Prevalence, risk factors and molecular identification of paramphistomid species in sheep from a Spanish endemic area

Paramphistomids are ruminal trematodes that cause important losses in tropical and subtropical regions. However, their presence in Europe has increased significantly in recent decades. In northwestern Spain, this trend has been confirmed in cattle, but data in sheep are scarce and not updated. Moreover, the paramphistomid species affecting sheep in the area have never been molecularly identified. To evaluate the prevalence of paramphistomid infections in sheep from northwestern Spain, 826 faecal samples from 25 sheep farms were collected and analysed via coproscopic techniques. In addition, the rumens of 85 roe deer from the same area were examined to detect adult paramphistomids. The species present were molecularly identified. Multivariate analyses for identifying the risk factors affecting the prevalence and egg shedding of rumen flukes were also performed.

Overall, 14% of the animals and 44% of the flocks were positive; the mean egg count was 20.5 eggs per gram of faeces. In contrast, no adult paramphistomids were found in roe deer. Older sheep, those from farms located in the central climatic area, without water throughs available on pastures and using their own manure to fertilize, were considered significantly more susceptible to infection with paramphistomids. With respect to egg shedding, animals from 37 to 72 months of age, farms under semiextensive management, and those coinfected with Fasciola hepatica presented significantly greater egg counts. Molecular identification revealed 100% similarity with Calicophoron daubneyi sequences from other European and Mediterranean countries.

The present study confirms the increase in the prevalence of paramphistomid infections in sheep in the area with high dissemination of the parasite, as previously reported in cattle, and represents the first molecular identification of C. daubneyi in sheep from Spain. Our results demonstrate that special attention should be given to adult animals since they are the main carriers and are responsible for environmental contamination. In addition, detecting risk areas and applying effective control management measures such as the installation of watering points on pastures seems essential for limiting infections in livestock, especially in sheep, since they are susceptible to developing clinical paramphistomidosis at any time in their lives. The absence of adult flukes in roe deer suggests that they represent less suitable hosts for this trematode than cattle and sheep, although more robust studies monitoring the situation in sympatric areas with domestic ruminants are needed.