Vet February 2017.indd

Trematodes are almost all hermaphrodite (schistosomes being the exception) flat worms (flukes) which have a two or more host life cycle, with snails featuring consistently as an intermediate host. Dogs and cats residing in Europe, including the UK and Ireland, are far less likely to acquire trematode or fluke infections, which means that veterinary surgeons are likely to be unconfident when they are presented with clinical cases of fluke in dogs or cats. Such infections are likely to be associated with a history of overseas travel. In contrast, the importance of the liver fluke, Fasciola hepatica to grazing ruminants is evident from the range and significance of this parasite in sheep and cattle. This importance has been reflected historically, in the research and development investment for chemotherapy, vaccinology, lifecycle intervention and animal welfare in livestock. For over half a century this investment has delivered a battery of treatments for fluke in cattle and sheep. This article aims to provide an update on fluke in ruminants whilst utilising the depth of knowledge about fluke in ruminants to provide a context for fluke in companion animals. The public health significance of fluke will also be reviewed briefly. KEY SPECIES A number of trematode species are potential parasites of dogs and cats. The whole list of potential infections is long and so some representative examples are shown in Table 1. A more extensive list of species found globally in dogs and cats has been compiled by Muller (2000). Dogs and cats are relatively resistant to F hepatica, so despite increased abundance of infection in ruminants, there has not been a noticeable increase of infection in cats or dogs. In ruminants, the most important species in Europe are the liver fluke, F hepatica and the rumen fluke, Calicophoron daubneyi (see Figure 1). The rumen fluke has been recognised relatively recently as a common species, exceeding the prevalence of liver fluke in Ireland in one survey where approximately 31% of sheep and 44% of cattle were infected (Anon, 2011). A third species in ruminants, Dicrocoelium dendriticum, occurs less commonly (see Table 1). Fasciola gigantica is another species exotic to Europe but a significant cause of disease in cattle and humans elsewhere. Examples of human infections are shown in Table 1.