Examination of Mycobacterium avium subspecies paratuberculosis mixed genotype infections in dairy animals using a whole genome sequencing approach

Many pathogenic mycobacteria are known to cause severe disease in humans and animals. M. avium subspecies paratuberculosis (Map) is the causative agent of Johne's disease a chronic wasting disease affecting ruminants such as cattle and sheep, responsible for significant economic losses in the dairy and beef industries. Due to the lack of treatment options or effective vaccines, mitigating losses can be difficult. In addition the early stages of Map infection may occur in asymptomatic hosts that continue to shed viable bacteria in their faeces, leading to the infection of other healthy animals. Using multi-locus short sequence repeat (ML-SSR) analysis we previously reported that individual Johne's positive dairy cattle from farms across the island of Newfoundland were infected by Map with multiple SSR-types simultaneously. The occurrence of multiple mixed genotype infections has the potential to change pathogen and disease dynamics as well as reduce the efficacy of treatments and vaccines. Therefore, we conducted whole genome sequencing (WGS) and single nucleotide polymorphism (SNP) analysis on a subset of these isolates for a more in-depth examination. We also implemented a PCR assay using two discriminatory SNPs and demonstrated the incidence of a mixed infection by three genotypically diverse Map isolates in a single animal. In addition results show that WGS and SNP analysis can provide a better understanding of the relationship between Map isolates from individual and different animals. In the future such studies on the occurrence of mixed genotype infections could potentially lead to the identification of variable pathogenicity of different genotypes and allow for better tracking of Map isolates for epidemiological studies.