Finding a Standard Course of Treatment for Bartonella infections

There are an estimated 7-15 different species of Bartonella bacteria that cause disease in people.¹ Infections with any one of these bacteria is referred to broadly as bartonellosis, and include Bartonella henselae infections, also known as cat scratch disease, Bartonella quintana infections, and Bartonella bacilliformis infections.²

There are approximately 20,000 cases of Bartonella henselae infections in the US annually.¹ It is primarily transmitted by fleas, but can also be transmitted by animal bites, scratches, or needle sticks.¹ Bartonella quintana infections are transmitted by body lice and it is unknown how many cases there are, and Bartonella bacilliformis infections are caused by sand flies in some regions of South America.²

If these infections progress, they can lead to serious complications and infections including endocarditis. Patients who are immunocompromised can be subject to serious clinical manifestations and require antimicrobial treatment. However, there is no standard course of treatment for these infections, and many doctors prescribe antibiotics based on limited data and case studies.³

“Severe disease is oftentimes found in immunocompromised patients. And in these patients, they need long, prolonged periods of antibiotics, similar to TB infection or Babesia or even Borrelia, the causative agent of Lyme disease,” Emily Olsen, PhD, said in an interview with Contagion. “And so basically, these patients have to be on antibiotics for long periods of time, sometimes even 6 months. From my approach, I'm hoping to find a treatment regimen that can essentially treat all forms of the different presentations of bartonellosis.”

From previous work done by Olsen and Monica Embers, PhD, professor of Microbiology and Immunology at Tulane University, they discovered that “B henselae treatment with single antibiotics in different media, as well as in DH82 canine macrophages, was ineffective in eliminating bacteria.”

They decided to expand their work in this area looking at different antibiotics, which were supported by case reports, as well as double and triple combination therapy in DH82 canine macrophages and biofilms.³ They tested doxycycline, gentamicin, azithromycin, azlocillin, rifampin, tobramycin, and clarithromycin.³

“We found that while monotherapy may inhibit growth extracellularly, it is ineffective when used against intracellular bacteria or pre-existing biofilms. We found that aminoglycosides in combination with either rifampin or azlocillin significantly reduced bacterial growth in multiple microenvironments,” they wrote.

Olsen and Embers presented these findings at ASM Microbe.

“I'm hoping that the way I approach the problem, which was 167 combinations, essentially, and whittling it down from there, will eliminate any kind of shot in the dark kind of antibiotic treatments, and so it will guide physicians on what patients can take. But of course, everything still has to go through animal models and clinical trials,” Olsen said.

As an underdiagnosed infection, Olsen believes it is important to recognize how it affects individuals.

“People who have Bartonella are really, truly suffering from this disease, and we really need to find an effective approach in treating them,” Olsen said.

References
1. Bartonellosis. Columbia University Medical Center. Accessed August 1, 2025. https://www.columbia-lyme.org/bartonellosis
2. About Bartonella. Centers for Disease Control and Prevention. March 3, 2025. Accessed August 1, 2025.
https://www.cdc.gov/bartonella/about/index.html
3. Multi-Drug Therapy is Required to Effectively Treat Bartonella Infection in Different Environments. ASM presentation.Session AAR-P-205. June 19-23, 2025. Los Angeles.