A newly confirmed bacterial species, Rickettsia finnyi, has been identified in dogs with symptoms resembling Rocky Mountain spotted fever.
Veterinary cases from across the United States have led North Carolina State University researchers to confirm a brand-new bacterial species in the Rickettsia family. The microbe, first spotted in dogs in 2018, has now been formally classified as Rickettsia finnyi. In dogs, infections have been linked to an illness that can look a lot like Rocky Mountain spotted fever (RMSF). So far, there is no evidence that the bacterium has infected people.
What makes the finding especially noteworthy is where these bacteria live and how they spread. Spotted fever group Rickettsia (which is transmitted by ticks) includes some of the most medically important tick-borne germs known, and the group already contains more than 25 species worldwide. The best known is R. rickettsii – which causes RMSF – and it is among the most dangerous members of the genus.
For pet owners and veterinarians, the challenge is that RMSF and related infections can start with broad, nonspecific signs. Dogs and people can develop fever and lethargy, along with symptoms tied to irritation of blood vessels, including swelling, rash, and pain. Those overlaps are one reason researchers pay close attention when a new Rickettsia shows up in clinical samples.
From Initial Cases to Species Confirmation
“We first reported the novel species of Rickettsia in a 2020 case series involving three dogs,” says Barbara Qurollo, associate research professor at NC State and corresponding author of the new study.
“Since then, we received samples from an additional 16 dogs – primarily from the Southeast and Midwest – that were infected with the same pathogen. We were also able to culture the new species from the blood of one of the naturally infected dogs in that group.”
These bacteria are notoriously hard to study. Rickettsia are intracellular, meaning they grow inside cells rather than thriving easily on a lab dish.
To formally establish a new species, researchers must culture it, sequence and publish its genome, and deposit the living samples in two biobanks so other scientists can verify the work and investigate the organism themselves. Qurollo’s team succeeded in culturing the bacterium from an infected dog, clearing a major hurdle that often slows progress in tick-borne disease research.
Challenges in Culturing and Possible Tick Transmission
“Rickettsia species are difficult to culture because these organisms grow inside of cells,” Qurollo says. “While we haven’t been able to confirm which tick species transmit it yet, we think it may be associated with the lone star tick, because a research group in Oklahoma found R. finnyi DNA in a lone star tick.”
The researchers named the new species Rickettsia finnyi, after Finny, the first dog they found it in.
“By naming it after an individual dog, we wanted to honor all companion dogs that have contributed to the discovery of new pathogens that could cause serious illness in both dogs and humans,” Qurollo says.
Reference: “Isolation and Characterization of Rickettsia finnyi, Novel Pathogenic Spotted Fever Group Rickettsia in Dogs, United States” by Praveen K. Korla, Michael G. Karounos, Sarah B. Clarke, Cynthia Robveille, James M. Wilson, Edward B. Breitschwerdt, Adam J. Birkenheuer and Barbara A. Qurollo, November 2025, Emerging Infectious Diseases.
DOI: 10.3201/eid3111.250681
The work was supported by the American Kennel Club Canine Health Foundation (grant number 02983).
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