If you are someone who thinks, “I grew up with mice around. I can’t get sick from them.” – think again. According to the Montana Department of Public Health and Human Services’ (DPHHS) Public Health and Safety Division, 39 cases of hantavirus have been reported in Montana from 1993 through March 2015. Ten of those cases have resulted in deaths. Hantavirus can occur at any time of the year, with the majority of Montana cases being contracted in the spring (46%) and summer (31%).
Rodents in North America known to carry hantavirus include the deer mouse, cotton rat, rice rat, and white-footed mouse. Both the deer mouse and white-footed mouse exist in Montana, however, the deer mouse has been identified as the reservoir of the virus by Montana DPHHS. Recent studies revealed that 13% of deer mice tested in Montana have antibodies to hantavirus in their blood and 75% that have the antibodies actually have the virus in their blood.
Deer mice range in color from pale grey to a dark reddish brown on the top of their tails and backs, with white legs, feet, and stomach. The deer mouse is found across Montana, lives in all terrestrial habitats, and is a year-round resident. The Centers for Disease Control and Prevention (CDC) describe Hantavirus Pulmonary Syndrome (HPS) as an acute, sometimes fatal, respiratory disease. While there are several types of hantavirus, the Sin Nombre Virus (SNV) is responsible for most of the cases in the U.S. and is found in the western and central United States. HPS is contracted when humans
encounter mice and rodents infected with hantavirus. The Montana State University MontGuide, “Hantavirus: What is it? What can be done about it?” states that the most common method of transmission is people inhaling airborne rodent urine, fecal, or saliva particles. It can be contracted when dried materials which contain rodent feces are disturbed and that material contacts broken skin, mucus membranes (i.e., eyes, nose, etc.), or is ingested in water or food that’s been contaminated. In rare instances, people bitten by rodents have become infected. SNV cannot be transmitted through human to human contact and domestic pets have not been known to carry it.
Hantavirus infection produces symptoms similar to the flu, including:
• Fever that does not respond to medication (101 to 104°F)
• Muscle and body aches (thighs, hips, back, and sometimes shoulders)
• Fatigue
The symptoms listed above are universal but some people also experience chills, nausea, vomiting, diarrhea, and abdominal pain.
Symptoms may appear one to six weeks after contact with the virus and usually occur within two to three weeks of exposure. The duration of symptoms varies, lasting from only a few hours to several days. Later stages of the infection, usually four to 10 days after the initial phase, are marked by severe, rapidly progressive respiratory failure. If you experience any of these symptoms and have been in a location where you may have come in contact with rodents, seek medical attention immediately. Tell your attending physician or practitioner that you have been in contact with rodents.
There is no cure, treatment, or vaccine for hantavirus. Infected individuals who seek medical attention and are placed in an intensive care unit may do better than those who are not. These patients are intubated and given oxygen therapy to help them through the most acute periods of respiratory stress.
HPS can be prevented by eliminating or minimizing contact with rodents. Take steps to ensure that your home, workplace, or campsite, etc. is free of easy-to-get food and that holes and gaps in and around foundations are blocked. If mice become a problem, examine your home’s exterior and interior for gaps that are more than ¼-inch in diameter and seal any that are larger with cement, lath screen or lath metal, wire screening, hardware cloth (less than ¼-inch grate size), or any other patching material. While caulk and expanding foam can reinforce the materials previously mentioned, they are usually not enough to stop a rodent on their own.
The following procedures are recommended by the CDC to clean up after mice and rats. First, always wear gloves. Spray urine and droppings until very wet with a disinfectant or a mixture of one part bleach and nine parts water. Let the droppings soak for five minutes. Use a paper towel to wipe up the droppings or urine. Dispose of the towel in an outside garbage container. Mop or sponge the area with a disinfectant or bleach solution. Do not sweep or vacuum up rodent droppings, nests, or over areas where urine is present. This can cause particles to become airborne and possibly become ingested. If you work in a high-risk environment, the CDC recommends the following:
• Know the symptoms and prevention measures of the disease.
• If you develop an illness with a fever or respiratory symptoms within 45 days of possible exposure to rodents or their nests, seek medical attention immediately. Communicate with your medical provider that you have been exposed.
• When cleaning rodent-infested areas, wear a respirator. Use one with the OSHA-approved Type 100 filter, commonly called a ‘HEPA filter.’
• People regularly exposed to rodent-infested areas should wear coveralls (disposable, if possible), rubber boots or disposable boot covers, rubber or plastic gloves, protective goggles, and a mask.
• Personal protective gear should be decontaminated upon removal. If coveralls are not disposable, they should be laundered on site or immersed in liquid disinfectant until they can be washed.
For more information about hantavirus, its symptoms, and how to prevent contracting it, contact your local MSU county or reservation Extension office or your local Environmental Health Department.