Canine Brucellosis
Overview
Brucellosis is one of the few venereal diseases among
dogs. It is associated with testicular atrophy. It causes sterilisation
(sometime obvious, sometimes not) in the male, embryonic re-absorption,
abortion, weak pups that die soon after birth and eventual sterility in
females. Males are contagious for months through their semen, females
are contagious for several weeks after the failed pregnancy.
Brucellosis may be passed to humans.
It can cause suppressed immune systems and sterility in humans. However,
brucellosis in this form cannot be passed back to animals or other
humans, as this disease is not adapted to humans.
Diagnosis can be quickly made, although animals
tested less than three weeks after exposure will show negative. False
positives are possible; follow up diagnosis with more reliable methods
should follow any initial positives.
Treatment for brucellosis was not generally very
successful in the early days and often very expensive. Extensive
antibiotic therapy, evaluation and additional testing added up quickly,
with no guarantee of success. No vaccine was or is available.
Modern veterinary medicine has greater success in
treating infected dogs. Surgical intervention with antibiotic treatment
is most effective
Any animal with brucellosis should not be bred,
and should be removed from the kennel or other breeding stock before
infecting the entire colony.
Dealing with infections in Kennel situations
Test all dogs present in unit - separate positive
and negative dogs - with positive
dogs, isolate individual dogs and treat with antibiotics and spay or
castrate. Negative dogs should be isolated where possible and treated
with antibiotics as a precaution if it is the intention that they may be
bred from once guaranteed cleared of infection. If there is no intention
to include them in future breeding programs, spay or castrate.
Re-test all dogs after 4 weeks.
Negative dogs that were negative
in previous tests should be retested monthly until clear on two
successive tests.
Positive dogs that were negative
in previous tests should be spayed or castrated (if this has not already
been done) and treated with antibiotics.
Test dogs monthly for 3 months until each individual
is negative on two successive tests following spaying, castrating and
treatment procedures on any that test positive.
Follow-up serology for 3 months post-treatment.
Isolation is important to prevent positive dogs
infecting negative dogs. Strict hygiene/disinfection procedures should
be followed using a broad spectrum disinfectant like Zircon S at
appropriate strengths with particular attention to the handling and
disposal of soiled material from the accommodation units. Protective
suits, masks and gloves are advised.
Good diet and a stress free environment will
greatly aid recovery of infected dogs.
Canine
Brucellosis Caused by Brucella canis
Paper
by - S. J. Shin and L. Carmichael - 1999
Diagnostic
Laboratory and Baker Institute for Animal Health, College of Veterinary
Medicine, Cornell University, Ithaca, New York, USA.
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Etiology
and Epidemiology
Canine brucellosis is caused by Brucella canis (B. canis), a rough,
small, gram-negative, intracellular bacterium. The canine brucella was
first recognized in 1966 as a cause of abortions and reproductive
failures and it has since been recognized in several countries. It is
especially common in Central and South America, in the southern states
of the United States, and has been diagnosed in commercial or research
breeding kennels (beagle) in several other countries, including Japan
and, more recently, in The People's Republic of China. The disease has
been reported sporadically in Europe. Humans may be infected; however,
dogs and other canine species are believed to be the only true hosts.
Natural infections occur most commonly after ingestion of contaminated
placental materials or aborted fetuses, vaginal discharges from infected
bitches that are in heat or who abort, and during breeding. Following an
abortion, organisms may be shed for several weeks or, intermittently,
for months. Males also may shed organisms in the urine, but bacterial
numbers are relatively low, except when urine is contaminated with
seminal or prostatic fluids. Prevalence data is meager, but
seroprevalence rates appear high (20 - 30%) in Mexico and
Central/South America. Estimates in the southern United States, Japan
have been reported to be 7 - 8% in stray dogs. Food-producing
animals are highly resistant. True prevalence rates are unknown and
other epidemiological aspects of canine brucellosis are lacking.
Clinical Signs
Clinical signs are associated principally with the reproductive tract.
In females, the most prominent sign is abortion after 45 - 55
days of gestation in about 75% of the cases. Early embryonic death and
resorption, or abortion 10 - 20 days after mating, may occur
in some cases. These may go unnoticed and the female may present with
the chief complaint of "failure to conceive". In males, the
main sign is epididymitis of one or both testes, and infertility.
Testicular atrophy and a moist scrotal dermatitis may be present. Semen
from infected males usually contains large numbers of abnormal sperm and
inflammatory cells, especially during the first 3 post-infection months.
