Maintenance of Subclinical Mycoplasma bovis Infections in American Bison (Bison bison) in the Absence of Detectable Transmission

Mycoplasma bovis is a growing threat to American bison (Bison bison) health and restoration efforts, causing significant mortality and disease in affected bison herds. Despite this, little is known about the epidemiology or clinical course of M. bovis infection in bison. In this study, we present continued observations from a cohort of naturally infected American bison, in which maintenance of subclinical M. bovis infections was previously reported. Most (8/11) surviving previously infected animals mounted a detectable immunoglobulin G (IgG) response that waned within 6-24 mo. Two bison mounted and maintained robust IgG antibody responses throughout the study period; one of these also remained quantitative PCR and culture positive throughout the study. One animal failed to mount a detectable IgG response despite becoming infected with M. bovis during the study. Also, naïve animals (n=4) were added to the environment where positive animals were previously kept, shared a water tank with known positive animals, and were finally added to the cohort and sampled at 3-mo intervals for a 2-yr follow-up period. The four naïve animals, and a calf born to one of them, remained M. bovis negative despite commingling with known positive animals in the cohort. We discuss limitations of current antemortem test approaches and the need for more accurate testing to support healthy bison restoration and management.