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Rats and Mice


Rats and mice that live in or near human dwellings are called commensal rodents. There are three species of commensal rodents in the U.S. They include: the roof rat, the Norway rat and the house mouse. Many other species of "wild" rodents live outdoors but may still occasionally be encountered by people.


Commensal, or domestic, rodents are of tremendous public health importance. They may eat or contaminate human food, carry ectoparasites such as mites and fleas into close human contact, cause allergies in sensitive individuals and be disease carriers. In addition to their uncleanliness, rats and mice gnaw through stored food packaging, eating portions of the product and contaminating it with their feces, urine and shed hairs. They also (mostly at night) contaminate food preparation surfaces such as counter tops, table tops and cookware.


Two notorious human diseases that are associated with rats and their fleas are murine typhus and plague. Both diseases occur in rats and can be transmitted from rat to rat and also from rat to human by fleas. Murine typhus is a spotted fever like infection. It is one of the most widely distributed arthropod-borne diseases. Plague, the disease that killed one-fourth of the population of Europe during the 14th century, still occurs in many parts of the world today with hundreds of cases reported annually. The disease, especially when it gets into the lungs, may be severe and often fatal.


Another human disease, leptospirosis, can also be acquired by contact with rats through their urine, feces, food, or water containing the causative organism. Leptospirosis may cause high fever, rash, severe headache, abdominal pain and sloughing of the skin.


Wild mice transmit another serious disease called hantavirus pulmonary syndrome. This is a rodent-borne virus that can cause severe respiratory problems and even death. Hantavirus is spread through the urine, saliva and feces of rodents, especially the deer mouse. Humans contract the disease by breathing dried particles of their urine or feces. This can occur by cleaning an indoor area that was infested by deer mice. Hantavirus causes a victim's lungs to fill with liquid. Symptoms can develop within one to six weeks and include muscle aches, fever and possibly chills, headaches, nausea, diarrhea, abdominal pain and coughing.


Roof Rat and Norway Rat


The roof rat, also called the black rat or ship rat, weighs only about 5 to 9 ounces. It has a long tail, a pointed nose and blackish fur.

The Norway rat is larger and more aggressive than the roof rat. As an adult the Norway rat can weigh between 12-16 ounces with a body length of 6-8 inches long. It has small ears, a blunt nose and small eyes. Their fur is shaggy and coarse with variations in color. The tail is scaly and shorter than the head and body combined. Their droppings are 1/4 to 1/2 inch in length and capsule shaped with blunt ends. They are usually shiny black, but color can vary depending on their diet.

Roof rats and Norway rats will leave behind foot tracks of about 3/4-1 inch, whereas mouse tracks measure 3/8 of an inch or less. Rats will also drag their tails, leaving a mark between their feet tracks. Unscented baby powder or flour lightly sprinkled can help you determine tracks and the rat's runway as they cross suspected areas. Gnawing holes from rats are about 2 inches or more in diameter. Both rat species will eat cereal grains, meats, fish, livestock, pet food and vegetables. In general, roof rats tend to nest in trees, vines, attics, ceiling voids, etc... Whereas Norway rats nest in burrows in the ground, behind equipment, in wall voids and the like.

House Mouse

The house mouse is small and slender and about 1-2 inches long excluding it's tail. It has large ears, a pointed nose and small eyes. The tail is as long as the head and body combined. Their fur color varies, but it is usually a light grey or brown. Their droppings (feces) are about 1/8-1/4 inch long and rod shaped. They gnaw small, clean holes about 1-1 1/2 inches in diameter.

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