Novel Rickettsia Species Infecting Dogs, United States.

James M Wilson,Nicholas B Juhasz,Barbara A Qurollo,Edward B Breitschwerdt,Henry S Marr,Joao Felipe De Brito Galvão,Carmela L Pratt

doi:10.3201/eid2612.200272

Abstract

In 2018 and 2019, spotted fever was suspected in 3 dogs in 3 US states. The dogs had fever and hematological abnormalities; blood samples were Rickettsia seroreactive. Identical Rickettsia DNA sequences were amplified from the samples. Multilocus phylogenetic analysis showed the dogs were infected with a novel Rickettsia species related to human Rickettsia pathogens.

Highlights

In 2018 and 2019, spotted fever was suspected in 3 dogs in 3 US states
We report similar illnesses among 3 dogs from different US states associated with tick exposures occurring in summer months
All 3 cases demonstrated fever, lethargy, and thrombocytopenia, abnormalities commonly associated with Rocky Mountain spotted fever (RMSF)

Summary

Examination and treatment

Febrile (39.8°C); lethargy; Febrile (40.1°C); lethargy; dehydration; examination. +/− hepatomegaly joint effusion (elbow, carpus, and tarsus); abdominal pain arthropathy; shifting leg lameness. For sequences from case 3: 23S-5S ITS, MT050448; htrA (17 kDa), MT050446; mmpA-purC ITS, MT066187; gltA, MT050445; and ompA, MT050447. By August 30, 2019, the dog’s anemia and thrombocytopenia worsened, despite treatment with doxycycline and prednisone. Prednisone and mycophenolate were administered for presumptive immune-mediated thrombocytopenia, and within 3 weeks, the platelet count normalized and titers increased by 4-fold. We obtained identical Rickettsia DNA gene sequences from each dog’s blood specimen. Multilocus phylogenetic tree of Rickettsia spp. obtained from a dog with Rocky Mountain spotted fever–type symptoms in 2019 (bold) compared with reference sequences. We used 2,576 nucleotides concatenated from regions within 3 genes (gltA, htrA, and ompA) and 2 intergenic spacer regions (23S-5S and mmpA-purC). We used the Rickettsia sequences from case 3 to generate a phylogenetic tree (Table 2) based on concatenated novel Rickettsia sp. We attempted cell culture isolation of the Rickettsia sp. from whole blood but were unsuccessful (Appendix, https://wwwnc.cdc.gov/EID/ article/26/12/20-0272-App1.pdf)

Conclusions

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