The Giant Liver Fluke: A Review, Intermediate Host Habitat, and Infection in a White-tailed Deer Population in Minnesota

Abstract

Fascioloides magna is a potential contributing factor to moose mortality across North America. Although the effect of this parasite on moose populations is debated, there is little evidence that F. magna infection alone will cause mortality. However, F. magna prevalence is increasing, and the additional parasite burden may be important in combination with other factors. F. magna has four primary life cycle stages with different developmental requirements that limit the habitats in which cervids can become infected. The least understood aspect of F. magna infection risk to cervids is the ecology of its snail intermediate hosts. Which snails are most important for F. magna transmission is not fully known. The habitat requirements and fine-scale distribution of these snails is also not well understood. However, snail hosts must overlap with cervid feeding or drinking in aquatic habitats for transmission of F. magna to occur. Moose feed on aquatic vegetation, but aquatic feeding in white-tailed deer and elk, the primary hosts of F. magna, is not well understood. Differences in aquatic feeding habits of moose and deer may generate different infection risks. Habitat use, population density, and age structure of sympatric deer and elk likely contribute to infection risk for moose. We suggest future research should focus on F. magna as a contributing factor, and not the direct cause of mortality in cervids. Examining the energetic cost and fitness losses associated with F. magna infection, followed by a comprehensive risk assessment using known habitat requirements of F. magna, lymnaeid snails, and cervid hosts would elucidate the risks and impacts of F. magna in North America.