Newly Discovered Tick-Borne Disease in Dogs Could Threaten Humans

A previously unknown tick-borne bacterium has been linked to several fatal infections in dogs across the United States, raising concerns that it may eventually spread to humans. The organism belongs to the same group responsible for spotted fever illnesses, many of which are known to infect people. Because related species often pose risks to humans, experts warn that this genus should always be viewed as potentially harmful.

Researchers at North Carolina State University successfully isolated the pathogen from a dog showing symptoms resembling Rocky Mountain spotted fever (RMSF), an illness transmitted through tick bites. Genetic sequencing confirmed the bacterium as a completely new member of the spotted fever family. It has been officially designated Rickettsia finnyi, named after Finny, the dog whose blood sample provided the first culture.

According to veterinary scientist Barbara Qurollo, the team first documented this novel Rickettsia species in 2020 in three canine cases. Since then, samples from sixteen additional infected dogsmostly from the Southeast and Midwesthave been analyzed, all carrying the same pathogen.

The infections produced moderate to severe clinical signs, including high fever, fatigue, and dangerously low platelet counts. Although most animals improved after receiving antibiotics, one dog died before a diagnosis could be made, another had to be euthanized, and a third relapsed following treatment and later died from nephrotic syndrome.

RMSF is among the most aggressive members of the Rickettsia group, but more than two dozen related species exist, several capable of causing illness in mammals. Advances in molecular diagnostics have revealed many of these species only recently. While humans and dogs are not central to the Rickettsia life cycle, both can act as incidental hostsespecially in regions where people, pets, and ticks share the same environment.

Because Rickettsia bacteria grow inside host cells, they are notoriously difficult to cultivate, yet culturing remains the only definitive way to identify them. Past experience shows that new species can go undetected for years; for instance, Rickettsia parkeri was known to infect animals long before the first human case was recognized in 2004, suggesting that earlier misdiagnoses may have occurred.

Genetic comparisons reveal that R. finnyi is closely related to other spotted fever pathogens. In laboratory tests, it demonstrated the ability to persist in mammalian cells for over 104 days, indicating that infected dogs could serve as a reservoir for the bacterium.

Although the transmitting tick has not been definitively identified, researchers suspect the lone star tick may be responsible. DNA from R. finnyi was previously detected in this species in Oklahoma, and its geographic distribution corresponds to the regions where infected dogs were found.

Scientists emphasize that understanding which ticks and animals host this emerging pathogen will be critical for reducing public health risks. The findings appear in the journal Emerging Infectious Diseases.

Author: Connor Blake