Disseminated Nocardiosis Caused by Nocardia farcinica in Two Puppy Siblings

SIMPLE SUMMARY: Clinical infections caused by bacteria belonging to the genus Nocardia spp. are sporadic in humans and animals living in tropical areas; however, recent reports suggest their increasing incidence, including in non-tropical countries. Systemic nocardiosis due to Nocardia farcinica may lead to neurologic manifestations in people and similar findings have been reported from infected dogs; therefore, dogs could represent a suitable experimental model for understanding the epidemiology and pathogenetic mechanisms of human infections. Despite Nocardia spp. not generally causing outbreaks, these may arise in human hospitals and, as reported with this study for the first time, in canine breeding establishments. Our case report describes the clinical, pathological and microbiological findings associated with fatal systemic infection by N. farcinica in two puppies, discussing the current epidemiology in humans and dogs, known pathogenesis and available diagnostics. Overall, our cases displayed pathologic and microbiologic similarities with previously reported human systemic N. farcinica infections. In light of the often difficult-to-treat nature of systemic nocardial infections, their neglected and re-emerging status, zoonotic nature and outbreak potential, investigation of canine models may help gain insights of the virulence, clinical-epidemiological features, predisposing factors and identification of Nocardia spp. strains isolated from human, animal and environmental sources. ABSTRACT: Systemic nocardiosis due to Nocardia farcinica has not been reported in canine outbreaks. Two 14-week-old female Dogue de Bordeaux siblings presented with fever and severe, acute onset limb lameness; traumatic lesions with evidence of infection were identified over the lame limbs of both dogs. The patients were euthanised owing to lack of therapeutic response and rapid escalation to systemic infection with central nervous system manifestations. The post-mortem changes consisted of multiple disseminated abscesses, mainly affecting the skin and subcutis at the limb traumatic injuries, local and hilar lymph nodes, lung, kidney and brain. Bacterial culture and identification via MALDI-TOF and 16S rRNA sequencing revealed Nocardia farcinica from several of these sites in both dogs. Clinical significance of the isolate was supported by cytology of the post-mortem organs’ impression smears showing numerous branching filamentous bacteria associated with inflammation. The organism displayed marked multidrug-resistance. No history of immunosuppression was available, and immunohistochemistry ruled out viral pathogens as canine distemper and parvovirus. N. farcinica should be considered as a potential differential cause of sudden lameness and systemic infection in dogs with traumatic skin lesions over the limbs. This is the first reported small-scale outbreak of systemic nocardiosis in dogs due to N. farcinica.