Bartonella Infection and Treatment

March 7, 2020

Bartonellosis is caused by infection with one of five Bartonella species of bacteria including Bartonella henselae, the bacterium that can cause “cat scratch” disease in people. The bacteria can be transmitted between cats by fleas and ticks and can be spread to people primarily by cat scratches and bites. and you should bring any concern to your physician. Most infected cats show no signs of illness and can remain infected for years or even for life if untreated. There is some controversy regarding pathogenicity in cats and the organism has been blamed for causing oral, respiratory, intestinal, and ocular diseases.including conjunctivitis, uveitis, blepharitis, chorioretinitis, and keratitis. Conjunctivitis attributed to Bartonella infection is commonly both chronic and refractory to a variety of treatments yet it responds rapidly to oral azithromycin therapy. The biggest differential for Bartonella conjunctivitis is FHV-1 conjunctivitis. Dual infection is also a possibility. While 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 challenging.. 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 (an infected but antibody negative cat is seen about 10% 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 limitations and are more expensive and time-consuming.


Bartonella infection is usually treated with a 3-week course of the oral antibiotic azithromycin or doxycycline. Control of flea problems is also important to prevent reinfection.

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.