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- Author or Editor: Tim E. Carpenter x
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Abstract
Objective—To assess relative costs and benefits of vaccination and preemptive herd slaughter to control transmission of foot-and-mouth disease (FMD) virus (FMDV).
Sample Population—2,238 herds and 5 sale yards located in Fresno, Kings, and Tulare counties of California.
Procedure—Direct costs associated with indemnity, slaughter, cleaning and disinfecting livestock premises, and vaccination were compared for various eradication strategies. Additional cost, total program cost, net benefit, and benefit-cost value (B/C) for each supplemental strategy were estimated, based in part on results of published model simulations for FMD. Sensitivity analyses were conducted.
Results—Mean herd indemnity payments were estimated to be $2.6 million and $110,359 for dairy and nondairy herds, respectively. Cost to clean and disinfect livestock premises ranged from $18,062 to $60,205. Mean vaccination cost was $2,960/herd. Total eradication cost ranged from $61 million to $551 million. All supplemental strategies involving use of vaccination were economically efficient (B/C range, 5.0 to 10.1) and feasible, whereas supplemental strategies involving use of slaughter programs were not economically efficient (B-C, 0.05 to 0.8) or feasible.
Conclusions and Clinical Relevance—Vaccination with a highly efficacious vaccine may be a cost-effective strategy for control of FMD if vaccinated animals are not subsequently slaughtered and there is no future adverse economic impact, such as trade restrictions. Although less preferable than the baseline eradication program, selective slaughter of highest-risk herds was preferable to other preemptive slaughter strategies. However, indirect costs can be expected to contribute substantially more than direct costs to the total cost of eradication programs. (Am J Vet Res 2003;64:805–812)
SUMMARY
From Aug 1985 through July 1986, 720 meat turkey flocks on 160 California premises were monitored and outbreaks of fowl cholera (Pasteurella multocida) were investigated. Data from 43 outbreak (case) flocks were compared with data from 43 nonoutbreak (control) flocks. Outbreak flocks, compared with control flocks, were more likely to be located on premises with higher maximal bird capacity and history of fowl cholera outbreaks. The overall impression was that flocks in larger, newer, more intensively managed premises were at greater risk of fowl cholera outbreaks than were other flocks.
Abstract
Objective—To develop a spatial epidemic model to simulate intraherd and interherd transmission of footand- mouth disease (FMD) virus.
Sample Population—2,238 herds, representing beef, dairy, swine, goats, and sheep, and 5 sale yards located in Fresno, Kings, and Tulare counties of California.
Procedure—Using Monte-Carlo simulations, a spatial stochastic epidemic simulation model was developed to identify new herds that would acquire FMD following random selection of an index herd and to assess progression of an epidemic after implementation of mandatory control strategies.
Results—The model included species-specific transition periods for FMD infection, locations of herds, rates of direct and indirect contacts among herds, and probability distributions derived from expert opinions on probabilities of transmission by direct and indirect contact, as well as reduction in contact following implementation of restrictions on movements in designated infected areas and surveillance zones. Models of supplemental control programs included slaughter of all animals within a specified distance of infected herds, slaughter of only high-risk animals identified by use of a model simulation, and vaccination of all animals within a 5- to 50-km radius of infected herds.
Conclusions and Clinical Relevance—The FMD model represents a tool for use in planning biosecurity and emergency-response programs and in comparing potential benefits of various strategies for control and eradication of FMD appropriate for specific populations. (Am J Vet Res 2003;64:195–204)
Abstract
Objective—To develop a model to evaluate the effect of vaccination against Tritrichomonas foetuson reproductive efficiency in beef herds.
Sample Population—A beef herd of 300 cows and 12 bulls (8 bulls ≤ 3 years old and 4 bulls > 3 years old).
Procedure—The model was developed by use of data for various risk factors and vaccine efficacy. The reference herd was considered to be one in which T foetus had been diagnosed and bulls were tested for T foetus before the breeding season. Five thousand iterations were run for each of 13 simulations, with each simulation representing a separate combination of risk factors.
Results—In all simulations, vaccination resulted in significantly higher calving incidence than nonvaccination. Shared grazing was found to be the most significant risk factor for a decrease in calving incidence attributable to T foetus infection, followed in importance by lack of testing before the breeding season and a higher proportion of old bulls. Combinations of risk factors contributed to a loss of income of up to 22%, some of which could be blunted by vaccination.
