The increase in the white-tailed deer population in Rainy River District has become a matter of some concern because of a parasite that can be fatal to moose.
Parelaphostrongylus tenuis—also known as meningeal worm or brain worm—is a slender, delicate roundworm found in the cranial cavity of cervids.
Due to physiological differences, the disease appears to do little damage to deer, but poses a serious threat to moose.
Ministry of Natural Resources area biologist Darryl McLeod said the recent trend of mild winters has pushed the range of deer northward to the point where—in Sunset Country at least—they now represent a potential threat to the indigenous moose population.
“We’ve found little evidence it is causing severe mortality among moose yet, but it is a concern to moose managers,” McLeod said from his office in Fort Frances.
“It’s normally found in deer, where it causes very little damage,” he noted.
The problem, said McLeod, is the fact there has not been a severe winter since the mid-1990s, when there were two back-to-back harsh ones in 1995-96 and 1996-97.
These resulted in a large kill-off of deer and pushed their boundaries south, where they had less contact with moose.
“This is a problem that is almost unique to Sunset Country,” McLeod remarked. “There are few other places where deer and moose co-exist to this degree.”
The MNR has been conducting tests on stool samples of deer and moose in an attempt to detect the larvae, which penetrate certain species of gastropods (snails and slugs) that act as intermediate hosts.
Deer and moose become infected by ingesting infected gastropods with their food.
In the final host, development of the larva into adult worms occurs in tissues of the central nervous system, particularly the spinal cord. Parasites leave tissues of the spinal cord after 20-40 days and move to the spinal membranes, where they mature.
Subsequently, they move into the cranial cavity, where they can cause weakness, fearlessness, lack of co-ordination, deafness, blindness, paralysis, and death.
When in moose, it often is called “moose sickness” or “blind staggering.”
Declines in the moose populations in New Brunswick, Nova Scotia, Maine, and Minnesota have been attributed to this disease.
McLeod said there is not yet a great deal of evidence to suggest brain worm is killing large numbers of moose in Sunset Country, but the situation is being monitored.
“Even given that, we have found very few cases of blind staggering so far,” he noted. “We usually detect it from our aerial surveys in the spring, when we see moose tracks going in circles.”
McLeod said the best thing for moose would be a good old-fashioned, harsh northern winter to knock down the deer population.
In other jurisdictions, such as Minnesota, the quota on deer tags has been increased.
There is talk of doing the same next year in the west end of the district, where the deer population appears to be particularly high.
(Fort Frances Times)
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