Chronically infected males may have no sperm, or reduced numbers of
immature sperm. Autoimmune (anti-sperm) antibodies are present and
probably contribute to male infertility. Nonspecific signs in both sexes
include lethargy, loss of libido, premature aging and generalized lymph
node enlargement. B. canis has been isolated from field cases of
diskospondylitis, a condition that also has been reproduced
experimentally in SPF dogs. Recurrent uveitis has been occasionally
reported in infected dogs after several weeks of infection.
Infected males harbor organisms in the prostate gland and epididymides
for several months. Bacteria are disseminated the seminal fluids and,
occasionally, urine. B. canis is short-lived outside the dog and is
readily inactivated by common disinfectants.
Diagnosis
The diagnosis of canine brucellosis requires laboratory confirmation.
Blood cultures are strongly recommended before declaring an animal
infected. Serological tests which are presently available to most
veterinarians in the U.S. are imprecise since surface antigens of rough
Brucella, such as B. canis, cross-react strongly with antibodies to
several other nonpathogenic bacterial species. The most commonly used
tests include:
Serological Tests
Rapid Slide Agglutination Test (RSAT) - The RSAT requires
brief treatment of serum with 2-mercaptoethanol (0.2M), and is available
in the U.S. as an office screening test (D-Tec CB; Symbiotics Corp.,
Kansas City, Missouri, USA.). The antigen is rose bengal-stained B.
ovis, which cross-reacts with B. canis. A negative slide test is strong
evidence that the dog is not infected, but only about 40% of dogs whose
sera agglutinate the slide test antigen are actually positive for canine
brucellosis. Thus, dogs positive on the slide agglutination test should
not be considered infected until additional serological tests are done -
blood cultures are always indicated because of the long and continual
periods of bacteremia. More than 50% of infected dogs have a bacteremia
lasting 1 year or longer. More specific antigens (B. canis M-) are now
available (NYS Diagnostic Laboratory, Cornell University), but they have
not been made commercially available (see (3) below).
Tube agglutination (TAT) and Agar Gel Immunodiffusion (AGIDcwa)
Tests - These tests utilize cell wall antigens and are
additional serologic methods available through diagnostic laboratories.
However, those tests also are flawed by false-positive reactions and
difficulties in interpretation, especially with "early" sera
or sera from chronically infected dogs. Results obtained by the RSAT,
TAT, and AGIDcwa tests should be confirmed by more specific tests
(below) and isolation attempts.
Improved Serodiagnostic Tests - Improved tests include: (1) A
RSAT that employs a mutant strain (less mucoid, "M-") of B.
canis that has high specificity (M-RSAT); (2) an agar gel
Immunodiffusion test (AGIDcpa) that employs cytoplasmic protein antigens
extracted from the bacterial cytoplasm. The protein antigens are highly
specific for the Genus Brucella and are useful in distinguishing between
infected and non infected dogs who possess antibodies that react in
agglutination or AGID (cell wall antigens) tests, noted above (1 &
2). (3) enzyme-linked immunosorption tests (ELISA) that employ as
antigen cell wall LPS extacts of B. canis M- or cytoplasmic proteins
extracted from B. abortus. Published results indicate significant
advantages of the improved tests noted above and the warrant serious
consideration for further development for use in diagnostic laboratories
or as veterinary office kits.
Indirect Fluorescent Antibody Test (IFAT) - An IFAT is used by
several diagnostic laboratories in the U.S., but data on its accuracy
have not been published. Results from Cornell University's Diagnostic
Laboratory indicate a high rate of false positive reactions with the IFA
test.
Blood Cultures
Despite improvements in serologic diagnostic methods, blood cultures
should always be performed when the disease is suspected. B. canis is
readily isolated from the blood on tryptose or trypticase soy media for
several months after infection. Cultures should be incubated aeobically,
since CO2 is inhibitory. Detailed methods are described in
the references (Alton et al, 1988). Many laboratories are insufficiently
familiar with the interpretation of canine brucellosis diagnostic
procedures, which has frequently resulted in the destruction of
non-infected dogs solely on the basis of agglutination test results
that, in fact, were false-positive reactions.
