Bovine and ovine rumen fluke in Ireland-Prevalence, risk factors and species identity based on passive veterinary surveillance and abattoir findings.

ABSTRACT

The prevalence of rumen fluke, the incidence of clinical paramphistomosis and the trematode's species identity were studied in cattle and sheep in the Republic of Ireland using passive veterinary surveillance (faecal examination and necropsy results; 2010-2013) and abattoir data. Based on faecal examination, the prevalence of rumen fluke was higher in cattle than in sheep. Rumen fluke prevalence in cattle and sheep fluctuated over the year and in most years (2011-2013), prevalence was higher in winter (December-February) than in summer (June-August). For 3 of 4 years studied, there was no correlation between monthly prevalence of rumen fluke and prevalence of liver fluke as estimated by faecal examination. At sample level, joint occurrence of rumen fluke and liver fluke was 1.1-2.0 times more common than would be expected under the assumption of independence. Based on necropsy data, a spike in deaths attributed to paramphistomosis was observed in 2012, when rainfall was unusually high. This spike in mortality was not accompanied by a spike in faecal prevalence, emphasizing that the incidence of disease, which is due to high burdens of juvenile rumen fluke in the gut, is not correlated with prevalence of infection, which is measured by faecal examination and reflects presence of adult fluke in the rumen. At slaughter, 52% of 518 cattle from 101 herds were positive for rumen fluke, compared to 14% of 158 sheep. Prevalence in cattle was higher than reported in most studies from mainland Europe and varied by animal category, age, sex, abattoir visit and location (county) of farm from which the animal was submitted for slaughter, but in multivariate analysis, only sampling month and county were significantly associated with detection of rumen fluke. The identity of rumen fluke in cattle and sheep was confirmed as Calicophoron daubneyi. Although C. daubneyi is thought to share an intermediate host snail with Fasciola hepatica, the differences in prevalence between host species and over time suggest that the epidemiology of C. daubneyi is distinct from that of F. hepatica. Further studies of the C. daubneyi life-cycle in ruminant hosts, intermediate snail hosts and the environment will be needed to gain a better understanding of modes of transmission and options for control of rumen fluke infection and disease.