Experimental Aerosol Inoculation of Mycobacterium bovis in North American Opossums (Didelphis virginiana)

Abstract

The goal of this study was to evaluate the susceptibility of North American opossums (Didelphis virginiana) to aerosol inoculation of Mycobacterium bovis at two dose levels in order to gain information on disease pathogenesis, fecal shedding of the organism, and the potential role that opossums play in the spread of this disease in nature. Six opossums received high dose (1ϫ10 7 colony forming units (cfu) by aerosol inoculation, six opossums received low dose (1ϫ10 3 cfu inoculation, and six opossums were sham-inoculated with sterile water and served as controls. Lungs were the most frequently infected tissues, with nine of 12 inoculated opossums positive for M. bovis on culture. Gross lesions consisted of multifocal pneumonia and enlarged lymph nodes. Microscopically, granulomatous pneumonia and granulomatous lymphadenitis associated with acidfast bacilli were present in eight of 12 inoculated opossums. Fecal shedding of M. bovis was uncommon at both inoculation doses. While opossums were highly susceptible to aerosol inoculation of M. bovis, they did not become emaciated or develop widely disseminated lesions. From this study, opossums may transmit tuberculosis by aerosol infection to other opossums in close contact and serve as a source of infection to carnivores that feed upon them, however, transmission of the disease to large herbivores by fecal shedding or direct contact may be less likely.

Epizootiologic Survey of Mycobacterium Bovis in Wildlife and Farm Environments in Northern Michigan

“…Although bovine TB surveillance conducted in west Texas, USA, did not identify any infected birds (Pillai et al, 2000), there has been discussion at TB scientific meetings on bovine TB in Michigan, USA (Patrick, 2003) about the possible physical transfer of disease organisms on the feet of birds. Although we did not collect and test birds for bovine TB infection, Fitzgerald et al (2003a) reported that Rock Pigeons can become infected under experimental conditions and can shed the bacteria in feces. Hill (2005) reported a sizable number of visits to Michigan, USA, farms by Wild Turkeys, including close contact with cattle.…”

“…Our results confirm these concerns based on bovine TB prevalence ($2.5%) in these species and their frequent occurrence in barns. Opossums and raccoons were experimentally infected with M. bovis, and some individuals shed the bacteria (Fitzgerald et al, 2003b;Palmer et al, 2002). However, we do not know whether naturally infected animals of these species would shed the bacteria in the wild or merely serve as dead-end or spillover hosts.…”

Evaluating wildlife-cattle contact rates to improve the understanding of dynamics of bovine tuberculosis transmission in Michigan, USA

“…Researchers from Michigan State University, USA reported it unlikely that bTBinfected opossums pose risk of pathogen transmission to large ruminants, although they can transmit pathogens via aerosol to other opossums in close contact (Fitzgerald et al, 2003). Such close contact within tightly knit family groups is a common characteristic of wildlife hosts of bTB (Fitzgerald et al, 2003).…”

“…Researchers from Michigan State University, USA reported it unlikely that bTBinfected opossums pose risk of pathogen transmission to large ruminants, although they can transmit pathogens via aerosol to other opossums in close contact (Fitzgerald et al, 2003). Such close contact within tightly knit family groups is a common characteristic of wildlife hosts of bTB (Fitzgerald et al, 2003). Both raccoons and opossums are found to share communal dens resulting in increased interaction when resources are abundant such as around feed stockpiled for livestock (Palmer et al, 2002;Atwood et al, 2009).…”

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

“…It has been established that Brushtail possums are an ideal host for tuberculosis due to the fact that they are highly susceptible to M. bovis , shed the organism through multiple routes and have shared dens [5, 7, 11]. Virginia opossum is a known natural host of tuberculosis in the state of Michigan in the United States and previous studies have shown them to be susceptible to M. bovis by aerosol inoculation [5, 6, 12]. Additionally, Virginia opossum utilizes shared dens, and in the state of Michigan, has a high potential for significant interaction with other animals harboring tuberculosis [8].…”