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  • Author or Editor: Andres M. Perez x
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Abstract

Objective—To estimate when foot-and-mouth disease virus (FMDV) would first be detected in bulk tank milk of dairies after exposure to FMDV.

Sample Population—Hypothetical dairy herds milking 100, 500, or 1,000 cows.

Procedures—For each day after herd exposure to FMDV, infection, milk yield, and virolactia were simulated for individual cows with low and high rates of intraherd transmission to estimate when a PCR assay would detect virus in bulk tank milk. Detection limits were based on assumptions for the number of virus genomes per milliliter of milk and for analytical sensitivity of a PCR assay.

Results—A mean of 10% of the cows was predicted to have FMD lesions from 7 to 8 days and from 13.5 to 15 days after herd exposure for herds with high and low intraherd transmission rates, respectively. Herd bulk milk volume decreased by 10% by 8.5 to 9.5 days and by 15 to 16.5 days after herd exposure for herds with high and low transmission rates, respectively. Mean times by which FMDV would be first detected in bulk milk were 2.5 days and 6.5 to 8 days after herd exposure, which were extended for 10 to 11 days and 17 to 18 days for herds with high and low transmission rates, respectively.

Conclusions and Clinical Relevance—PCR screening of bulk milk for FMDV would likely detect FMDV in dairy herds several days sooner than might be expected for owner reporting of clinical signs and thus should be worthy of consideration for regional, national, or global FMD surveillance.

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in American Journal of Veterinary Research

Abstract

Objective—To characterize the temporal and spatial distribution and reproductive ratio of vesicular stomatitis (VS) outbreaks reported in Mexico in 2008.

Animals—Bovine herds in Mexico in which VS outbreaks were officially reported and confirmed from January 1 through December 31, 2008.

Procedures—The Poisson model of the space-time scan statistic was used to identify periods and geographical locations at highest risk for VS in Mexico in 2008. The herd reproductive ratio (Rh) of the epidemic was computed by use of the doubling-time method.

Results—1 significant space-time cluster of VS was detected in the state of Michoacan from September 4 through December 10, 2008. The temporal extent of the VS outbreaks and the value and pattern of decrease of the Rh were different in the endemic zone of Tabasco and Chiapas, compared with findings in the region included in the space-time cluster.

Conclusions and Clinical Relevance—The large number of VS outbreaks reported in Mexico in 2008 was associated with the spread of the disease from the endemic zone in southern Mexico to areas sporadically affected by the disease. Results suggested that implementation of a surveillance system in the endemic zone of Mexico aimed at early detection of changes in the value of Rh and space-time clustering of the disease could help predict occurrence of future VS outbreaks originating from this endemic zone. This information will help prevent VS spread into regions of Mexico and neighboring countries that are only sporadically affected by the disease.

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in American Journal of Veterinary Research

Abstract

Objective—To determine the association between soil type and paratuberculosis in cattle.

Sample Population—Soil samples and test results for paratuberculosis in 92 Indiana cattle herds.

Procedure—Testing records from herds in which ≥ 20 cattle were tested for paratuberculosis by use of an ELISA between 1998 and 2002 were identified. Soil type was characterized on the basis of herd location. Clusters of herds with seroprevalence greater than the median seroprevalence were identified. Association between clusters and soil types was estimated by logistic regression, adjusted for herd type (dairy or beef).

Results—A spatial cluster of greater than the median seroprevalence was identified in northeast Indiana. Soils with low silt content were associated (odds ratio [OR], 7.2; 95% confidence interval [CI], 2.1 to 24.5) with this cluster. Adjusting for herd type did not substantially alter this association (OR, 6.7). Herds located in areas with sandy loam (OR, 6.2; 95% CI, 1.4 to 27.4) and loam (OR, 3.6; 95% CI, 1.0 to 13.2) soils were also more likely to be within the cluster of greater than the median seroprevalence. Herds located in areas of silt loam soils were less likely (OR, 0.2; 95% CI, 0.1 to 0.7) to be included in this cluster.

