Epidemic simulation of a foot and mouth disease outbreak in Minnesota.

Foot and mouth disease (FMD) is a primary transboundary livestock disease of international concern. Outbreaks of the disease have recently occurred in several countries that were previously FMD-free. For countries with limited direct experience of this disease, modelling is a useful tool for the study of a potential outbreak. The objectives of this study were to determine specific FMD risk parameters for Minnesota and the United States (USA) and to use these parameters to create a baseline FMD outbreak model for Minnesota. Of specific interest was to assess whether the type of herd in which the outbreak began (a dairy herd or a large-scale swine herd) influenced the basic model outcomes of outbreak size and duration, and to examine the effects of depopulation and movement controls. The mean values for disease duration, outbreak duration and number of farms and animals infected were larger in the scenario with a dairy index herd. The results of these two outbreak models demonstrated the entire spectrum of FMD outbreak types; that is, from limited, focal outbreaks to widespread, uncontrolled outbreaks. The findings from this study provide details of a baseline model that emergency preparedness planners can use to evaluate response strategies for a potential incursion of FMD into the USA. These findings are also of value for all countries as veterinary authorities develop or adjust their FMD emergency response plans.

Probability of introducing foot and mouth disease into the United States via live animal importation.

Foot and mouth disease (FMD) continues to be a disease of major concern for the United States Department of Agriculture (USDA) and livestock industries. Foot and mouth disease virus is a high-consequence pathogen for the United States (USA). Live animal trade is a major risk factor for introduction of FMD into a country. This research estimates the probability of FMD being introduced into the USA via the legal importation of livestock. This probability is calculated by considering the potential introduction of FMD from each country from which the USA imports live animals. The total probability of introduction into the USA of FMD from imported livestock is estimated to be 0.415% per year, which is equivalent to one introduction every 241 years. In addition, to provide a basis for evaluating the significance of risk management techniques and expenditures, the sensitivity of the above result to changes in various risk parameter assumptions is determined.

Triggers for foot and mouth disease vaccination in the United States.

In the United States, the national policy for foot and mouth disease (FMD) vaccination lacks clarity. To better understand what potential Incident Commanders see as important 'triggers' or factors to consider for implementing vaccination as a control strategy, the authors presented seven such individuals with an FMD outbreak scenario that started in north-western Illinois and spread across state lines by the end of the fifth week. The scenario had four infected premises at the end of week one, 13 at the end of week two, and 60 (including both infected and previously depopulated premises) by the end of week five. Two individuals favoured vaccination the first week of the outbreak scenario, one did not want to vaccinate during the scenario, and the remainder wanted vaccination at some time during the scenario. Respondents ranked nine specific factors to take into consideration when deciding whether or not to vaccinate. Of these, the capability to manage the outbreak by stamping out ranked first. Many of the issues raised in this report are applicable to other countries that are currently FMD-free without vaccination.

A review of economic tools for the assessment of animal disease outbreaks.

This paper demonstrates how currently underutilised economic modelling techniques can enrich the analysis of animal disease problems. Increasingly, analyses of animal health programmes are expected to address a range of economic and social questions. These expectations can be addressed by better integration of epidemiological modelling with economic techniques whose application to animal health has not been thoroughly discussed in past reviews. This paper describes a range of economic models that can be applied in animal health research and provides guidance for determining the appropriate method given the issues at hand. The complexity of some of these approaches underlines the importance of multidisciplinary research and education.

Enhancing economic models for the analysis of animal disease.

This paper discusses how economic tools can be targeted and combined to enhance their usefulness in analyses of animal disease problems. It briefly reviews the most commonly used economic modelling techniques to clarify the applicability of specific economic methods to different problems in animal health analysis. The paper then reviews applications of these methods in the literature and suggests how further research could integrate and improve different economic approaches and link epidemiological and economic methods to address a wider range of issues at different scales of analysis.

Pork producers' attitudes, knowledge, and production practices that relate to on-farm food safety.

