An Examination of Gross Lesions Associated with Bovine Tuberculosis in the U.S.

Understanding the gross lesion distribution associated with bovine tuberculosis (bTB) and the relationship between antemortem test results is important for optimizing surveillance activities. Antemortem diagnostic test results and postmortem examination results from animals infected with bTB in the United States are routinely collected during surveillance and outbreak response. From 2017 to 2022, data were compiled and analyzed from 403 infected animals, representing both beef and dairy cattle from a variety of herds with different levels of disease prevalence. Overall, 95.3% of cattle infected with Mycobacterium bovis presented with gross lesions. Most cattle had lesions in one anatomic region. Lesions of the thorax and head were most common with 42.4% of infected cattle having lesions in only the thorax, 18.4% having lesions only in the head, and 15.6% having lesions in both the head and thorax. The most frequently affected tissues were the mediastinal, tracheobronchial, and medial retropharyngeal lymph nodes. Results of antemortem skin tests were not found to be associated with lesion count or location. This analysis presents an updated look at the current state and presentation of bTB in the U.S., makes use of data collected in the field, and can help guide future bTB surveillance and control strategies.