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First evidence of pyrazinamide-susceptible Mycobacterium bovis, sub-lineage La1.1, in Ireland

E Roycroft(1,2) S Mok(1,2) M Blair(5) Á O'Halloran(1) J Keane(2,3) J Wagener(1,2) B Boyle(1,2) D Brites(4) M Fitzgibbon(1,2)

1:Irish Mycobacteria Reference Laboratory; 2:Trinity College Dublin; 3:St. James's Hospital, Dublin, Ireland; 4:Swiss Tropical and Public Health Institute; 5:Mallow General Hospital, Cork, Ireland

Ireland has a strong agricultural sector. In 2021, the dairy herd alone totalled 1.6 million. Mycobacterium bovis is a zoonotic infection that could potentially infect any animal, domestic or wild, already present or introduced into the country. Its incidence is low, but not decreasing at a desirable rate. In 2022/2023, over 5% of human isolates received at the Irish Mycobacteria Reference Laboratory (IMRL) were lineage Bovis. The cattle/wildlife interface has been recognised as a potential source of transmission by the government more notably than the animal/human interface. To date, all human M bovis isolated has been intrinsically resistant to pyrazinamide (PZA).

Here, we present the first evidence of PZA-susceptible (La1.1) M. bovis in Ireland (May 2023). It was isolated from a sputum sample from an elderly patient in the rural southwest. The patient had no documented occupational history but he had kept some exotic animals in a park at his home. Phenotypic drug susceptibility testing showed that the isolate was susceptible to rifampicin, isoniazid, ethambutol, streptomycin and PZA. Whole genome sequencing was performed and the isolate was compared with other publicly-available global La1.1 strains (reference strain AF212297). It was more closely related to strains from Malawi than those found in Uganda, suggesting the possibility of further delineating this sub-lineage. More strains of La1.1 would be required to investigate this.

Without the collaboration of stakeholders under a One Health policy, the true molecular epidemiology of zoonotic tuberculosis cannot truly be measured. Until then, the threat to humans from M. bovis remains.

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