pathogens Article Systemic Mycobacterium kansasii Infection in Two Related Cats Petra ˇ Cerná 1,2, † , Jordan L. Mitchell 3, * , † , Joanna Lodzinska 3 , Paola Cazzini 3 , Katarina Varjonen 4 and Danièlle A. Gunn-Moore 3 1 Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado, CO 80528, USA; petra.cerna@colostate.edu 2 The University of Veterinary and Pharmaceutical Sciences Brno, 612 42 Brno, Czech Republic 3 The Royal (Dick) School of Veterinary Studies and The Roslin Institute, Easter Bush Campus, University of Edinburgh, Midlothian EH25 9RG, UK; jlodzins@exseed.ed.ac.uk (J.L.); Paola.Cazzini@ed.ac.uk (P.C.); Danielle.Gunn-Moore@ed.ac.uk (D.A.G.-M.) 4 AniCura Djursjukhuset Albano, Rinkebyvägen 21A, 182 36 Danderyd, Sweden; katarina.varjonen@anicura.se * Correspondence: jordan.mitchell@ed.ac.uk † These authors have joint credit as first author. Received: 26 October 2020; Accepted: 16 November 2020; Published: 18 November 2020   Abstract: Mycobacterial infections are a major concern in veterinary medicine because of the difficulty achieving an etiological diagnosis, the challenges and concerns of treatment, and the potential zoonotic risk. Mycobacterium kansasii, a slow-growing non-tuberculous mycobacteria, causes disease in both humans and animals. While infections have been well described in humans, where it may be misdiagnosed as tuberculosis, there are fewer reports in animals. Only four cases have been reported in the domestic cat. This case report describes systemic M. kansasii infection in two sibling indoor-only cats that presented two and half years apart with cutaneous disease that was found to be associated with osteolytic and pulmonary pathology. Infection with M. kansasii was confirmed in both cats by polymerase chain reaction on fine-needle aspirate of a lumbosacral soft tissue mass in one cat and on a tissue punch biopsy of a skin lesion in the other; interferon-gamma release assay inferred M. avium-complex and M. tuberculosis-complex infection in the two cats, respectively. Both patients made a full recovery following antimicrobial therapy with rifampicin, azithromycin, and pradofloxacin (plus N-acetyl cysteine in cat 2). This report highlights successful treatment of systemic M. kansasii mycobacteriosis in the cat and the challenge of accurately diagnosing this infection. Keywords: feline cutaneous mycobacteriosis; non-tuberculous mycobacteria; Mycobacterium kansasii; diagnostics; treatment 1. Introduction Mycobacterial infections in cats are increasingly recognised throughout many parts of the world, including Great Britain [1], continental Europe [2–5], Australia [6], and North America [7]. Broadly speaking, mycobacteria can be divided into two groups: the non-tuberculous mycobacteria (NTM) [8], and the Mycobacterium (M.) tuberculosis-complex (MTBC), which includes the causative agents of tuberculosis (TB) in cats, i.e., M. bovis and M. microti—the vole bacillus [1,9]. There are over 150 NTM species [10], many of which are important pathogens in their own right e.g., M. avium subsp. paratuberculosis, the causative agent of Johne’s disease in cattle and sheep [11], while others are opportunistic environmental saprophytes [12]. Historically, the NTM have been categorized based on their growth characteristics [13]; however, some species of mycobacteria cannot be cultivated in Pathogens 2020, 9, 959; doi:10.3390/pathogens9110959 www.mdpi.com/journal/pathogens