Bartonellosis—more than what the cat scratched in
Over the past three decades, the field of Bartonella research has grown substantially. Currently, there are more than 36 recognized Bartonella species that are transmitted by an array of vectors (e.g. fleas, keds, lice, sand flies, ticks). Many Bartonella species are zoonotic, causing disease in people and animals. Cats and dogs serve as the reservoir for many of the Bartonella species; however, other animals (e.g. rodents, rabbits, sheep, coyotes) are frequently involved. As diagnostic techniques improve and research expands, our understanding of these bacteria and their role in human, canine and feline disease is evolving rapidly.
Cat scratch disease …
Bartonella is best known as the zoonotic agent of cat scratch disease (CSD). Caused by the bacteria Bartonella henselae, cats are infected by the cat flea (Ctenocephalides felis). People acquire CSD through the scratch or bite of an infected cat. It is actually B. henselae in flea feces present on the cat’s claws or teeth that transmits infection. Disease in people often manifests as a pustule at the site of the scratch or bite and may progress to regional lymphadenopathy and low-grade fever.
Typically, CSD is self-limiting but severe illness can occur (particularly in immunocompromised individuals), resulting in bacillary angiomatosis, peliosis or endocarditis. It is estimated that more than 12,000 people are diagnosed with CSD annually in the United States. Young children are at increased risk of CSD—making up one-third of diagnosed cases—with the elderly at increased risk for severe disease.
… and beyond
Zoonotic cat scratch disease only scrapes the surface when it comes to this bacterial invader. Several Bartonella species have been implicated in disease in cats and dogs. In cats, B. henselae and B. clarridgeiae are the most common culprits of subclinical infection and clinical disease. In dogs, B. vinsonii subsp. berkhoffii and B. henselae are considered most common.
For dogs and cats, subclinical infection (a positive result on tests such as polymerase chain reaction [PCR], culture or serology) in an otherwise healthy animal is the most common presentation to veterinary teams. Animals infected with Bartonella species may develop a chronic bacteremia that can last for months to years. This bacteremia is most common in younger cats (less than 1 year of age). Seroprevalence (positive antibody test results) can be particularly high in shelter, stray and feral animals (or multicat households) with an outdoor lifestyle or high cat-to-cat contact. This is likely due to higher risk of flea and tick exposure, along with scratch and bite behaviors in larger cat or dog groups. Blood transfusion may also be a risk for infection.
Clinical signs in dogs and cats
Bartonellosis is an important consideration in dogs (and less frequently cats) with infectious endocarditis or myocarditis that often results in congestive heart failure. This may present clinically as heart murmur, cough, trouble breathing and myriad systemic signs (e.g. fever, lethargy, lameness, neurologic abnormalities). Most cats infected with Bartonella species have no signs of disease (subclinical) or have vague intermittent signs that may emerge with stress, immunocompromise, coinfection with another pathogen or concurrent illness. Less frequently, infection with Bartonella species in dogs and cats has been associated with a wide range of clinical signs and inflammatory diseases (e.g. granulomatous disease, pancreatitis, peliosis hepatis). More work is needed to determine the role and management of Bartonella infection in these conditions.
Getting definitive on the diagnosis
Diagnosis of bartonellosis in cats and dogs can be challenging. This is mainly due to the difficulty with test result interpretation (e.g. subclinical infection) and the vague or intermittent nature of clinical signs. A combination of consistent clinical signs, exposure history (e.g. shelter, stray, flea and tick exposure) and a positive culture (blood or tissue) or PCR result is needed to confirm diagnosis. Screening healthy animals (sometimes requested because of zoonotic concerns, especially with immunocompromised owners) is generally not advised.
Treatment tips for cats and dogs
Doxycycline or a combination of antimicrobials is usually recommended for treatment of clinical bartonellosis. However, pet owners should be made aware that therapy is infrequently curative and is used to reduce bacterial load, improve disease signs and improve patient quality of life. Note: Treatment is recommended only for animals with overt clinical signs.
Zero in on zoonosis and vector (flea and tick) control
In the clinic, shelter and at home, prevention should focus on reducing or eliminating fleas, flea dirt and ticks and, as possible, preventing animal scratches and bites. To reduce risk, make sure owners know the human disease risk (notably CSD) and educate them on the need for precautions such as avoiding bites and scratches and lowering the burden of fleas and flea dirt. In particular, educate and discourage immunocompromised individuals from playing with or owning young cats.