From mice to men
Researchers hope Portland hantavirus study will prove the value of biodiversity
For Luis Ruedas and his Portland State University graduate students, the discovery that hantaviruses exist in Portland parks was just the first step toward what could be a much larger discovery.
Now they are using their research into the virus and its rodent hosts to test a hypothesis that could have vast implications.
Their theory is: The more biological diversity an area contains, the less likely it is that deadly viruses will break out there and spread to humans.
Ruedas, 42, explains that if the theory holds up, 'then we have an objective criterion for conservation. It's not that it hurts humanity or our souls are going to be poorer when a species dies out.
'No. We have to promote conservation because if we don't promote conservation, then you're going to get sick. And that's all there is to it.'
Mysterious mouse disease
Hantavirus pulmonary syndrome was first identified by scientists in 1993, after a handful of young, physically fit people fell mysteriously ill in the 'Four Corners' area of the Southwest, where the borders of Colorado, Utah, Arizona and New Mexico meet. Those infected with the mysterious disease perished very rapidly from unidentified lung problems.
An investigation by local researchers and the U.S. Centers for Disease Control found that the disease had been spread by deer mice that were carrying a previously unknown type of hantavirus.
The CDC researchers learned that the virus spreads from mouse to mouse during aggressive encounters, such as fights between males during mating season. People generally catch the virus either by touching something contaminated with mouse urine and then touching their noses or mouths, or by breathing air in confined areas such as crawl spaces where tiny particles of rodent urine or droppings are in the air.
Since the Four Corners outbreak, the disease has resurfaced in Louisiana, New York, Canada, Argentina and throughout the Western Hemisphere. Five people have caught it in Oregon during the last decade. Three died.
In spite of the discovery that the virus exists in Portland, the public health risk does not appear high, Ruedas says.
Preliminary results show that about 15 percent of the deer mice captured in Forest Park carry the virus, compared with about 5 percent in Tryon Creek State Park.
The researchers will keep close watch over their findings to assess any possible health threats. But for now, what's interesting to Ruedas and his team is their consistent findings of a lower infection rate in areas of higher biodiversity. That's the big question they'll be studying over the next three years in five Portland area parks.
Beginnings of a theory
Ruedas, who holds a doctorate in wildlife and fisheries sciences from Texas A & M, first began studying hantaviruses in 1995 as part of his postdoctoral work at the University of New Mexico.
He later traveled to Panama as an investigator for the CDC to investigate an outbreak of hantaviruses there. That's where he and a colleague first came up with the seeds of the theory that he is trying to nail down in Portland Ñ that biodiversity is good for human health.
Born in Madrid, Spain, the son of a U.N. official, the trilingual Ruedas has traveled the globe for his research. He has taught in Puerto Rico, gathered museum specimens in the Philippines and documented two previously unknown bat species on the island of Sulawesi, Indonesia.
The potential relationship between his expertise in hantaviruses and his lifelong infatuation with biodiversity first occurred to him in January 2000 in Panama. He found that the virus did not exist in a more biologically diverse area of Panama, near where the outbreak occurred. Later, while he was back to crunching numbers in Atlanta for the CDC, his theory began to take form.
Previous research has long hinted at a relationship between biodiversity and human health. Scientists studying the ecology of lyme disease and malaria have noted that the diseases spread most efficiently when there are many mosquitoes or ticks of one species and relatively little species diversity. It's a theory known as the dilution effect: The impact of a disease is diluted by the number of species present.
For Ruedas to build on this research, he says, his evidence must be objective and indisputable. But he allows that he is not objective going into the effort. 'I like nature,' he says. 'It does hurt my soul when a species dies.
'But how am I going to make other people care? It's like religion. You can't convince a person to become a Buddhist or a Christian or anything else. They have to come to it independently, based on faith.
'If I ask someone to come to my system of beliefs based on my faith, it's a waste of time. It's pointless. There has to be an objective criterion. And this is my objective criterion.'
A meticulous methodology
When Ruedas and his students started their research in Portland, they knew they needed to find virus-carrying mice, quantify the biodiversity in the area that the mice were found, and then investigate the relationship between the virus and the biodiversity.
That's the purpose of the hundreds of live traps that are being meticulously set within Forest Park, Tryon Creek State Park, Oxbow Regional Park, Tualatin Wildlife Refuge and Powell Butte Park.
Deep in a fern-filled forest of mossy cedars and big-leaf maples, two of Ruedas' graduate students, Phil Jones and Laurie Dizney, spent a recent afternoon hauling a truckload of live traps with duct tape straps to a carefully mapped area.
Using cat food and sardines for the small traps, peanut butter and oats for the bigger ones, they bait the traps and add some cotton, so the trapped animal can burrow in and nest for the night.
Then they set the traps along carefully laid-out lines through the forest. Each line is like the spoke in a bicycle wheel 200 meters in diameter. There are 12 spokes in all, with 12 bait stations each, making 145 stations if you count the center. It's a methodology that's been scientifically proved to show actual densities of animals, rather than estimates.
Jones and Dizney and any volunteers they can round up check the traps every morning for four days. They identify and count the animals they capture and don respirators to take blood samples from potential virus hosts. They send the blood samples to a research lab in New Mexico, where they are tested for the virus.
In spite of an encounter with a trapped skunk, a serious lack of funding and $1,000 in vandalism damage to the traps in Powell Butte Park, Jones and Dizney say that the research is progressing well. It's much too early to draw any conclusions, they say, but the preliminary evidence appears to support Rueda's hypothesis.
Jones, a 33-year-old graduate of the University of Missouri, left a corporate position with a Midwestern biotech firm to move to Portland. His goal is to use DNA studies to find out exactly which type of hantavirus exists in Portland, and exactly which types of mice carry them.
It's unclear, for example, whether the Portland mice are the same as those found in the Four Corners outbreak of 1993, or different mice, possibly carrying a different virus.
The more scientists learn about the mice and their viruses, the better they will be able to gauge the threat to public health here and to stem an outbreak if one occurs.
Dizney, 39, got into the fitness business after college, and now that she's returned to school to pursue her doctorate, her conditioning proves useful, as she lugs around the wire-mesh traps for hours on end.
Dizney's job is to keep careful track of the numbers of animals, the species diversity and density, and how the numbers relate to weather patterns, mating seasons and biodiversity.
Like Ruedas, she makes a clear connection between her research and conservation. 'We're trying to get a legitimate reason to preserve these nice diverse areas,' she says.