Objective—To determine whether cats exposed at a
residence were infected with Mycobacterium bovis,
whether the tuberculin skin test can identify cats
infected with M bovis, and whether an ELISA could
identify tuberculosis-infected cats.
Animals—20 domestic cats exposed to a cat with
laboratory-confirmed disseminated M bovis infection.
Procedure—Cats were administered a tuberculin
skin test and monitored for 72 hours. Blood and fecal
samples were collected. Cats were then euthanatized,
and postmortem examinations were performed.
Tissues were examined grossly and histologically
for signs of mycobacteriosis. Pooled tissue
samples and fecal samples were submitted for
mycobacterial culture. Blood samples were examined
for evidence of tuberculosis by use of a comparative
Results—4 cats had positive responses for the
ELISA, and 2 cats had suspicious responses. All
tuberculin skin tests yielded negative results. No
gross or histologic lesions of tuberculosis were
detected in any tissues, and mycobacteria were not
isolated from tissues or feces obtained from the 20
Conclusions and Clinical Relevance—All cats that
had positive or suspicious responses for the ELISA
were offspring of the cat with tuberculosis. Evidence
of tuberculosis was not seen in other cats at the residence,
the owner, or the attending veterinarian. The
most likely source of tuberculosis for the infected cat
was through the consumption of M bovis-infected
wildlife carcasses or offal. Because M bovis is endemic
in wildlife in northeastern Michigan, there is a risk
of exposure to tuberculosis in companion animals,
their owners, and attending veterinarians. (Am J Vet
OBJECTIVE To describe use of whole-genome sequencing (WGS) and evaluate the apparent sensitivity and specificity of antemortem tuberculosis tests during investigation of an unusual outbreak of Mycobacterium bovis infection in a Michigan dairy herd.
PROCEDURES All cattle in the index dairy herd were screened for bTB with the caudal fold test (CFT), and cattle ≥ 6 months old were also screened with a γ-interferon (γIFN) assay. The index herd was depopulated along with all barn cats and a dog that were fed unpasteurized milk from the herd. Select isolates from M bovis–infected animals from the index herd and other bTB-affected herds underwent WGS. Wildlife around all affected premises was examined for bTB.
RESULTS No evidence of bTB was found in any wildlife examined. Within the index herd, 53 of 451 (11.8%) cattle and 12 of 21 (57%) cats were confirmed to be infected with M bovis. Prevalence of M bovis–infected cattle was greatest among 4- to 7-month-old calves (16/49 [33%]) followed by adult cows (36/203 [18%]). The apparent sensitivity and specificity were 86.8% and 92.7% for the CFT and 80.4% and 96.5% for the γIFN assay when results for those tests were interpreted separately and 96.1% and 91.7% when results were interpreted in parallel. Results of WGS revealed that M bovis–infected barn cats and cattle from the index herd and 6 beef operations were infected with the same strain of M bovis. Of the 6 bTB-affected beef operations identified during the investigation, 3 were linked to the index herd only by WGS results; there was no record of movement of livestock or waste milk from the index herd to those operations.
CONCLUSIONS AND CLINICAL RELEVANCE Whole-genome sequencing enhanced the epidemiological investigation and should be used in all disease investigations. Performing the CFT and γIFN assay in parallel improved the antemortem ability to detect M bovis–infected animals. Contact with M bovis–infected cattle and contaminated milk were major risk factors for transmission of bTB within and between herds of this outbreak.