Health Status and Drivers of Endoparasite Infection in a Low-Density Moose (Alces alces) Population.

At their southern range limits in North America, moose (Alces alces) experience increased overlap with white-tailed deer (Odocoileus virginianus) and associated parasites through shared habitat use. Moose persist at low densities in New York state, USA, and are incidental hosts to multiple pathogenic endoparasites. Understanding the contributions of endoparasitism to moose morbidity and mortality requires investigation into their health status and drivers of parasite infection. We summarized health data from 60 live-captured and 191 opportunistically necropsied moose (spanning 2000-23) and used generalized linear modeling to assess the determinants of moose infection by giant liver fluke (Fascioloides magna) and meningeal worm (Parelaphostrongylus tenuis). Despite 98% of live moose having good or excellent body condition, 75% were potentially infected with at least one internal parasite species. Hematologic analyses of live moose indicated elevated eosinophil and lymphocyte counts. Infestations with winter tick (Dermacentor albipictus) were common on live-captured New York moose (74%), although intensities were considerably lower than on moose in neighboring states. Necropsied moose were commonly infected with F. magna and P. tenuis, but most often succumbed to trauma from vehicle collisions. Density of white-tailed deer, definitive host to both endoparasites, was the primary driver of P. tenuis infection in moose. For F. magna, moose age and sampling year were positively associated, whereas deer density and road density were negatively associated with moose infection probability. Limiting deer densities in core moose areas may help reduce the risk of P. tenuis infection, and targeted management efforts could promote resilience of small moose populations to multiple parasites.