Multivariate spatially-structured variability of ovine helminth infections

Abstract

A cross-sectional survey was carried out on 2004-2005 in the Campania region, southern Italy, to study the multivariate geographical distribution of four different sheep helminths, i.e. Fasciola hepatica (liver fluke), Calicophoron (Paramphistomum) daubneyi (rumen fluke), Dicrocoelium dendriticum (lancet fluke), and the gastrointestinal strongyle Haemonchus contortus. A series of multivariate Bayesian hierarchical models based on square root transformation of faecal egg counts were performed. The results were consistent with theoretical knowledge of the biology and epidemiology of the four studied helminths. In particular, the impact of common intermediate hosts (F. hepatica and C. daubneyi share the same intermediate host species) was quantified and evidence of previously unknown ecological components was given. D. dendriticum was correlated to F. hepatica and H. contortus was found not to be spatially associated with the previously mentioned helminths.

Keywords

• disease mapping, shared component models, hierarchical Bayesian model, veterinary epidemiology, helminths.