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Most Live-captured New York Moose Were in Good Condition Despite Frequent Endoparasite Evidence

A wild moose cow standing beside her calf
Research · Disease, parasites & microbiology

A long-term health assessment of moose (Alces alces) in New York, USA found a striking contrast between outward condition and parasite exposure. Among 60 live-captured animals, 98% were rated in good or excellent body condition, yet 75% showed evidence consistent with possible infection by at least one internal parasite. The study also used records from 191 moose examined after death between 2000 and 2023.

The two datasets provided different kinds of information. Live captures allowed standardised assessments of body condition, blood values and parasite exposure, while the necropsy records came opportunistically from animals that were found dead or killed. The latter therefore reveal pathology and recorded causes of death, but are not a random sample of mortality in the wider population.

Parasite exposure was common despite good body condition

Most live-captured moose appeared physically robust, but parasite-related findings were widespread. Blood tests showed elevated eosinophil and lymphocyte counts, changes that can accompany immune responses but do not by themselves identify a particular infection.

Winter ticks (Dermacentor albipictus) were found on 74% of live-captured animals. Infestation intensity was nevertheless much lower than in neighbouring states where severe winter-tick outbreaks can cause major blood loss and poor condition. The New York results therefore show that a parasite can be widespread without reaching the extreme burdens seen elsewhere.

White-tailed deer were central to meningeal-worm risk

Among the necropsied moose, infections with the meningeal worm Parelaphostrongylus tenuis and the giant liver fluke Fascioloides magna were common. White-tailed deer (Odocoileus virginianus) are the normal definitive hosts of both parasites, whereas moose are incidental hosts in which infection can cause serious disease.

White-tailed deer density was the strongest predictor of meningeal-worm infection in moose, consistent with deer acting as the main source of environmental transmission. Giant-liver-fluke infection followed a more complicated pattern: older animals and samples from later years had higher estimated infection probability, while the associations with deer density and roads did not fit a simple transmission explanation.

Trauma, especially vehicle collisions, was the most frequent immediate cause of death recorded among the necropsied animals. Because those carcasses were collected opportunistically, this should not be treated as an estimate of how moose across New York usually die.

The authors’ clearest management implication concerns meningeal worm: reducing white-tailed deer density in core moose areas could lower exposure risk. More broadly, they argue that parasite pressure should be considered alongside other stressors even when most live animals appear to be in good body condition.

Sources and image credit

  1. Grauer, J. A., Fuller, A. K., Frair, J. L., Hynes, K., Behling-Kelly, E., & Schuler, K. L. (2026). Health status and drivers of endoparasite infection in a low-density moose (Alces alces) population. Journal of Wildlife Diseases, 62(2), 311–327.Author and institutional publication records list the article online on 30 January 2026; PubMed later indexes the issue/e-publication in April 2026.

Image: U.S. Fish and Wildlife Service / Wikimedia Commons. Moose cow and calf; illustrative species photograph. · Public domain · Source

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