Animal tuberculosis in a free-ranging fallow deer in northwest Italy: a case of “lucky strain survival” or multi-host epidemiological system complexity?

We report the first case of Mycobacterium bovis infection in a free-living fallow deer (Dama dama) in northwest Italy, the epidemiological analysis (i.e., tracing source and dissemination during outbreaks), and the potential source of infection in a historically animal tuberculosis (aTB)-free area. Gross lung and lymph node lesions were histologically consistent with a severe parasitic bronchopneumonia due to lungworms associated with severe mycobacterial infection. The lesions contained numerous densely packaged, acid-fast bacilli, raising suspicion of an active, open form of aTB. Acid-fast organisms were characterized as M. bovis SB0120-ETR 45533, one of the most common profiles in Italy. Epidemiological investigation into the most recent outbreaks caused by M. bovis SB0120-ETR 45533 within a 50-km radius of where the fallow deer was retrieved disclosed two different situations: one case involving a water buffalo (Bubalus bubalis) in 2008 and one involving a donkey in 2016. Analysis of spoligotype and VNTR-type pattern circulating and recorded in northwest Italy from 1999 to 2014 suggested that in the cases of the donkey and the fallow deer, the source of infection was most likely attributable to spillover from outbreaks in domestic species: cattle and water buffalo, respectively. According to the European Commission, aTB status of livestock does not depend on aTB cases in wildlife (Council Directive 64/432/33C of 26 June 1964); nevertheless, the primary aim of aTB eradication should include global monitoring of all susceptible species if the re-emergence of M. bovis from established wildlife reservoir is to be prevented.