Ted Nugent made cat scratch fever (actually
called cat scratch disease) nearly a household name with his song,
but most people still know very little about this infection other
than it involves a fever spread by cat scratches. In fact, it
involves infection by a bacterium called Bartonella
henselae, which is spread by fleas. Classically, cats transmit
the organism when they are parasitized by fleas, scratch
themselves, and get infected flea dirt (digested host's blood
excreted by fleas) in their claws, and scratch a person or another
cat with their dirty claws. Cats can also harbor
Bartonella in their mouths and transmit the infection via
bites or groom their feet and self-infect their claws.
The Human Disease
Infection with Bartonella henselae in
the immunocompetent person leads to cat scratch disease. The
inoculation site (a bite or scratch) develops a small red bump (a
papule.) About 2 to 3 weeks following contact with the infected
cat, the lymph node in the area of the contact will swell and
become painful and a fever develops. These signs generally resolve
on their own and the condition is minor.
If the patient does not have a competent immune
system, one of several much more serious syndromes can result. The
infection goes deeper into the body causing spleen enlargement, and
potentially encephalitis, heart valve infection, and other
conditions. These syndromes may be observed rarely in people who
are immunocompetent.
How Likely Is it for a Cat to Be
Infected?
Since fleas carry the bacteria, cats with
insufficient flea control are at highest risk. This means cats
living in climates that are warm and humid (conditions fleas thrive
best in) are most likely to be infected. If conditions are right,
up to 40% of cats in an area may be infected. If a person is
diagnosed with cat scratch disease, there is a 90% chance that the
cats they own will be found infected as well.
Do Infected Cats Get
Sick?
This is a highly controversial question as there
is some evidence that Bartonella henselae infection may be
one cause of the progressive oral disease of the cat called plasma
cell stomatitis. It has been suggested that Bartonella infection
may be the root of numerous chronic inflammatory conditions of the
cat. With such high numbers of infected cats present regionally (up
to 40%), it is going to be difficult to prove one way or the other
whether there is a real association or just coincidence.
Many cats with Plasma Cell
Stomatitistest strongly positive for
Bartonella henselae but this may simply reflect a high
incidence of exposure in the community. These cats often show
tremendous improvement in their oral disease with antibiotics
focussed on eradication of Bartonella; however, since
secondary infections are common with plasma cell stomatitis,
antibiotic response is common. The jury is still out and the
controversy rages on, but there is certainly nothing harmful in
treating a cat with plasma cell stomatitis for Bartonella,
though the medication (azithromycin) is somewhat expensive.
Other than this controversy over chronic
illnesses, if there are symptoms of infection they are mild,
transient, and similar to those of humans: fever, swollen lymph
nodes, and muscle pain.
Can Dogs Get Infected?
The short answer is: yes. Fleas may carry the
infection as they do for cats plus it appears that ticks may also
be carriers. As with cats, dogs are not believed to get sick from
this infection except for the minor flu-like symptoms described
above.
Is My Cat Infected?
There are five tests available to detect
Bartonella henselae: ELISA, IFA, PCR, culture, and Western
blot. All the tests have pros and cons and no method seems to shine
above the others.
The ELISA, IFA, and Western blot tests are tests
for antibody detection, the idea being that if antibodies against
Bartonella are there then Bartonella must be there as
well. For most diseases where antibody levels are used to establish
a diagnosis, a minimum "titer" or antibody amount is considered
necessary to say, "Yes, this patient is infected." The problem for
Bartonella is that no such guidelines have been
established. Making matters worse, we know that up to 11% of cats
with Bartonella organisms happily circulating in their
bloodstreams will not make antibodies and will thus test negative.
At least this means that when the test is negative there is an 89%
or greater chance that the cat is truly negative.
The most reliable test is the blood culture;
however, several consecutive cultures are needed, as the organism
tends to only circulate intermittently. A positive culture is proof
of infection though a negative culture may simply not have been
taken at the time when organism is circulating.
PCR is a very sensitive DNA test for the presence
of Bartonella DNA but because the organism only
intermittently circulates, this may not offer much advantage over
culture (except that results can be obtained slightly
sooner).
In humans, a delayed hypersensitivity skin test
is used, as part of the diagnostic criteria for cat scratch disease
but this test has not been useful in cats. In this test, similar to
the Tuberculosis test most of us are familiar with, a scratch on
the skin is made and a reaction to the introduced antigens may
occur either right away or in approximately 48 hours (delayed
hypersensitivity reaction). Cats are poor delayed hypersensitivity
responders.
Treatment of Cats
Right now the most reliable treatment seems to be
Azithromycin, which clears 83% of infected cats. The course of
treatment is approximately 3 weeks. Other antibiotics have been
less promising.
Prevention of Human Infection Guidelines from The
Centers For Disease Control and Prevention
Infection with Bartonella
Prevention of Exposure
1. HIV-infected persons,
particularly those who are severely immunosuppressed, are at
unusually high risk for developing relatively severe disease due to
infection with Bartonella, which can be transmitted from
cats. These persons should consider the potential risks of cat
ownership. Persons who acquire a cat should adopt or purchase an
animal aged greater than 1 year that is in good health.
2. Although declawing
is not generally advised, HIV-infected persons should avoid rough
play with cats and situations in which scratches are likely. Any
cat-associated wound should be washed promptly. Cats should not be
allowed to lick open wounds or cuts of HIV-infected persons.
3. Care of cats should
include flea control.
4. No evidence
indicates any benefits to cats or their owners from routine culture
or serologic testing of the pet for Bartonella
infection.
Prevention of Disease
5. No data support
chemoprophylaxis (i.e., preventive drug treatment) for
Bartonella-associated disease.
Prevention of Recurrence
6. Relapse or
reinfection with Bartonella has sometimes followed a
course of primary treatment. Although no firm recommendation can be
made regarding prophylaxis in this situation, long-term suppression
of infection with erythromycin or doxycycline should be
considered.
By Wendy C. Brooks, DVM,
DipABVP