A survey was distributed by mail to a random selection of Illinois pig farmers marketing 1,000 or more pigs in 1998 to assess their knowledge, attitude and behavior regarding on-farm food safety. Valid responses were received from 353 of the 946 surveys mailed (37.3%). Pork production accounted for more than 50% of gross agricultural revenues among 65.0% of respondents, and 91.2% were classified as "owner-operators." Knowledge of food-borne pathogens was mixed, with correct responses to questions as follows: Trichina, 80.4%; Salmonella, 58.5%; Toxoplasma, 19.9%; and Campylobacter, 12.8%. Producers strongly agreed that food safety was a shared responsibility at every level of the food chain, including the farm level, with an average score for all steps in the pork chain of 4.5 on a scale from 1 (not important) to 5 (very important). When asked whether third party verification of on-farm practices was important, 51.2% agreed and 48.8% either disagreed or neither agreed nor disagreed. Associations between demographic categories and knowledge of and attitudes toward food safety were detected for herd size, proportion of agricultural receipts from pig production, grower versus birth-to-market production, age categories, and whether the respondent owned the pigs or facilities. Many (53.4%) were willing to apply a suggested food safety practice, even if there was no net profit for the practice. Findings suggest that Illinois pork producers accept an important role in pork food safety and express a willingness to participate but have knowledge gaps that should be filled.

Comparison of serologic testing and slaughter evaluation for assessing the effects of subclinical infection on growth in pigs.

OBJECTIVE: To compare serologic testing with slaughter evaluation in assessing effects of subclinical infection on average daily weight gain (ADG) in pigs. DESIGN: Cohort study. ANIMALS: 18 cohorts (30 to 35 pigs/cohort) of pigs on/farms. PROCEDURE: Blood samples were collected, and pigs were weighed at 8, 16, and 24 weeks of age. Sera were tested for antibodies to porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (SIV), transmissible gastroenteritis virus (TGEV), pseudorabies virus, Mycoplasma hyopneumoniae, and Actinobacillus pleuropneumoniae. At slaughter, skin, nasal turbinates, lungs, and liver were examined. Associations between ADG and results of serologic testing and slaughter evaluation were examined by use of multiple linear regression. RESULTS: Pathogens that had a significant effect on any given farm during any given year and the magnitude of that effect varied. However, at 16 and 24 weeks of age, a higher antibody titer was consistently associated with a lower ADG. Mean differences in ADG between seropositive and seronegative pigs were 18 g/d (0.04 lb/d) for SIV, 40 g/d (0.09 lb/d) for PRRSV, 38 g/d (0.08 lb/d) for M hyopneumoniae, and 116 g/d (0.26 lb/d) for TGEV. Of the evaluations performed at slaughter, only detection of lung lesions was consistently associated with a decrease in ADG. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that subclinical infection with any of a variety of pathogens commonly found in swine herds was associated with a decrease in ADG. Serologic testing was more effective than slaughter evaluation in assessing the impact of subclinical infection on ADG in these pigs.

Benefit-cost analysis of the national pseudorabies virus eradication program.

An epidemiologic model of pseudorabies virus (PRV) in swine was developed. This model was used to project future herd-to-herd disease transmission under alternative eradication or control programs over 20 years (1993 to 2012). With current PRV eradication program funding, it was projected that prevalence would be 23% in higher-risk states in the United States, 10% in moderate-risk states, and 1% in lower-risk states. Increased funding for the PRV eradication program was projected to reduce PRV prevalence substantially. Productivity and economic impacts of PRV also were estimated for the average size farrow-to-finish operation. These impacts included mortality for preweaning, nursery, growing/finishing, and breeding hogs; market weights and number of market hogs sold; farrowing rates, number of live pigs per litter, and number of litters per sow-year. Profitability was estimated to be $6/cwt less for PRV-infected herds than for uninfected herds. Aggregate effects of PRV eradication programs were estimated by use of economic welfare analysis. For all PRV eradication program alternatives analyzed, consumers were the major beneficiaries of the program because of reduced prices and increased consumption of pork. Estimates of the value of economic welfare impacts under the current program with an assumed parallel supply-curve shift were determined: consumers gained $336.5 million; producers gained $35.9 million; government expenditures were $197.1 million; and the benefit/cost ratio of the program was 1.89. Economic welfare measures were projected to increase substantially with increased PRV eradication program funding. Economic welfare measures also were estimated under other assumptions.

