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Using animal performance data to evidence the under-reporting of case herds during an epizootic: application to an outbreak of bluetongue in cattle.

Nusinovici S, Monestiez P, Seegers H, Beaudeau F, Fourichon C - PLoS ONE (2014)

Bottom Line: This system did not allow a precise estimation of the extent of the epizootic.This interpolation was based on the spatiotemporal dynamic of confirmed case herds reported in 2007.Overall, results indicate that performance data can be used to evidence the under-reporting during an epizootic.

View Article: PubMed Central - PubMed

Affiliation: INRA, UMR1300 Biology, Epidemiology and Risk Analysis in animal health, Nantes, France; LUNAM Université, Oniris, Ecole nationale vétérinaire, agroalimentaire et de l'alimentation Nantes-Atlantique, Nantes, France.

ABSTRACT
Following the emergence of the Bluetongue virus serotype 8 (BTV-8) in France in 2006, a surveillance system (both passive and active) was implemented to detect and follow precociously the progression of the epizootic wave. This system did not allow a precise estimation of the extent of the epizootic. Infection by BTV-8 is associated with a decrease of fertility. The objective of this study was to evaluate whether a decrease in fertility can be used to evidence the under-reporting of cases during an epizootic and to quantify to what extent non-reported cases contribute to the total burden of the epizootic. The cow fertility in herds in the outbreak area (reported or not) was monitored around the date of clinical signs. A geostatistical interpolation method was used to estimate a date of clinical signs for non-reported herds. This interpolation was based on the spatiotemporal dynamic of confirmed case herds reported in 2007. Decreases in fertility were evidenced for both types of herds around the date of clinical signs. In non-reported herds, the decrease fertility was large (60% of the effect in reported herds), suggesting that some of these herds have been infected by the virus during 2007. Production losses in non-reported infected herds could thus contribute to an important part of the total burden of the epizootic. Overall, results indicate that performance data can be used to evidence the under-reporting during an epizootic. This approach could be generalized to pathogens that affect cattle's performance, including zoonotic agents such as Coxiella burnetii or Rift Valley fever virus.

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Related in: MedlinePlus

Experimental variogram of the observed dates of detection of Bluetongue virus serotype 8 clinical signs of reported case herds (dots) and the fitted nested model of semivariogram (solid black line) which is the sum of a nugget effect, an exponential and a Gaussian variogram model.The gaussian component which is kept for kriging is shown in red dashed line.
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pone-0100137-g002: Experimental variogram of the observed dates of detection of Bluetongue virus serotype 8 clinical signs of reported case herds (dots) and the fitted nested model of semivariogram (solid black line) which is the sum of a nugget effect, an exponential and a Gaussian variogram model.The gaussian component which is kept for kriging is shown in red dashed line.

Mentions: Figure 2 shows the experimental semivariogram of the observed dates of clinical signs detection in case herds. Some case herds located in the same municipality were detected at different periods of the epizootic. These point pairs had thus a large semivariance, giving a pure random term (nugget effect) of 640 day2 and a fitted exponential semivariogram model with a semi-variance of 127 day2 and a range of 9.9 km. The fitted gaussian semivariogram model had a semi-variance of 243 day2 for a scale parameter (sd) of 82 km that is equivalent to an effective range of about 160 km. The fitted nested semivariogram model, plotted in black in Figure 2, shows the suitability of the fitted model for all distances larger than 10 km. The Gaussian component of the variogram model, in red dashed line, was used to map mid-to-long-range variation by Universal Kriging, filtering short range variation (5 to 10 km) and semivariance due to location uncertainty inside the municipality level. Figure 3 shows the location of the 8,313 cattle herds used as the data sample and the predicted values of the kriging model for the dates of clinical detection of the disease in the outbreak area. Predicted dates of clinical suspicion were expressed as a number of days since the first clinical case detected the 31st July 2007 among cattle herds.