Conclusions and Clinical Relevance—Highest calving incidence is achieved when all bulls are tested for T foetus before the breeding season and all bulls with positive culture results are culled. Avoiding all risk factors is better than vaccinating, but when this is not feasible for a given herd, the results of this simulation indicate that proper vaccination can decrease economic losses attributable to abortions caused by T foetus. (Am J Vet Res 2004;65:770–775)
Abstract
Objective—To estimate direct and indirect contact rates on livestock facilities and distance traveled between herd contacts.
Sample Population—320 beef, dairy, goat, sheep, and swine herds, 7 artificial insemination technicians, 6 hoof trimmers, 15 veterinarians, 4 sales yard owners, and 7 managers of livestock-related companies within a 3-county region of California.
Procedure—A questionnaire was mailed to livestock producers, and personal and telephone interviews were conducted with individuals.
Results—Mean monthly direct contact rates were 2.6, 1.6, and 2.0 for dairies with < 1,000, 1,000 to 1,999, and ≥ 2,000 cattle, respectively. Mean indirect contact rates on dairies ranged from 234 to 743 contacts/ mo and increased by 1 contact/mo as herd size increased by 4.3. Mean direct monthly contact rate for beef herds was 0.4. Distance traveled by personnel and vehicles during a 3-day period ranged from 58.4 to 210.4 km. Of livestock arriving at sales yards, 7% (500/7,072) came from ≥ 60 km away, and of those sold, 32% (1,180/3,721) were destined for a location ≥ 60 km away. Fifty-five percent (16/29) of owners of large beef herds observed deer or elk within 150 m of livestock at least once per month.
Conclusions and Clinical Relevance—Direct and indirect contacts occur on livestock facilities located over a wide geographic area and at a higher frequency on larger facilities. Knowledge of contact rates may be useful for planning biosecurity programs at the herd, state, and national levels and for modeling transmission potential for foot-and-mouth disease virus. (Am J Vet Res 2001;62:1121–1129)
Abstract
Objective—To assess concurrently the effects of moderate ligamentous suspensory apparatus injury (MLSAI), racing-speed exercise, and horseshoe characteristics on risk of catastrophic suspensory apparatus failure (SAF) or metacarpal condylar fracture (CDY) in forelimbs of racehorses.
Sample population—Cadavers of 301 Thoroughbred racehorses (108 with SAF, 33 with CDY, and 160 control horses).
Procedure—A cross-sectional epidemiologic study was used to describe distributions and relationships between MLSAI, exercise, and horseshoe variables. Logistic regression was used to assess potential risk factors for developing SAF and CDY.
Results—Exercise variables were more highly associated with age than height of a steel bar affixed to the ground surface of the front of a horseshoe (ie, toe grab) or sex. Marginal associations were detected between MLSAI and age and height of toe grab. Higher risk for developing SAF was associated with MLSAI, use of a pad on a horseshoe, longer interval since last period of ≥ 60 days without a race or timed workout (ie, layup), 2 to 5 career races, and higher intensity of recent exercise. Higher risk for developing CDY was associated with MLSAI, male horses, age between 2 and 5 years, higher intensity of recent exercise, and longer interval since layup.
Conclusions and Clinical Relevance—Recognition of MLSAI and rehabilitation of affected horses should reduce incidence of SAF and CDY. Horses in long-term continuous training with recent high-intensity exercise are at greater risk for injury. Use of pads in horseshoes was associated with SAF, although the relationship may not be causal. (Am J Vet Res 2004;65:1508–1517).
Abstract
Objective—To evaluate a Markov-chain model for the development of forelimb injuries in Thoroughbreds and to use the model to determine effects of reducing sprint distance on incidence of metacarpal condylar fracture (CDY) and severe suspensory apparatus injury (SSAI).
Sample Population—Weekly exercise and injury data for 122 Thoroughbreds during racing or training.
Procedure—Weekly data were used to construct a Markov-chain model with 5 states (uninjured [UNINJ], palpable suspensory apparatus injury [PSAI], SSAI, CDY, and lost to follow-up [LOST]). Transition probabilities between UNINJ and PSAI were estimated as a function of weekly sprint distance by use of linear regression analysis. The model was used to predict distributions of annual CDY and SSAI incidences in southern California racehorses and was validated by using CDY incidence reported by racetrack practitioners. The model was modified by reducing the number of sprint distances that were > 6 furlongs (> 1.20 km) by 20%, and CDY and SSAI incidences were compared with those generated by the baseline model.
