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 assess phylogenetic relationships
among Mycobacterium bovis isolates by use of random
amplified polymorphic DNA polymerase chain
reaction (RAPD-PCR) fingerprinting and to relate genetic
profiles of isolates to epidemiologic characteristics.
Animals—400 cattle with tuberculosis.
Procedure—Mycobacterium bovis was isolated from
various organs of cattle slaughtered in 6 geographic
regions of Mexico. Most cattle were adult Holsteins
from large herds that did not participate in a tuberculosis
control program. Four random primers and 2
selected primers were used in RAPD-PCR fingerprinting
of 88 isolates. Pairwise genetic distance between
isolates was obtained and subjected to cluster analysis
with bootstrapping to test for levels of support.
Results—98 different fragments were obtained; there
was broad genetic diversity among isolates, and each
isolate had a unique RAPD-genotype, including those
originating from the same herd. Clustering by geographic
location, affected organ, or severity of lesion
was not detected. Linkage disequilibrium analysis suggested
that M bovis was highly clonal and that mutations
develop at a rapid rate among isolates.
Conclusions and Clinical Relevance—Use of RAPDPCR
could not differentiate M bovis isolates by epidemiologic
characteristics or identify common
sources of infection. (Am J Vet Res 2000;61:90–95)