We Herd You Had TB

BACKGROUND:  In July 2013, the North Dakota Department of Health (NDDoH) was notified of a patient diagnosed with active tuberculosis (TB) disease. The investigation revealed the patient was from Mexico and employed at a local dairy whose primary duties required extensive direct contact with dairy cattle.

METHODS:  Interview with the case identified 13 named contacts. Difficulties in identifying the causative agent lead to a delay in appropriate treatment. Culture results confirming Mycobacterium bovis were not available until mid-November. Sensitivity results showed the expected pyrazinamide resistance but also a low-level resistance to isoniazid (INH). The ND Board of Animal Health was notified of the case and conducted whole herd testing on 319 dairy cattle resulting in 11 caudal fold (CF) responders. Testing was also done on the dairy farmer’s 161 beef animals resulting in no caudal fold responders.

RESULTS: The case received directly observed therapy (DOT) through a contractual agreement with a local clinic.  In December 2013, the case had to return to Mexico for approximately two months.  Follow up care was coordinated with Cure TB to ensure DOT would continue when the dairy worker returned to Mexico.  The case has successfully completed DOT. Three of the 11 initial reactive cattle were positive for M. bovis.  Results on Cows A, B, and C were culture and PCR positive, PCR positive, and culture positive, respectively. Two additional whole dairy herd tests were conducted with no evidence of active disease.  The herd was released from quarantine on November 4^thand will undergo annual herd tests for the next five years.

CONCLUSIONS: Early collaboration and communication between agencies allowed for a prompt and comprehensive investigation. This collaboration also led to a one-health approach for education efforts targeting dairy employees and employers as well as the general public. To better understand disease transmission, the human isolate and the two cattle isolates were sent for whole genome sequencing. The human case and Cow A were identical and Cow C was similar but not identical, but both strains of M. bovis were found to be of Mexico origin. The cavitary disease of the human and the small grossly visible lesions in Cow A, suggest that the human case was further along in active disease progression. That finding, along with the Mexico-origin of the TB strains, North Dakota raised cattle and the epidemiological investigation, it is likely that the dairy worker transmitted the disease to the cattle.