Factors affecting serum selenium and vitamin E concentrations in dairy cows.

Supplementation of selenium and vitamin E to enhance disease resistance in dairy cattle has become common, particularly to prevent periparturient reproductive disorders and mastitis. To establish reference values for serum vitamin E and selenium concentrations in postparturient dairy cattle and to determine whether serum concentrations of these micronutrients varied with season and stage of lactation, cows from a stratified random sample of 50 herds were studied for 1 year. Blood samples were collected from each of the 50 study herds twice, from the 10 most recently parturient cows or from 10% of the herd, whichever was greatest. Mean concentration of vitamin E and selenium was 2.55 micrograms/ml and 78.12 ng/ml, respectively. Vitamin E concentrations were significantly (P < 0.05) higher during the summer and fall than during the winter and spring. Selenium concentrations were significantly (P < 0.05) lower during the summer and fall than during the winter and spring. Herd, season of blood sample collection, and time since parturition were significant (P < 0.02) in explaining variation in vitamin E and selenium concentrations.

Productivity and profitability differences between pseudorabies-infected and pseudorabies-noninfected farrow-to-finish swine herds.

Productivity and economic effects of pseudorabies were estimated for a mean-size, farrow-to-finish swine enterprise. A Delphi technique was used to elicit productivity effects from an expert panel. Enterprise budgets for pseudorabies-infected and noninfected herds were constructed by use of these productivity estimates, as well as by use of economic data from secondary sources. Data examined to determine effects on productivity included preweaning, nursery, and growing/finishing pig mortality; breeding hog mortality; feed conversion; labor; and veterinary services and medication expenses. Results indicated that profitability was lowered in infected herds by approximately $6/cwt of swine produced.

Predicting the number of herds infected with pseudorabies virus in the United States.

Epidemiologic modeling of the likely herd-to-herd transmission of pseudorabies virus (PRV) was developed to assess the progress and potential for the PRV-eradication program in the United States. The herd-to-herd transmission of PRV over a 20-year period (1993 to 2012) in the United States was simulated under various scenarios, which included variable program-funding levels and variable prevalences. A transition model (Markov process model) was used to predict yearly changes in herd prevalence of PRV infection. Five mutually exclusive states of nature for herds were assumed: uninfected and not vaccinated; uninfected and vaccinated; known to be infected and not vaccinated; known to be infected and vaccinated; and infected, but not known to be infected. Three prevalences for states in the United States were assumed: higher prevalence, moderate prevalence, and lower prevalence. Three funding levels were assumed: no eradication program, continued funding at the current level, and increased funding of 25%. Estimates made by an expert panel for determining probabilities in the state-transition matrices were used. A model also was developed, and was considered to be the most optimistic scenario likely under increased funding of 25%. The most optimistic estimates of the probabilities that still lay within the range of estimates made by the expert panel were used for this model. Only the optimistic transmission matrices allowed for total eradication of PRV.(ABSTRACT TRUNCATED AT 250 WORDS)

Costs of clinical mastitis and mastitis prevention in dairy herds.

