Severe pneumonia in a street rat (Rattus norvegicus) caused by Rodentibacter rarus strain RMC2

Background: Rodents are one of the most dangerous reservoirs and carriers of infectious diseases. Gradually, rats have become predominant in cities, sometimes staying in close vicinity to humans, pets and other animals. Consequently, they tend to increase the transmission risk of pathogens. Case Description: Here, we report an original case of bacterial pneumonia in a street rat (Rattus norvegicus). The rat was found dead on a street in the chief town of Marseille (France) after being run over by a car. The necropsy of the corpse revealed generalized granulomatous pneumonia in almost all the pulmonary lobes. Lung lesions, predominantly multiple fibro-inflammatory areas are preassembly to the witness of an infectious etiology. Bacterial isolation was performed from lung tissues. Colonies were identified by MALDI-TOF MS and confirmed by 16S rRNA sequencing. The following bacteria were identified: Staphylococcus cohnii, Bordetella bronchiseptica, B. parapertussi, Corynebacterium glucuronolyticum, Pelistega suis and Rodentibacter rarus. Based on histopathological diagnosis and the avoidance approach, the most likely etiological agent of the pneumonia is therefore R. rarus, a little-known Pasteurellales bacterium that is closely related to R. pneumotropicus. Conclusion: These data emphasize the severity of R. rarus infection in rodents. Thus pointing out a potential risk for other animals (dogs, cats, birds) as well as humans. The health monitoring program for rodents and rabbits pasteurellosis should now include R. rarus. Therefore, the pathological effect of Rodentibacter species and/or strains needs to be better explored