Abstract
Zoonotic tuberculosis is a risk for human health, especially when animals are in close contact with humans. Mycobacterium tuberculosis was cultured from several organs, including lung tissue and gastric mucosa, of three captive elephants euthanized in a Swiss zoo. The elephants presented weight loss, weakness and exercise intolerance. Molecular characterization of the M. tuberculosis isolates by spoligotyping revealed an identical profile, suggesting a single source of infection. Multilocus variable-number of tandem-repeat analysis (MLVA) elucidated two divergent populations of bacteria and mixed infection in one elephant, suggesting either different transmission chains or prolonged infection over time. A total of eight M. tuberculosis isolates were subjected to whole-genome sequence (WGS) analysis, confirming a single source of infection and indicating the route of transmission between the three animals. Our findings also show that the methods currently used for epidemiological investigations of M. tuberculosis infections should be carefully applied on isolates from elephants. Moreover the importance of multiple sampling and analysis of within-host mycobacterial clonal populations for investigations of transmission is demonstrated.
Highlights
Infections with several members of the Mycobacterium tuberculosis complex (MTBC) can cause tuberculosis (TB) in both captive and free-ranging wildlife species, representing a considerable zoonotic risk[1,2,3,4]
While in some species, such as cattle, M. tuberculosis infections are self-limiting and persistence of the pathogen into the population does not occur without exposure to humans[11,17], cases where M. tuberculosis was maintained for a prolonged time within certain wildlife populations have been reported[14]
In contrast to the trunk wash results, necropsy and bacteriological culture confirmed shedding of M. tuberculosis based on the positive culture results from the trunk mucosa, tracheobronchial and pharyngeal swab in two out of three elephants
Summary
Infections with several members of the Mycobacterium tuberculosis complex (MTBC) can cause tuberculosis (TB) in both captive and free-ranging wildlife species, representing a considerable zoonotic risk[1,2,3,4]. Modern phylogenetic analysis defined MTBC into seven major lineages adapted to humans and two lineages adapted to various wild and domestic animal species[7]. Some wildlife species are recognized for their role of maintenance host, acting as a reservoir and transmitting the pathogens into domestic livestock, companion animals or human beings[5,9]. While in some species, such as cattle, M. tuberculosis infections are self-limiting and persistence of the pathogen into the population does not occur without exposure to humans[11,17], cases where M. tuberculosis was maintained for a prolonged time within certain wildlife populations have been reported[14]. The privacy rights of the zoo were fully protected and the obtained data were de-identified
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