A stratified random sample of 50 Ohio dairy herds, monitored for 1 year between March 1988 and May 1989, was used to estimate the component costs of clinical mastitis per cow-year overall and by organism, the component costs of an episode of clinical mastitis overall and by organism, and the incidence of clinical mastitis by organism. Each herd was visited monthly by a veterinarian who conducted on-farm interviews and completed standardized data-collection forms designed to elicit economic information about the on-farm costs of clinical mastitis and mastitis prevention. Producers collected milk samples prior to treatment of clinical mastitis cases. Culturing methods allowed identification of 18 specific mastitis pathogen classifications. Annual costs estimated were on a per cow-year and clinical episode basis. The monthly mean population of cows monitored was 4,068. Mastitis prevention cost $14.50/cow-year, whereas the cost incurred by producers because of clinical cases of mastitis was $37.91. Organisms prevalent in the cows' environment caused the most costly types of mastitis. Disregarding contaminated samples and episodes for which no milk samples were taken, mastitis for which 2 organisms were isolated accounted for 35.5% of costs of clinical mastitis, followed by cases for which Escherichia coli (21.3%) was isolated, cases for which culturing yielded no growth (8.6%), and cases for which esculin-positive Streptococcus spp (6.4%), Klebsiella spp (5.7%), esculin-negative CAMP-negative Streptococcus spp (5.1%), Enterobacter spp (4.8%), coagulase-negative Staphylococcus spp (4.1%), coagulase-positive Staphylococcus spp (3.0%), S agalactiae (2.5%), and Bacillus spp (1.2%) were isolated.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of contagious pathogens of bovine mastitis and use of mastitis control practices.

A cross-sectional study of 1,032 dairy herds in Ohio was conducted to determine the prevalence of the major contagious pathogens of mastitis (Streptococcus agalactiae and Staphylococcus aureus) and the use of common mastitis control measures. Herd owners were surveyed by mail concerning their use of mastitis control measures. The survey focused on treatment of nonlactating cows, postmilking teat dipping, culling practices, milking machine maintenance, treatment for clinical mastitis, and premilking hygiene practices. Nearly 90% of questionnaires were returned. The prevalence of Streptococcus agalactiae and Staphylococcus aureus was determined by use of bulk-tank milk samples. Most herds (n = 802) met the criteria for classification into 1 of 4 groups: (1) Free of contagious pathogens, as determined by inability to isolate coagulase positive staphylococci (CPS) and esculin-negative CAMP positive streptococci (ENCPS) from 3 bulk-tank milk samples, (2) CPS, but not ENCPS, isolated from at least 1 sample, (3) ENCPS, but not CPS, isolated from at least 1 sample, (4) both ENCPS and CPS isolated from at least 1 sample. The number of herds in which both ENCPS and CPS were isolated was low; therefore, these herds were grouped with herds in which ENCPS alone was isolated for the evaluation of mastitis control practices related to herd pathogen status. Herd somatic cell count (SCC) was determined using Dairy Herd Improvement Association data by calculating the geometric mean SCC from individual cow test day SCC. Twelve months of SCC data from 741 herds were included in this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of oral administration of a calcium-containing gel on serum calcium concentration in postparturient dairy cows.

Various nutritious nutritional-supplement gels are being marketed for use in veterinary medicine. This study was designed to determine whether serum calcium, phosphorous, or magnesium concentrations were different between cows given a gel containing calcium chloride as its active ingredient (treated) and cows given inert carrier gel (control). The study revealed a significant (P < 0.01) increase in serum total calcium concentration within 5 minutes of administration of a calcium gel given to cows within 1 hour of parturition. Serum total calcium concentration had returned to baseline value by 24 hours after calcium gel administration. Serum inorganic phosphorus concentration also increased significantly (P < 0.05) after treatment. Significant changes in serum magnesium concentrations were not detected.

Impact of expenditures for veterinary services and medical supplies on dairy farm productivity and profitability.

The value of the marginal product (VMP) for veterinary services and medical supplies (VETMED), and the profit maximizing level of VETMED were estimated for dairy producers. Data from the Pennsylvania Farmers Association-Dairy Farm Business Analysis system during the years of 1986 to 1990 were used to evaluate the functional relationship between production and expenditures for VETMED. Other input variables examined were man-year equivalents of labor, asset values, value of feed fed, and culling rate. Data were screened to reflect economically viable dairy farms in Pennsylvania, and 173 such farms participated for each of the 5 years analyzed. The VMP was estimated for 1990. Profit maximizing levels for VETMED were estimated for 1990 holding other input variables at their mean values. Mean expenditures for VETMED were $2,606/farm, or $43/cow in 1990. The VMP for VETMED was estimated to be $3.22 or $4.98, depending on the method of calculation. In other words, the marginal dollar spent on VETMED generated $3.22 ($4.98) in additional revenue from milk production. The profit maximizing level of expenditures for VETMED was $138/cow, substantially more than the mean, indicating the potential for farms in this data set to improve profitability through additional expenditures on VETMED.

