LAUSR

Abstract: This study investigated a previously unreported species of Helicobacter and associated cardiac inflammation in common degus (Octodon degus) at the Bronx Zoo. Lymphohistiocytic and/or lymphoplasmacytic cardiac inflammation was identified in 109 of 242 degu necropsies between 2000 and 2022. Polymerase chain reaction (PCR) targeting the Helicobacter 16S gene was performed on frozen cardiac tissue from 50 degus with (n = 27) or without (n = 23) carditis. Testing was positive in 16 degus with moderate or severe carditis, negative in 11 degus with minimal or mild carditis, negative in 22 degus without carditis, and positive in one degu without carditis. A positive correlation between PCR positivity and cardiac inflammation was identified from a Fisher's exact test (P < 0.01). Steiner staining was positive for intralesional spiral-shaped bacteria in cardiac tissue from PCR-positive degus (n = 10) and negative in PCR-negative degus (n = 33). Three nondegu rodents with carditis were also PCR positive for the novel Helicobacter. Chromogenic in situ hybridization (CISH) analysis targeting Helicobacter sp. nucleic acid in cardiac tissue was positive in 16 PCR-positive degus with carditis, negative in 33 PCR-negative degus, and positive in the three PCR-positive nondegu rodents. DNA sequencing, sequence alignment and comparison with known Helicobacter spp. through phylogenetic analysis showed that this bacterium, provisionally named Helicobacter sp. ‘degu’, is likely novel and forms a unique branch point within a larger clade that contains Helicobacter spp. from reptile hosts. Further studies are needed to elucidate a causative role for this bacterium as a pathogen in degus and assess implications for captive animal management and disease risk for degus and other Rodentia species.