Objectives—To determine epidemiologic factors
associated with tuberculosis (TB) in dairy cattle
slaughtered in 6 important regions for milk production
Procedure—Tissue specimens with lesions typical of
TB were obtained during routine inspection of carcasses
at abbatoirs between July 1996 and January
1997. Infection with Mycobacterium organisms was
confirmed by histologic examination and bacteriologic
culture. Species identification was made by use of
selective growth medium, conventional biochemical
tests, and radiometric procedures. Epidemiologic
information for affected cattle was obtained by personal
interviews with cattle dealers and owners.
Results—400 (16%) of 2,500 cattle carcasses had
gross lesions typical of TB. Of the 400 infected cattle,
336 (84%) had lesions in ≥ 1 lymph node. Infection
was confirmed in 87% of cattle with gross lesions by
histologic examination, in 77% by bacteriologic culture
at a laboratory in the United States, and in 59% by
bacteriologic culture at a laboratory in Mexico. Most
cattle were adult females in fair to good body condition
that came from large herds (> 500 cattle) and
were not included in the Mexican TB control program.
Conclusions and Clinical Relevance—Mean prevalence
of lesions typical of TB in dairy cattle at 6 locations
in Mexico was 16%. Mycobacterium infection
was confirmed by various techniques in most lesions.
Recognition of typical gross lesions at slaughter may
expedite TB control procedures. (Am J Vet Res 2000;
Objective—To determine the feasibility of qualifying individuals or groups of Yellowstone National Park bison as free from brucellosis.
Sample—Serum, blood, and various samples from live bison and tissues taken at necropsy from 214 bison over 7 years.
Procedures—Blood was collected from bison every 30 to 45 days for serologic tests and microbiological culture of blood for Brucella abortus. Seropositive bison were euthanized until all remaining bison had 2 consecutive negative test results. Half the seronegative bison were randomly euthanized, and tissues were collected for bacteriologic culture. The remaining seronegative bison were bred, and blood was tested at least twice per year. Cow-calf pairs were sampled immediately after calving and 6 months after calving for evidence of B abortus.
Results—Post-enrollment serial testing for B abortus antibodies revealed no bison that seroconverted after 205 days (first cohort) and 180 days (second cohort). During initial serial testing, 85% of bison seroconverted within 120 days after removal from the infected population. Brucella abortus was not cultured from any euthanized seronegative bison (0/88). After parturition, no cows or calves had a positive test result for B abortus antibodies, nor was B abortus cultured from any samples.
Conclusions and Clinical Relevance—Results suggested it is feasible to qualify brucellosis-free bison from an infected herd following quarantine procedures as published in the USDA APHIS brucellosis eradication uniform methods and rules. Latent infection was not detected in this sample of bison when applying the USDA APHIS quarantine protocol.