Ask Dr. Richards: 11/03

Question: My 14-year-old cat was diagnosed with disease caused by Bartonella following a month long illness (high fever, vomiting, loss of appetite and lethargy). Surgery for an inflamed abdominal lymph node did not alleviate the signs.

Fortunately, I was able to take her to a major veterinary referral center for the diagnosis. I was told that some research indicates that this disease is symptomatic in many more cats than are being diagnosed because many veterinarians are unfamiliar with the signs and available tests. How can we heighten awareness among veterinarians and cat owners so that cats can be treated with the antibiotics that can save them?

Answer: One way to heighten awareness is via this column, so Ill do my part. But combating the lack of awareness is only part of the solution. When it comes to determining whether a disease in a particular cat is caused by a species of the bacteria, Bartonella – usually Bartonella henselae – things arent nearly as straightforward as we would hope. In fact, the deeper you look, the more complex it becomes.

Cat-scratch disease (CSD) in humans was first described in the early 1930s, and today its estimated that more than 20,000 cases – usually mild and requiring no treatment – occur every year in the United States. Disease in immunocompromised people can be very serious, even fatal. It wasnt until 1983 that bacteria were determined to be the cause, and it took an additional nine years before Bartonella bacteria were recognized as the chief offenders.  

Cats are known to carry the organism and are believed to be the major source of human infections.  Although varying a lot depending on the part of the country, upwards of 80 perfect of cats – particularly older cats, feral cats and flea-infested cats residing in warm, humid climates – show evidence of exposure to Bartonella.

Roughly half this number either continuously or intermittently harbors bacteria in their bloodstream, sometimes for long durations of time. Most of these infected cats are perfectly healthy. Even the majority of cats infected artificially in laboratory studies have only mild and transient disease characterized by short periods of fever, listlessness and loss of appetite. In some, the lymph nodes will become enlarged, while fewer still may experience nervous system disorders. 

For various reasons, many veterinary scientists conjecture that Bartonella may play a role in some chronic cat diseases, especially those with the signs seen in experimental infections and certain kinds of eye and mouth disease. But at this time, Bartonella has not been proven to contribute to any chronic illness in cats.

Its going to be difficult to prove, too, and will probably require large epidemiologic studies to clearly establish a link between infection and disease. To complicate things even more, diagnosis of infection – both in sick or healthy cats – is difficult, and usually relies on a combination of antibody tests, blood cultures, and tests using polymerase chain reaction (PCR). These are performed at only a few laboratories in the country and the results must be cautiously interpreted: Some infected cats will be missed, but even if a cat is found to be infected, Bartonella may have nothing whatsoever to do with the disease.  Even worse, treatment with antibacterial medication doesnt reliably clear infection, although it may reduce the number of bacteria. Nonetheless, if infection is diagnosed in a cat with the signs describe above, then antibacterial treatment is certainly justified and, as in the case with your kitty, may be life sparing.

Prevention is Better Than Cure
Bartonella is believed to be transmitted from cat to cat by fleas, and in most cases, people probably become infected through contamination of cat scratches or bites with flea feces. To reduce the likelihood of CSD occurring in the family, avoid rough play with cats, maintain meticulous flea control, wash cat-inflicted wounds right away and dont allow cats to lick any cuts or wounds on people. There is no evidence that declawing cats reduces the risk, nor does giving antibacterial medication. A couple of other recommendations if a family member is immunocompromised (AIDS patient, undergoing chemotherapy, organ transplant recipient, etc.) and thus at higher risk of serious disease: You might consider adopting an adult cat (kittens are more often implicated in cases of CSD) and asking your veterinarian to perform an antibody test. Cats with no antibody are less likely to be infected.