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Facts about Brucellosis
1. What is brucellosis?
It is a contagious, costly disease of ruminant 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.
2. How serious is brucellosis?
Considering the damage done by the infection in animals-decreased
milk production, weight loss in animals, loss of young, infertility,
and lameness, it is one of the most serious diseases of livestock.
The rapidity with which it spreads and the fact that it is transmissible
to humans makes it all the more serious.
3. What disease agents cause brucellosis?
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 and bison; 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 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.
4. What are the signs of brucellosis?
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.
5. How is brucellosis spread?
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.
6. What is being done to fight brucellosis?
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 June 30, 2000, 44 States, plus Puerto Rico and the U.S.
Virgin Islands, were free of brucellosis. Six States currently
have a herd infection rate of less than 0.25 percent and are considered
to be in Class A status. There are no States in Class B (herd
infection rate between 0.26 percent and 1.5 percent) or Class C
status (herd infection rate greater than 1.5 percent).
7. What about free-ranging bison herds?
The presence of brucellosis in free-ranging
bison 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.
8. How do epidemiologists help fight brucellosis?
Epidemiologists are specially trained veterinarians who 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.
9. How costly is brucellosis to the livestock industry?
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.
10. How effective is the Brucellosis Eradication Program?
At the beginning of the program, brucellosis was widespread throughout
U.S. livestock, but eradication efforts have had dramatic results.
In 1956, there were 124,000 affected herds found by testing in the
United States. By 1992, this number had dropped to 700 herds,
and as of June 30, 2000, there were only 6 known affected herds
remaining in the entire United States. USDA, 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.
11. What is the basic approach to eradication?
The basic approach has always been to 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.
12. How is infection found in cattle?
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 checked 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 one 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.
13. What happens when evidence of disease is found by surveillance
testing?
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
check neighboring herds and others that may have received animals
from the infected herd. All possible leads to additional
infection are traced.
14. How does the brucellosis ring test (BRT) surveillance work?
The BRT 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.
15. How does market cattle identification (MCI) work?
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.
16. Which animals are eligible for MCI testing?
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.
17. Why is identification of market cattle important?
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.
18. What are the advantages of MCI?
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.
19. What is a blood agglutination test?
It is an effective method of diagnosing brucellosis. To pinpoint
infection within a herd, a blood sample is taken from each animal
and tested in the field or at a laboratory. The blood serum is mixed
with a test fluid or antigen containing dead Brucella organisms.
When the organisms in the test fluid clump together in a reaction
known as agglutination, the test is positive.
20. What is the brucellosis card test?
It is a rapid, sensitive, and reliable procedure for diagnosing
brucellosis infection. It is similar to the blood agglutination
test but 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.
21. Are there any other tests for brucellosis?
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 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.
22. What animals are eligible for testing?
With certain exceptions, herd tests must include all cattle and
bison over 6 months of age except steers and spayed heifers.
23. What is the incubation period of brucellosis?
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.
24. Can brucellosis in animals be cured?
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.
25. Can brucellosis be prevented?
The disease may be avoided by employing good sanitation and management
practices. 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.
26. What about vaccination?
For cattle and bison in heavily infected areas or replacement animals
added to such herds, officials recommend vaccinating heifers with
an approved Brucella vaccine. 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.
27. How does the vaccine work?
Brucella abortus vaccine produces a bodily response that
increases the animal's resistance to the disease. However,
vaccination is not 100-percent effective in preventing brucellosis;
it typically protects about 65 percent of the vaccinated cattle
from becoming infected by an average exposure to Brucella.
28. Is Strain 19 the only approved Brucella vaccine?
No. 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.
29. Is Strain RB51 vaccine approved for use in bison?
As of June 2000, B. abortus Strain RB51 had not yet been
approved for use in bison. Preliminary studies indicate that
RB51 is safe and efficacious in bison calves. However, in
order for RB51 to be conditionally licensed in bison, additional
safety and efficacy trials must be completed.
30. Where or when is calfhood vaccination most important?
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 are not official vaccinates and
they are beyond the age at which they should have been vaccinated.
31. Where is vaccination less important?
In many areas of the country, low herd infection rates coupled
with improvement in the detection of early infection through BRT,
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.
32. How does brucellosis affect humans?
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.
33. What are the main sources of human infection?
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 in 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.
34. How common is human brucellosis in this country?
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. Sixty two (62) cases of brucellosis
in humans have been reported to the Centers for Disease Control
and Prevention for 1998 (provisional data).
35. Can people get brucellosis by eating meat?
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.
36. How can people be protected from brucellosis?
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.
For additional information, contact:
USDA, APHIS, Veterinary Services
National Animal Health Programs
4700 River Road, Unit 43
Riverdale, MD 20737-1231
Telephone (301) 734-7708
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