Using animal performance data to evidence the under-reporting of case herds during an epizootic: application to an outbreak of bluetongue in cattle.

Nusinovici S, Monestiez P, Seegers H, Beaudeau F, Fourichon C - PLoS ONE (2014)

Experimental variogram of the observed dates of detection of Bluetongue virus serotype 8 clinical signs of reported case herds (dots) and the fitted nested model of semivariogram (solid black line) which is the sum of a nugget effect, an exponential and a Gaussian variogram model.The gaussian component which is kept for kriging is shown in red dashed line.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4061093&req=5

pone-0100137-g002: Experimental variogram of the observed dates of detection of Bluetongue virus serotype 8 clinical signs of reported case herds (dots) and the fitted nested model of semivariogram (solid black line) which is the sum of a nugget effect, an exponential and a Gaussian variogram model.The gaussian component which is kept for kriging is shown in red dashed line.
Mentions: Figure 2 shows the experimental semivariogram of the observed dates of clinical signs detection in case herds. Some case herds located in the same municipality were detected at different periods of the epizootic. These point pairs had thus a large semivariance, giving a pure random term (nugget effect) of 640 day2 and a fitted exponential semivariogram model with a semi-variance of 127 day2 and a range of 9.9 km. The fitted gaussian semivariogram model had a semi-variance of 243 day2 for a scale parameter (sd) of 82 km that is equivalent to an effective range of about 160 km. The fitted nested semivariogram model, plotted in black in Figure 2, shows the suitability of the fitted model for all distances larger than 10 km. The Gaussian component of the variogram model, in red dashed line, was used to map mid-to-long-range variation by Universal Kriging, filtering short range variation (5 to 10 km) and semivariance due to location uncertainty inside the municipality level. Figure 3 shows the location of the 8,313 cattle herds used as the data sample and the predicted values of the kriging model for the dates of clinical detection of the disease in the outbreak area. Predicted dates of clinical suspicion were expressed as a number of days since the first clinical case detected the 31st July 2007 among cattle herds.

Bottom Line: This system did not allow a precise estimation of the extent of the epizootic.This interpolation was based on the spatiotemporal dynamic of confirmed case herds reported in 2007.Overall, results indicate that performance data can be used to evidence the under-reporting during an epizootic.

View Article: PubMed Central - PubMed

Affiliation: INRA, UMR1300 Biology, Epidemiology and Risk Analysis in animal health, Nantes, France; LUNAM Université, Oniris, Ecole nationale vétérinaire, agroalimentaire et de l'alimentation Nantes-Atlantique, Nantes, France.

ABSTRACT
Following the emergence of the Bluetongue virus serotype 8 (BTV-8) in France in 2006, a surveillance system (both passive and active) was implemented to detect and follow precociously the progression of the epizootic wave. This system did not allow a precise estimation of the extent of the epizootic. Infection by BTV-8 is associated with a decrease of fertility. The objective of this study was to evaluate whether a decrease in fertility can be used to evidence the under-reporting of cases during an epizootic and to quantify to what extent non-reported cases contribute to the total burden of the epizootic. The cow fertility in herds in the outbreak area (reported or not) was monitored around the date of clinical signs. A geostatistical interpolation method was used to estimate a date of clinical signs for non-reported herds. This interpolation was based on the spatiotemporal dynamic of confirmed case herds reported in 2007. Decreases in fertility were evidenced for both types of herds around the date of clinical signs. In non-reported herds, the decrease fertility was large (60% of the effect in reported herds), suggesting that some of these herds have been infected by the virus during 2007. Production losses in non-reported infected herds could thus contribute to an important part of the total burden of the epizootic. Overall, results indicate that performance data can be used to evidence the under-reporting during an epizootic. This approach could be generalized to pathogens that affect cattle's performance, including zoonotic agents such as Coxiella burnetii or Rift Valley fever virus.

Show MeSH
Related in: MedlinePlus