The prevalence and development of digenean parasites within their intermediate snail host, Galba truncatula, in a geographic area where the presence of Calicophoron daubneyi has recently been confirmed

Abstract

During the past decade, rumen fluke (Calicophoron daubneyi) has established as a prominent parasite of livestock within numerous European countries. Its development and spread is enabled by the presence of its intermediate snail host G. truncatula. However, the dynamics of this stage of the C. daubneyi lifecycle is yet to be recorded in numerous northern European countries including the UK. Here, the prevalence of C. daubneyi along with F. hepatica, H. cylindracea and other parasites infecting G. truncatula snails on 10 Welsh farms was recorded using morphological and PCR techniques. A total of 892 G. truncatula snails were collected between May and October 2016. The prevalence of C. daubneyi in sampled G. truncatula snails (4%) was lower compared to F. hepatica (5.6%). No association in prevalence between these species was recorded. Haplometra cylindracea was found infecting 8.2% of G. truncatula snails, with its prevalence within G. truncatula populations negatively associated with F. hepatica cercariae prevalence (P=0.004). Generalized estimation equation (GEE) linear regression models identified the levels of respective fluke eggs shed onto pasture as the main significant association between prevalence levels of both C. daubneyi and F. hepatica within G. truncatula populations (P<0.001). However, equivalent prevalence levels of C. daubneyi and F. hepatica within G. truncatula populations were associated with higher C. daubneyi egg outputs and lower F. hepatica egg outputs from livestock grazing the G. truncatula habitats. Only one of 36C. daubneyi infected G. truncatula snails was found harbouring its cercarial stages, a significantly lower proportion compared to the 29 of 50 F. hepatica infected G. truncatula harbouring its respective cercariae (P<0.05). These results signify that C. daubneyi may be less adept at infecting and developing in the UK's native G. truncatula populations in comparison with F. hepatica. However, C. daubneyi has previously demonstrated its ability to progressively adapt to an intermediate host in a new environment. If C. daubneyi were to adapt to infect and develop more efficiently in UK G. truncatula populations, paramphistomosis risk would significantly increase leading to increased livestock losses. Questions are also raised regarding potential interaction between digenean species at intermediate snail host level, which could impact subsequent livestock trematodosis risk.

Keywords: Calicophoron daubneyi; Fasciola hepatica; Galba truncatula; Generalized estimation equation (GEE); Haplometra cylindracea; UK.