Results—The model accurately fit development of injuries in the sample population but overestimated development of injuries in the southern California racehorse population. Development of and recovery from PSAI were correlated with distance run at high speeds. Reducing by 20% the number of sprints run at distances > 6 furlongs significantly reduced modeled annual CDY and SSAI incidence by 9%.
Conclusions and Clinical Relevance—Reducing the number of sprints at distances > 6 furlongs, particularly among horses with PSAI, reduces risk of CDY and SSAI. (Am J Vet Res 2003;64:328–337)
Abstract
Objective—To describe cardiac lesions and identify risk factors associated with myocarditis and dilated cardiomyopathy (DCM) in beach-cast southern sea otters.
Animals—Free-ranging southern sea otters.
Procedure—Sea otters were necropsied at the Marine Wildlife Veterinary Care and Research Center from 1998 through 2001. Microscopic and gross necropsy findings were used to classify sea otters as myocarditis or DCM case otters or control otters. Univariate, multivariate, and spatial analytical techniques were used to evaluate associations among myocarditis; DCM; common sea otter pathogens; and potential infectious, toxic, and nutritional causes.
Results—Clusters of sea otters with myocarditis and DCM were identified in the southern aspect of the sea otter range from May to November 2000. Risk factors for myocarditis included age, good body condition, and exposure to domoic acid and Sarcocystis neurona. Myocarditis associated with domoic acid occurred predominantly in the southern part of the range, whereas myocarditis associated with S neurona occurred in the northern part of the range. Age and suspected previous exposure to domoic acid were identified as major risk factors for DCM. A sample of otters with DCM had significantly lower concentrations of myocardial L-carnitine than control and myocarditis case otters.
Conclusions and Clinical Relevance—Cardiac disease is an important cause of death in southern sea otters. Domoic acid toxicosis and infection with S neurona are likely to be 2 important causes of myocarditis in sea otters. Domoic acid–induced myocarditis appears to progress to DCM, and depletion of myocardial L-carnitine may play a key role in this pathogenesis. (Am J Vet Res 2005;66:289–299)
Abstract
Objective—To investigate the epidemiologic and financial impacts of targeted sampling of subpopulations of cows, compared with random sampling of all cows, for classification of dairy herd infection status for paratuberculosis.
Animals—All cows from 4 infected herds with a low-to-moderate prevalence of paratuberculosis and from 1 noninfected herd in California.
Procedure—The infection status of each cow was classified on the basis of results of an ELISA or combined ELISA and fecal culture results. Thirteen sampling schemes designed to randomly sample cows on the basis of lactation number, stage of lactation, and milk production were evaluated. Sampling without replacement was used to obtain a probability of herd detection of paratuberculosis for each evaluated sampling method and for simulated sample sizes between 30 and 150 cows. Marginal cost-effectiveness analysis was used to determine the cost increase relative to the increase in detection probability.
Results—Sampling cows in the third or higher lactation and ≥200 days into lactation yielded the highest detection probability in most instances, resulting in a detection probability that was 1.4 to 2.5 times that obtained by sampling 30 cows in the second or higher lactation. Costs of testing via the alternative method with a 95% detection probability were approximately $300 lower in a high-prevalence herd (31%) and $800 lower in a low-prevalence herd (9%), compared with use of the reference method.
Conclusions and Clinical Relevance—Detection of herds with paratuberculosis could be improved, and costs of testing substantially reduced by sampling targeted groups of cows.
Abstract
Objective—To evaluate the application of a vaccine in a population of animals.
Sample Population—Field-trial data from the literature.
Procedure—A spreadsheet simulation model was constructed to estimate the impact of a vaccination program, assuming various population sizes, transmission rates, and vaccine efficacies.
Results—Total effectiveness (proportion of affected animals [ie, cases] avoided) increased with the vaccinated proportion of the population. However, with a highly efficacious vaccine, this relationship discontinued after a sufficient vaccination proportion was reached, reflecting herd immunity. Evaluation of a case study indicated that what may be considered a poor vaccine on the basis of its low efficacy may protect a substantial portion of the population if the vaccine is administered to a sufficient number of susceptible animals. Further investigation of a case study of horses indicated that evaluating a vaccine based solely on its efficacy could greatly underestimate its value.
Conclusions and Clinical Relevance—When evaluating a vaccine applied to a population, in addition to the vaccine efficacy, the vaccination rate, cost of the vaccine, potential disease transmission rate, and number and cost of cases avoided must also be considered. Efficacy may underestimate vaccine value in terms of the reduction of indirect cases typically avoided when vaccination is applied in a population. (Am J Vet Res 2001;62:202–205)