Naturally transmitted <i>B. bronchiseptica</i> infections begin in the nasal cavity before growing and spreading to the lower respiratory tract.

<p>Index HeJ mice were inoculated with 100(<b>A</b>) nasal cavity, (<b>B</b>) trachea, or (<b>C</b>) lungs of individual recipient HeJ mice after being housed with an index case for 5, 7, 10, 12, and 14 days. The dashed line indicates the limit of detection. Graph represents findings of a single experimental iteration.