University of Montana researcher Angela Luis has been awarded a National Science Foundation grant to study how diversity of competitor species affects infectious disease transmission in wildlife – specifically hantavirus in deer mice.
Luis earned the five-year, $2.5 million grant from NSF's Ecology and Evolution of Infectious Disease Program. She is an associate professor of population and disease ecology in the University's W.A. Franke College of Forestry and Conservation.
The goal of the study is to learn more about how to predict increases in hantavirus in rodents, and, ideally, help prevent its spread to humans, Luis said. While transmission to humans is rare, hundreds have died from the infection in the U.S., and hantaviruses have killed tens of thousands of people worldwide.
The study's underlying principles also could apply to other wildlife-based human diseases. Luis said this is especially important as biodiversity disappears rapidly and infectious diseases increasingly spill over from wildlife to humans.
The big question for this study is how do competitors affect transmission of disease."
Angela Luis, Researcher, University of Montana
Within an ecosystem, species interact with one another. In Montana, for example, a mountain lion might prey on an elk calf. Other species – called competitors – jockey for resources. Deer mice, say, compete with montane voles for habitat and food.
Changes in biodiversity – how many species and what species are on the landscape – can affect all sorts of things, including how disease is spread among animals and from animals to humans. How exactly that works, though, is still up for debate.
Luis said there is debate among disease ecologists centered around the ideas of "dilution" and "amplification" – whether increased species diversity decreases or increases disease risk, respectively – and, specifically, when to expect one process or the other.
In some ecosystems, increasing competitor diversity decreases disease risk. This is called the dilution effect because higher species diversity dilutes out infection.
"The idea is that if you have a more diverse community, you'll have less disease transmission," Luis said. "It's a nice public health message, right? If we are protecting biodiversity, we are protecting ourselves."
However, as Luis explains, that's not always the case.
"You don't always see that correlation. You sometimes see the opposite," she said.
A more diverse community also sometimes can increase disease risk – the amplification effect.
"Sometimes if you have more wildlife around, you have more wildlife around that could infect humans," she said. "The dilution effect is not universal."
Current scientific research hasn't fully uncovered when to expect one effect over another, and it's unknown how these competing forces may work within one disease system.
Luis' new project will examine potential causes of dilution and amplification and how they interact to help move beyond the debate and instead clarify which mechanisms are most important in determining disease transmission. It also will identify any patterns about when one process might occur over the other.
"We're starting to say, it depends, and that's what I'm trying to get at," she said. "What does it depend on? Why do you sometimes get more of one than the other? Let's look at what's driving the pattern."
Luis will study three ways that competitors could affect hantavirus transmission rates in deer mice:
- First, competitors can reduce host density, reducing the number of mice across the landscape.
- Second, they can impact contact rates by changing the way mice interact with one another.
- Finally, they can impact immunity by stressing mice. When mice are stressed out, their immunity generally drops, leaving them more vulnerable to disease.
The project will consist of three phases.
In the first phase, Luis' team will monitor natural populations of deer mice at three long-term field sites. This involves trapping deer mice and competitors to understand what the community looks like and how many of those animals are infected with hantavirus.
The second phase involves manipulating populations.
"We built these six big enclosures at Bandy Ranch that are about 30 meters by 30 meters," Luis said. "We can put a certain number of deer mice in there and a certain number of competitors in there and see how they are changing the deer mice's behavior and immunity."
The third component involves analyzing long-term datasets from Montana and from the Southwest spanning 25 years, showing how competitors have affected deer mice populations.
At the end of the study, researchers also will conduct a broad analysis, fitting all of the research findings together to come up with mathematical models that predict when you might expect dilution or amplification in certain scenarios.
Amy Kuenzi, a professor at Montana Tech, is co-principal investigator on the grant. The grant also will help fund three UM doctoral students, a postdoc position, a lab manager position and a number of undergraduate field technician roles.
"The landscape is changing – largely from humans – through all these different anthropogenic things like habitat loss or conversion, climate change," Luis said. "All of these things that people are doing affect the wildlife communities on the landscape, which can affect transmission of nasty things back to them.
"As we've seen with the pandemic, zoonotic disease outbreaks – 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."
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