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The moose, the slug and the deadly brainworm: MN scientist tries to solve a mystery

Oct 30, 2017 03:18PM ● Published by Editor

By  | dorrick@pioneerpress.com | Pioneer Press
PUBLISHED: October 28, 2017 at 7:00 am | UPDATED: October 28, 2017 at 5:10 pm

The solution to a mystery that’s killing Minnesota’s moose could come down to slug and snail DNA contained in moose and deer droppings.

And a University of Minnesota scientist eager to analyze that poop is looking for the public’s help.

In an uncommon approach to academic research, Tiffany Wolf, assistant professor of veterinary population medicine at the U’s College of Veterinary Medicine, is turning to crowdfunding — public donations of any amount — to pay for sensitive testing to search for the DNA of snails and slugs that transmit “brainworm,” a parasite that causes up to 30 percent of natural mortality in Minnesota’s troubled moose population.

Tiffany Wolfassistant professor of veterinary population medicine at the University of Minnesotas College of Veterinary Medicine is researching how moose acquire brainworm a fatal parasite Courtesy University of Minnesota
Tiffany Wolf

“We’re trying to lay the groundwork for a new research project, and we’re trying to connect with regular Minnesotans who care about the moose,” Wolf said. “We get calls all the time from agencies and even private citizens asking how they can help. This is one way.”

Her goal: $6,000. You can donate here.

If that financial target sounds modest, that’s because the scope of the work is small — for now, at least.

But the question it’s asking isn’t.

MOOSE DISAPPEARING

It’s unclear how long Minnesota will still have moose.

In 2006, the state held an estimated 8,840 adults. Today, the population is a little under half that. It appears to have leveled off in recent years, but researchers say they’re not sure the moose will be able to rebound any time soon because survival is poor among adults.

Among the threats: a warmer climate, wolves, habitat changes, winter ticks, liver flukes, and the fatal parasite known as brainworm.

A BRAINWORM’S JOURNEY

Brainworm naturally lives part of its life in whitetail deer — with no ill effects to the deer, despite a wild and crazy (and kind of gross) ride. Here’s how it works:

Illustration by Natalie Sacco  New York State Department of Environmental Conservation
(Illustration by Natalie Sacco / New York State Department of Environmental Conservation)

A larva gets eaten by a deer and migrates through the body, making its way to nearthe brain over the course of three or four months. Now an adult, it makes eggs. It then tunnels to the lungs and lays the eggs.

The eggs hatch, and the deer partially coughs up these new larvae, swallows them, and poops them out.

When a ground-dwelling slug or a snail wanders over a larva, the larva sneaks into the gastropod through the foot, that little flat part a snail or slug uses to move around.

It lives in the terrestrial gastropod — “an intermediate host” — until a deer inadvertently eats it while munching on leaves of plants or trees.

The cycle begins again: a happy ending for the deer and brainworm.

But when the parasite — Parelaphostrongylus tenuis — gets into moose, it’s deadly. “It’s like they don’t have the right roadmap for the moose,” Wolf said. The parasite gets lost and eventually invades the brain of the moose.

This debilitates the moose, causing it to walk in circles, unable to eat or evade predators. The moose dies, along with the brainworm. Unhappy ending for both; the moose is a “dead-end host.”

An adult brainworm P tenuis on thespinal cord of a moose submitted for diagnosis Courtesy New York State Department of Environmental Conservation
Adult brainworm on spinal cord of moose. (Courtesy New York Department of Environmental Conservation)

Wolf, who has been researching moose in northern Minnesota for several years, primarily with the Grand Portage Band of Lake Superior Chippewa, said between 25 percent and 30 percent of collared moose that died were infected with brainworm.

So brainworms are a big deal for anyone looking to help the moose.

KILL ALL THE DEER?

There’s one obvious way to tackle the brainworm problem: Kill the deer that live among the moose.

A map shows the ranges of deer elk moose and caribou in Minnesota before European settlement Courtesy Minnesota Department of Natural Resources

Different slugs and snails prefer different plants and micro-habitats. So knowing which gastropods carry brainworm could help biologists and land managers figure out what food is problematic for the moose.

Exactly how to use all that to save the moose isn’t clear. That’s too many steps ahead, said Wolf.

“Are there things in the environment that we can manipulate that could reduce the brainworm prevalence? We don’t know,” she said. “It’s a really complex system, and there doesn’t appear to be just one thing killing the moose. In complex systems, there isn’t just one lever to pull.”

After all, when Europeans first arrived in Minnesota, whitetail deer were less prolific. Deer were prevalent in the southern and central part of the state, while elk generally bordered the moose range on one side, and caribou on the other. Elk and caribou are essentially gone now, and deer — along with their brainworms — have filled the void.

For years, the Minnesota Deparment of Natural Resources has sought to keep deer numbers relatively low in the remaining moose range in the northeastern part of the state, primarily by allowing enough deer-hunting permits to keep deer density down.

That policy has often been unpopular with hunters — a formidable voice in the state. Wolf knows that.

“Right now, everybody thinks if we need to save the moose, we need to suppress the deer population, and that’s not palatable for some people,” she said. “Maybe we do have to suppress the deer population, but maybe we can target the gastropods as well.”

BRAINWORM-SLUG MYSTERY

Scientists might be able to do something about the brainworm problem, but first they have to unravel a mystery surrounding it: Which slugs and snails carry it?

Every time they look for brainworm-infected gastropods in the woods, they find almost none. In fact, the brainworm-infection rates of gastropods in the wild are so low that it seems far-fetched that so many deer and moose would be infected.

This is where Wolf’s new project comes in.

The traditional way for scientists to gather wild gastropods for study is a tried-and-true technique involving … wet cardboard.

That’s it: Lay some wet cardboard in the woods, and slugs and snails will come. Except not if they’re infected with brainworm — perhaps.

That’s the question Wolf is posing: What if the wet-cardboard method — hallowed in annals of malacology though it may be — is the problem?

“We’re taking a step back and thinking about how we’re studying the system,” she said. “We may find that the wet-cardboard approach was successful, and that it really is an exceptionally low prevalence (of brainworm). “But for me to rest peacefully, I need to think about sample bias.

“When we bait species, we might introduce some bias. Sometimes parasite infections can change a species’ behavior.”

In other words, maybe the snails and slugs that become infected act differently — even though they seem to live out healthy lives. Maybe they don’t like wet cardboard. And maybe, just maybe, some of them tend to gravitate toward certain types of moose food.

SAVING MOOSE FROM SLUGS?

So here’s what Wolf wants to do: First, gather up piles and piles of moose and deer dung. (Actually, she’s already done that, but she’ll want more.)

Second, look for trace DNA — similar to environmental DNA, aka “eDNA” — of snails and slugs. The $6,000 she needs will pay for this part.

The DNA testing should confirm which gastropods are the vectors for brainworm. (The common marsh slug is a prime suspect.)

Different slugs and snails prefer different plants and micro-habitats. So knowing which gastropods carry brainworm could help biologists and land managers figure out what food is problematic for the moose.

Exactly how to use all that to save the moose isn’t clear. That’s too many steps ahead, said Wolf.

“Are there things in the environment that we can manipulate that could reduce the brainworm prevalence? We don’t know,” she said. “It’s a really complex system, and there doesn’t appear to be just one thing killing the moose. In complex systems, there isn’t just one lever to pull.”


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