The impact of introduced hosts on parasite transmission: opisthorchiid infections in American mink (Neovison vison)

Introduced animals may be considered at an advantage over native competitors because they have escaped natural parasites. In some cases however, generalist parasites in a novel environment can use introduced species as an alternative or reservoir host. This can change the dynamics of parasite populations, with implications for epidemiology. The key factor determining the impact of an alternative host is its ability to maintain a reproductively successful parasite and contribute to the transmission potential of that parasite. The digenean Pseudamphistomum truncatum is found in native otters Lutra lutra in Britain and has been reported in introduced American mink Neovison vison. To investigate whether introduced mink are competent hosts and to ask how mink compare with otters as hosts, we compared parasite prevalence, intensity and fecundity between the two host species in a region where both are common. Although prevalence was not statistically different between otters and mink (48 %, n = 27, compared to 33 %, n = 21 respectively), mean parasite intensity was higher in mink (253 ± 145 standard error parasites/infected host, compared to 46 ± 18 in otters). Parasite fecundity was lower in mink (mean egg count/parasite/host = 622 ± 64) than in otters (1,204 ± 108), and this difference was not confounded by host or parasite size or by intraspecific competition among parasites. Assuming the parasite eggs are equally viable from otters or mink, mink are not only a competent host for P. truncatum, but because of the higher parasite intensity in mink, they can potentially spread c.3 times as many parasite eggs to intermediate hosts, than otters. The naturalisation of mink to new habitats may therefore contribute to trematode infections in native fauna.