Surveillance of Bovine Tuberculosis and Risk Estimation of a Future Reservoir Formation in Wildlife in Switzerland and Liechtenstein

Abstract

Bovine tuberculosis (bTB) caused by Mycobacterium bovis or M. caprae has recently (re-) emerged in livestock and wildlife in all countries bordering Switzerland (CH) and the Principality of Liechtenstein (FL). Comprehensive data for Swiss and Liechtenstein wildlife are not available so far, although two native species, wild boar (Sus scrofa) and red deer (Cervus elaphus elaphus), act as bTB reservoirs elsewhere in continental Europe. Our aims were (1) to assess the occurrence of bTB in these wild ungulates in CH/FL and to reinforce scanning surveillance in all wild mammals; (2) to evaluate the risk of a future bTB reservoir formation in wild boar and red deer in CH/FL. Tissue samples collected from 2009 to 2011 from 434 hunted red deer and wild boar and from eight diseased ungulates with tuberculosis-like lesions were tested by direct real-time PCR and culture to detect mycobacteria of the Mycobacterium tuberculosis complex (MTBC). Identification of suspicious colonies was attempted by real-time PCR, genotyping and spoligotyping. Information on risk factors for bTB maintenance within wildlife populations was retrieved from the literature and the situation regarding identified factors was assessed for our study areas. Mycobacteria of the MTBC were detected in six out of 165 wild boar (3.6%; 95% CI: 1.4–7.8) but none of the 269 red deer (0%; 0–1.4). M. microti was identified in two MTBC-positive wild boar, while species identification remained unsuccessful in four cases. Main risk factors for bTB maintenance worldwide, including different causes of aggregation often resulting from intensive wildlife management, are largely absent in CH and FL. In conclusion, M. bovis and M. caprae were not detected but we report for the first time MTBC mycobacteria in Swiss wild boar. Present conditions seem unfavorable for a reservoir emergence, nevertheless increasing population numbers of wild ungulates and offal consumption may represent a risk.

Detection and Molecular Characterization of Mycobacterium microti Isolates in Wild Boar from Northern Italy

“…bovis is the most frequently isolated agent, but occasionally M. microti is also isolated from wild boar (34,36). In the area of study, the presence of M. bovis was marginal, with only four positive samples isolated in 2005 (2) and 2006 (2) from CO and VA.…”

“…As a result of these examinations, the presence of Mycobacterium strains in wild boar was reported (27,36,41). Both M. bovis and M. microti were isolated from wild boars in this area, and recently, M. microti was also detected using direct real-time PCR in tissue samples from two wild boars from a neighboring area in Switzerland (34).…”

“…In particular, the presence of MTBC in the wild boar has been reported in several European countries, including Italy (27)(28)(29)(30)(31)(32)(33)(34).…”

Zoonotic Aspects of Tuberculosis: Disease of the past or re-emerging zoonosis?

“…This could at least partially be attributed to the fact that over half of the infected humans diagnosed in BTB free countries originated from another country where they contracted M. bovis prior to immigration. In other cases zoonotic TB could have come from infected cattle or other species present in officially tuberculosis free countries (European Food Safety Authority 2013; Schoning et al 2013).…”

“…Although the risk for zoonotic transmission is very low, undiagnosed bovine cases progressing to advanced stages of disease may present a source of infection in isolated cases as reported in Germany, The Netherlands, Austria and Switzerland (Schoning et al 2013), (www.promed.org).…”