Epidemiology of select species of filarial nematodes in free-ranging moose (<i>Alces alces</i>) of North America

North American moose (Alces alces) are a culturally and economically valued species. Recent population declines raise concern for the survivability of this natural resource. The Minnesota population has experienced the most dramatic decline, with a 60% loss in total numbers since 2006. Nematode parasites, particularly some species of filarids, are important pathogens of moose and could be contributing to morbidity and mortality. This study investigates the eco-epidemiology of two filarial parasites of moose: Rumenfilaria andersoni and Elaeophora schneideri. By surveying cervid species from six U.S. states, we discovered R. andersoni was present in moose from all sample locations with prevalence varying between 20-40%. This suggests R. andersoni is distributed throughout North America. We also observed R. andersoni in white-tailed deer (Odocoileus virginianus) but not elk (Cervus canadensis) or caribou (Rangifer tardanus). Sequence analysis of R. andersoni suggested the existence of two distinct clades. Molecular screening of Minnesota tabanid flies discovered 1.5% harbored R. andersoni, with only Chrysops spp. deerflies containing R. andersoni DNA. This is the first report of R. andersoni in moose and white-tailed deer herds within the contiguous U.S. and the first time horseflies have been implicated as the vector. Molecular surveys for parasitic nematodes in brain tissues from Minnesota moose that died from unknown causes revealed 63% produced 18S sequences closely aligning with E. schneideri, a neurological pathogen of moose previously unreported in Minnesota. Molecular screening of Minnesota tabanid flies revealed E. schneideri was present in the environment and transmission could occur locally. Prevalence ranged between 0-100% per trapping site, with Chrysops spp. and Hybomitra spp. horseflies implicated as vectors. This is the first report of Chrysops spp. serving as a carrier of E. schneideri and the first report of E. schneideri in Minnesota, suggesting E. schneideri is an emerging pathogen in the Minnesota herd. Together these data demonstrate the presence of multiple parasitic nematode species in vulnerable moose populations, yet it is still unclear what the implications are for herd health. Further research is warranted to determine if a link between nematode infections and declining moose populations exists.