Nontuberculous Mycobacteria in Horses: A Narrative Review

SIMPLE SUMMARY: The incidence of diseases caused by nontuberculous mycobacteria (NTM) has increased in the past few years in both human and veterinary medicine. It was once thought that horses are immune to NTM infections, but there have been recent findings of NTM isolates within horses experiencing gastrointestinal, respiratory, and reproductive disorders. This literature describes the manifestations of NTM in horses, evaluates the efficacy of diagnostic and treatment methods, and discusses the zoonotic threat horses may pose in spreading NTM. Horses with NTM are most commonly presented for gastrointestinal infection, placentitis and abortion, respiratory distress, musculoskeletal abnormalities, and lymphadenitis. As of right now, genotyping diagnostic methods are the gold standard, but there has yet to be an effective treatment developed for NTM in both humans and horses. Lastly, the exact risk horses pose as a zoonotic threat to humans remains unclear, warranting further investigation. ABSTRACT: Nontuberculous mycobacteria (NTM) infections are increasing in human and veterinary medicine. Although horses were initially thought to be resistant to NTM infection, reports of horses suffering from gastrointestinal, respiratory, and reproductive diseases associated with NTM have increased in the last few decades. The aim of this literature review is to summarize the mycobacteria species found in horses, describe clinical manifestations, diagnostic and treatment approaches, and public health concerns of NTM infection in horses. Clinical manifestations of NTM in horses include pulmonary disease, lymphadenitis, soft tissue, bone infections, and disseminated disease. NTM are also linked to granulomatous enteritis, placentitis, and abortions. Currently, diagnostic methods for NTM are limited and include acid-fast microscopy, bacterial cultures, species-specific PCR assays, and gene sequencing. In humans, NTM treatment guidelines are available, but their application appears inadequate and inconsistent. In horses, treatment guidelines for NTM infections are not available. NTM are a serious public health threat as 70% of people with untreated acquired immunodeficiency syndrome (AIDS) have a chronic pulmonary disease caused by NTM. Thus, it is essential that we gain a better understanding of NTM infections in horses and their zoonotic potential.