Researchers have identified a new type of rickettsia bacteria that can cause significant illness in dogs and humans.
This new, as yet unnamed species, originally identified in three dogs, belongs to the group of typhus Rickettsia, which also includes Rickettsia rickettsii, the bacteria that cause Rocky Mountain Spotted Fever (RMSF).
Rickettsia pathogens fall into four groups; Of these, the spotted fever group Rickettsia (which transmit ticks) is the most commonly known and contains the most commonly identified species. There are more than 25 species of tick-borne rickettsia species in the typhus group worldwide, with R. rickettsii being one of the most virulent and dangerous.
For dogs, R. rickettsii is the only known typhus rickettsia group that causes clinical disease in North America. Symptoms of RMSF in dogs and humans are similar, including fever, lethargy, weight loss, and symptoms related to vascular inflammation such as swelling, rash, and pain.
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Blood samples were taken from three dogs from three different states (Tennessee, Illinois, and Oklahoma) exposed to ticks and RMSF-associated symptoms to test for R. rickettsii in 2018 and 2019. While the samples reacted positive to antibody tests for R. rickettsii, the DNA they received was only 95% similar to R. rickettsii when the researchers amplified the polymer pathogen DNA from the samples using the polymerase chain reaction (PCR).
“Antibodies from the other spotted fever group, Rickettsia, often react to RMSF in antibody tests,” says Barbara Qurollo, Associate Research Professor at North Carolina State University and the corresponding author of a paper describing the work. “To make sure what we’re dealing with, we also look at the genetic information using PCR and found that this is a new organism.”
The initial PCR work prompted Qurollo and James Wilson, a PCR technician at NC State and lead author of the study, to pursue the new bacteria. They performed additional PCRs to amplify different genes, examined five different regions of the bacterial DNA, and compared them to the sequenced DNA of other Rickettsia groups. They also performed a phylogenetic tree analysis which enabled them to firmly place the new rickettsia in the typhus group.
Before naming this new Rickettsia species, Qurollo and colleagues would like to cultivate the organism in order to be able to better characterize the new species. Until now, it has been difficult to cultivate Rickettsia species from a small amount of a clinical specimen.
“We’ll keep looking for this rickettsia species, determining its geographic range, and trying to better characterize it – it’s a slow process, but high on our radar,” says Qurollo. “So far we have discovered this new Rickettsia species in 2020 in four other dogs in the Southeast and Midwest of the United States.
“We are also asking vets to collect ticks from dogs that show symptoms whenever possible, and we are working with researchers in Oklahoma to collect ticks in the area for testing. This helps us determine which types of ticks can transmit these particular bacteria.
“Another question we want to answer is whether this new species of rickettsia also infects humans. Dogs are great watchmen for tick-borne diseases – they are frequently exposed to ticks and can become infected with many of the same tick-borne pathogens that infect humans. We hope that we can take a one-health approach to this new pathogen and also work with scientists in human medicine. “
The work appears in the journal Emerging Infectious Diseases. The PCR work took place in the NC State’s Vector Borne Disease Diagnostics Lab at the College of Veterinary Medicine.