Bacteriological and molecular detection of Mycobacterium bovis in cattle with inconclusive results to intradermal tuberculin tests.

A dairy herd (77 cows) from Rio de Janeiro, Brazil, with a history of tuberculosis infection was tested by a comparative cervical test (CCT). Seventeen cows were reactive and seven were inconclusive (swelling ≥ 2.0 mm and ≤ 3.9 mm, respectively). All of these 24 cows were slaughtered and necropsied ; samples from lungs and lymph nodes were collected for multiplex polymerase chain reaction (PCR) and culturing. Infection was confirmed in 23/24 (95.8%) of the slaughtered animals (five by culturing, four by PCR, and 14 by both tests). All cows with inconclusive results at CCT were confirmed as infected. Although slaughter of inconclusive reactor cows is not mandatory in many countries, our study provided evidence to support the slaughter of these cows, at least during an outbreak.