Rats & Hantavirus

Jefferson County Public Health (JCPH) protects residents against diseases that can be spread by animals, including rats. Generally, rats are simply a nuisance and do not pose a public health risk in Colorado.

However, according to the Centers for Disease Control and Prevention (CDC) [external link], rats and mice spread more than 35 diseases worldwide. These diseases can be spread to humans directly, through handling of rodents, through contact with rodent feces, urine or saliva, or through rodent bites. Diseases carried by rodents can also be spread to humans indirectly, through ticks, mites or fleas that have fed on an infected rodent.

In Colorado, Hantavirus [external link] is a disease of concern carried by deer mice. Information about other diseases that can be carried by rodents [external link].

The primary strategy for preventing human exposure to rodent diseases is effective rodent control in and around the home. The guide below has helpful information for effective rat control. 

For additional information about rodent control, please visit: the CDC rodent index [external link]. You can also contact Duane Dominguez, Environmental Health Specialist at JCPH, at 303-271-5745.

Download a helpful fact sheet about rats in and around homes.


A Guide for Safe and Effective Rat Control

The following information provides detailed directions for effective and nontoxic control of rats that you can use to keep your home, business or property free of rats — or remove them after they’ve appeared.

Why are Rats Here?

  • Residences and businesses provide everything a rat needs to survive — food, water and shelter.
  • Rats have reproductive peaks in the spring and in the fall. The average female rat can wean 20 or more offspring a year. Rats in cities and towns normally live for five to 12 months.
  • Rats will eat any food that people or their pets consume. They may also store hoarded food in walls, furniture and appliances. In cities, there is ample food from bird feeders, dog pens, vegetable gardens, chicken coops, garbage cans, dumpsters and compost piles.
  • Unless disturbed, a rat colony may infest the same alley, basement or, building year after year; construction and building renovations may cause them to disperse to other areas.

Prevent Rats From Becoming a Problem: How to Rodent-Proof Your Home or Business

Sanitation and exclusion (keeping pests from entering) are the most important ways to prevent a rodent infestation in the first place or to keep them from coming back once you treat a problem. While cats and owls are predators of rats, there are usually not enough to keep rodent numbers down. Additionally, some house cats don’t have the inclination to prey on adult rats.

Take these steps to rodent-proof your home or business:

1. Manage exterior landscaping. Avoid low-lying shrubs and vines, such as creeping juniper, next to buildings and fences. Remove tree branches within five feet of the building. Mow tall grass and weeds. Don’t give rats a place to hide.

2 .Remove clutter both inside and outside the building. Remove boxes, rubbish and other debris that may have accumulated. Do not store firewood against house or building. Remove old furniture, vehicles and appliances from your property. Don’t give rats a home.

3 .Manage food sources. Store large bags of dog food or birdseed in metal or heavy-duty plastic cans. Pick up pet food dishes at night. Secure compost piles and recycling bins so that they are inaccessible to rodents. Remove animal waste (feces) every day from your yard. Animal waste contains undigested pet food that rats will eat. Don’t provide food sources.

4. Keep dumpsters and garbage cans clean and secure. Dumpsters should be an adequate size so that there is no overflow. There should be no leaks or breaks under or on the sides. Lid covers should be in place (and used). Drain plugs should be in place. Dumpsters containing food trash should be stored 25 to 50 yards from buildings.

5. Use a durable trashcan with a tight-fitting lid. Do not put out trash in plastic bags. Rats will chew through them and feast on your leftovers.

6. Rodent proof houses, garages, sheds and other buildings by sealing any potential entrances. Conduct a detailed inspection of the building for entry points. A rat can enter an opening the size of its skull — ½ inch high and ¾ inch wide. In order to exclude both rats and mice, seal any hole larger than ¼ inch. Potential entry points include garage doors, door thresholds, chimneys, exterior lines (electrical, water, gas) leading through walls, openings in building foundations and dryer vents. Make sure doors, windows and screens fit tightly. Coarse steel wool, copper mesh, wire screen and lightweight sheet metal are excellent materials for plugging gaps and holes. Rats are likely to gnaw away plastic sheeting, wood, caulking and other less sturdy materials.

Do you have a rat problem?

Inspect your home, business, yard and surroundings. If you answer yes to the questions below, you might have a rat problem.

