This document summarizes the updated recommendations
from the Centers for Disease Control and Prevention (CDC) for rodent control
in and around homes and workplaces. The information is adapted from the
Morbidity and Mortality Weekly Report, July 26, 2002; Vol. 51; No. RR09.
Rodent control in and around buildings remains the
primary strategy in preventing hantavirus infection. Rodent infestation
can be determined by direct observation of animals, or inferred by observation
of their nests or feces on floors or in protected areas (e.g., closets,
kitchen cabinets, drawers, wall voids, furnace and water heater cabinets,
behind ventilation screens), or from evidence that rodents have been gnawing
on food or other objects. The interiors and exteriors of all buildings
should be carefully inspected at least twice a year for any openings where
rodents could enter and for conditions that could support rodent activity.
If any evidence of rodent infestation is detected inside the buildings,
precautions should be taken. The guidelines in the "Worker Protection"
section should be followed if a building is associated with a confirmed
case of hantavirus disease or if evidence of heavy rodent infestation
is present (e.g., piles of feces or numerous nests or dead rodents).
Consult an NPS Integrated Pest Management (IPM)
Coordinator for assistance with severe or persistent infestations. Recommended
control measures include rodent-habitat elimination, rodent proofing,
good sanitation practices, and trapping. Your IPM Coordinator can help
you establish a comprehensive rodent management strategy.
Preventing Rodents from Entering Buildings by
- Look for and seal up all gaps and holes inside
and outside the building that are >¼ -inch (>6 mm) in diameter.
Inside the structure, look for and seal up all gaps and holes underneath,
behind, and inside kitchen cabinets; inside closets; around floor air
vents and dryer vents; around the fireplace; around windows and doors;
behind appliances (e.g., dishwashers, clothes washers, and stoves);
around pipes under the kitchen and bathroom sinks; around all electrical,
water, gas, and sewer lines (chases); and beneath or behind water heaters,
radiators, and furnaces and around their pipes that enter the building.
Outside the building, look for and seal all gaps and holes around windows
and doors; between the foundation of the structure and the ground; under
doors without thresholds, door sweeps, or weatherstripping; around electrical,
water, gas, and sewer lines (chases); and around the roof, eaves, gables,
and soffits. In addition, look for unscreened attic vents and crawlspace
vents. In trailers, look for and seal holes and gaps in the skirting,
between the trim and metal siding, around utility lines and pipes and
ducts, around roof vents, and around the trailer tongue.
- Seal all entry holes >¼-inch (>6
mm) in diameter that are inside and outside the building with any of
the following: cement, lath screen or lath metal, wire screening, hardware
cloth (<¼-inch grate size), steel wool, STUF-FIT* or other
patching materials. Caulk and expanding foam can be used to reinforce
any repairs where lath metal, hardware cloth, steel wool, or STUF-FIT
are the primary materials. Expanding foam alone is effective about 90%
of the time.
- If rodent burrows are found under foundations
or trailer skirtings, construct a barrier around the entire foundation
using 14-inch-wide (35 cm), <¼-inch (<6 mm) mesh, 16-19
gauge hardware cloth. Bend the hardware cloth lengthwise into a right
angle, with two sides of approximately 7 inches (18 cm). Secure one
side of the hardware cloth tightly to the building siding. The other
side should be buried at least 2 inches (5 cm) below ground level and
extend away from the wall.
Additional information is available in the NPS guide
for rodent proofing structures (Mechanical
Rodent Proofing Techniques).
Precautions for the Outsides of Buildings
- Place woodpiles and
stacks of lumber, bricks, stones, or other materials >100 feet from
- Store grains and animal feed in rodent-proof
- Remove, from the vicinity of buildings any food
sources that might attract rodents.
- Keep pet food covered and stored in rodent-proof
containers. Allow outdoor pets only enough food for each meal, then
store or discard any remaining food from feeding dishes.
- Avoid using bird feeders near buildings. If they
must be placed near the building, use "squirrel-proof" feeders
and clean up spilled seeds each evening.
- Dispose of garbage and trash in rodent-proof
containers with tight-fitting lids.
- Haul away trash, abandoned vehicles, discarded
tires, and other items that might serve as rodent nesting sites.
- Mow grass closely, and cut or remove brush and
dense shrubbery to a distance of at least 100 feet from structures.
