Time series analysis of the prevalence of Ascaris suum infections in pigs using abattoir condemnation data

Abstract

In most regions of the world, condemnations of porcine livers are almost always due to parasitic Ascaris suum infections. Thus, accurate data for all abattoirs in a region will reflect the prevalence of this disease in the pig population of that region. In Northern Ireland, a computerized information database retrieval system for abattoir data has been available since 1986. The information recorded by the system details the specific cause and location of all condemnations in cattle, sheep and pigs for all abattoirs in Northern Ireland since 1969. In this paper, results of analysis of a subset of these data (1969 to 1989) for pigs is presented and a univariate time series model identified for the recorded prevalence of condemnations due to cirrhotic lesions in pig livers. The results of the analysis demonstrate a very highly significant upward trend in the occurrence of Ascaris suum infections. The residual terms for the model were correlated with the corresponding time series of all the key meteorological variables. The association between the level of lesions and the mean level of air temperature over the early summer period is highlighted. The overall proportion of variation accounted for in the time series of the annual level of cirrhotic condemnations was 96%.