The “B” Word…Bartonellosis
By: Alan Klag, DVM, DACVIM
Board-Certified Internal Medicine Specialist
Chief of Internal Medicine Service
Veterinary Specialty & Emergency Center
Bartonella, a rather fragile gram negative rod bacterium, was first recognized as the cause of Cat Scratch Fever in people and also the title of a famous Ted Nugent song for those of my age group (see below).
Prior to the identification of this organism, people, predominantly children, were presenting with significant lymphadenopathy, often leading to false suspicions and fears of lymphoma and other infectious disease prior to biopsy. Many of the children and adolescents with the illness were noted to have been scratched or bitten by a cat within a few weeks of onset of the signs.
Image courtesy of Wikipidia
Although the term Cat-Scratch Disease (CSD) was first described over 80 years ago, the bacterium was not determined until decades later.
The predominant species of Bartonella in people and cats is Bartonella henselae. It is thought that the cat flea, ctenophalus felis, is the vector leading to inoculation of patent B. henselae organisms into the bloodstream. Blood transfusion and cat bites are also potential sources of introduction of organisms. More recently, it has become apparent that Bartonella organisms can cause significant illness in the dog and veterinary interest in the organism typically revolves around illness in the dog.
Cats are known to be reservoirs of the organisms and can carry the organism for months or longer, typically with no clinical signs. Occasionally, they can have a short febrile episode at onset or develop clinical signs when immunosuppressed, however, for the most part, they are quite resistant to illness from the organism. Thus, it is rarely indicated to investigate for Bartonella in a cat unless one is trying to understand whether a particular cat may be a carrier of the organism.
From a public heath perspective, good flea control is important, as well as a general hygiene protocol such as making sure that children in particular wash their hands after handling cats and that situations where they might be scratched or bitten by a cat be avoided. In cases of lymphadenopathy in people, especially when localized and painful, exposure to cats should be considered and mentioned to the physician.
Dogs are more susceptible to illness when infected with Bartonella. They may carry Bartonella vinsonii subsp. berkhoffii, Bartonella henselae, and other Bartonella species. Most widely recognized syndromes include endocarditis, myocarditis, granulomatous lymphadenitis and other granulomatous inflammatory disease as well as cardiac arrhythmias (likely due to either endocarditis or myocarditis).
The actual prevalence of illness in dogs due to Bartonella is unknown and somewhat dependant on who you are speaking to. Some feel that it is very much undiagnosed due to the difficulty in finding the organisms and others feel that it is mentioned too frequently for the true incidence of the illness. In our practice, it is rare for us to obtain a definitive diagnosis of Bartonellosis in dogs, however, there are cases that show typical cytologic or histopathologic granulomatous inflammation that respond to appropriate antibiotic therapy where the diagnosis is suspected but unproven.
This is where the challenge lies. Serology, PCR on tissue, blood or other fluid as well as culture from tissue or blood are available, however, the latter is quite challenging.
PCR testing should be done by a reputable lab experienced in doing PCR for Bartonella and serology only indicates exposure but does not prove active infection.
Our experience at VSEC is that very few dogs that we test are serology positive for any species of Bartonella, mirroring studies that indicate the worldwide seroprevalance for Bartonella in dogs is low.
This finding is consistent with the fact that dogs do not likely serve as a reservoir for the organisms/are not healthy carriers. Given these findings, a positive serology titer, especially a higher titer, should always be taken seriously and is suggestive of active Bartonellosis.
The challenge is not so much with a seropositive dog, but rather with the seronegative ones as the thought is that many infected dogs will not seroconvert so other testing such as PCR should be considered in cases where suspicion is high. Another option is to repeat serology after several weeks to ensure no seroconversion when the initial titers are negative.
This is another subject of debate in that some feel that resistance to various antibiotics is not uncommon and that there is no one antibiotic that is consistently effective. Combination antibiotics are sometimes advised. If this is true, then using lack of response to treatment to any given antibiotic cannot be relied upon to refute the diagnosis, making Bartonellosis an even greater diagnostic challenge.
The antibiotics that are most commonly used for Bartonella include quinolones and doxycycline. Amoxicillin and Rifampin have also been used. Any dog suspected to have Bartonellosis should be treated for 4-6 weeks, as the organism can be difficult to clear, even with an effective antibiotic.
Dr. Alan Klag is a board-certified internal medicine specialist at the Veterinary Specialty & Emergency Center. The Veterinary Specialty & Emergency Center operates state-of the-art emergency and specialty veterinary hospitals that are open 24/7/365 in Levittown PA, Philadelphia PA and Conshohocken PA. For more information about our world-class emergency and specialty care, please visit VSEC on the web at www.VSECVET.com.