Conclusions and Clinical Relevance—Spatial distribution of herds with greater than the median seroprevalence of paratuberculosis was associated with soil characteristics. Survival of Mycobacterium avium subsp paratuberculosis may be enhanced by silt or sand content in loamy soils. These results may be used to modify paratuberculosis control programs. ( Am J Vet Res 2004;65:10–14)

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in American Journal of Veterinary Research

Abstract

Objective—To estimate the time of seroconversion to the New Jersey serotype of vesicular stomatitis virus (VSNJV) in sentinel cattle of dairy herds located at high and low elevations in southern Mexico and to determine the factors associated with an increase in VSNJV transmission.

Animals—471 dairy cattle in 4 free-ranging dairy herds located at high and low elevations in southern Mexico.

Procedures—Serum samples from all cattle were screened by use of serum neutralization (SN) tests for antibodies against VSNJV. Cattle with SN titers < 1:20 were designated as sentinel cattle and tested every 10 weeks for seroconversion to VSNJV (SN titer ≥ 1:80). A Cox proportional hazards regression model was used to compare the hazard for seroconversion between sentinel cattle located at high and low elevations and kept under similar management and nutritional conditions.

Results—Hazard of VSNJV seroconversion was significantly higher for sentinel cattle located at high elevations, compared with the hazard for sentinel cattle located at low elevations. Dairy cattle located at high elevations seroconverted to VSNJV more frequently during the rainy season and the beginning of the dry season.

Conclusions and Clinical Relevance—Seroconversion to VSNJV was more likely in dairy cattle in southern Mexico located at high elevations than in dairy cattle located at low elevations. These findings should contribute to understanding the dynamics of VSNJV infection in endemic areas and should be useful in the design of effective preventive and control strategies to decrease the impact of future VSV incursions.

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in American Journal of Veterinary Research

Abstract

OBJECTIVE To measure incidence and estimate temporal and spatial dynamics of porcine reproductive and respiratory syndrome virus (PRRSV) infection in US sow herds.

ANIMALS 371 sow herds in the United States from 14 production companies.

PROCEDURES The exponentially weighted moving average was used to monitor incident PRRSV infections for onset of an epidemic. The spatial scan statistic was used to identify areas at significantly high risk of PRRS epidemics. A χ2 test was used to estimate whether there were significant differences in the quarterly and annual PRRS incidence among time periods, and a bivariable logistic regression model was used to estimate whether PRRSV infection during a given year increased the odds of that herd being infected in the following year.

RESULTS During the 4-year period of this study, 29% (91/319; 2009 to 2010), 33% (106/325; 2010 to 2011), 38% (135/355; 2011 to 2012), and 32% (117/371; 2012 to 2013) of the herds reported new infections. Weekly incidence was low during spring and summer and high during fall and winter. The exponentially weighted moving average signaled the onset of a PRRSV epidemic during the middle 2 weeks of October each year. Disease incidence was spatially clustered. Infection in the previous year increased the odds of infection in 2010 to 2011 and 2011 to 2012.

CONCLUSIONS AND CLINICAL RELEVANCE Results indicated a striking repeatability in annual PRRSV temporal and spatial patterns across 4 years of data among herds from 14 production companies, which suggested that efforts to control PRRSV at a regional level should continue to be supported.

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in American Journal of Veterinary Research

Abstract

Objective—To use mathematical modeling to assess the effectiveness of control strategies for porcine reproductive and respiratory syndrome (PRRS) virus on a swine farm.

Sample—A hypothetical small, medium, or large farrow-to-weaning swine farm in the Midwestern United States.

Procedures—Stochastic models were formulated to simulate an outbreak of PRRS on a farm. Control strategies assessed in those models included none (baseline) and various combinations of mass immunization, herd closure, and gilt acclimatization. Nine different models resulting from the combination of low, moderate, or high PRRS virus virulence and small, medium, or large herd size were simulated. A stabilized status, the outcome of interest, was defined as the absence of positive PCR assay results for PRRS virus in 3-week-old piglets. For each scenario, the percentage of simulations with a stabilized status was used as a proxy for the probability of disease control.

Results—Increasing PRRS virus virulence and herd size were negatively associated with the probability of achieving a stabilized status. Repeated mass immunization with herd closure or gilt acclimitization was a better alternative than was single mass immunization for disease control within a farm.

Conclusions and Clinical Relevance—Repeated mass immunization with a PRRS modified-live virus vaccine with herd closure or gilt acclimitization was the scenario most likely to achieve a stabilized status. Estimation of the cost of various PRRS control strategies is necessary.

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in American Journal of Veterinary Research