Lining the small intestine with mycobacteriophages protects from <i>Mycobacterium avium</i> subsp. <i>paratuberculosis</i> and eliminates fecal shedding

Johne's disease (JD), a chronic, infectious enteritis caused by <i>Mycobacterium avium</i> subsp. <i>paratuberculosis</i> (MAP), affects wild and domestic ruminants. There is no cure or effective prevention, and current vaccines have substantial limitations, leaving this disease widespread in all substantial dairy industries causing economic, and animal welfare implications. Mycobacteriophages (MPs) have been gaining interest in recent years and are proposed as a promising solution to curtailing MAP infection. Using a well-validated infection model, we have demonstrated the preventative potential of MPs to protect dairy calves against MAP infection. Calves were supplemented daily with a phage cocktail from birth till weaning at 2 m of age and inoculated with MAP at 2 wk of age. Infection status was measured for 4.5 mo through blood, fecal, and postmortem tissue samples. Our findings highlight the remarkable efficacy of orally administered MPs. Notably, fecal shedding of MAP was entirely eliminated within 10 wk, in contrast to the infected control group where shedding continued for the entirety of the trial period. Postmortem tissue culture analysis further supported the effectiveness of MPs, with only 1 out of 6 animals in the phage-treated group testing positive for MAP colonized tissues compared to 6 out of 6 animals in the infected control group. Additionally, plaque assay results demonstrated the ability of phages to persist within the intestinal tract. Collectively, these results underscore the potential of orally administered MP cocktails as a highly effective intervention strategy to combat JD in dairy calves and by extension in the dairy industry.