Experimental Aerosol Inoculation and Investigation of Potential Lateral Transmission ofMycobacterium bovisin Virginia Opossum (Didelphis virginiana)

Abstract

An endemic focus of Mycobacterium bovis (M. bovis) infection in the state of Michigan has contributed to a regional persistence in the animal population. The objective of this study was to determine if Virginia opossums (Didelphis virginiana) contribute to disease persistence by experimentally assessing intraspecies lateral transmission. One wild caught pregnant female opossum bearing 11 joeys (young opossum) and one age-matched joey were obtained for the study. Four joeys were aerosol inoculated with M. bovis (inoculated), four joeys were noninoculated (exposed), and four joeys plus the dam were controls. Four replicate groups of one inoculated and one exposed joey were housed together for 45 days commencing 7 days after experimental inoculation. At day 84 opossums were sacrificed. All four inoculated opossums had a positive test band via rapid test, culture positive, and gross/histologic lesions consistent with caseogranulomatous pneumonia. The exposed and control groups were unremarkable on gross, histology, rapid test, and culture. In conclusion, M. bovis infection within the inoculated opossums was confirmed by gross pathology, histopathology, bacterial culture, and antibody tests. However, M. bovis was not detected in the control and exposed opossums. There was no appreciable lateral transmission of M. bovis after aerosol inoculation and 45 days of cohabitation between infected and uninfected opossums.

Performance of Diagnostic Tests for Bovine Tuberculosis in North American Furbearers and Implications for Surveillance

“…Examination of pathology and mycobacterial culture results from early in the course of surveillance led to the conclusion that furbearers in Michigan were likely to be spillover hosts only (Bruning‐Fann et al., , ) and were likely playing no significant role in the maintenance of bTB nor its transmission to livestock (de Lisle et al., ; Schmitt et al., ). Since that time, data from a variety of experimental (Palmer et al., ; Johnson et al., ; Berentsen et al., ; Fenton et al., ) and field (Berentsen et al., ) studies in multiple species have thus far confirmed those early conclusions. Although unsupported by the accumulated data, some continue to believe that furbearers play a significant role in cattle herd infections (Atwood et al., ; Witmer et al., ).…”

Surveillance and movements of Virginia opossum (Didelphis virginiana) in the bovine tuberculosis region of Michigan

“…While numerous studies on captive inoculated medium-sized mammals have stated that smalland medium-sized mammals likely do not shed enough M. bovis to be considered as reservoirs for M. bovis [15,18], medium-sized mammals such as brushtail possum in New Zealand and badgers in the UK and Ireland are considered primary reservoirs of M. bovis [41,42]. Although overall sample size limited statistical significance, 13 positive medium-sized mammals were from within the bTB core area while only one was from outside the bTB core area.…”

“…Although overall sample size limited statistical significance, 13 positive medium-sized mammals were from within the bTB core area while only one was from outside the bTB core area. While numerous studies on captive inoculated medium-sized mammals have stated that small- and medium-sized mammals likely do not shed enough M. bovis to be considered as reservoirs for M. bovis [15, 18], medium-sized mammals such as brushtail possum in New Zealand and badgers in the UK and Ireland are considered primary reservoirs of M. bovis [41, 42]. Furthermore, prevalence of M. bovis in free-ranging white-tailed deer has held steady for the past 4 years at just below 2% [43] which is lower than prevalence for opossum and raccoon in our study.…”

“…Previous research has documented considerable shedding of M. bovis by free-ranging European badgers but little similar information exists for medium-sized mammals in Michigan [15,16]. Studies have shown that opossum are susceptible to aerosolized inoculation [15], but lateral transmission was not documented when infected opossum were cohabited with naive opossum for 45 days [18]. Studies have shown that opossum are susceptible to aerosolized inoculation [15], but lateral transmission was not documented when infected opossum were cohabited with naive opossum for 45 days [18].…”

“…Surveillance of medium-sized mammals in Michigan for M. bovis has found that numerous mammals may be spillover hosts but little research has been conducted to understand the amount of shedding for free-ranging mammals other than white-tailed deer (but see [17]). Studies have shown that opossum are susceptible to aerosolized inoculation [15], but lateral transmission was not documented when infected opossum were cohabited with naive opossum for 45 days [18]. Several species of mammals have been documented to use stored feed and farm structures (e.g.…”