Trim the limbs off any trees or shrubs that overhang or touch the building.
- Use concrete foundations in new construction
of sheds, barns, and outbuildings. The top of the foundation should
be at least 6 inches above ground level.
- Place spring-loaded snap traps in outbuildings
and in areas that might likely serve as rodent shelter, within 100 feet
around buildings; use these traps continuously, replacing the bait periodically.
For instructions concerning the safe use and cleaning of spring-loaded
snap traps and the disposal of trapped rodents, see "Precautions
for Inside of Buildings," below.
Precautions for the Insides of Buildings
- Keep food and water covered and stored in rodent-proof
- Keep pet food covered and stored in rodent-proof
containers. Allow pets only enough food for each meal, then store or
discard any remaining food. Do not leave excess pet food or water out
- If storing trash and food waste inside, do so
in rodent-proof containers, and frequently clean the inside and outside
of the containers with soap and water.
- Wash dishes, pans, and cooking utensils immediately
- Remove leftover food and clean up all spilled
food from cooking and eating areas.
- Clean empty aluminum cans or other empty containers
prior to storage.
- Dispose of trash and garbage on a frequent and
regular basis, and pick up or eliminate clutter.
- Keep items (e.g., boxes, clothes, blankets) off
of the floor to prevent rodents from nesting in them.
- Repair water leaks and prevent condensation from
forming on cold water pipes by insulating them. Deny rodents access
to moisture (e.g., mop closets, boiler rooms, catch basins under potted
plants, and areas around aquarium tanks). Useful indicators for the
identification of sources of moisture are growth of mold, mildew, or
other fungi inside buildings.
- Keep exterior doors and windows closed unless
protected by tight-fitting metal screens.
- Use spring-loaded snap traps with a small amount
(the size of a pea) of peanut butter as bait. Place the trap perpendicular
to the baseboard or wall surface, with the end of the trap containing
the bait closest to the baseboard or wall. Place traps in areas where
rodents might be entering the building. Spring-loaded traps can be painful
or even dangerous if they close on fingers; they should be handled with
caution, and placed were children and pets cannot reach them. Live trapping
or the use of sticky boards is not recommended.
In the western United States (west of the 100th
meridian, a line from mid-Texas through mid-North Dakota), a risk of plague
transmission to humans from fleas exists. Use insect repellent (containing
N,N-diethyl-m-toluamide [DEET]) on clothing, socks, and hands to reduce
the risk of flea bites when picking up dead rodents and traps. In cases
of heavy rodent infestation in indoor spaces in the western United States,
use an insecticide before trapping. Contact your NPS Public Health Consultant
to find out if plague is a danger in the area, and, together with the
IPM Specialist, for advice on appropriate flea-control methods. The use
of repellents and insecticides must be reviewed and approved by the appropriate
NPS IPM Specialist.
- Continue trapping
for at least 1 additional week after the last rodent is caught. As a
precaution against reinfestation, use several baited, spring-loaded
traps inside the building at all times in locations where rodents are
most likely to be found. The bait must be replaced occasionally to keep
- Examine traps regularly. To dispose of traps
or trapped animals, wear rubber, latex, vinyl, or nitrile gloves. Spray
the dead rodent with a disinfectant or chlorine solution. Wait 10 minutes
after thoroughly soaking the rodent to ensure deactivation of the virus,
then either take it out of the trap by lifting the spring-loaded metal
bar and letting the animal fall into a plastic bag or place the entire
trap containing the dead rodent in a plastic bag and seal the bag. Place
the rodent into a second plastic bag and seal it. Dispose of the rodent
in the double bag by burning it or placing it in a covered trash can
that is regularly emptied. Contact the state or local health department
concerning other appropriate disposal methods.
- If the trap will be
reused, decontaminate it by immersing and washing it in a disinfectant
or chlorine solution and rinsing afterward.
- For severe or persistent
infestations, contact an NPS IPM Specialist.
When resident mice are removed from buildings without
measures to prevent reentry, they are replaced almost immediately by other
mice from the outside. Therefore, indoor rodent-trapping will be unsuccessful
in reducing rodent infestations without simultaneous efforts to rodent-proof
*STUF-FIT is a soft copper-mesh material that might
be preferable to steel wool because it does not rust and is not easily
pulled apart by rodents. It can be obtained from pest control supply houses
or from Allen Special Products (telephone 800-848-6805).