Montana mice may hold the secret to how viruses spread

Researchers are studying how climate change and biodiversity affect viruses’ jump from animals to people.

 

For the past 20 years, Amy Kuenzi has spent three days of every month traveling to a ranch near Gregson, Montana, and setting out traps that contain peanut butter and oats. Her quarry is deer mice. She takes blood samples, looks for scars and fleas, and attaches ear tags.

“Mice are fairly trap happy and easy to catch,” she said. “But it can be kind of a miserable job in the winter.”

Kuenzi’s goal is to better understand how a type of hantavirus called Sin Nombre spreads through these mouse populations.

Kuenzi, a professor of biology at Montana Technological University, and her colleague Angie Luis, a professor of biology at the University of Montana, are among a growing number of researchers working to predict where viruses may be likely to spill over from animals to humans. Sixty percent of human diseases, including the Sin Nombre hantavirus, originate in animals, and two-thirds of those originate in wildlife.

By understanding hantavirus and the complex ecology that governs it, Kuenzi and Luis also hope to create a model system to better understand the ecology of many other viruses, including coronaviruses.

The researchers have built six large enclosures at the Bandy Ranch, a University of Montana research facility. There, they can study how deer mice behave when they’re the sole occupants and then introduce the mice’s main rodent competitors, voles, to see how mouse populations, mouse behavior, and disease prevalence change.

“We are trying to understand that as we stress animals, as we add or remove competitors, how does that change the transmission?”

“We’re asking how competitors affect the transmission of disease,” Luis said of the research, recently funded with a $2.5 million National Science Foundation grant. “We are trying to understand that as we stress animals, as we add or remove competitors, how does that change the transmission?”

Researchers in Montana are studying how a type of hantavirus called Sin Nombre spreads through populations of deer mice. Understanding this could help researchers predict where viruses may be likely to spill over from animals to humans.
( Lydia Zuraw/KHN illustration; Getty Images; CDC/Cynthia Goldsmith

The role of biodiversity in zoonotic diseases is complex and can have both positive and negative effects. For example, competition from other rodents can lower deer mice numbers and reduce how often the mice interact, limiting infections. At the same time, the presence of more competitors can stress deer mice, and stress in animals has been shown to lower their immunity and greatly increase their viral load.

Climate change is also a factor. Warmer temperatures and fluctuations in rain and snow are changing habitats, which can affect infection rates. The first recognized outbreak of hantavirus in humans, in 1993, is thought to have been driven by a wet winter that provided more food for mice.

The Montana study area has only two main rodents, making it a simple system for carrying out research. Kuenzi and Luis are also gathering data in the Southwest, where Sin Nombre is far more prevalent — and complicated. “At one site in Arizona, we caught 29 species of rodent-sized small mammals,” Kuenzi said. The larger number of species appears to decrease the prevalence of the disease, Luis said.

Sin Nombre, Spanish for “without a name,” is one of several types of hantavirus. It is transmitted through the inhalation of airborne particles from mouse droppings. The disease is rare in humans but can be deadly. In 1993, the first known outbreak was on the Navajo Nation in the Southwest. It killed 13 people, half of those it infected.

The disease is most prevalent in rural areas, where mice and other rodents are common, and public health officials urge people to take special care when cleaning homes or buildings that have been closed for the winter or when working in areas like crawl spaces or vacant buildings where rodents may be present.

In 2012, Sin Nombre in tent cabins in Yosemite National Park killed three people. In 2004, the deputy superintendent of Glacier National Park died from the disease. From Sin Nombre’s discovery in 1993 through 2019, fewer than 900 infections were reported in the U.S.

The hope for the research in Montana is that it will lead to recommendations on how to manage land in ways that don’t increase the prevalence of the disease.

This is just one thread in the tapestry of disease ecology. The long list of factors that increase the possibility that pathogens will spill over from animals to humans is getting a lot of attention from researchers around the world in response to the pandemic caused by SARS-CoV-2. Viral outbreaks are a product of the ways that humans are altering the natural world, though researchers are seeking to determine precisely how.

In the big picture, research from the past 20 years shows that keeping nature intact will help minimize the risk of another pandemic. “Evidence is mounting that biodiversity dilutes out disease,” Luis said. “As we lose biodiversity, we see greater disease prevalence.”

“As we lose biodiversity, we see greater disease prevalence.”

When animals can move to find food when they need to and avoid humans and domestic animals, “we are not going to see spillover events,” said Raina Plowright, a professor at Montana State University, who studies the disease ecology of bats.

Activities that bring people into contact with wildlife — such as farming, logging, and building homes in wild areas, all of which change the ecosystem — may amplify the risk of spillover.

It could, for example, drive the competitors of deer mice out completely. “Deer mice like disturbance,” Luis said. As land is developed, species that compete with deer mice may scatter, and without competitors, deer mice increase in number. With more mice come more encounters between them and the spread of Sin Nombre.

Early studies of biodiversity and disease took place in upstate New York, where the fragmentation of forest habitat by development had led to the loss of foxes, owls, hawks, and other predators. Those changes drove a five-fold surge in the number of white-footed mice, which are potent reservoirs for the bacteria that cause Lyme disease.

But the idea that biodiversity has protective effects is more complicated than first thought. “There are lots of exceptions to this idea that biodiversity dilutes out disease,” Luis said. “You can get both positive and negative effects of biodiversity at the same time. There is an overall dilution effect because competitors lower the density of deer mice,” she said, but there might be amplification from stress caused by competitors.

