Health Threats to School Children from Rats and Mice
Jerome Goddard, Ph.D.
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Medical Importance. Rats and mice which live in or near human dwellings are called commensal rodents. There are three species of commensal rodents in the U.S.- the Norway rat, the roof rat, and the house mouse. Many other species of "wild" rodents live outdoors - but still may 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, there can be direct effects (not indirect such as disease transmission) of rodents on health such as biting. A study found an average of 500 cases of human rat bite per year in New York City between 1947 and 1953.1 In addition, one public health official estimated that more than 45,000 persons are bitten by rats nationwide each year.1 Rat bites may become infected with a wide variety of bacterial organisms, and there is a medical condition called "rat bite fever".

As to their uncleanliness, rats and mice gnaw through stored food packaging, eating portions of the product, but - perhaps more significantly - contaminating it with their feces, urine, and shed hairs. They also (mostly at night) contaminate food preparation surfaces such as table tops, food production machinery, and cookware in cafeterias. Cafeteria workers returning to work in the morning may think the counter tops are clean, when, in fact, they are covered with tiny drops of urine and hairs. Also, when rats or mice heavily infest a building, the place may become infested with human-biting mites and fleas (from the rodents), as well as taking on a generalized foul odor from the urine. Large areas inside buildings become drenched with urine over time, creating a disagreeable "mousey odor".2

Two notorious human diseases are associated with rats and their fleas - plague and murine typhus. Both diseases occur in rats and get transmitted from rat to rat and from rat to people by fleas. Murine typhus -- a spotted fever like infection -- is one of the most widely distributed arthropod-borne diseases, occurring in ports and coastal areas worldwide. Currently, in the U.S., it is restricted to southern Texas and parts of southern California.3 Plague - the disease that killed one-fourth of the population of Europe during the 14th century - still occurs in many parts of the world, with hundreds of cases reported annually. The disease - especially when it gets in the lungs - may be severe and often fatal. In the U.S., sporadic cases occur mostly in Arizona, California, Colorado, and New Mexico.3 Another human disease, leptospirosis, can also be acquired by contact with rats, their urine, or soil, food, or water containing the causative organism.4 Leptospirosis may cause high fever, rash, severe headache, abdominal pain, and sloughing of the skin.

Wild mice transmit another serious disease. Hantavirus pulmonary syndrome 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. The disease causes a victim's lungs to fill with liquid. Symptoms include muscle aches, fever and possibly chills, headaches, nausea, diarrhea, abdominal pain and coughing. The symptoms develop within one to six weeks after exposure. Hantavirus cases are known to occur mainly in the Southwestern United States and eastward to Pennsylvania.

In addition to disease transmission, introduction of ectoparasites, and food contamination, scientists are now finding out that rats and mice can produce asthma and allergies in the same way cockroaches and dust mites do. There will certainly be more research and new findings in this area in the near future. Apparently, people with allergies can develop hypersensitivity to proteins in rodent urine, causing asthma attacks. Results of skin tests on asthmatic children in major U.S. cities have shown that up to 18% of them have sensitivity to mice and 20% to rats.2,5 In one study, 95% of inner city homes had detectable mouse allergen inside.5 This study obviously points out the need for better rodent control in human dwellings.

Biology of the Pest Species Involved. The house mouse is a small rodent, weighing only ½ to 1 ounce as an adult. Mice are usually dark gray color on the back and light gray on the belly. They may live their entire lives inside buildings, where they eat almost anything. However, they seem to prefer grains, meats, peanut butter, and sweet liquids. The Norway rat, also called the brown rat, wharf rat, or sewer rat, is the most widely distributed rat in the U.S., being found in all 50 states. It is a thick and stocky animal, weighing about 12 to 16 ounces, and with coarse brown fur and a blunt nose. The tail is shorter than the head and body length combined. In contrast, the roof rat (also called the black rat or ship rat) weighs only about 5 to 9 ounces, has a long tail, pointed nose, and blackish fur. Both rat species will eat cereal grains, meats, fish, livestock or pet food, and vegetables. In general, Norway rats nest in burrows in the ground, behind equipment, in wall voids, and the like, whereas roof rats nest in trees, vines, attics, ceiling voids, etc.

Control Options and Health Effects from Non-use of Pesticides. Control of rats and mice involves sanitation to remove food, water, and harborage areas for the pests, exclusion of rodents from buildings (plugging all entry points in a building), mechanical trapping/removal, and baiting with pesticides (rodenticides). Note: rodenticides are placed in tamper-resistant containers to prevent human exposure to the product.

If traditional pesticides (rodenticide baits, in this case) are not available to pest control personnel for the removal of commensal rodents in/around schools, then successful elimination of the pests -- and their associated health risks -- will be extremely difficult, if not impossible. Pesticides should be considered as important "public health tools" in the removal of rodents. Failure to have such tools available to pest control personnel servicing schools will ultimately lead to children being exposed to rats and mice, their bites, and the diseases they carry. In addition, there may be possible liability on the school's part for not having provided a safe, pest-free environment.

References
1. Weber WJ: Diseases Transmitted by Rats and Mice. Fresno, California: Thomson Publications, 1982.

2. Corrigan B: Mice just as important as roaches in allergy studies. Pest Control Technology Magazine (online), GIE Media, Cleveland, Ohio, February 7, 2001.

3. Goddard J: Physician's Guide to Arthropods of Medical Importance. 3rd ed. Boca Raton, FL: CRC Press, 2000.

4. Benenson AS, ed: Control of Communicable Diseases Manual. 16th ed. Washington, DC: American Public Health Association, 1995.

5. Phipatanakul w, Eggleston PA, Wright EC, Wood RA: Mouse allergen. I. The prevalence of mouse allergen in inner city homes. J Allergy Clin Immunol 2000; 106: 1070-1074.

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