Prevention and Control
Attempts to develop a suitable vaccine which would induce immunity, yet
not provoke serological responses that interfere with the diagnosis,
have not been successful. Presently, the development of a vaccine is
considered undesirable since the brucella vaccines which have been
studied offered only moderate protection and vaccinated dogs developed
antibodies which would confuse the serodiagnosis. Prevention of
infection and elimination of infected dogs should be the principal
control strategy in kennels.
Prevention requires yearly testing of all breeding stock and the testing
of all dogs to be introduced into a kennel. In the United States, the
New York State Diagnostic Laboratory at Cornell University is recognized
as the principal, and most reliable, testing lab. Only proved
non-infected dogs should be bred. In the United States, females in
breeding kennels are commonly tested by the RSAT before their expected
estrus. At least 3 weeks should be allowed to perform further tests to
ascertain whether a seropositive test indicates actual infection or a
false-positive result. Two negative tests done at 4 - 6 week
intervals should be required for all dogs to be introduced into breeding
colonies. The two tests will detect dogs who may be incubating the
disease. If a bitch aborts, assume infection until it is proved
otherwise. Bitches who abort should be kept isolated and the premises
must be disinfected. If a male dog loses interest in mating, or develops
testicular abnormalities and poor fertility, it should be examined for
brucellosis.
Treatment
Treatment is not recommended for dogs in breeding kennels, and where
dogs cannot be isolated and accurately monitored following antibiotic
therapy. Treatment is expensive and cures are difficult to achieve,
especially in chronically infected males. Repeated blood cultures and
serologic monitoring is required for at least 3 post-treatment months
before a dog can be declared negative. Recrudescence of the infection
after the cessation of antibiotic treatment is common. Even if the
organism can be successfully eliminated, males frequently remain sterile
because of irreversible damage to the testes and epididymides. Spaying
or castration is believed to reduce the risk of transmission from
infected dogs; however, this hypothesis has not been tested
experimentally and neutering does not eliminate organisms from the body.
All neutered dogs should receive a course of antibiotics. The most
successful and practical treatment results have been obtained with a
combination of a tetracycline drug, e.g., tetracycline hydrochloride,
doxycycline, minocycline, and streptomycin administered during the first
3 months of infection. More than 80% cure rates have been achieved in
kennels, where dogs initially diagnosed as infected were euthanised and
additional ("early") cases were treated. Unfortunately,
dihydrostreptomycin
is unavailable for treatment of dogs in the United States. A cure is
more difficult to achieve in chronic infections.
If available, dihydrostreptomycin
(10 mg/kg IM bid) is given for the initial 7 days of treatment together
with a tetracycline antibiotic (25 mg/kg orally tid), which is continued
for 4 weeks. During the last 7 days of tetracycline therapy,
streptomycin is again given. In some instances where the first course
failed, a second course of treatment has been successful. Since
streptomycin is no longer available in the USA for treatment of dogs,
gentamicin has been recommended by some clinicians as a substitute
antibiotic. However, there is insufficient data to recommend gentamicin,
and preliminary studies indicate that its efficacy is unsatisfactory,
except in very early cases - i.e., in dogs infected for less than
1 - 2 months. Treatment is not recommended for breeding dogs,
or when long-term (3 months) follow-up is unlikely. Treatment failures
are especially common in infected males where organisms are commonly
sequestered in the prostate gland and epididymides.
Testing and elimination of infected dogs is the only proven method of
eradication of B. canis from an infected kennel. An attempt should be
made to identify the source of the infection - unfortunately, this has
rarely been accomplished since breeders are reluctant to admit
culpability.
Management of infected kennels/dogs is time
consuming and expensive. Veterinarians must be prepared to address
owners' concerns and render judicious advice, which may vary according
to circumstances. Prevention is essential to avoid the ordeal of
infection in a breeding kennel. As soon as canine brucellosis is
diagnosed in a kennel, vigorous measures must be implemented until the
disease has been eradicated. Infected kennels should be quarantined,
even though most states/countries do not have formal regulations. Lack
of such measures has lead to widespread, even international, spread of
B. canis infection.
Public Health Significance
Humans are susceptible to B. canis, but infections are uncommon and they
are usually mild. Approximately 40 cases of human infection have been
reported in several countries, however the actual number is unknown
since cases are rarely diagnosed, or reported. Symptoms are usually
vague - prolonged febrile illness with lymph node
enlargement. Most natural infections have been acquired through close
contact with infected dogs. Laboratory infections also have been
reported. Unlike the dog, infected humans usually respond rapidly to
antibiotics (tetracycline's or tetracycline's + streptomycin).
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