NATURAL INFECTION OF RED DEER WITH BOVINE TUBERCULOSIS

Six bovine tuberculosis-free red deer hinds were introduced in October 1993 to a 1.8 ha enclosure, within a larger field study site known to contain tuberculous possums, and kept there for 9 months. A Mycobacte rium bovis-infected possum was found in the vicinity of the deer enclo sure 3 weeks after the introduction. Subsequently, a further eleven in fected possums were found in the area. The deer were monitored by repe ated composite antibody detection ELISA and lymphocyte transformation assays for tuberculosis, interpreted in parallel, by skin testing and by routine culturing of samples collected from potential excretion sit es. Lymphocyte transformation assay evidence of M. bovis infection in four hinds was first observed 4 months after introduction. One other h ind became bovine tuberculin lymphocyte transformation assay positive in the 5(th) month. Positive or equivocal bovine reactivity remained e vident at most test episodes. A comparative cervical skin test perform ed in July 1994, shortly before slaughter, was positive in these five hinds. Mycobacterium bovis was recovered off swabs from the oropharyng eal tonsils of two hinds during routine sampling. Detailed necropsy of the six deer revealed a single typical tuberculous lesion in only one , but culturing of various tissue specimens ascertained that the five blood test and comparative cervical skin test-positive animals were al l infected. Mycobacterium bovis was cultured from the oropharyngeal to nsils of four and medial retropharyngeal lymph nodes of two of the dee r with no typical gross lesions. Six additional tuberculosis-free hind s were introduced to the enclosure in April 1994 and kept there for 12 months. Four of these animals showed a positive lymphocyte transforma tion assay response to M. bavis after 9 weeks, but no significant reac tivity thereafter. Concurrent observational studies suggest that five of the first six deer probably became infected through dose inspection and investigation of the tuberculous possums, although the possibilit y of deer-to-deer transmission cannot be totally excluded. The likely deer-possum contact, and thus exposure to M. bovis, was related to the curiosity and social ranking of the hinds. The second group appear to have had transient exposure to M. bovis, possibly caused by direct co ntact with the infected hinds introduced earlier. This group never sho wed any curiosity toward, or interaction with, possums during the peri ods of observation.