NR AXSL
AU Maurella,C.
TI Modelling the within Herd Prevalence of Scrapie in Goats
QU International Conference - Prion 2007 (26.-28.9.2007) Edinburgh International Conference Centre, Edinburgh, Scotland, UK - Book of Abstracts: Epidemiology, Risk Assessment and Transmission P04.14
IA http://www.prion2007.com/pdf/Prion Book of Abstracts.pdf
PT Konferenz-Poster
AB
Natural scrapie in goats was first reported in France. Other cases were then described in UK, Canada, Cyprus and Greece. Some of them occurred after contact with scrapieaffected sheep but some did not. In Italy, the first case of natural scrapie in goats was diagnosed in 1997. In that year a sudden rise in scrapie incidence involving both sheep and goats was attributed to a potentially contaminated vaccine. Such spikes in the incidence incite to investigate on the reasons why epidemic changes happen.
Aim of the study was to investigate risk factors accounting for the variability of within herd prevalence among the different outbreaks of natural scrapie in goats since it was confirmed in Italy.
A generalized linear latent mixed model was applied to model within herd prevalence (cases per 10,000 tests) using the data coming from the 45 goat scrapie outbreaks (14 mixed flocks of sheep and goats and 31 goat-only herds) that have been reported since the first case of natural scrapie to date. Using a hierarchical logistic regression, this model allows to multiply random effects not just by a single variable but by a linear combination of variables. The statistical unit was established to be the sheep. The levels we included in the model were: herd, region and the use of a particular vaccine; the explanatory variables were age, breed, husbandry and genotype.
As all the scrapie cases had the same genotype (222Q/Q), showing a significant association with scrapie status any further statistical analysis which included the genotype as a variable was precluded. Moreover the results show a difference in the presence of the disease associated with the fixed effects; however no large random effects were evident.
An adequate statistical modelling of the disease in goats has to account for the clustering of the animals in herds and regions: the mixed model applied in this work has contributed to identify factors associated to the spreading and the persistency of scrapie in the Italian goat herds during the last years.
AD C. Maurella, Istituto Zooprofilattico Sperimentale di Piemonte, Liguria e Valle d'Aosta, Italy
SP englisch
PO Schottland
EA pdf-Datei und Poster (Posterautoren ergänzt um P.L. Acutis, F. Ingravalle, M.C. Bona, M. Caramelli und G. Ru)