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UI Hygienic Lab offers tips for guarding against hantavirus infection

IOWA CITY, Iowa -- During the fall and winter months, houses or outbuildings can provide a haven for mice and other rodents. They're a nuisance for sure, but they pose a more serious health risk: the spread of hantaviruses.

Hantaviruses include several different strains, some of which cause hantavirus pulmonary syndrome (HPS). This life-threatening disease is marked by flu-like symptoms -- high fever, severe body aches, chills, troubled breathing and cough -- which progress rapidly to severe lung disease. There is no known cure or vaccine for HPS. In the United States, the disease's mortality rate is high -- about 37 percent.

The illness first made headlines in 1993 when health officials in the Southwestern United States investigated a cluster of deaths among young people in the region. Researchers learned that the disease was caused by a hantavirus and transmitted by infected mice. Since then, more than 170 cases of the illness have been identified among humans in 28 states.

The first confirmed case of HPS in Iowa occurred last spring and caused the death of a north-central Iowa man who resided in a rural area near Alden.

There are at least 10 strains of hantavirus worldwide, of which four have been identified as causing HPS in humans. The primary carrier of the HPS strain is the deer mouse. It is four to nine inches in length from head to tail and ranges in color from pale gray to reddish brown, with white fur on its belly and feet. The deer mouse is highly adaptable and is found in different habitats, including human residences and rural areas, but generally not in urban areas.

"The virus is transmitted mainly in the airborne particles of rodent urine, droppings or saliva," says Dr. Tom Gahan, virologist at the University of Iowa Hygienic Laboratory. "However, transmission also may occur when fresh or dried materials contaminated by rodent droppings come into contact with broken skin, are introduced into the eyes or, possibly, ingested in contaminated food or water. People also have become infected after being bitten by rodents." In South America, a strain of the HPS virus appears to be transmissible from human to human, but this has not been documented in the U.S.

"Researchers at the Centers for Disease Control and Prevention (CDC) have implicated strain differences to account for this distinction," says Dr. Mary Gilchrist, director the UI Hygienic Laboratory, "but we still have a lot to learn about this disease."

Last August, Mike Birmingham, a field researcher at the Hygienic Laboratory, and researchers from the CDC, the Iowa Department of Public Health and Iowa State University spent three days collecting blood, tissue and organ samples from rodents on the farmstead of the Alden man who died from HPS. The researchers trapped about 25 rodents, including deer mice, whitefooted mice, shrews and prairie voles. Shrews are not known to carry hantaviruses, Birmingham notes, while voles are known to carry some strains of hantavirus, but not the strains that cause HPS in humans.

The Hygienic Laboratory and the CDC divided the rodent samples, and both laboratories did analyses to compare results. They did not find the HPS-causing strains in the mice they had collected, but did detect in two vole samples antibodies to a hantavirus strain that's currently being studied to see if it causes the disease in humans.

"Actually, the people from the CDC weren't all that surprised," Birmingham says, "because we just didn't catch that many mice for testing. With the '93 outbreak in the Southwest, there was a massive infestation of mice, probably due to climatic factors."

Some scientists have speculated that hantavirus infection in the U.S. is prevalent during wet weather seasons, particularly pronounced El Niño years, Gilchrist notes. "If this is the case, we might see more infections in humans this winter," she says.

People at a higher risk for hantavirus infection include families who move into homes, particularly in rural areas, that rodents have infested; campers and hikers; electricians, plumbers and others who work in crawl spaces; and farmers who clean barns, outbuildings and grain storage areas. "Especially in the fall and winter, as rodents look to move indoors, people need to be aware. The best prevention is to keep all rodents from entering your home and to carefully clean and disinfect areas where rodents have been detected," Gilchrist says.

The Hygienic Laboratory offers these tips for guarding against hantavirus:

* Keep your home and/or any outbuildings clean. Keep all grains or other edible materials like birdseed in rodent-proof cans. Eliminate storage of stuffed furniture or other potential sources of rodent bedding in outbuildings. Ventilate all areas of the house or outbuildings before cleaning.

* Prevent rodent entry and dispose of any rodents in your home. Use steel wool or cement to seal any holes in your house.

* Use outside control measures. Cut grass and brush within 100 feet of the house. Move woodpiles, gardens, trash cans and animal feeders at least 100 feet from the house.

* Disinfect areas where rodents may have been. Always wear rubber gloves during cleanup. To minimize dust, do not vacuum or sweep before mopping.

For more information on hantaviruses and HPS prevention, contact the UI Hygienic Laboratory at (319) 335-4500, or the Iowa Department of Public Health at (515) 281-5787. Hantavirus information from the CDC can be found by calling 1-800-532-9929 or visiting the CDC World Wide Web page at