Scientists discover new species of tick-borne bacteria dangerous to dogs

Researchers at North Carolina State University’s (NCSU) College of Veterinary Medicine have identified a new species of Rickettsia bacteria—and a new vector for Rocky Mountain spotted fever (RMSF) in dogs.

According to a new study, the previously unknown species belongs to the Rickettsia genus, which also contains Rickettsia rickettsii, tick-borne bacteria that cause RMSF in both dogs and humans. The researchers discovered the new species while working out of NCSU’s Vector-Borne Disease Diagnostic Lab.

Rickettsia pathogens are categorized into four groups, with the RMSF group containing more than 25 species worldwide. Of these, R. rickettsii is one of the most virulent, and the only bacteria in the RMSF group known to cause clinical disease among dogs in North America.

The symptoms of RMSF in dogs are similar to those in people: fever, lethargy, weight loss, rash, and pain, among others. Over the past couple of years, three dogs in different states—Tennessee, Illinois, and Oklahoma—exhibited symptoms of RMSF.

When the researchers sequenced the DNA in blood samples collected from those three dogs, they only got a 95% match to R. rickettsii—so they dug deeper.

Corresponding author Barbara Qurollo, MS, DVM, an associate research professor of Small Animal Internal Medicine at NCSU, told NEWStat how they discovered the new species.

“We tested for Rickettsia by both polymerase chain reaction (PCR), which detects the actual pathogen DNA in a blood sample, and serology, which detects antibodies made by the patient against spotted fever group Rickettsia.”

Qurollo said the PCR test is designed to identify DNA from a wide range of Rickettsia pathogens—even some that have not yet been discovered. “When we sequenced the DNA of the organism in the sick dogs’ blood and compared it with other known Rickettsia, we realized this was a Rickettsia species that had not been reported yet.” The serology test showed that the dogs were also antibody positive, she added, “as would be expected if the dog was sick due to RMSF.”

All three dogs showed clinical signs of RMSF, including fever and abnormally low blood platelet levels. And the new species seems to be thriving after the initial study: Qurollo and her colleagues discovered the new species in four other dogs whose samples were sent to the Vector-Borne Disease Diagnostic Lab.

As to what part of the country this new species of bacteria might be native to, Qurollo says they’re still investigating. “But the [infected] dogs lived primarily in the southern and midwestern US.”

Whether or not the new species is capable of infecting humans is unknown, but Qurollo said her team is working on that too, and they plan to collaborate with public health officials to eventually test human samples.

Another unknown: the new species’ name.

Qurollo said it could be a while before it has one: “Once we know more about the organisms, we’ll then suggest a name.”

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