Mycobacterium microti at the Environment and Wildlife Interface

Abstract

An unexpected high presence of Mycobacterium microti in wild boar in Northern Italy (Garda Lake) has been reported since 2003, but the factors contributing to the maintenance of this pathogen are still unclear. In this study, we investigated the presence of M. microti in wild rodents and in water and soil samples collected at wild boar aggregation areas, such as watering holes, with the aim of clarifying their role in M. microti transmission. In total, 8 out of 120 captured animals tested positive for the Mycobacterium tuberculosis complex (MTBC) as assessed by real-time PCR, and six samples were confirmed to be M. microti. A strain with a genetic profile similar to those previously isolated in wild boars in the same area was isolated from one sample. Of the 20 water and 19 mud samples, 3 and 1, respectively, tested positive for the presence of MTBC, and spacer oligotype SB0118 (vole type) was detected in one sample. Our study suggests that wild rodents, in particular Apodemus sylvaticus, Microtus sp. and Apodemus flavicollis, play roles in the maintenance of M. microti infections in wild boar through ingestion or by contact with either infected excreta or a contaminated environment, such as at animal aggregation sites.

Keywords: Mycobacterium microti; Mycobacterium tuberculosis complex; environmental samples; rodents.

Figure 1

Map of the study area: (A) = Italy with the macro region area denoted; (B) = Lombardy region and Lake Garda area, BS represents Brescia Province; (C) = Alto Garda Bresciano Park area denoted in green; (D) = Gargnano area with study sites. Red circles indicate sites positive for M. microti (9 and 11 positive rodent samples; 10 and 12 positive environmental samples). 1 = Via Costa 1; 2 = Via Costa 2; 3 = Passo di Magno 1; 4 = Passo di Magno 2; 5 = Briano; 6 = Lama; 7 = Navone; 8 = Fa; 9 = Sembrune; 10 = Bocca Lovere; 11 = Bertu; 12 = Praa 1; 13 = Praa 2; 14 = Praa 3. Further details on the sites can be found in Table S1 (Supplementary Materials).