Objective—To develop a mathematical model to simulate infection dynamics of Mycobacterium bovis in cattle herds in the United States and predict efficacy of the current national control strategy for tuberculosis in cattle.
Design—Stochastic simulation model.
Sample—Theoretical cattle herds in the United States.
Procedures—A model of within-herd M bovis transmission dynamics following introduction of 1 latently infected cow was developed. Frequency- and density-dependent transmission modes and 3 tuberculin test–based culling strategies (no test-based culling, constant [annual] testing with test-based culling, and the current strategy of slaughterhouse detection–based testing and culling) were investigated. Results were evaluated for 3 herd sizes over a 10-year period and validated via simulation of known outbreaks of M bovis infection.
Results—On the basis of 1,000 simulations (1,000 herds each) at replacement rates typical for dairy cattle (0.33/y), median time to detection of M bovis infection in medium-sized herds (276 adult cattle) via slaughterhouse surveillance was 27 months after introduction, and 58% of these herds would spontaneously clear the infection prior to that time. Sixty-two percent of medium-sized herds without intervention and 99% of those managed with constant test–based culling were predicted to clear infection < 10 years after introduction. The model predicted observed outbreaks best for frequency-dependent transmission, and probability of clearance was most sensitive to replacement rate.
Conclusions and Clinical Relevance—Although modeling indicated the current national control strategy was sufficient for elimination of M bovis infection from dairy herds after detection, slaughterhouse surveillance was not sufficient to detect M bovis infection in all herds and resulted in subjectively delayed detection, compared with the constant testing method. Further research is required to economically optimize this strategy.
Objective—To assess seasonal variation in prevalence
of Listeria monocytogeneson ruminant farms and identify
management practices associated with ruminant listeriosis
and fecal shedding of L monocytogenes.
Study Design—Case-control study.
Sample Population—2,056 samples of feces, feed,
soil, and water from 24 case farms with listeriosis
and 28 control farms without listeriosis.
Procedure—Samples were collected and evaluated
via bacterial culture for L monocytogenes. Univariate
associations between farm management practices
and listeriosis and fecal shedding of L monocytogenes
were assessed. Multivariate models were
developed to identify farm management practices
associated with listeriosis and fecal shedding of L monocytogenes.
Results—The prevalence of L monocytogeneson cattle,
goat, and sheep farms was seasonal, especially in
fecal samples, with peak prevalence in winter. Although
the prevalence of L monocytogenes in feedstuffs from
small-ruminant farms also peaked during winter, the
bacterium was detected at a constant rate in cattle farm
feedstuffs throughout the year. Farm management
practices, animal health and hygiene, and feedstuff quality
and storage were associated with ruminant listeriosis
and fecal shedding of L monocytogenes.
Conclusions and Clinical Relevance—Results suggest
that the prevalence of L monocytogenes on ruminant
farms is seasonal, management practices are
associated with ruminant listeriosis and fecal shedding
of L monocytogenes, and the epidemiologic features
of listeriosis differ in cattle versus small ruminants.
Awareness of risk factors may be used to develop control
measures to reduce animal disease and introduction
of L monocytogenes into the human food chain.
(J Am Vet Med Assoc 2005;227:1808–1814)
Objective—To determine the radiographic methods
that best predict the development of osteoarthritis in
the hip joints of a cohort of dogs with hip dysplasia
and unaffected dogs.
Animals—205 Labrador Retrievers, Greyhounds, and
Labrador Retriever-Greyhound crossbred dogs.
Procedure—Pelvic radiography was performed when
the dogs were 8 months old. Ventrodorsal extendedhip,
distraction, and dorsolateral subluxation (DLS)
radiographs were obtained. An Orthopedic
Foundation for Animals-like hip score, distraction
index, dorsolateral subluxation score, and Norberg
angle were derived from examination of radiographs.
Osteoarthritis was diagnosed at the time of necropsy
in dogs ≥ 8 months of age on the basis of detection
of articular cartilage lesions. Multiple logistic regression
was used to determine the radiographic technique
or techniques that best predicted development
Results—A combination of 2 radiographic methods
was better than any single method in predicting a cartilage
lesion or a normal joint, but adding a third radiographic
method did not improve that prediction. A
combination of the DLS score and Norberg angle best
predicted osteoarthritis of the hip joint or an unaffected
hip joint. All models that excluded the DLS score
were inferior to those that included it.
Conclusions and Clinical Relevance—A combination
of the DLS score and Norberg angle was the best
predictor of radiographic measures in 8-month-old
dogs to determine whether a dog would have normal
or osteoarthritic hip joints. (Am J Vet Res 2003;64:1472–1478)
Objective—To determine the duration of fecal shedding of and serologic response to Salmonella spp after natural infection in dairy calves and characterize Salmonella organisms recovered from these herds.
Animals—Calves from 2 dairy herds (A and B) in the northeast United States that were identified at the beginning of a Salmonella outbreak.
Procedures—Fecal samples were collected twice per week (herd A) or once per week (herd B); blood samples were collected for serologic testing once per week in both herds. Bacteriologic culture of fecal samples was performed, and Salmonella isolates were characterized by serotype, pulsed-field gel electrophoresis (PFGE) pattern, and antimicrobial resistance profile.
Results—All Salmonella isolates from herd A were serovar Typhimurium var Copenhagen, had the same PFGE pattern, and were resistant to at least 9 antimicrobials. All isolates from herd B were Salmonella Typhimurium, represented 2 PFGE patterns, and were susceptible to all antimicrobials evaluated. The estimated duration of fecal shedding was 14 days in herd A and 9 days in herd B. Few calves were seropositive for antibody against Salmonella lipopolysaccharide within the first week after birth (0 of 20 in herd A and 13 of 79 in herd B) or seroconverted (6 in herd A and 4 in herd B). Fecal shedding was more common in calves that seroconverted, but overall, there was not a strong association between seropositivity and fecal shedding of Salmonella organisms.
Conclusions and Clinical Relevance—Although the herds differed in serologic response and Salmonella subtype, the duration of fecal shedding among calves was similar between herds.