Rodents are members of the order Rodentia, a sub-category of the class Mammalia. They consistute the largest category of mammals, making up about 40 percent of that class. Some familiar members of the order are beavers, guinea pigs, hamsters, mice, porcupines, rats, and squirrels.
An associated anatomical feature in rodents is the presence of a relatively large jaw and jaw muscles adapted to produce the chewing and gnawing action associated with the animal's dentition. The powerful muscles pull the lower jaw back and forth during chewing and gnawing. Most rodents are primarily herbivores, although some are carnivorous, with insects a popular secondary food. They have evolved a wide variety of lifestyles, ranging from the tree homes of flying squirrels to burrows of gophers and mole rats to aquatic capybaras.
Rodents are responsible for at least 35 human diseases worldwide. These diseases can be contracted in one of two ways, direct contact or indirect contact with a rodent. In the former case, a pathogen may be transmitted from a rodent to a human when a person comes into contact with saliva, feces, or urine from an infected animal. For example, one might accidentally rub against rodent feces or urine or inhale dust that contains small amounts of feces or urine. In some cases, a person might actually pick up a contaminated rodent, such as a pet rat or pet guinea pig that has become infected with a pathogen. The pathogen is then transmitted by accidental inhalation or ingestion of the pathogen or through contact with an open sore or wound in the skin. It some cases, a person may become infected as a result of being bitten by a rodent. Some diseases that are transmitted directly from rodent to human are the following:
Indirect disease transmission involves an intermediary stage between the rodent carrier of a disease and the ultimate human host for the pathogen that causes the disease. For example, Lyme disease is transmitted when a tick (in the United States, the blacklegged tick [or deer tick, Ixodes scapularis] or the western blacklegged tick [Ixodes pacificus]) bites a rodent whose blood is contaminated with the Borrelia burgdorferi bacterium. When the tick then later bites a human, it transmits that bacterium in its saliva to the human bloodstream. Some diseases that are transmitted indirectly from rodents to humans include the following:
Every disease listed here has its own characteristic methods of diagnosis, treatment, and prognosis.
A preliminary diagnosis of a rodent-related disease can often be made on the basis of characteristic signs and symptoms, along with a patient history that might reveal situations in which the patient may have been exposed to rodents or other disease-transmitting vectors. A confirmatory diagnosis often depends on bloodwork through which the causative agent can often be identified through microscopic analysis or other testing.
Bacterial infections are most effectively treated by one or more antibiotics, the specific choice made being based on the infection involved. For example, the drugs of choice for treating babesiosis are atovaquone in conjunction with azithromycin or clinamycin and quinine. Treatment of cutaneous leishmaniasis generally makes use of pentavalent antimony (such as sodium stibogluconate) and treatment for RMSF usually makes use of doxycycline.
Generally speaking, rodents tend to be a more serious source of disease in regions that lack adequate levels of sanitation. Garbage piles, for example, tend to attract rats and mice, who then become a primary host for pathogens responsible for a variety of human diseases. So the first recommendation in efforts to reduce rodent-associated disease is to maintain as high a level of sanitation as possible. In developed nations, where solid waste disposal, sewage treatment, and other sanitation procedures tend to be common, the problem of rodent control often becomes one for individual households or businesses. The Centers for Disease Control and Prevention (CDC) recommends a three-prong effort to control rodents in the home and the workplace. The three prongs are Seal Up! Trap Up! Clean Up!
The Seal Up! aspect of this progrm involves identifying apertures through which rodents can enter a building and sealing those apertures. Rodents are clever animals who will find and utilize openings almost anywhere, from cracks in basement walls to openings along roof lines. The Trap Up! aspect of the program refers, as the name suggests, to the use of traps to capture and kill rodents such as rats and mice. The CDC recommends traditional spring traps that kill a rodent rather than a live trap because the latter may allow the rodent to defecate or urinate within the building, leaving behind any pathogens that it may be carrying. Finally, the Clean Up! stage of the program emphasizes sanitary procedures that will discourage rodents from congregating near a building, procedures such as storing food in tight containers, keeping outdoor grills clean, hanging bird feeders at a distance from the main house, using a tightly fitting lid on garbage cans, and keeping composting devices at sufficient distance from the house to discourage rodents from entering the premises.
Humans have been using a variety of chemicals for centuries in their efforts to bring the rodent population under control. At one time, the most popular rodenticides were compounds containing a heavy metal, such as arsenic or thallium. Somewhat later, chemists developed other compounds that acted by interrupting the normal blood clotting process in an animal, causing a rodent to begin hemorrhaging and eventually bleeding to death. The anticoagulant warfarin was once a popular ingredient in such products. Some objections were long raised to the use of such products believing that they were accompanied by severe pain and discomfort by the drugged animal, who often took days or weeks to die after ingesting the poison. Probably a more serious concern with such rodenticides was their potential for harm to humans who accidentally ingested the product.
As a result of these concerns, chemists have developed a second generation of rodenticides that, while still potentially unpleasant for the rodent, are safer for use in human environments. These products make use primarily of the poisons bromethalin, chlorophacinone, and diphacinone. The U.S. Environmental Protection Agency (EPA) has warned chemical manufacturers that rodenticides produced after June 4, 2011, that do not meet its new and higher standards for rodenticide safety will face the probability of action by the agency for removal of their older and more risky products.
See also Hantavirus infections ; Lyme disease ; Sanitation .
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David E. Newton, EdD