Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 26, 2000
Publication Date: N/A
Interpretive Summary: In 1994, a free-ranging, white-tailed deer (Odocoileus virginianus) in Michigan was diagnosed with tuberculosis due to Mycobacterium bovis. Subsequent surveys in northeast Michigan have identified the first known epidemic of tuberculosis in white-tailed deer. Information is lacking on the pathogenesis and transmissibility of M. bovis infection in white-tailed deer. In order to determine the efficiency with which deer transmit tuberculosis to each other, and the routes by which such transmission occurs, we exposed non-inoculated deer to experimentally inoculated deer. Sixty-nine days after co-mingling, all in-contact deer were infected and subsequently developed tuberculosis. Experimentally inoculated deer shed M. bovis in nasal secretions, saliva, feces, and urine. In-contact infected deer also shed M. bovis in nasal secretions and saliva. Hay and pelleted feed in some pens were found to contain M. bovis at multiple times throughout the experiment. This study shows that tuberculous deer efficiently transmit M. bovis to other deer in close contact. Lesion distribution in in-contact exposed deer suggests aerosol transmission as a likely means of infection, however, contamination of shared feed also must be considered. Wildlife managers in tuberculosis endemic areas should discourage practices that encourage unnatural gathering of deer, such as artificial feeding. Gathering increases the likelihood of direct and indirect transmission of tuberculosis.
Technical Abstract: Surveys of free-ranging deer in Michigan have identified the first known epidemic of tuberculosis in white-tailed deer. Information is lacking on the transmissibility of Mycobacterium bovis among deer. To determine the efficiency and routes of transmission between deer we exposed non-inoculated deer to deer that had been experimentally inoculated by intratonsilar instillation of 2x10*8 CFU of M. bovis. Two in-contact deer were penned with 2 experimentally inoculated deer; each pen having a single source of water, hay, and pelleted feed. Sixty-nine days after introduction, all in-contact deer manifested delayed type hypersensitivity (DTH) reactions to M. bovis purified protein derivative (PPD). All experimentally inoculated deer were removed one-hundred-twenty days after inoculation. One-hundred-fifty-nine days after introduction, 4 new non-inoculated deer were housed with the remaining original in-contact deer such that 2 new in-contact deer were penned with 2 original in-contact deer. One-hundred days after introduction, all new in-contact deer demonstrated DTH to M. bovis PPD. At 180 days after introduction of new in-contact deer, deer were euthanized and examined. All in-contact exposed deer developed tuberculosis. Lesions were most common in the lung and pulmonary lymph nodes. Experimentally inoculated deer shed M. bovis in nasal secretions, saliva, feces, and urine. In-contact infected deer also shed M. bovis in nasal secretions and saliva. Hay and pelleted feed contained M. bovis at multiple times during the experiment. Tuberculous deer efficiently transmit M. bovis to other deer in close contact. Lesion distribution suggests aerosol transmission, however, contamination of shared feed also must be considered.