Development of a model of natural infection with Mycobacterium bovis in white-tailed deer

The objective of this study was to develop a suitable experimental model of natural Mycobacterium bovis infection in white-tailed deer (Odocoileus vir ginianus), describe the distribution and character of tuberculous lesions, and to examine possible routes of disease transmission. In October 1997, 10 mature female white-tailed deer were inoculated by intratonsilar instillat ion of 2 x 10(3) (low dose) or 2 x 10(5) (high dose) colony forming units ( CFU) of M. bovis. In January 1998, deer were euthanatized, examined, and ti ssues were collected 84 to 87 days post inoculation. Possible routes of dis ease transmission were evaluated by culture of nasal, oral, tonsilar, and r ectal swabs at various times during the study. Gross and microscopic lesion s consistent with tuberculosis were most commonly seen in medial retrophary ngeal lymph nodes and lung in both dosage groups. Other tissues containing tuberculous lesions included tonsil, trachea, liver, and kidney as well as lateral retropharyngeal, mandibular, parotid, tracheobronchial, mediastinal , hepatic, mesenteric, superficial cervical, and iliac lymph nodes. Mycobac terium bovis was isolated from tonsilar swabs from 8 of 9 deer from both do sage groups at least once 14 to 87 days after inoculation. Mycobacterium bo vis was isolated from oral swabs 63 and 80 days after inoculation from one of three deer in the low dose group and none of four deer in the high dose group. Similarly, M. bovis was isolated from nasal swabs 80 and 85 days aft er inoculation in one of three deer from the low dose group and 63 and 80 d ays after inoculation from two of four deer in the high dose group. Intrato nsilar inoculation with M. bovis results in lesions similar to those seen i n naturally infected white-tailed deer; therefore, it represents a suitable model of natural infection. These results also indicate that M. bovis pers ists in tonsilar crypts for prolonged periods and can be shed in saliva and nasal secretions. These infected fluids represent a likely route of diseas e transmission to other animals or humans.