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What is brucellosis?
Brucellosis is an infectious disease caused by the
bacteria of the genus Brucella. These bacteria are
primarily passed among animals, and they cause
disease in many different vertebrates. Various Brucella
species affect sheep, goats, cattle, deer, elk, pigs, dogs,
and several other animals. Humans become infected by
coming in contact with animals or animal products that
are contaminated with these bacteria. In humans
brucellosis can cause a range of symptoms that are
similar to the flu and may include fever, sweats,
headaches, back pains, and physical weakness. Severe
infections of the central nervous systems or lining of the
heart may occur. Brucellosis can also cause long-lasting
or chronic symptoms that include recurrent fevers, joint
pain, and fatigue.
Brucellosis is not very common in the United States, where100 to
200 cases occur each year. But brucellosis can be very common
in countries where animal disease control programs have not
reduced the amount of disease among animals.
Brucellosis is a disease caused by a bacteria, Brucella canis.
It is found throughout the world. It is spread through contact
with aborted fetuses and discharges from the uterus of
infected bitches, during mating, through maternal milk and
possibly through airborne transmission in some cases. The
bacteria enters the body through mucous membranes and
spreads from there to lymph nodes and the spleen. It also
spreads to the uterus, placenta and prostate gland as well as
other internal organs at times.
In female dogs, infection leads to abortion or early death of
infected puppies. Infected females may have no other clinical
signs. In some cases there may be decreased fertility rather
than abortion. This may be due to resorption of fetuses early
in their development.
The most common sign of brucellosis infection in a
healthy-appearing bitch is abortion between days 45 to 59 of
gestation. The vaginal discharge associated with abortion is
typically brown or greenish gray in color. This vaginal
discharge and fetuses contain large numbers of Brucella
bacteria. Other dogs and humans should not come in contact
with these secretions. When an infected bitch aborts, spread
throughout a kennel can be very rapid. The persistent
discharge after abortion contains extremely high numbers of
organisms for 4 to 6 weeks. Milk also serves as another
contaminant to the environment. Infected bitches may deliver
both living and dead puppies. These surviving puppies are
infected and will shed bacteria in their secretions.
Bitches infected with B. canis may appear infertile. These
bitches typically do conceive a litter, but resorb the fetuses
early during gestation. Brucellosis should always be
considered when a dog is examined for infertility.
In male dogs, infection of the testicles can lead to infertility
due to anti-sperm antibodies developed as the body attempts
to fight off the bacterial infection. The testes may atrophy
after the initial period of swelling. Scrotal enlargement or
infection of the skin over the scrotum may be seen.
In both female and male dogs there may be infection of spinal
discs (diskospondylitis) which can cause back pain and rear
leg weakness or even paralysis. Eye inflammation may be
seen in either sex.
It is not usually possible to culture Brucella canis bacteria
from the blood or affected tissues so diagnosis is usually
done by titer testing. There is a kit available to veterinarians
for testing in their office. It is usually best to retest any dogs
found positive on this test with other testing methods since
there is a fairly high rate of false positives using the in-house
test kit.
The Rapid Slide Agglutination Test (RSAT) is a widely used screening
test for brucellosis in dogs. A blood sample is taken from the dog to be
tested, and serum is separated. Patient serum is mixed with heat-killed
Brucella ovis on a microscope slide. B. ovis is used because it is
similar to B. canis. Agglutination of the serum sample is suspicious for
B. canis infection. This test is highly sensitive, and false-positive
reactions do occur. A false positive is a test that appears positive in a
dog that is not infected with the disease. These false-positive
reactions are caused by cross- reactions with Bordetella
bronchiseptica (the kennel cough agent), Pseudomonas, Moraxella,
and other gram negative bacteria. Thus if the RSAT is negative, it is
safe to assume that the dog does not have brucellosis. However, if
RSAT is positive, further testing is necessary to determine if the
patient is infected with Brucella canis. Typically, the 2-mercaptoethanol
tube agglutination test (2- ME TAT) is used in these patients. Few falsepositives result with this test. A dog that tests positive with the 2-ME
TAT should have the results confirmed using an agar gel
immunodiffusion test (AGID), or blood culture.
Brucellosis is very difficult to treat successfully. A
combination of minocycline and streptomycin is thought to
be most effective but is expensive. Tetracycline can be
substituted for the minocylcine to reduce costs but also
lowers the effectiveness of treatment. All infected animals
should be neutered or spayed to prevent sexually related
transmission. All infected animals should be considered to be
lifelong carriers of the disease, even if treated.
Dogs with brucellosis should never be used for breeding
and euthanasia is the only solution to the problem. These
animals are a potential source of infection for other dogs and
humans. Combination therapy of aminoglycosides and
tetracyclines has been tried, but the treatment only makes the
infected dog test "false" negative, when in fact the dog is still
very infectious and very much contagious. A breeding bitch
in a kennel should be permanently separated from the other
dogs to minimize the chance of spread. Euthanasia is the
only true remedy for a dog that has tested positive for
brucellosis using the AGID test which is the blood culture.
Remember that a neutered, spayed, and/or antibiotic treated
dog is still a source of infection to other dogs and humans so
this is not a proper option to exercise, even though some
vets are wrongly doing so.
Unfortunately, there is no vaccine available for the prevention or
treatment of brucellosis. Any new additions brought into the breeding
kennel should be isolated for at least one month, and should have two
negative brucellosis tests one month apart before being allowed into the
kennel. Stud dogs that are actively breeding should be tested at least
once every three months. Dogs and bitches competing regularly in field
trials should be tested once per month and kept segregated from the main
kennel area where breeding studs, brood bitches, and puppies are kept.
Brucellosis-infected bitches should not be bred, even with artificial
insemination, due to the risk of contamination from vaginal discharge,
milk, and puppies. If a dog or bitch in the main kennel area does test
positive for brucellosis, the entire kennel must be tested. Several tests
should be done on each dog, each one a month apart, to make sure that
all positive animals are identified, and then immediately destroyed and
properly disposed of.
It would probably be best not to breed dogs without testing
both the male and female for this disease. Breeding should
be a deliberate choice -- not a random event! For breeding
kennels, routine isolation of new dogs would be a very good
idea. After isolation and negative tests at entry into the
kennel and one month later, it should be safe to let the new
dog mix with the others in the kennel. If infection is
suspected at any time, quaternary ammomium (like Roccal
Rx) and iodophor (Betadine Rx) disinfectants can kill Brucella
organisms in the kennel to limit spread of the disease.
Humans are generally infected in one of three ways: eating or
drinking something that is contaminated with Brucella, breathing in
the organism (inhalation), or having the bacteria enter the body
through skin wounds. The most common way to be infected is by
eating or drinking contaminated milk products. When sheep,
goats, cows, or camels are infected, their milk is contaminated
with the bacteria. If the milk is not pasteurized, these bacteria can
be transmitted to persons who drink the milk or eat cheeses made
it. Inhalation of Brucella organisms is not a common route of
infection, but it can be a significant hazard for people in certain
occupations, such as those working in laboratories where the
organism is cultured. Inhalation is often responsible for a
significant percentage of cases in abattoir employees.
Contamination of skin wounds may be a problem for persons
working in slaughterhouses or meat packing plants or for
veterinarians. Hunters may be infected through skin wounds or by
accidentally ingesting the bacteria after cleaning deer, elk, moose,
or wild pigs that they have killed.