Kevin Lafferty is an ecologist with the U.S. Geological Survey’s Western Ecological Research Center in Santa Barbara, California, and studies the ecology of parasites. Focusing on the ecology of mice and hantavirus makes sense, he said: “If wild rodents … are going to become more abundant because we disturb the environment, then those particular diseases might be the kind of things we should worry about.”

However, the broad notion of protecting biodiversity to prevent disease is “wishful thinking,” he said. “That’s a vague and ineffective way to solve human health problems,” Lafferty said. Instead, he added, researchers should focus on how the viruses’ hosts respond to the environment.

Luis agreed that more work needs to be done on a complicated topic. “Outbreaks that are moving from animals to humans have only become more common over the last 30 to 40 years,” Luis said. “This is not the last pandemic. We need to understand how what we are doing leads to these outbreaks.”

Jim Robbins is a veteran journalist based in Helena, Montana. His latest book is the The Wonder of Birds: What they Tell Us about the World, Ourselves and a Better Future.

We welcome reader letters. Email High Country News at [email protected] or submit a letter to the editor. See our letters to the editor policy.

KHN (Kaiser Health News) is a national newsroom that produces in-depth journalism about health issues. Together with Policy Analysis and Polling, KHN is one of the three major operating programs at KFF (Kaiser Family Foundation). KFF is an endowed nonprofit organization providing information on health issues to the nation.

High Country News Classifieds
  • MEMBERSHIP AND OFFICE MANAGER - FRIENDS OF THE INYO
    Friends of the Inyo - Donor database management & reporting, IT/HR, and office administrative support. PT or FT. Partly remote OK but some in-office time...
  • NORTHERN NEW MEXICO PROJECT MANAGER
    New Mexico Land Conservancy is seeking a qualified Northern New Mexico Project Manager to provide expertise, leadership and support to the organization by planning, cultivating,...
  • GRAPHIC AND DIGITAL DESIGNER
    Application deadline: December 17, 2022 Expected start date: January 16, 2023 Location: Amazon Watch headquarters in Oakland, CA Amazon Watch is a dynamic nonprofit organization...
  • EXECUTIVE DIRECTOR
    Eugene, Ore. nonprofit Long Tom Watershed Council is seeking a highly collaborative individual to lead a talented, dedicated team of professionals. Full-time: $77,000 - $90,000...
  • GIS SPECIALIST
    What We Can Achieve Together: The GIS Specialist provides technical and scientific support for Geographic Information System (GIS) technology, data management, and visualization internally and...
  • LOWER SAN PEDRO PROGRAM MANAGER
    What We Can Achieve Together: The Lower San Pedro Program Manager directs some or all aspects of protection, science, stewardship and community relations for the...
  • FOREST RESTORATION SPATIAL DATA MANAGER
    What We Can Achieve Together: The Forest Restoration Spatial Data Manager fills an integral role in leading the design and development of, as well as...
  • WATER PROJECTS MANAGER, SOUTHERN AZ
    What We Can Achieve Together: Working hybrid in Tucson, AZ or remote from Sierra Vista, AZ or other southern Arizona locations, the Water Projects Manager,...
  • SENIOR STAFF THERAPIST/PSYCHOLOGIST: NATIVE AMERICAN STUDENT SPECIALIST
    Counseling Services is a department strategically integrated with Health Services within the Division of Student Services and Enrollment Management. Our Mission at the Counseling Center...
  • THE NATURE CONSERVANCY IS HIRING A LOCAL INITIATIVES COORDINATOR
    The Nature Conservancy in Wyoming seeks a Local Initiatives Coordinator to join our team. We're looking for a great communicator to develop, manage and advance...
  • LAND AND WATER PROTECTION MANAGER - NORTHERN ARIZONA
    We're Looking for You: Are you looking for a career to help people and nature? Guided by science, TNC creates innovative, on-the-ground solutions to our...
  • SENIOR CLIMATE CONSERVATION ASSOCIATE
    The Greater Yellowstone Coalition (GYC) seeks a Senior Climate Conservation Associate (SCCA) to play a key role in major campaigns to protect the lands, waters,...
  • EXECUTIVE DIRECTOR
    The Southern Nevada Conservancy Board of Directors announces an outstanding opportunity for a creative leader to continue building this organization. SNC proudly supports Nevada's public...
  • CORTEZ COLORADO LOT FOR SALE
    Historic tree-lined Montezuma Ave. Zoned Neighborhood Business. Build your dream house or business right in the heart of town. $74,000. Southwest Realty
  • ENVIRONMENTAL AND CONSTRUCTION GEOPHYSICS
    - We find groundwater, buried debris and assist with new construction projects for a fraction of drilling costs.
  • STRAWBALE HOME BESIDE MONTEZUMA WELL NAT'L MONUMENT
    Straw Bale Home beside Montezuma Well National Monument. Our property looks out at Arizona fabled Mogollon Rim and is a short walk to perennial Beaver...
  • ATTORNEY AD
    Criminal Defense, Code Enforcement, Water Rights, Mental Health Defense, Resentencing.
  • LUNATEC HYDRATION SPRAY BOTTLE
    A must for campers and outdoor enthusiasts. Cools, cleans and hydrates with mist, stream and shower patterns. Hundreds of uses.
  • LUNATEC ODOR-FREE DISHCLOTHS
    are a must try. They stay odor-free, dry fast, are durable and don't require machine washing. Try today.
  • PROFESSIONAL GIS SERVICES
    Custom Geospatial Solutions is available for all of your GIS needs. Affordable, flexible and accurate data visualization and analysis for any sized project.