  • Do you see rats traveling along fences or walls? Rats forage for food mainly at dusk and again prior to dawn, but, if the area is quiet and undisturbed, they may forage during the daytime.
  • Have you found rat nests behind boxes or in drawers in the garage?
  • Have you seen rat droppings? Fecal pellets are ¾ inches long and ¼ inch in diameter, smooth, rectangular in shape, dark colored and usually found in small groups. Look for droppings (one rat produces 40 to 50 pellets a day) in a 100-foot radius around outside dog pens or areas used to store pet food, birdseed or chicken seed. 
  • Are there rat droppings in your recycle bins or in/around your garbage cans?
  • Have you seen burrows and/or digging? Rats live in subterranean burrows. Burrows are about 3 inches in diameter; the entrance looks compacted and smooth. An active burrow is free of cobwebs and debris. In urban and suburban areas, rats often burrow around buildings, beneath slabs and alongside building foundations. Junk and clutter on the ground, as well as areas with dense vegetation, are also favored. Look in these areas around both residential and commercial structures:
  • Alongside walls of gardens raised using railroad ties
  • Beneath low-lying bushes
  • Along fence supports where dense vegetation (ivy, Virginia creeper, etc.) is covering fence
  • Under slab walkways
  • Under low-lying decks, along garage walls or storage sheds
  • Under compost piles or chicken coops
  • Are there smooth, well-packed “runways,” such as worn-down paths in the grass? Runways are used between the nest and food source, and the average distance a rat travels from its nest is 25 to 100 feet. Rats usually travel along structural lines, such as a fence or wall. Indoors, rats prefer continual body contact with at least one vertical surface such as a wall near ground or floor level.
  • Have you seen gnawing damage around openings — shallow, parallel grooves left by incisors? Each mark is about 4 mm in width.
  • Are there defunct sewer system lines in your neighborhood?
  • Do you have woodpiles or wood stored on the ground? Have you noticed remnants of rat nests when stacking or unstacking firewood?
  • Are there rub marks caused by the rats rubbing their fur along wall/floor junctions and at regularly used openings?
  • Have you ever had to remove a drowned rat from your swimming pool or hot tub?
  • Have you heard gnawing, scrambling or squeaking noises in the walls? Is there a musky smell?

Best Practices for Eliminating Rats — Use Snap Traps

Snap traps are lethal traps that quickly and humanely kill rats as they attempt to eat thRat Trape bait. There are several advantages to using snap traps.

  • They provide a quick solution to a rodent emergency.
  • Using traps will minimize the chances of decomposing rodent odors and fly problems.
  • Most mechanical traps can be reused many times.
  • They are nontoxic, which means they are less likely to harm children, the environment or other animals

Although it takes patience and strategy, snap traps are an effective and a nontoxic method to eliminate a rodent infestation. However, it is important that rat traps are used safely to ensure that people, particularly children, pets and non-target animals do not accidentally encounter the traps. When placing traps indoors, place traps in darkened corners, along walls or behind appliances and objects.

You may wish to hire a professional to install traps. But ensure that you understand the principles for effective trapping and don’t assume that a pest control service will use these techniques unless you require it when you hire them. 

Using Traps Effectively

If you choose to trap on your own property, follow these guidelines.

  • Rats are cautious of new objects. Place the trap(s) in the location where there is the most rodent activity. For example, if there is a hole in the floor or wall used by the rodents, place several traps in the area, but away from the opening. You can also place traps 8 to 12 inches away from runways. Avoid placing traps directly in the line of frequently used travel lanes.
  • Monitor areas where the rat might travel, such as runways or burrow openings. You can apply talcum powder to monitor suspected areas or use video cameras with low-light options and wide-angle lenses. These techniques may provide the clues needed to reveal the rat’s secretive behavior. Some professionals have used thermal imaging devices to locate elusive rats in hard-to-reach areas.
  • Place rat traps about 10 to 20 feet apart. Use as many traps as are practical so trapping time will be short and decisive.
  • Place traps unset and baited for 2 to 3 days prior to setting the traps. Place baits in a small trail leading towards the snap trap, as well as on the edges of the trap. This lets the rat associate food with the new object.
  • In a building, place traps along a wall so that they extend from the wall at right angles, with the trigger end nearly touching the wall. Rats like to touch surfaces, like a wall, when they move.
  • Place different kinds of bait in traps. Divide up the traps with meats, peanut butter or even nesting material, such as soft strips of cloth. If rats are not attracted to the trap, try enticing them with a gourmet option, such as fresh meat or shrimp.
  • Whenever possible, eliminate the rat’s regular food source. Remember that rats are wary of new things, so, if there is abundant food elsewhere, it is not likely to try “new” food in a trap.
  • For personal hygiene, wear disposable gloves when installing or recovering any animal traps. However human odors on traps are not likely to deter most rodents.
  • If these steps are followed carefully, the majority of rats will most likely be caught on the first night. Install many traps at the beginning. Continue trapping for three to four more nights and continue watching for signs of rats.

Make sure that you rodent-proof your property and follow the guidelines for removing food and shelter to prevent another infestation.

Why NOT to Use Poison or Other Types of Traps

Poison baits or rodenticides, which are pesticides that kill rodents, are not recommended because of the risk to children, pets, non-target animals such as hawks or other birds of prey, coyotes or bobcats, and environmental concerns.

Rodenticides can harm pets or non-target animals by “secondary poisoning,” where the pet or animal preying on a poisoned rat is also poisoned. An example is when a cat, dog or bird of prey eats a rodent that is dying or has been killed by rodenticides.

Rodenticides are applied as a bait, which contains an attractive food plus a toxin. Rodent baits can be dangerous to children, pets or non-target animals from ingestion of the bait. Bromethalin is one type of rodenticide that poisons the central nervous system. Most other rodenticides are blood-thinning drugs called anticoagulants.