Parasitic Brain Worm Linked to Declining Moose Populations in North America

The majestic moose, a symbol of resilience and strength, faces a silent killer: a parasitic worm that infiltrates its brain. Researchers at Washington State University have uncovered compelling evidence that Eleaophora schneideri, also known as the arterial worm, may be a significant contributor to the decline of moose populations in certain regions.

A Microscopic Menace

The study, published in the Journal of Wildlife Diseases, is part of a three-year collaborative project on moose mortality with Idaho Fish and Game and the University of Idaho. Researchers examined the remains of recently deceased Shiras moose in Idaho between March 2020 and July 2022. While the parasitic roundworm E. schneideri was absent in moose from north Idaho, it was found in half of the adult moose studied in the southeastern part of the state.

“The microfilaria are just scattered throughout their brains, and even though the damage from each is miniscule, they’re basically shot-gunning the whole brain,” said Kyle Taylor, a pathologist at WSU’s Washington Animal Disease Diagnostics Laboratory. “We hypothesize the cumulative effects of large numbers of microfilariae in the brain may be associated with increased morbidity or chance of mortality, with mortality more likely in cases with larger numbers of worms.”

The Subtle Signs of Infection

E. schneideri is primarily transmitted by tabanid flies, such as horse and deer flies. Mature worms can measure up to 4.5 inches and are most commonly found in the carotid arteries near the head and neck, where they mate and release microfilariae into the bloodstream. Infection can lead to a condition called elaeophorosis, which disrupts the host’s circulation system and can cause blindness, abnormal behavior, damage to the ears and muzzle, and even death.

The researchers suspect that the subtle but widespread damage to the brain caused by the worms may be reducing the fitness of moose, potentially increasing their risk of predation and, in some cases, causing death. “We really need to have an understanding of all the issues related to moose population decline, and this parasite appears to be a factor,” Taylor emphasized.

Keyword phrase: parasitic brain worm in moose

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