With new funding from the Environment and Natural Resources Trust Fund, researchers from the University of Minnesota, Grand Portage Band of Lake Superior Chippewa, and Virginia Tech University are collaborating to improve moose survival and health by mapping brainworm transmission in northern Minnesota.
Five years of data — collected and analyzed by the same collaborators from 2013–2018 — reflect that brainworm is associated with 25–33 percent of mortalities among the declining Minnesota moose population.
“Historically, moose were the primary subsistence species to the Grand Portage Band of Lake Superior Chippewa,” says Seth Moore, director of biology and environment at the Grand Portage Band of Chippewa. “But harvests have declined in recent years following declines in Minnesota moose populations.”
Moose are a culturally vital species to the Grand Portage Band, Moore continued.
“Researching moose health and sustainability with an intention to improve management is critical to reversing the declining trend,”he said. “We hope to learn how and where brainworm transmission occurs on the landscape so that we can manage habitats to reduce that risk.”
Brainworm is spreading to moose in northern Minnesota by the increased population of white-tailed deer in the region — a result of warming temperatures up north due to climate change. Less severe winters and shallower snow depths lead to higher deer survival rates and an increasing population trend in deer.
White tailed deer, the definitive hosts, shed brainworm larvae in their pellets. The larvae then mature in an intermediate host- one of several species of terrestrial snails and slugs — before becoming infectious to moose and other ungulates. Moose ingest infected snails when they browse vegetation. The matured larvae then migrate to meningeal tissue, which surrounds the moose’s brains and nervous systems. Rather than remaining there, as they do in deer, the matured larvae tunnel through moose brain and spinal tissue. The result for infected moose is neurological disease and often death.
Now, few options for mitigating the spread of brainworm exist, other than controlling white tailed deer populations. This new project presents an opportunity for a novel approach to mitigating the spread of brainworm. Instead of controlling white tailed deer populations in Grand Portage, the researchers hope to track brainworm’s movement across moose and deer habitats. They hope to observe the natural landscape and climate barriers to the spread of this disease, and manipulate those obstacles in future mitigation efforts.
“Generally speaking, there is some reluctance to reduce deer density on the landscape to the level that would halt transmission of brainworm from deer to moose,” said Tiffany Wolf, assistant professor, Veterinary Population Medicine, University of Minnesota College of Veterinary Medicine. “The transmission of this parasite requires a third host — snails and slugs — and that presents additional opportunities to impact transmission. It’s certainly a complex pathway, and there are a lot of gaps in our knowledge about where and when transmission to moose occurs. But, thanks to this support, we have an opportunity to close some of those gaps.”
The Legislative-Citizen Commission on Minnesota Resources recommended this work for funding from the Minnesota Legislature, which recently awarded roughly $400,000 over the course of three years — from 2020 to 2022 — to the project. In the project’s first phase, the researchers will use spatial analysis to pinpoint areas of habitat where moose and deer overlap. They will then identify specific landscape and climatic characteristics of those spaces and create a spatial risk map of where brainworm is most likely to be transmitted across the two species.
Snails and slugs are known intermediate hosts of brainworm, but which species are most important in the transmission of the disease is still unknown. In the project’s second year, the researchers will collect deer and moose pellet samples to identify and quantify snail and slug species consumption. They will then identify which snail and slug species are primary diet components in each moose habitat type.
Lastly, the scientists will map the parasite’s genetics to look for patterns of transmission across the landscape. They will collect fecal samples from across habitats in Grand Portage, where a high density of deer are currently being studied. By mapping brainworm population genetics, the scientists can describe gene flow of the parasite and identify, and eventually leverage, natural landscape barriers that impact transmission.
“The Minnesota Legislature has helped us further our college’s mission by supporting this work,” says Molly McCue, DVM, MS, PhD, interim associate dean for research at the University of Minnesota College of Veterinary Medicine. “They have emboldened our talented researchers to help solve some of the issues faced by Minnesota, and we are incredibly grateful for their investment in our work.”
Early support through UMN crowd-funding and the Van Sloun Foundation facilitated the development of tests these researchers used on genetic material recovered directly from fecal samples. These tests will be used again in this project, allowing the researchers to genetically profile the parasite and detect snail and slug DNA in feces.