Preventing Meningeal Worm with Poultry

Minimize meningeal worm with poultry and habitat modification

Preventing Meningeal Worm with Poultry

Reading Time: 8 minutes

Meningeal worm (Paralaphostrongylus tenuis), also known as brainworm or deer worm, is spread between white-tailed deer and domestic goats, sheep, and other livestock and causes severe neurological problems. Snails act as an intermediate host and vector. When small ruminants consume snails, the larvae migrate through the animal’s brain and spinal cord and can be fatal. Researchers have looked at several poultry predators to mitigate snail populations in the hopes of reducing rates of transmission.

Rachel White, PhD Candidate and Assistant Professor of Sustainable Agriculture and Livestock at the University of Maine Cooperative Extension, pursued a PhD to provide meaningful and scientifically backed approaches to real challenges that farmers face. She’s personally lost sheep to meningeal worm and wanted to explore both the risk factors of transmission and ways to reduce that risk. “Producers have used poultry as an integrated pest management option to combat pests such as beetle and fly larvae,” White explains. “For gastropods, or snails and slugs, in particular, there are limited studies that look at the efficacy of using ducks on agricultural systems, largely targeting aquatic snails. Here in the Northeast, where there are many small farms (200 or fewer animals), losing livestock to parasites such as meningeal worm really makes a financial and emotional impact on the farmer.”

How is meningeal worm spread?

“I call meningeal worm a ‘phantom parasite’ because, unlike other small ruminant parasites, this one has no diagnostic for confirming infection,” White says. Understanding the lifecycle of the worm is important in figuring out mitigation options. In the worms’ natural hosts — white-tailed deer — the infective larvae migrate up the central nervous system without harm to the deer and take residence in the brain cavity where they reproduce. Venous circulation carries the eggs to the lungs, where they hatch into first-stage larvae. From there, they migrate to the esophagus, where they’re swallowed and then released in the feces.

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Third stage (infective) larvae, within snails 10x. Photo Credit: Rachel White
Third stage (infective) larvae, within snails 20x. Photo credit: Rachel White

The larvae penetrate the foot (soft tissue) of the gastropod and develop into third-stage larvae. The third stage is the infective phase, which harms livestock and other wild cervids. When a goat, sheep, or other non-deer host consumes an infected gastropod, they become a “dead-end” host for the worm. They don’t reproduce within the livestock host, so fecal egg counts won’t be detected.

What do meningeal worms do to goats?

“Detection is determined by either differential diagnosis based on symptoms — ataxia (unbalanced gait), hind-end paralysis, blindness, head tilting, and, on occasion, neck and spine hair loss from scratching, or by necropsy,” White says. If they’re feral, they may lose their fear of humans. Identifying the risk factors for meningeal worms is important because rabies has many similar effects

White says even necropsies can be challenging since the larvae are microscopic (~1000 micrometers), and lesions may be missed. Symptoms typically appear 3 to 5 months after initial ingestion of an infected gastropod. She adds this is typically seen in the late fall or early winter since the ruminants most likely encountered and ate the gastropods in the spring when the snow melted and conditions were optimal for gastropod reproduction. When animals eat high doses of larvae, their symptoms can be noticed sooner.

“Different species have different sensitivities to the dose of larvae ingested,” White says. “For instance, goats seem more sensitive to lower amounts, like 5 to 8 larvae, than other animals like sheep. Alpacas are extremely sensitive, with as little as 3 to 5 larvae causing debilitating illness. In my work examining over 6,000 snails, the most I’ve found was 33 larvae — enough to affect larger species like a cow or horse or cause rapid illness and death in sheep and goats. Animals can recover from brainworm infection by an intensive anthelmintic protocol, though they may carry an abnormal gait or other symptoms for the rest of their lives.”

Identify Risk Factors

White recommends that farmers evaluate their operations to determine their risk before implementing a biological control such as poultry. “Areas without white-tailed deer presence and low or no terrestrial gastropods likely have no risk due to the fact that those two host types need to be present for the worms to transfer into livestock.”

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Whitetail deer, Photo Credit: Rachel White

Terrestrial snails and slugs prefer moist and humid conditions to move and survive. Areas with deer overlap on grazing landscapes, combined with gastropods, are a recipe for increased risk. Even if deer only visit pastures in the winter, the first-stage larvae will survive the freezing temperatures and become viable in the spring. In general, 4 in every 100 snails carry meningeal worm.

Here are factors that White says increase transmission risk:

  • Overlap of white-tailed deer, gastropods, and livestock.
  • Wet landscapes (though not always).
  • An abundance of snails. White’s worst case involved walking across a pasture and hearing the audible crunch of stepping on hundreds of snails.
  • “Hot spot” areas with few snails but heavy deer presence. White has a client who has apple trees located between two paddocks. Deer and a hundred or so snails funnel into this tight irrigated space directly adjacent to the goat pens.
  • Biodiverse and broad-leaf plants. Burdock, stinging nettle, and dandelion are plants with a large leaf surface area that captures morning dew or rain and holds moisture. They also have tap roots that draw moisture down into the soil. These plants make little microclimates where the snails and slugs hang out and persist, even in drought conditions.
  • Gastropod species, size, and behavior. In White’s work, most gastropods collected were the amber snails in the family Succinidae. The larger the snail, the longer it has lived and the greater likelihood it carries larvae. These snails are active climbers compared to other snails that mostly move on the ground. Goats and sheep are more likely to accidentally eat a snail that’s climbing tall vegetation. Snails are also most active at night, in the morning, and in humid or wet conditions.
  • High and retained soil moisture. According to White’s research, the most at-risk farms were those with the best pasture and soil management, combined with biodiverse vegetation that included grasses, clover, and dandelions. These farmers intensively rotated their animals every 1 to 2 days and never overstocked their grazing space. Soil moisture was high even in summer drought. This creates ideal conditions for snail survival throughout the grazing season.

