A long-term study in Merino sheep experimentally infected with Mycobacterium avium subsp. paratuberculosis: clinical disease, faecal culture and immunological studies

Two longitudinal experiments involving Merino sheep challenged with either bovine or ovine strains of Mycobacterium avium subsp. paratuberculosis (Map) have been conducted over a period of 54 and 35 months, respectively. Blood samples for the interferon-gamma test, the absorbed ELISA and faecal samples for bacteriological culture were taken pre-challenge and monthly post-challenge. Infections were induced with either a bovine or ovine strain of Map in separate experiments with infections being more easily established, in terms of faecal bacterial shedding and clinical disease when the challenge inoculum was prepared from gut mucosal tissue than cultured bacteria. The patterns of response for shedding and clinical disease were similar. Cell-mediated immune responses were proportionally elevated by at least an order of magnitude in all sheep dosed with either a bovine or ovine strain of Map. Conversely, antibody responses were only elevated in a relatively small proportion of infected sheep. Neither of the clinically affected tissue challenged sheep developed an antibody response despite the presence of persistent shedding and the development and decline in cell-mediated immunity. The results indicated that for sheep the interferon-gamma test may be useful for determining if a flock has been exposed to ovine Johne's disease.     

Salmonella in captive and wild Tasmanian devils (Sarcophilus harrisii) in Tasmania

Translocation of Tasmanian devils (Sarcophilus harrisii) is a common strategy for recovery of the species as carried out by the Save the Tasmanian Devil Program. Dasyurids including the endangered Tasmanian devil are well known to asymptomatically harbour the zoonotic bacteria Salmonella enterica in their intestinal tracts. Testing for Salmonella is a routine component of pretranslocation health testing, so a statewide microbiological survey of captive and wild devils was implemented in order to understand prevalence and common Salmonella serotypes, and inform decision-making when positive cultures are identified. This preliminary study identified a significantly higher proportion of Salmonella isolations in wild compared with captive devils. Mississippi and Typhimurium were the most common serotypes, followed by Lexington, Bovismorbificans, Kottbus and Amsterdam. Given the common finding of Salmonella in wild devils and the range of serotypes involved, in addition to numerous isolations in domestic species and humans, it is unlikely that the release of small numbers of captive devils to the wild in Tasmania poses a significant risk to the destination ecosystem. Ongoing monitoring of devils is required as the stress of acclimatisation could predispose devils to clinical disease. Appropriate personal protective attire is pertinent to protect personnel handling animals from this zoonotic infection.