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New species of infectious Rickettsia bacteria found in dogs

Researchers at NC State University have identified a new species of Rickettsia bacteria that could cause disease in dogs and humans. The new species is part of the group that includes Rickettsia rickettsii, a bacteria that is carried by ticks and causes Rocky Mountain Spotted Fever (RMSF).

Rickettsia pathogens are categorized into four groups, with the spotted-fever group containing more than 25 species worldwide. Of these, R. rickettsii is one of the most virulent and dangerous. It is also the only known spotted fever group Rickettsia that causes clinical disease among dogs in North America

The symptoms in dogs are similar to those in people, including fever, lethargy, weight loss, swelling, rash, and pain. Over the last couple of years, three dogs across different states – Tennessee, Illinois and Oklahoma – exhibited the symptoms of RMSF. 

When researchers at NC State sequenced the DNA in blood samples collected from the dogs, they did not get a complete match to R. rickettsii. 

“Often, antibodies from other spotted fever group Rickettsia will cross-react in antibody tests for RMSF,” said study co-author Professor Barbara Qurollo. “So to be sure what we’re dealing with, we also look at the genetic information via PCR and that’s how we found that this is a new organism.”

In collaboration with PCR technician and study first author James Wilson, Professor Qurollo conducted further tests to take a closer look at five different regions of the bacteria’s DNA. The team also used a phylogenetic tree analysis to place the new Rickettsia firmly within the spotted fever group.

“We’re going to continue looking for this Rickettsia species, determine its geographical range and try to better characterize it – it’s a slow process, but high on our radar,” said Professor Qurollo. 

“So far in 2020 we’ve detected this new Rickettsia species in four more dogs residing in the southeastern and midwestern U.S. We’re also asking veterinarians to collect the ticks associated with dogs who show symptoms when possible, and we’re collaborating with researchers in Oklahoma to collect ticks in the environment for testing. This will help us determine what tick species may be transmitting this particular bacteria.”

“Another question we would like to answer is whether this new Rickettsia species also infects people. Dogs are great sentinels for tick-borne diseases – they have high rates of exposure to ticks and the ability to become infected with many of the same tick-borne pathogens that infect people. We hope to take a ‘One Health’ approach to this new pathogen and collaborate with scientists in human medicine as well.”

The study is published in the journal Emerging Infectious Diseases.

By Chrissy Sexton, Staff Writer

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