Chemical, Physical, and Biological Controls

Luckily, White says there are several ways to mitigate a booming snail population.

  • Various synthetic and chemical molluscicides are marketed for snail and slug control. However, these products might not be ideal for pasture application or garden use, and may not be allowed for organic production.
  • Biological control is typically less expensive and more environmentally friendly than chemicals. Biological strategies can also incorporate native and introduced predators and competitors. Natural predators of terrestrial gastropods include various species of salamanders, frogs, toads, turtles, snakes, birds, rodents, ants, and other gastropods.
  • Habitat modification can include eliminating natural habitats like installing water drainage, picking up debris, or disturbing the habitat by mowing, raking, or rototilling. Creating barriers with gastropod-toxic plants, concrete barriers, or salt may also reduce the risk.
  • Creating barriers for the deer could be another option. While a (minimum) six-foot fence would be needed, snails can cross barriers effortlessly. “Intensive land use practices, such as timber harvesting, mowing, and overgrazing, have correlated with a decline of snail abundance in forested and grassland environments,” White says. “Other organic methods include plucking snails and slugs directly, trapping (using beer), altering irrigation or eliminating wet areas, [and] plant barriers, such as fragrant herbs, may prove useful in preventing and controlling gastropods.”

How can poultry mitigate meningeal worms?

Ducks have been known to reduce terrestrial and aquatic snail populations for thousands of years. White says that some breeds may perform better than others. “In one study, active foraging breeds, like Khaki Campbell ducks, were more effective at consuming golden apple snails than docile meat breeds, like Muscovy. My study, though it hasn’t yet gone through peer review, has shown that Rhode Island Red laying hens (around 200) rotated roughly every four days in a 25,000-square-foot pasture significantly reduce snail populations after exposure to pastures.”

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Khaki- Campbell ducks. Photo credit: Rachel White

White says that not all animals have a palate for slugs and snails. Like children, some animals must be trained to enjoy escargot! Although ducks and geese are usually in aquatic environments where gastropods are ubiquitous, their appetite might be influenced by where they were raised. “These ducks in the lab were older, and I think they lived in a barn,” White says. “So, we actually taught them how to eat snails. It took two weeks for us to slowly start giving them noninfected snails to learn how to eat them.”

Active foraging duck breeds are preferred over heavy meat breeds; the same is true for chickens. “Laying hens going all over the place are pretty effective. Broilers, which just want to sit and get fat, aren’t ideal. Freedom Rangers are a little smaller and designed to be efficient foragers. They might be more efficient than the Rhode Island Reds. I haven’t done this comparison.”

Other fowl possibilities.

Guinea fowl are another species that White is interested in since they’re always out and traveling. “Because there’s a lot of anecdotal evidence that poultry is effective on ticks, I would say, target your foraging breeds and go from there.”

To rule out any potential effects of meningeal worm on birds, White inoculated snails with P. tenuis larvae and fed them to ducks. No ducks developed neurological symptoms, though around 24% of larvae were expelled in the bird’s feces. And since poultry digestive systems are so similar, White imagines the larvae would pass through a chicken in the same way.

“If a farmer identified that their animal’s risk of getting meningeal worm was high and they wanted to incorporate pastured poultry, my recommendation would be to introduce poultry in the spring, when snail numbers are highest, and ahead of grazing animals.”

Traditionally, an integrated pest management strategy would incorporate poultry after the livestock to scratch the manure into the ground and pick at the fly larvae. In White’s research, you would flip the order by introducing poultry before those animals get on pasture to preemptively reduce gastropod populations. White also recommends mowing the field to reduce any microclimate reservoirs where snails might be hiding.

Laying hens in rotation. Photo credit: Rachel White

One risk to animals and humans near chickens is salmonella. “The same farmer with the hot-spot apple tree area won’t use poultry because they’re an organic goat dairy and can’t risk the chance of exposure to salmonella,” White explains. “This bacteria can last 7 to 10 days in the environment in dry conditions and months in puddles or manure lagoons.”

White says to introduce mammals onto poultry-treated areas at least two weeks post-treatment. Producers who choose to have poultry cohabitate with other livestock may want to consider sending a fecal sample to a veterinary diagnostic lab to rule out any pathogenic bacteria.

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Kenny Coogan with ducks. Photo credit: Kenny Coogan.

KENNY COOGAN earned a master’s degree in Global Sustainability and has published over 400 articles on pets, livestock, and gardening. He lives on a 1-acre homestead with a flock of Pekin ducks, managing a permaculture-style landscape. Coogan also runs a successful carnivorous plant nursery in Tampa. Listen to Coogan co-host podcasts by visiting Mother Earth News and Friends Podcast.


Originally published in the 2024 Fall issue of Goat Journal and regularly vetted for accuracy.

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