Common Rats

Size: Rats are larger rodents that may grow to a body length of 10 to 12 inches. Seldom will a rat weigh more than one pound.
Color: Can vary from gray to brown to black.

Introduction:

Norway rats, found throughout the U.S., have a heavier body, smaller eyes and ears, and a shorter tail. Found in coastal states, roof rats have long tails, thin bodies, and large eyes and ears. Rats are more prevalent in urban and rural areas, and are found in homes less often than mice because of their larger size.

Rats are extremely important pests on the farm. Hamilton (1947) states, "On the farm, rats eat incredible quantities of foodstuffs, destroy poultry, lay waste the stored fruits and vegetables, and riddle buildings with their sharp teeth. Rats tear down growing corn, eat melons, pumkins and tomatoes on the vines, and even take an appreciable toll of cherries, climbing the tree in search of the fruit." Rats also are a major problem to the poultryman. They destroy feed, carry disease and kill chicks. Various estimates suggest That rats destroy or contaminate at least 20 percent of the world's food supply.

Diseases Carried By Rats

Disease organisms may be transmitted directly through the rodent's bite, carried from the rodent (i.e.,vectored) by a flea, tick or mite which bites man and transfers the pathogen, or by contamination of food or water with feces or urine.

Hantavirus

By now, most avid readers of newspaper, pest control trade magazines, and a variety of other publications have probably heard about hantavirus. The disease has various strains that may induce symptoms as minor as high blood pressure or as deadly as pulmonary collapse due to fluid buildup and the overwhelming of the body defenses. The hantavirus strain know as hantavirus pulmonary syndrome (HPS; also sometimes referred to as Muerto Canyon hantavirus or Four Corners hantavirus) was first identified in 1993 in New Mexico and is one of the deadliest known strains of the disease. It produces pneumonia-like symptoms that can quickly become severe; 40% of the more than 100 cases of HPS that has been documented in the U.S. since 1993 have been fatal. The various strains of hantavirus occur in different rodents, primarily mice. The Four Corners strain is known to occur in field mice or deer mice and is transmitted to humans through dried fecal material. This mouse is commonly found in rural areas and occasionally suburban areas, but rarely in urban settings. Most urban cases of hantavirus are likely due to the victim visiting a rural area and contracting the disease there, then returning home. It should be noted that none of the three most common urban rodent pests --the house mouse, the norway rat, or the roof rat -- have been found to carry hantavirus. When in a suburban setting, where dried mouse feces are present, it is best to err on the side of safety and assume the worst.

Salmonella

Associated with exposure to rotting food, salmonellosis may occur after contact with infested droppings of either rats or mice. The salmonella bacteria can enter victims via the mouth, by inhalation, or through direct contact with open cuts or sores. The disease is also commonly associated with bird infestations.

Plague

The great plague of London that killed more than half of the city's inhabitants, and the "black death" that devastated Europe for more than 50 years in the 14th century, killing some 25,000,000 individuals, were in part due to the abundance of rats. The plague-infected rats carry plague-infected fleas which in turn infect man. Fortunally, such epidemics no longer devaste Europe, yet it is estimated that from 1898 to 1923 11 million lives were lost from the plague in India, China, Mongolia and other parts of Asia. Plague is a bacterial disease of the circulatory and respiratory systems. The germ Yersinia pestis, which invades the body, was discovered independently in 1894 by the Japanese investigator Kitsato. At the time it was established that rat plague and human plague were identical. In man, plague may manifest itself in four ways:

( 1 ) Bubonic plague. Here the blood is infested and the bacilli are arrested in the lymph glands, particulary in those of the groin and under the armpits, resulting in inflamed glands or buboes which suppurate. This is the most common form of plague and results from the bite of a flea. The mortality may range from 40 to 70 percent. It should be noted bubonic plague also can be contracted by contact of the abraded skin with infected dust or body fluids.

( 2 ) Septicemic plague. In most serious cases the lymph glands fail to arrest the bacilli, which appear in large numbers in the blood. Numerous hemorrhages occur under the skin, which turn black, accounting for the name "Black Death". This form of plague also is spread by the bite of an infected flea, but since the disease in this case is very virulent, death nearly always results.

( 3 ) Pneumonic plague. Here, where the bacilli are in the lungs, we have the most dangerous form of plague from a public health standpoint, since it is spread so readily through contact and coughing, as well as by the consumption of contaminated food. This form of plague nearly always results in mortality above 90 percent. It is now thought that the initial 14th century European plague outbreak was of this form, since the spread was so rapid.

( 4 ) Sylvatic plague. This form of plague wherein the virulence is greatly diminished. Groundsquirrels presumably contracted the plague in San Francisco in 1900, so now it is enzootic or established in wildlife in this country. This form of plague was first discovered in 1908 and gradually spread throughout the West. It is now found in ground squirrels, wood rats, deer mice and woodchucks. Silver (1927) states: "The sylvatic form of the plague is apparently not highly contagious to man, as an average of only about one human case each year has been reported. The menace, however, remains a most disturbing one because of the ever-present possibilities that house rats may become reinfested in the population centers and that human cases of bubonic plague contracted from native rodents may develop the secondary, or pneumonic form, which is highly contagious directly from person to person." Elsewhere in the world, plague remains active. Major endemic (and enzootic) foci occur in Africa, Asia and South America. Murinetyphusfever. USPHS (1948) states there are two kinds of typhus fever, "epidemic or European, and endemic or murine. The epidemic form is transmitted from person to person by body lice, while murine typhus is contracted from domestic rodents, probably both rats and mice, rats being the more active in spreading infection. If louse-infested individuals contract murine typhus, the infection may then be transmitted by the patient's lice to other people."