Bartonellosis is caused by infection with one of five Bartonella species of bacteria including Bartonella henselae. This is the bacterium that can cause "cat scratch" disease in people. The bacteria can be transmitted between cats by fleas and ticks. The bacteria can be spread to people primarily by cat scratches and bites. Most infected people do not become ill. However, since it is a potentially zoonotic disease (can be transmitted from animals to humans), you should bring any concern to your physician. Cats can remain infected for years or even for life if untreated. Most infected cats show no signs of illness. There is some disagreement amongst veterinarians as to what Bartonella infection can do to cats. The organism has been blamed for causing a variety of problems in cats including oral, respiratory, intestinal, and ocular diseases.
Potential Ocular Effects of Bartonella Infection:
Bartonella infection in cats has been implicated as causing conjunctivitis, uveitis, blepharitis, chorioretinitis, and keratitis.
The conjunctivitis attributed to Bartonella infection is commonly both chronic and refractory to a variety of treatments. Yet it can respond rapidly to oral azithromycin therapy. The biggest differential for Bartonella conjunctivitis is herpesviral conjunctivitis. Dual infection is also a possibility.
We mostly think of Bartonella as a pathogen in cats but there is at least one report of it causing ocular effects in dogs as well.
Proving that Bartonella infection is the cause of a cat's clinical signs can be difficult. Diagnosis is made by evaluating the clinical signs in conjunction with a blood test to look for a high level of antibodies to this organism. Drawbacks to this type of testing include the facts that there can be false negatives (meaning the cat is infected but antibody negative; occurs up to 11% of the time) and that a positive titer might only indicate exposure to the organism and not active infection. Other diagnostic tests available include blood culture and PCR but these tests have their own drawbacks and can be more expensive and time-consuming.
Bartonella infection is usually treated with a 3-week course of the oral antibiotic azithromycin. This course of therapy has been shown to clear infection in 83% of affected cats. If repeat testing (see below) indicates inadequate therapy, another course of treatment will probably be recommended. Control of flea problems is also important to prevent re-infection. The main side effects of azithromicin therapy are gastrointestinal ones (vomiting, decreased appetite, and diarrhea). If side effects occur, please let us know right away.
Evaluation of Bartonella Therapy:
Six months following therapy, repeat blood testing is advised to assess the adequacy of treatment. This is an "antibody titration test". Titers are determined by serial dilutions on both the pre-and post-treatment blood samples. This testing is much more involved than the initial testing. It is therefore more time-consuming and more expensive. It can take as long as one month to get these results compared to about 10-14 days for the initial blood test. Keep in mind that this follow-up testing is still important even if the ocular signs have resolved. Otherwise, there is potential for ocular signs to recur and/or for health problems to show up in other organ systems.