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Bob’s eye looked
strange.
Normally a bright-eyed, active young cat, Bob, a 2-year
old Manx belonging to Michelle Prager, was feeling out
of sorts. His activity level had dropped over the past
day or two, and his left eye had an unusually cloudy
appearance.
On physical examination, Bob had a high fever (104
degrees). All body systems checked out fine, except for
his eyes. Bob’s right iris was its usual green color,
but his left iris had a reddish tinge to it. The pupil
was slightly smaller in that eye, and the anterior
chamber – the space between his iris and his cornea –
was a bit murky. Bob’s eye wasn’t clear, but the
diagnosis was: anterior uveitis, a type of inflammation
involving one of the inner layers of the eye.
Treatment of uveitis consists of topical and oral
anti-inflammatory drugs, and most cases respond fairly
readily. However, determination of the cause of uveitis
in cats can be frustrating. It is important to establish
a primary cause of feline uveitis, since this may lead
to more specific therapy, may affect long-term
prognosis, may identify a contagious disease that could
affect other cats in the household, and may even
identify a disease that could have public health
significance. Common causes of uveitis in cats include
viral diseases such as feline leukemia virus (FeLV),
feline immunodeficiency virus (FIV), feline infectious
peritonitis (FIP), protozoal diseases such as
toxoplasmosis, and systemic fungal diseases.
I tested Bob for these disorders, and prescribed topical
medication while waiting for the test results, which
would be available in a few days. All tests came back
negative. This was not surprising, as a definitive cause
for feline uveitis is determined in less than 50% of
cases. Bob’s eye, however, responded quickly to
treatment. The cloudiness disappeared, and both eyes
returned to their beautiful green color.
Eight months later, Bob was back. So was his uveitis and
fever. I had ruled out most common causes of uveitis in
cats. Could this be Bartonella?
In the past decade, the field of veterinary medicine has
been abuzz with excitement, and confusion, over the
significance of Bartonella as a cause of illness in
cats. Unfortunately, what we don’t know about Bartonella
still exceeds what we do know.
For many years, the cause of a disease syndrome in
humans that was frequently associated with contact with
kittens or cats, remained unknown. The syndrome, called
Cat Scratch Disease (CSD) was characterized by fever,
malaise, and lymph node enlargement. In 1992, the
mystery was solved, as a new organism, Rochalimaea
henselae, was discovered to be the causative agent for
CSD. In 1993, the organism was renamed Bartonella
henselae.
“Bartonella is a bacterial organism that can infect
people as well as animals. Cats are the main reservoir
of infection, and the prevalence of infection is fairly
high”, says Dr. Mike Stone, board certified internist at
Tufts University. “Of the approximately 60 million pet
cats in the United States, at least 20% are infected
with Bartonella.” Exposure to fleas or flea feces is the
most important factor in transmission of the disease to
cats. The odds that a cat will be infected with
Bartonella is greatest in young cats, cats that go
outdoors, and cats that have fleas.
When people contract
a Bartonella-associated illness, a history of close
contact with (or being scratched by) a cat or kitten is
usually discovered. During grooming, cat claws are often
contaminated with infected flea feces or infected cat
blood. When a cat scratches, the organism is thus
deposited into the skin. There have been, however, a few
documented cases of people with Bartonella-associated
illness that have not been in contact with cats. It is
suspected that these people have picked up the organism
through contact with fleas, or flea feces in the
environment.
In people, infection with Bartonella can cause a variety
of illnesses, depending on the immune status of the
person. People with competent immune systems are more
likely to develop classical Cat Scratch Disease.
Antibiotic therapy is believed to have no significant
effect on the course of CSD in people, and most cases
resolve on their own. In immunocompromised people,
however, Bartonella infection can result in more serious
illness.
Bartonella infection in cats is a bit more mysterious.
Cats that have been experimentally injected with
Bartonella have been reported to develop a variety of
symptoms, including fever, loss of appetite, enlarged
lymph nodes, aggressive behavior, and generalized
tremors. The significance of these findings is debatable
because of differences in study design, and because
experimental inoculation does not necessarily reflect
what happens when cats are infected naturally. Most
naturally infected cats show no clinical signs of
illness. There are only a few published studies
regarding natural infection. In one study from
Switzerland, sick seropositive cats (those with
antibodies against Bartonella and presumably infected)
were more likely to have oral disease and urinary tract
disease than sick seronegative cats. However, healthy
control cats in that study were just as likely to test
positive as the sick cats, so it is impossible to say
whether it was the Bartonella that caused the illness in
the sick cats, or whether their being Bartonella-positive
was just a coincidental finding. In another study from
Japan, cats that were co-infected with Bartonella and
FIV were at increased risk for developing gingivitis and
lymph node enlargement. One study in the United States
revealed that sick cats who tested positive for
Bartonella were more likely to have blood in their urine
than sick cats who tested negative for Bartonella.
The one body system that does seem to be affected by
Bartonella is the eyes. Reports of human eye diseases
caused by Bartonella prompted others to look for similar
diseases in cats. “Bartonella is an emerging infection
that is considered responsible for uveitis in human
beings, cats, and less commonly in dogs”, says Dr.
Stefano Pizzirani, a veterinary ophthalmologist at the
Cumming’s School of Veterinary Medicine at Tufts
University. A number of feline eye disorders have since
been attributed to Bartonella. (See sidebar).
