Using the National Cattle Register to estimate the excess mortality during an epidemic: Application to an outbreak of Bluetongue serotype 8

Abstract

National Cattle Registers have been widely used to examine animal movements and their role in disease transmission, but less frequently for other epidemiological applications. Our study shows how routinely collected identification data can be used to evaluate the population impact of an epidemic in cattle and to derive an indirect estimate of the associated mortality. We adapted a method developed by Human health agencies, based on the modelling of historical mortality fluctuations, to analyze the evolution of mortality in a cattle population subjected to a Bluetongue serotype 8 (BT8) outbreak. Between 01/07/2007 and 01/07/2008, 21,017 cattle died in the considered population whereas 16,691 deaths were expected according to the model. 43% of the 4326 extra deaths were found in calves less than 7 days of age, but excess mortality was found in each age group. The temporal distribution of extra-deaths, described at a weekly scale, suggests that they were related to the BT8 epidemic. The presented method could be an appreciable tool for estimating the global burden of epidemics since it is based on data already routinely collected in each European Member State. This study was conducted retrospectively but considering the promptness of the notification system, the method could be used to monitor the evolution of epidemics in near-real time.

Standardized analysis of German cattle mortality using national register data

“…The levels of age-stratified cattle mortality are comparable to previous reports (Roy, 1990;Gardner et al, 1990;Karuppanan et al, 1997;Gulliksen et al, 2009;Thomsen et al, 2004Ortiz-Pelaez et al, 2008;McConnel et al, 2008;Maher et al, 2008;Perrin et al, 2010;Dechow and Goodling, 2008;Dechow et al, 2011;among others). For example, dairy cow mortality risks of 0.02-0.035 in Denmark 1990-1999(Thomsen et al, 2004), 0.048 in North America 2002(McConnel et al, 2008, mortality rates of 0.051-0.066 in Sweden 2002(Alvasen et al, 2012 have been reported.…”

“…In consequence, a substantially increased mortality in a holding makes violated model assumptions likely. These may include welfare problems, insufficient health care or feeding practices, and infectious diseases like Bluetongue, FMD, and BSE (de Vries et al, 2013;Stevenson, 2003;Perrin et al, 2010). These and any other possibilities remain to be analyzed when examining mortality in a concrete deviant holding.…”

“…A comparable stratification by five current age bands and two breeds was used on a regional level by Perrin et al (2010Perrin et al ( , 2012. In the present study, the stratification by age, breed, sex, and holding size was found reasonably robust to model expected deaths per holding and also to estimate national herd-level mortality rates.…”

“…In this study, a Poisson regression model was used, similar to Perrin et al (2010), but predicting the number of expected deaths per holding. Thereby, the determination of deviant mortality in any holding, but also at regional level is possible.…”

Syndromic surveillance system based on near real-time cattle mortality monitoring

“…As other authors (Perrin et al, 2010;Barker et al, 2011;Dorea et al, 2013) we used weekly timescales to avoid the irregular weekday effect observed on the daily time series. Using the week as timescale brings stability into the models, however it also includes certain information bias and some timeliness reduction (Perrin et al, 2012).…”