# Widespread *Mycobacterium microti* detection in French wildlife in 2015

Lorraine Michelet, Krystel de Cruz, Yohann Phalente, Claudine Karoui, Sylvie Hénault, María Laura Boschiroli

Université Paris-Est, Laboratoire National de Référence de la Tuberculose, Unité de Zoonoses Bactériennes, Laboratoire de Santé Animale, ANSES, 94706 Maisons-Alfort Cedex, France

Corresponding author: maria-laura.boschiroli@anses.fr

*Mycobacterium microti* is a member of the *Mycobacterium tuberculosis* complex (MTBC), a group of major human and animal pathogens such as *M. tuberculosis* and *M. bovis*. *M. microti* was originally described as the cause of tuberculosis (TB) in wild rodents, but it can also infect other animal species and has even been described as a potential zoonotic agent (Cavanagh and others 2002; Panteix and others 2010).

A recent retrospective study reported 35 animal cases in France between 2002 and 2014 (Michelet and others 2015). It revealed an increasing number of cases in the last years due to the introduction of confirmatory molecular diagnostic tools that overcome the inherent mycobacteriology difficulties for TB diagnosis. Surprisingly, since the beginning of 2015, 20 new cases have been confirmed, which means that there has been an increase of 36% in the 12-year cumulated *M. microti* reported cases over only 9 months.

Since 2013, the wildlife TB surveillance program, Sylvatub, has disclosed the presence of this mycobacterium in wildboar and badgers (Rivière and others 2013). They represented 50% of all animal *M. microti* cases in 2013 (5 of 10 cases), 66% in 2014 (2 of 3 cases) and finally reached 85% in 2015 (17 of 20 cases). The peak of detection in these two wildlife species is mainly explained by the introduction of systematic first-line molecular tools for TB detection early in 2015.

These recent results suggest that *M. microti* prevalence in animals has been underestimated until recently. Furthermore, the presence of this pathogen has been described more and more often in wildlife in other countries (Boniotti and others 2014; Schoning and others 2013). The European wildboar and the badger seem particularly susceptible to *M. microti* infection, raising concerns about the identification and management of MTBC members in wildlife (Chiari and others 2015; Smith and others 2009). On the one hand, as regards livestock and wildlife bovine TB monitoring, this mycobacterium could lead to bovine TB confounding diagnosis, especially where its geographic distribution overlaps with that of *M. bovis*. On the other hand, even if *M. microti* is considered a rare human pathogen, its potential to cause clinical illness in humans has been demonstrated; its wide distribution in wildlife and in the environment could thus constitute a risk factor. In conclusion, further studies are needed to better characterize the epidemiology of this pathogen whose consequences for animal and human public health could have been undervalued until present.
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