Bartonella and Cat Scratch Disease

Ted Nugent made Cat Scratch Fever (actually called “Cat Scratch Disease”) nearly a household name with his song in the late seventies 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 bacteria of the genus "Bartonella." There are 24 Bartonella species,

Bartonella henselae

Bartonella henselae

14 of which can infect humans and five of which are harbored by cats.

Cat scratch fever cover

 

The five Bartonella species harbored by cats are spread by fleas. The most well studied and most common Bartonella organism is Bartonella henselae 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.

flea dirt on cat

Flea dirt looks like black specks in
the pet’s fur. On close inspection
some of the specks are comma
shaped. The “dirt” is actually
flea excrement consisting of
dried blood from the host. The
flea dirt drops from the coat along
with flea eggs (which are white).
The newly hatched flea larvae
consume the flea dirt as food.

THE HUMAN DISEASE

Infection with Bartonella henselae in the immunocompetent person leads to “cat scratch disease.” The innoculation site (a scratch from a claw containing bits of flea dirt) develops a small red bump (a “papule.”) About 2-3 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.

For more detail on the Cat Scratch Disease in humans we recommend:

HOW LIKELY IS IT FOR A CAT TO BE INFECTED?

cat in grass mf

(Photocredit: Morguefile.com)

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 where fleas thrive best) 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.

This sounds somewhat concerning for the cat-owners in a flea area but it is important to realize that an infected cat cannot transmit the infection without a claw full of flea dirt. If the fleas are removed from the infected cat, there will be no flea dirt in the coat and no risk of disease transmission.

DO INFECTED CATS GET SICK?

Cat 2 mf

(Photocredit: Morguefile.com)

This is a highly controversial question. It was only relatively recently discovered (1992) that cats themselves were more than simple carriers of Bartonella henselae and that they could actually become infected themselves. Several illnesses seem to have been associated with Bartonella infection (fever, deep eye inflammation, lymph node enlargement, muscle pain, reproductive failure, and bacterial heart valve deposits called “endocarditis.”)

stomatitis mouth

Cat with Plasma cell Stomatitis

There is some evidence that Bartonella henselae infection may be one cause of the progressive oral disease of the cat called
Plasma Cell Stomatitis though this remains controversial. It seems that cats co-infected with Bartonella henselae and the Feline Immunodeficiency Virus have an increased incidence of Plasma Cell Stomatitis compared to what would be expected from either infection alone.

Further, many cats with Plasma Cell Stomatitis test strongly positive for Bartonella henselae though this may simply reflect a high incidence of exposure in the community. Some cats show tremendous improvement in their oral disease with antibiotics focused on eradication of Bartonella; however, since secondary infections are common with Plasma Cell Stomatitis, antibiotic response is not surprising. 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; lasting results have been reported in some individuals.

It has been suggested that Bartonella infection may be at 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.

CAN DOGS GET INFECTED?

dog in field mf

(Photocredit: Morguefile.com)

The short answer is: yes though the species of Bartonella they get is Bartonella vinsonii rather than Bartonella henslae. Fleas may carry the infection as they do for cats plus it appears that ticks may also be carriers. Since there are numerous infectious agents spread by ticks and it is not unusual for a dog to have multiple tick-borne infections it is very difficult to determine which infection is causing which signs.

 

 

IS MY CAT INFECTED?

There are 5 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 mimimum “titer” or antibody amount is considered necessary to say “yes, this patient is infected.” The problems 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 THE CAT

An assortment of antibiotics have been used against Bartonella henselae in cats: azithromycin, amoxicillin, doxycycline, enrofloxacin, erythromycin and probably others. Efficacy has been mixed and Bartonella henselae rapidly becomes resistant to therapy.Treatment is currently recommended for cats showing symptoms of disease; if the goal is to reduce potential for human infection, this is best accomplished with flea control. Studies are on-going to determine which antibiotic is best for sick cats. Presently, doxycycline is leading the list of recommended medications but this may change.

PREVENTION OF HUMAN INFECTION:
GUIDELINES FROM THE CENTER FOR DISEASE CONTROL

Prevention of Exposure

  • HIV-infected people, 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 people should consider the potential risks of cat ownership. People who acquire a cat should adopt or purchase an animal aged greater than 1 year that is in good health.
     
  • 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.
     
  • Care of cats should include flea control.
     
  • 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

  • No data support chemoprophylaxis (i.e. preventive drug treatment) for Bartonella-associated disease. In simpler terms, if a suspicious cat scratch has occurred, there is no point in using medication to prevent infection.

FURTHER REFERENCES

www.winnfelinehealth.org/health/csd.html

www.cdc.gov/healthypets/diseases/catscratch.htm

Page last updated: 11/6/2014