find more information on Brucellosis?
A. For additional information, contact:
USDA, APHIS, Veterinary Services
National Center for Animal Health Programs
Eradication and Surveillance Staff
4700 River Road, Unit 43
Riverdale, MD 20737-1231
Telephone: (301) 734-7708
or visit our Web site at http://www.aphis.usda.gov/vs/.
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