Effects of environment and management on mortality in preweaned dairy calves.

Forty-eight herds participating in the 1988/1989 Ohio National Animal Health Monitoring System dairy project were monitored for 1 year to determine the effects of environment and management on mortality in preweaned calves. Environmental factors were evaluated by veterinarians during monthly visits to the herds. Management procedures were measured through the use of a questionnaire administered near the end of the project. Mortality in preweaned calves was calculated for each herd by using data from project records on calf mortality and animal inventory, which were collected monthly by veterinarians. Relationships between the management/environment variables and calf mortality were examined by use of analysis of covariance. Herd size, days on a nipple feeder, navel disinfection, type of housing, and whether each calf observed with diarrhea was treated with antibiotics were the variables that had an impact on herd mortality. These variables explained approximately 39% of the variation in mortality among herds.

Managerial risk factors of intramammary infection with Streptococcus agalactiae in dairy herds in Ohio.

Dairy herds in Ohio were selected by stratified random sampling for participation in a disease-monitoring study to relate Streptococcus agalactiae intramammary prevalence to herd management and environmental conditions. Of 48 herds studied, 27 herds had at least 1 cow infected with this pathogen. Management and environmental conditions were assessed by direct observation as well as by an interview with the dairy producers. One-way ANOVA or chi 2 analysis, with presence or absence of Streptococcus agalactiae as the dependent variable, was used to test each of 70 independent variables. Variables found significant at P less than 0.20 were further evaluated by use of logistic regression. Our sample size permitted only 4 independent variables to be simultaneously evaluated by logistic regression. The most predictive risk factors were identified as poor teat and udder hygiene, poor environmental sanitation, large herd population, and use of a shared washcloth for premilking cleaning of teats and udders.

Salmonella infections in neonatal dairy calves.

To estimate herd prevalence of Salmonella spp, fecal specimens were obtained for culture from neonatal calves of 47 Ohio dairy herds. Of the 452 calves tested, 10 calves from 7 farms were culture-positive. Salmonella serotypes isolated were S dublin, S typhimurium, S enteritidis, S agona, S mbandaka, and S montevideo. Bulk tank milk filters from these dairies were also submitted for culture. Salmonella sp was isolated from 1 of the 50 filters, and 2 calves from this herd were found to be shedding Salmonella sp of the same serotype.

Risk factors for abomasal volvulus and left abomasal displacement in cattle.

A hospital-based case-control study was conducted to evaluate and compare risk factors for abomasal volvulus (AV) and left displaced abomasum (LDA) in cattle. Medical record abstracts were derived from 17 North American veterinary schools by the Veterinary Medical Data Program for all cattle admitted between Jan 1, 1977 and Dec 31, 1986, and for those with a diagnosis of AV or LDA. From a total of 108,956 individual cattle records, 1,036 cases of AV and 7,695 cases of LDA were identified, with a ratio of LDA to AV cases of 7.4 to 1. In-hospital mortality was 23.5% for AV and 5.6% for LDA. Age, breed, gender, and season each had significant (P less than 0.05) effects on risk for AV and LDA. Risk for AV and LDA increased with increasing age, with greater risk in cattle aged 4 to 7 years. Dairy cattle were at higher risk of developing AV (adjusted odds ratio, 36.4) and LDA (adjusted odds ratio, 95.2) than were beef cattle. The odds of AV in Brown Swiss cattle were significantly (P less than 0.0001) lower, and the odds of LDA in Guernsey cattle were significantly (P less than 0.0001) higher than those in Holstein cattle. Female cattle were also at higher risk of developing AV (adjusted odds ratio, 3.3) and LDA (adjusted odds ratio, 29.1) than were male cattle. The odds of AV and LDA varied considerably throughout the year, with the lowest number of cases observed in autumn. Seasonal development of AV differed significantly (P less than 0.0001) from that of LDA, with the odds of AV and LDA being highest in January and March, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)