UNIVERSITY OF UTAH MEDIA RELEASE
Contacts:Denise Dearing, biologist - office (801) 585-1298Lee Siegel, university science news specialist - cell (801) 244-5399, office (801) 581-8993Rachel Mackelprang, biologist - (after Feb. 13)- office (801) 581-4333
HANTAVIRUS COMMON IN MICE NEAR OFF-ROAD RECREATION AREA
Feb. 10, 2001 - University of Utah biologists found nearly 30 percent of deer mice were infected with hantavirus around central Utah sand dunes popular with people who ride off-road vehicles (ORVs).
The scientists said more research is needed to determine if the high infection rate among deer mice near the federal Bureau of Land Management's Little Sahara Recreation Area was caused by ORV traffic that has created dirt roads and trails. They theorize that when ORVs denude rodent habitat, the animals are crowded into remaining areas of vegetation, leading to increased fighting, biting and scratching that allows the virus to be spread among mice when saliva and blood enter their wounds.
"We found an unusually high prevalence of hantavirus in deer mice we caught near the Little Sahara Recreation Area in central Utah," said Rachel Mackelprang, the study's principal author and a senior in biology at the University of Utah. "Given the previous research and all-terrain vehicle use, the unusually high prevalence could be due to the habitat being disturbed by off-road vehicles."
"It's a hypothesis we need to test," said study co-author Denise Dearing, an assistant professor of biology at the university. "From what we know about small-mammal ecology and transmission of hantavirus, it seems that human disturbance [of the landscape] could alter transmission of hantavirus" among rodents.
Dearing said researchers simply do not know if increased prevalence of hantavirus among mice raises the risk of transmission to humans. Mackelprang said she doubts there is any increased danger to the thousands of people who camp and ride ORVs in the area.
"We presume the danger to people camping there is minimal because hantavirus is transmitted to humans as an aerosol" or dust that people inhale when mouse feces or urine become airborne, Mackelprang said. "Humans usually get it in enclosed spaces like a garage or basement they are sweeping out. If you are outdoors, there is no chance of breathing such concentrated dust."
Mackelprang said ORVs usually kick up sand from areas denuded of vegetation, rather than creating finer dust or aerosol particles from vegetated areas inhabited by the mice.
Nevertheless, Dearing added, "without further research we really don't know how higher prevalence [of hantavirus in deer mice] will affect people in the outdoors."
The study by Mackelprang, Dearing and Stephen St. Jeor, a virologist at the University of Nevada, Reno, has been accepted for publication in the May-June issue of the journal Emerging Infectious Diseases, but is expected to appear in the journal's online edition in the next week or so. The journal is published by the federal Centers for Disease Control and Prevention (CDC).
The hantavirus in the mice at Little Sahara is a strain known as the Sin Nombre virus, which was identified as the cause of an outbreak of potentially deadly hantavirus pulmonary syndrome (HPS) that was first recognized in May 1993 in the Four Corners states of Utah, New Mexico, Arizona and Colorado.
From the time of that outbreak through Dec. 7, 2000, 277 cases of hantavirus pulmonary syndrome have been reported in the United States, and 38 percent resulted in death, according to the CDC, which listed a total of 14 cases in Utah.
Data for the new study were collected when Mackelprang and Dearing trapped deer mice, wood rats (also known as packrats), pinyon mice, kangaroo rats, pocket mice and sagebrush voles in non-dune areas around Little Sahara during three seasons in 1999: May 29-31, July 10-12 and Oct. 7-9. Those areas are riddled with dirt roads and trails from ORVs, and often provide unimproved campsites for people unable to find space at official campgrounds.
The biologists set up three live animal traps at about 40 wood rat nesting sites called middens, which are 7-foot-diameter, 2-foot-high mounds made of thousands of sticks. The traps were baited with oats, peanut butter and cotton, which rodents like as nesting material.
Captured rodents were anesthetized briefly so blood samples could be obtained. St. Jeor tested the blood samples for the presence of antibodies to hantavirus. In some viral diseases, antibodies indicate past infection but not necessarily current infection. Deer mice infected with hantavirus remain infected chronically, so the antibodies indicate which mice are infected, Dearing said.
Of 212 deer mice captured during the three trapping periods, the antibody test indicated 63 were infected, for a prevalence of 29.7 percent. That was almost three times greater than the infection rate found in other studies of similar habitats within the Great Basin of Utah and comparable to the infection rate seeing among deer mice in areas where the 1993 hantavirus pulmonary syndrome outbreak happened, Dearing and Mackelprang said.
The study also found hantavirus antibodies in four of 37 pinyon mice that were tested, or 10.8 percent, although the biologists do not know if the deer mice spread the virus to pinyon mice or vice versa. Hantavirus infection was not found in other species at Little Sahara, including the wood rats.
Mackelprang and Dearing cite several arguments to support the hypothesis that disturbance of the landscape by ORVs may be responsible for the high prevalence of hantavirus among deer mice around Little Sahara.
First, studies in Kansas and Europe have shown that when rodent habitats are disturbed - either by roads or when fields are mowed to create unmowed "islands" of grassy habitats - the density of deer mouse population increases dramatically. Second, those studies show deer mice in such fragmented habitats travel farther than mice in undisturbed areas.
Third, other research has shown small rodents living in denser populations become more susceptible to infection than rodents that are less crowded. Fourth, an earlier CDC study found only 11 percent of deer mice were infected with hantavirus in four other Great Basin sites with habitat similar to the scrub and pinyon-juniper habitats around Little Sahara.
Dearing said the researchers did not set out to study how ORV use affects hantavirus prevalence in rodents, but instead chose to study Little Sahara because wood rats occupy the area and, in previous work, Dearing had found that wood rats there sometimes carry hantavirus.
Mackelprang said she is an inactive member of the Sierra Club, and Dearing has donated to environmental groups. Both believe there should be a balance between protecting fragile landscapes and having land available for enthusiasts who enjoy riding ORVs such as trucks, dune buggies, motorcycles and small three- and four-wheeled all-terrain vehicles (ATVs). But they said their study is not an effort to combat ORV use.
"We want to emphasize we are not on a vendetta against ATVs," Mackelprang said. "This is just what we found, and a hypothesis that seems to fit the data."
Dearing said that if scientists can learn how transmission of hantavirus is affected by human disturbances to the landscape, "maybe we can do things to reduce transmission to humans. For example, when people put a cabin in the woods, if they clear the area around the cabin [for fire safety] and then deer mice move into the cabin, it is essentially creating a habitat 'island.' Maybe by leaving some brush to make that 'island' more continuous with the rest of the habitat, you might reduce the density of deer mice" near and inside the cabin.
Dearing plans to apply to the National Institutes of Health for a five-year grant of $650,000 to test the hypothesis that ORV damage to the landscape increases hantavirus prevalence among deer mice. If the funding is approved, she plans to compare hantavirus infection rates in rodents in undisturbed and disturbed areas.
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