Brain Worm in a Moose in Cape Breton Highlands National Park

The Canadian Wildlife Health Cooperative (CWHC), Atlantic Region at the Atlantic Veterinary College, University of Prince Edward Island, have diagnosed “parelaphostrongylosis”, commonly referred to as “brain worm” in a bull moose submitted from Cape Breton Highlands National Park. The moose was observed on French Mountain located in the highlands alongside the Cabot Trail on November 8, 2018. It was unable to stand, had neurologic deficits in its hind limbs, and had significant hair loss and skin abrasions over the rump consistent with vehicle collision, although none had been reported to Park staff. Based on the moose’s inability to stand, it was humanely euthanized and a field necropsy was performed.

The moose was in excellent body condition and no conclusive cause of injury could be determined despite an extensive examination. The head and lungs were removed and submitted to CHWC for further evaluation. Histologically, there were multiple lesions of inflammation and necrosis throughout the brain. In one section, an adult nematode worm was observed embedded within the parenchyma consistent with Parelaphostrongylus tenuis.

Parelaphostrongylosis is caused by P. tenuis, a nematode worm that normally completes its lifecycle in white-tailed deer. In this species, the adult nematodes live in the membrane covering the deer’s brain where they produce eggs that are passed in the deer’s feces into the environment. The eggs hatch into larva that infect intermediate hosts (snails or slugs) which are inadvertently consumed by grazing deer (definitive host) to complete the lifecycle.  When another herbivore species, such as a moose, consumes the infected slug or snail, the parasite penetrates the brain or spinal cord tissue creating a great deal of damage. Neurologic deficits are often observed and their location and severity depend on the extent of tissue damage caused by P. tenuis.

Parelaphostrongylosis has been reported in both mainland Nova Scotia, where it has been implicated as a factor in the decline of the mainland moose population, and on Cape Breton Island. Infections in Cape Breton moose are thought to be rare as white-tailed deer prefer habitat located in river valleys and moose prefer habitat located in the highlands. As the two preferred historic habitats have minimal overlap, limited opportunities exist for moose to consume the infected intermediate hosts.


We erroneously stated that it was the first case in Cape Breton. Corrected on February 15, 2019.

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1 Response

  1. And yet the Department of Natural Resources allows a moose hunt every year. I own a small inn that gets many guests from all over the world. When they leave, if they haven’t seen a moose, they are extremely disappointed often writing in the guest book that they loved everything about Cape Breton except they didn’t see a moose. If they did, they were quite thrilled!

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