Biodiversity cuts back on rates of hantavirus infection

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In ecology and epidemiology, there’s a phenomenon known as the “dilution effect.” The premise is this: the greater the diversity within an ecosystem, the lower the prevalence of zoonotic pathogens. The effect has been reported for a number of diseases, and in a new study University of Utah biologists Laurie Dizney (now at the University of Portland) and M. Denise Dearing have shed some light on how it might work for hantavirus in a population of deer mice in the high desert of Utah.

Deer mice are the natural hosts for the Sin Nombre hantavirus, or SNV. When contracted by humans, the virus can lead to the sometimes fatal Hantavirus Pulmonary Syndrome.

To test the dilution effect in a deer mouse population, the researchers trapped 155 of the rodents on BLM land in Juab County, Utah, and implanted small microchips inside them. They also took a small blood sample to test for SNV infection. Then they distributed an array of feeding trays in the desert, half in areas of high biodiversity and half in areas of low biodiversity. Half of the trays were placed in “protected” spots, offering a bit of protective cover to the hungry mice, while half were left exposed. “Bolder” mice were expected to feed more often at exposed stations, while “shy” ones would prefer to forage at the protected feeders. Each feeding station was equipped with a microchip scanner, to identify the mice when they came to eat, and a camera.

Over the course of nearly seven weeks of data collection, Dizney and Dearing collected more than 3,000 hours of information from the chip scanners and around 1,000 hours of video footage. The videos not only allowed them to look for interactions among deer mice, but also to see what other species were visiting the feeding stations: pinyon mice, western harvest mice, Great Basin pocket mice, Ord’s kangaroo rats, and others.

SNV was four times more prevalent at the collection sites with less biodiversity than those with more biodiversity. That’s despite similar density and demographics of the deer mouse populations.

Deer mice categorized as bold were three times more likely to be infected than those classified as shy. There were proportionally more bold mice in the low biodiversity areas.

This study, while it only offers correlations, is consistent with other previous research, which together imply that infection is the consequence of the boldness-related behaviors, rather than the cause. That’s because the infection is spread through aggressive interactions, and bolder mice are more likely to behave aggressively.

The researchers say that mouse behavior helps to explain the dilution effect. In areas of greater biodiversity, mice are better served by being a bit more timid. That’s because more biodiversity means a greater risk of predation. But with less biodiversity, mice can afford to be riskier, especially if that risk holds the potential for better foraging opportunities or the chance to find other mice to mate with. Unfortunately, that also comes along with the increase in pathogen transmission.

The bottom line is that greater biodiversity appears to buffer the spread of disease, at least for this strain of hantavirus. In societal conversations regarding conservation, one question that is frequently asked is just how conservation benefits humans, and while many argue that wildlife conservation is important for its own sake, here is yet another tool in the advocate’s toolbox. Ecosystems have their own sort of immune systems, and healthier, more robust ecosystems are better equipped to minimize the rate of infection. And that’s good news not just for animals, but also for humans. After all, we all suffer from many of the same diseases– Jason G. Goldman | 06 January 2016

Source: Dizney, L., & Dearing, M. D. (2016). Behavioural differences: a link between biodiversity and pathogen transmission. Animal Behaviour, 111, 341-347. DOI: 10.1016/j.anbehav.2015.11.006.

Header image: Hantavirus-infected deer mouse via Wikimedia Commons