At the 2017 Western Veterinary Conference in Las Vegas, Nevada, Edward Breitschwerdt, DVM, DACVIM, and Christopher Woods, MD, discussed Bartonella infection from both human and animal perspectives, covering epidemiology, disease manifestations, potential risk to veterinary personnel, and the role of veterinarians in education and prevention.
Bartonellosis is a zoonotic bacterial infection that can lead to serious disease in animals and humans. At the 2017 Western Veterinary Conference in Las Vegas, Nevada, Edward Breitschwerdt, DVM, DACVIM, and Christopher Woods, MD, discussed Bartonella infection from both human and animal perspectives, covering epidemiology, disease manifestations, potential risk to veterinary personnel, and the role of veterinarians in education and prevention.
Our understanding of the Bartonella genus is changing rapidly, said Dr. Breitschwerdt, a professor of medicine and infectious diseases at North Carolina State University College of Veterinary Medicine in Raleigh. Advances in diagnostic technology have enabled the discovery of new Bartonella species (the current count is 36). New vectors and reservoir hosts have also been identified.
According to the Centers for Disease Control and Prevention, the most common human diseases caused by Bartonella worldwide are cat-scratch disease (caused by Bartonella henselae, vectored by cat fleas, and transmitted to people via cat scratches), trench fever (caused by Bartonella quintana and transmitted by human lice), and Carrión disease (caused by Bartonella bacilliformis and transmitted by sand flies). Reservoir hosts such as cats are usually asymptomatic carriers of the bacteria.
However, the potential spectrum of bartonellosis—and thus the potential risk to animals and humans—is wider. “We don’t know exactly who is at risk,” said Dr. Breitschwerdt, “but we do know that everyone sitting in this room is at risk. That’s the most important message that I’d like to be transmitted to you today.”
Epidemiology and Pathogenesis
Bartonella are fastidious bacteria that do not grow well in culture. The genus is closely related to Brucella, noted Dr. Breitschwerdt. These bacteria are “extremely difficult to diagnose, extremely difficult to treat, and we never know if we’ve actually cured the patient and eliminated this infection.”
Bartonella can invade many cell types, including bone marrow progenitor cells, erythrocytes, and endothelial cells. Evidence suggests that some Bartonella species can suppress the immune response, potentially predisposing patients to coinfections with other organisms.
Bartonella are maintained in mammalian reservoir hosts and transmitted between hosts by arthropod vectors. Reservoir and vector species vary according the species of Bartonella. For B. henselae, the main reservoir species are domestic dogs and cats, and the most well-known vector is the cat flea. Recent research indicates that ticks can also transmit the organism. Known mammalian hosts for various Bartonella species include rodents, rabbits, cats, dogs, ruminants, several wildlife species, and humans. In general, vector-borne disease organisms do not necessarily cause serious illness in their adapted host species but can cause severe signs in other species.
More than one Bartonella species can be transmitted from fleas to cats, said Dr. Breitschwerdt. The organisms can pass via flea feces into the environment, where, according to a recent study, they are viable for up to 9 days. Flea control is of paramount importance, he said. “We need to think of [the cat flea] as a threat risk to the family.”
Clinical Signs in Dogs and Cats
The full spectrum of disease caused by bartonellosis is not yet known, said Dr. Breitschwerdt. Sequelae of Bartonella infection in animals may include the following:
“We now know that Bartonella kills cats,” he added. Certain strains of Bartonella can induce myocarditis and endocarditis in cats even though cats are usually asymptomatic hosts.
Clinical Signs in Humans
Dr. Woods, an infectious disease specialist at the Duke Global Health Institute in Durham, North Carolina, described human manifestations of bartonellosis through a series of case reports.
Infective endocarditis may be misdiagnosed because of the difficulty in growing Bartonella in culture. “Bartonella endocarditis is one of the most frequent causes of culture-negative endocarditis,” especially in areas of the world that do not have access to the newest diagnostic technology, he said. The session included a video of a physician describing his own experience with Bartonella endocarditis. He ultimately required an aortic valve replacement.
Visceral abscesses are “a well-known, very infrequent complica- tion of cat-scratch disease,” Dr. Woods said. He described splenic abscesses in a man and visceral abscesses in a 4-year-old boy who had cat-scratch disease. The boy’s mother also developed endometritis (leading to a miscarriage) secondary to bartonellosis.
Although cat-scratch disease is usually a self-limiting condition, Dr. Woods said, complications can occur. Neurologic complications can include encephalopathy, transverse myelitis, radiculitis, cerebellar ataxia, optic neuritis, and seizures. Most acute neurologic manifestations resolve within several weeks, he noted, but some patients have chronic deficits. Dr. Woods stated that some bartonellosis patients have concurrent mental health problems (partly because of the stress of having this difficult-to-diagnose condition), but occasionally this can manifest as “Bartonella psychosis.” He described one teenage bartonellosis patient who eventually began to have hallucinations and was diagnosed with schizophrenia. Her symptoms resolved after appropriate antibiotic treatment.
Dr. Woods described the case of a veterinarian who developed deterioration of the hip joint and required hip arthroplasty. B. henselae was isolated from the excised femoral head.
Sequelae of a Needlestick Injury
One month after sustaining a needlestick while aspirating a skin lesion on a dog with a history of ehrlichiosis, a veterinarian developed headache, fever, and paresthesia in one arm. Polymerase chain reaction testing revealed Bartonella vinsonii. Her clinical signs resolved after antibiotic treatment.
Occupational Risk and the Role of Veterinarians
Veterinarians and veterinary technicians are at particular risk for bartonellosis, said Dr. Woods. In a study of veterinary personnel recruited from a large veterinary conference and a veterinary teaching hospital, 28% had at least one Bartonella species detectable in blood samples. Symptoms such as headaches and irritability were more common in participants with positive results for Bartonella. “Persistent bacteremia is frequent in self-identified high-risk populations,” he concluded.
“I believe this genus will be the biggest challenge for our profession in the context of public health,” said Dr. Breitschwerdt. He suggested that in the future when veterinarians treat a pet with fleas, the main concern will be zoonotic disease risk, not necessarily the pet’s skin condition. “The goal,” he stressed, “is to educate the family as to the risk that those fleas are posing to them.”
With regard to vector-transmitted infectious diseases, veterinarians “are the most important part of the public health infrastructure in the United States of America,” Dr. Breitschwerdt concluded. Veterinarians receive education about diseases transmitted by fleas and ticks, unlike most physicians in the United States, he said. “You cannot diagnose a disease process that is not on your differential list.”
Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University in 1994. After an internship at Auburn University College of Veterinary Medicine, she returned to North Carolina, where she has been in companion animal general practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing.