These vertebrates that expose humans to
disease organisms without benefit of an arthropod vector that cause important human
disease includeds domestic (house mouse, rat) and wild or sylvan rodents. These
animals can infect humans directly with diseases such as tularemia, leptospirosis, arenavirus, hantavirus, ratbite fever,
lymphocytic choriomeningitis and salmonellosis (food poisoning). They also may serve as reservoirs for diseases
transmitted by ectoparasites, such as tick-borne relapsing fever, Colorado
tick fever, Rocky Mountain spotted fever, plague, murine typhus, rickettsial pox,
ehrlichiosis, babesiosis and tularemia.
RODENTS
Domestic or urban and sylvan (wild)
rodents occasionally are targeted for control measures. These rodents not only have the
potential to be annoying and to cause structural damage, but they also threaten by putting
on risk human health. Three species of urban rodents, Mus musculus (house mouse), Rattus
norvegicus (Norway rat) and Rattus rattus (roof rat), create the principal
rodent problems.
HOUSE MOUSE
The most common household rodent is the
house mouse, which resembles the roof rat in that they both have large ears, pointed
muzzles and slender bodies. Small, slender, dusky-gray rodent with a slightly pointed
nose; small, black, protruding eyes; and large, scantily haired ears. House mice are
considered among the most troublesome and economically important rodents in the U.S.
Although they are commonly found living in man-made structures, they are also well adapted
to living outdoors, commonly inhabitants of grassy fields and cultivated grain crops.
These wild populations often move into buildings when weather becomes severe. With poor
vision and by being color-blind, mice use their sense of smell to locate food items and
recognize other individual mice. House mice have acute hearing and readily respond to
unusual noises as a means of detecting and escaping danger. However, they become
accustomed to repetitive, ordinary noises, and as a result, their activities may be more
visible than those of rats. An important sensory factor is touch. Mice use the long,
sensitive whiskers on the nose and above the eyes as tactile sensors. The whiskers and
guard hairs enable the mice to travel easily in the dark along runways close to walls.
House mice feed on a wide range of foods, although they seem to prefer cereals over other
items. In particular, most mice favor the germ of grains. Peak feeding periods are at dusk
and just about dawn. Due to their small size, mice must feed several times during a
24-hour period and thus are active day and night. They normally range 10 to 30 feet from
the nest, which is often lined with soft materials such as cotton or paper and may be
built in walls, cabinets, upholstered furniture or other convenient spaces. Urine and
droppings mark the trail for others. Unlike some rats, mice are poor swimmers.
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Rats
We find two types of urban rats, the Norway rat and the Roof rat. The Norway rat is a
burrowing rodent. It has a blunt muzzle, small eyes and short, close-set ears, with
whitish-gray hair on the belly. Its nearly naked, scaly tail is dark on the top and light
on the underside and is shorter (6 to 8½ inches) than the combined length of the head and
body (7 to 10 inches). Adults weigh 12 to 18 ounces. The feces are capsule-shaped and
about ¾ inch long. Norway rats can be found in warehouses, farm buildings, houses,
sewers, rubbish dumps, woodpiles and building foundations. They are good climbers and can
reach a distance of 13 inches while standing on the ground and jump 24 inches vertically.
The Norway rat has relatively poor vision but keen senses of smell, touch, taste and
hearing. The sense of touch is served by long whiskers on the snout. The home range is
often 100 to 150 feet. Norway rats are mainly nocturnal, but they may be active in
undisturbed places during the day. They feed on virtually anything edible. The roof rat
(black or ship rat) is somewhat smaller and is a more agile climber. It has several color
phases, a slender body, prominent ears and large eyes. Roof rats have large, membranous
ears and sharply pointed muzzles. The unicolored, nearly hairless tail (7½ to 10 inches)
is usually longer than the head and body combined (6½ to 8 inches). The adult weights 8
to 12 ounces, and the feces differ from those of the Norway rat in that they are about ½
inch long and spindle-shaped. Serious pest populations of roof rats are confined along the
southern and western coastal areas of the country. Normally rats and mice are nocturnal,
so recognition of various signs is necessary in determining population levels. Some of
these signs are burrows, gnawing activity, fecal droppings, runways, rub marks, tracks and
carcasses. Reproduction, mortality and movement into an area determine the potential size
of rodent populations, whereas physical environment, food, shelter, water, predation, and
competition control the actual population size.
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