Novel Rickettsia Species in Dogs
Susan Little, DVM, PhD, DACVM (Parasitology), Oklahoma State University
In the Literature
Wilson JM, Breitschwerdt EB, Juhasz NB, et al. Novel Rickettsia species infecting dogs, United States. Emerg Infect Dis. 2020;26(12):3011-3015.
The Research …
Although tick-borne infection is commonly encountered in veterinary medicine, identifying the specific pathogen responsible can be difficult. Emergence of novel agents that can induce similar and, at times, severe disease increases the challenge. Diagnostic tests for tick-borne infection have been developed and validated to identify known, established organisms, but a diverse array of potential pathogens cycle in nature.
This study describes a novel spotted fever group of Rickettsia spp that caused severe disease in 3 dogs infected in the central and southern United States. Although attempts to culture the organism were unrewarding, researchers sequenced identical Rickettsia-specific targets from the blood of the 3 patients. All sequences were identical to each another and unique from other known Rickettsia spp.
The dogs shared a history of tick exposure in a region with heavy tick populations and were presented in the summer with fever, lethargy, and thrombocytopenia, leading to suspicion of tick-borne illness. All 3 patients were seropositive for antibodies reactive to Rickettsia spp on immunofluorescent assay (IFA) testing. One dog also had neutrophilic polyarthritis, which is occasionally reported in dogs with Rocky Mountain spotted fever.
One dog had protein-losing nephropathy and was euthanized after developing nephrotic syndrome. The remaining 2 dogs recovered after receiving doxycycline, prednisone, and supportive care. The novel organism was identified via PCR and sequencing of Rickettsia-specific nucleic acid targets from the blood of all 3 patients.
Studies like this are critical to understanding the diversity of tick-borne pathogens that threaten canine health. Spotted fever group Rickettsia spp cause cross-reacting antibodies detected on IFA tests, leading to a suspicion that as-yet-unrecognized agents like the one described here may be widespread.
Dogs are important sentinels for tick-borne infection risk in humans. The potential zoonotic risk posed by this agent warrants further consideration.
… The Takeaways
Key pearls to put into practice:
Novel tick-borne agents continue to be described. Recognizing classic clinical signs may allow for a successful outcome, even if the disease is caused by an unrecognized organism.
Ticks transmit a wide variety of infectious organisms. Focusing on consistent tick preventives and avoiding areas with intense tick populations can help limit risk for disease and protect dogs from infections.
Spotted fever group Rickettsia spp also infect humans. Novel infections provide another opportunity to raise awareness among pet owners about the zoonotic risk of tick-borne pathogens.