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We Herd You Had TB

Posted By Dee Pritschet, Beth Carlson, DVM, Susan Keller, DVM, Tracy Miller, PhD, Monday, December 1, 2014
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In July 2013, the North Dakota Department of Health (NDDoH) was notified of a patient presumptively 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. Due to the potential animal-human interaction, a collaborative investigation ensued between the NDDoH, the North Dakota Department of Agriculture-Animal Health Division and Board of Animal Health (NDDA-AHD and BOAH).

In November 2013, the BOAH conducted whole herd testing on 319 cattle. 11 cattle responded to the caudal fold (CF) tuberculin test and were then tested using the comparative cervical test (CCT). One cow (Cow A) was classified as a reactor to the CCT and was subsequently euthanized. Cow A had a small visible granuloma in a lymph node on necropsy, suggesting acute infection. The herd was quarantined when the first reactor was identified. The 10 remaining CF suspect animals were euthanized and tested for tuberculosis, resulting in two additional positives. Cow A was positive for Mycobacterium bovis (M.bovis) on both polymerase chain reaction (PCR) and culture testing, Cow B was PCR-positive only, and Cow C was culture-positive only. Neither Cow B nor Cow C showed any gross lesions.

Testing was also done on the dairy farmer’s 161 beef animals resulting in no caudal fold responders. In January 2014, a second dairy herd test was completed and six additional caudal fold responders were identified. These animals were shipped to slaughter; no gross lesions were found on examination, and all laboratory tests were negative for tuberculosis. A subsequent herd test of all dairy and beef cattle in April identified seven additional responders which had no evidence of TB at post-mortem examination or upon laboratory testing. In October of 2014, all cattle were again tested and found to be negative. The herd was released from quarantine on November 4th and will undergo annual herd tests for the next five years.

Difficulties in identifying the causative agent in the initial human case led to a delay in appropriate treatment. Culture results confirming M.bovis were not available until mid-November. TB treatment drug sensitivity results showed the expected pyrazinamide resistance but also a low-level resistance to isoniazid (INH).

The case lived in a remote area, so the NDDoH contracted with a local clinic to provide directly observed therapy (DOT). In December 2013, the case had to return to Mexico for approximately two months. Follow-up care was coordinated with the border initiative Cure TB to ensure DOT would continue when the dairy worker returned to Mexico. The dairy worker has since returned to the United States where he successfully completed his treatment.

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 case isolate and the two cattle isolates were sent to the National Veterinary Services Laboratories for whole genome sequencing. The human isolate had the same single nucleotide polymorphisms (SNP) profile as Cow A. The isolate recovered from Cow C, while very similar to Cow A and the human strain, was divergent by seven separate unique SNPs, which suggests another strain of M. bovis is present. Both of these TB strains indicate a Mexico origin, yet both Cow A and Cow C were born, raised, and had never been outside of North Dakota.

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 Mexican origin of the TB strains, North Dakota cattle, and further epidemiological data—support the likelihood that the dairy worker transmitted the disease to the cattle.

At the North Dakota Department of Health, Dee Pritschet is the HIV/AIDS Surveillance Coordinator and TB Controller and Tracy K. Miller, PhD, MPH is the state epidemiologist. At North Dakota Department of Agriculture, Susan Keller, DVM is State Veterinarian and Beth Carlson, DVM is Deputy State Veterinarian. To learn more, see the CSTE Infectious Disease Steering Committee page.

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