To muddy the waters even further, many of the Bartonella
studies are based on serological tests. Serological
tests detect antibodies against the organism, confirming
that the cat has been exposed to Bartonella. The
presence of antibodies does not necessarily mean that
the cat has an active Bartonella infection. In fact, it
is possible for a cat to be exposed to Bartonella,
develop antibodies against it, and then eliminate the
infection from its body. Because the antibodies remain
in the bloodstream, these cats will test positive on a
serological test, despite having defeated the infection.
I ran a serologic test on Bob. He tested positive for
Bartonella.
Some veterinarians feel that culturing the blood is a
better method to prove a cat is infected with Bartonella,
because a positive blood culture proves that the cat is
infected with the organism. Again, the results should be
viewed cautiously because a positive culture proves the
cat is infected, but it does not prove that the cat is
clinically ill from the infection.
Culturing the blood is a technically difficult process,
and it may take weeks before a positive result is
obtained because the organism is a slow grower. Another
test, called PCR, can be used for diagnosing Bartonella
infection, however, this test requires special
laboratories and is costly. A positive PCR test suggests
that the cat is infected, but again, it does not prove
that the cat is clinically ill from the Bartonella
infection.
The bottom line on diagnosis is that some tests prove
exposure, and some confirm infection, but there is no
single test that can definitively prove a cat is sick
from a Bartonella infection. If a veterinarian is
determined to blame Bartonella for a cat’s particular
illness, at minimum the following criteria should be
met:
• The illness is one that has at least been
reported to be associated with Bartonella infection
• Other possible causes of the cat’s illness have
been ruled out
• The cats tests positive for Bartonella (either
by serology, culture, or PCR)
• The cat responds to drugs that are known to be
effective against Bartonella
Azithromycin has been mentioned as an effective
antibiotic in the treatment of Bartonella infections.
The fluoroquinolones (for example Baytril®, Orbax®,
Zeniquin®)
are also effective, as is doxycycline and rifampin.
Bob satisfied the criteria listed above. He had uveitis,
a condition known to be caused by Bartonella. The other
common causes of uveitis – FeLV, FIV, FIP, Toxoplasmosis
– were ruled out. His serologic test for anti-Bartonella
antibodies was positive, and he responded to
azithromycin, an antibiotic known to have anti-Bartonella
activity. Was Bartonella the cause of Bob’s uveitis? We
still can’t be certain. “Among the diseases affecting
the eye, uveitis represents a challenging diagnosis
because many causes may be responsible, and diagnostic
tests are uncertain”, says Dr. Pizzirani. “Many cases
are, in fact, classified as idiopathic – the cause
cannot be determined.”
Veterinarians and cat owners must always keep in mind
that serologic tests do not prove current infection, and
the antibiotics used for the treatment of Bartonella
infections in cats are broad spectrum antibiotics that
may be effective against other organisms that can cause
illnesses resembling those caused by Bartonella. In
other words, even when the above criteria are satisfied,
at the present time it is still not possible to
definitively attribute the cause of a cat’s clinical
illness to Bartonella.
What about testing healthy cats for Bartonella? “Routine
testing of healthy cats, either by serology or culture,
is probably not necessary, except in certain
circumstances”, says Dr. Stone. “For example, it might
be advantageous for a veterinary blood bank to know the
Bartonella status of their donors, or a cat breeder to
know the status of their breeding stock. People with
immunosuppressive disorders may want to know the
Bartonella status of a cat before considering adoption,
as a negative cat may be a safer pet for them.” But
there are disadvantages as well. “A positive antibody
test might cause someone to classify the cat as
dangerous even though the cat may have eliminated the
infection and is now partially immune to it. Another one
of my fears is that cat who test positive might be
needlessly euthanized. And of course, there’s the
expense of testing, which can be considerable,
especially in a multi-cat household.” Dr. Stone also
cautions that a negative test – either by culture,
serology, or PCR – should not give owners a false sense
of security. “If preventative measures aren’t taken,
cats can easily become infected.” Because exposure to
fleas is the most important factor in the transmission
of Bartonella to cats, conscientious flea control is of
paramount importance. Cats should be kept indoors to
minimize the risk of fleas, and adding stray cats or
cats from shelters to the household should be done
cautiously, with extra attention paid to flea control.
Guidelines for preventing opportunistic infections among
HIV-positive people have been published previously. To
minimize the occurrence of Bartonella-associated illness
in people, the American Association of Feline
Practitioners has adapted these recommendations, which
include:
• Year-round flea control
• Adopting only healthy cats that are free of fleas and
are > 1 year of age
• Regular trimming of cat claws
• Avoiding scratches and bites
• Prompt and thorough washing of cat-associated wounds,
followed by professional medical advice
Bob, meanwhile, remains bright-eyed (though not
bushy-tailed; he is, after all, a Manx). It is clear
that further work needs to be done to determine exactly
what medical conditions can be attributed to Bartonella
infection in cats.
Sidebar: Feline eye disorders associated with Bartonella
• Uveitis – inflammation of some of the internal
structures of the eye, including the iris
• Retinitis – inflammation of the retina
• Conjunctivitis – inflammation of the soft
tissues surrounding the eye
• Keratitis – inflammation of the cornea
• Blepharitis – inflammation of the eyelids
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