12/18/2025
New Tick-Borne Bacterium Rickettsia finnyi Linked to Severe Illness in Dogs, Possible Human Risk.
A newly identified tick-borne pathogen, Rickettsia finnyi, has been linked to severe and sometimes fatal infections in dogs across the southeastern and midwestern United States. Scientists warn that the bacterium—closely related to species that cause Rocky Mountain spotted fever—may also pose a threat to humans.
Researchers at North Carolina State University have successfully cultured the bacterium from a sick dog showing symptoms similar to Rocky Mountain spotted fever, including fever, lethargy, and dangerously low blood platelet counts. Genome sequencing confirmed the organism represents a previously unknown species within the spotted fever group.
Since first detecting the pathogen in 2020, the NC State team has identified R. finnyi in 17 dogs. While most recovered with antibiotic treatment, several suffered severe complications, and at least two died. Laboratory tests show the bacterium can survive in mammalian cells for more than 100 days, raising concerns that pets could act as reservoirs.
Although the tick species responsible for transmitting the pathogen remains unconfirmed, researchers suspect the lone star tick, whose geographic range overlaps with the dogs’ locations and in which R. finnyi DNA has been detected. Given that many Rickettsia species can infect both animals and humans, scientists emphasize the need for close surveillance to determine possible public health risks.
The findings were published in Emerging Infectious Diseases.
