3.4 Dating estimates
The park was inaugurated in 1977 and personal communications from a previous employee indicates that TB cases in the park date back from the 1980’s. Thus, to better elucidate M. bovis introduction, we estimated the ages of the MRCAs (most recent common ancestor) of theM. bovis strains circulating in the safari park and results are shown in Table 1. Accordingly, the dating estimates of the MRCAs of each of the three M. bovis clusters (1 to 3, Figures 3 and 4) from the safari park ranged from 10 to 40 years before present (BP) (Table 1). In addition, the MRCA of clusters 1 and 2 dated from 23 to 47 years ago, which is also within the time frame of the park existence. In contrast, the MRCA of clusters 1, 2 and 3 dated from 50 to 103 years ago, which is older than the park inauguration. Thus, for clusters 1 and 2, and for cluster 3, it is possible that they are products of two different introduction events at the beginning of the safari park, evolving into different strains over time through persistent animal to animal transmission. Finally, another introduction event pertains to isolate TB013S13L, with a MRCA dating back from 25 to 77 years ago. The MRCA ofM. bovis and M. caprae was dated from 630 to 1,644 years BP, similar to a previous study (Zimpel et al., 2020).