Rodents

RODENTS (Rodentia), an order of mammals, mostly small or medium-sized; herbivorous. Of the teeth, the incisors are especially well developed; they wear down when gnawing food but possess unlimited growth; there are no canines; the molars have a folded surface; between them and the incisors there remains a free space. The total number of teeth ranges from 16 (mice and moles) to 28 (rabbits). In the first case, the dental formula has the following appearance: . 1-1 0-0 ™У=¹⁶; in the second: ^г1-1' з-з m|El-26. The lower jaw can move forward and backward and in both directions, which, in connection with the shape of the surface of the molars, facilitates more perfect grinding of hard-to-digest plant food. They are plantigrade. Their stomach is simple. The penis is disc-shaped with a deciduous sheath. The order of Rodents is divided into many families; some of them have great importance for man. The harm caused by Rodents to man is determined by a) spoiling food products, stocks, household items, furnishings, water pipes, and buildings, b) the ability of Rodents to be reservoirs of viruses transmitted to man, or to suffer from diseases common to man, c) the possession of parasites, also transmitted to man or domestic animals. Some Rodents are of benefit to man, since a) they provide him with furs, b) they are used as food, c) they secrete products having medicinal value, and d) they serve as laboratory animals for various experiments, mainly parasitological, infectious, and chemotherapeutic, for diagnostic tests and for therapeutic measures, for example for the preparation of anti-rabic vaccine. The following Rodents are of greatest importance for man: 1. Sciuridae - squirrel family. a) Ground squirrels, or steppe inhabitants, living in burrows dug in the soil. They feed on grass and grain in the field, devouring both stems and seeds, and are therefore large agricultural pests. They go into hibernation even under artificial keeping in warmth. They have great importance in the spread of plague (see). In the USSR the most important species of ground squirrels are: Citellus suslicus, the spotted ground squirrel (southern USSR up to the central provinces); Citellus pygmaeus (=C. mugosaricus and C. musicus) - B. Ekaterinoslav province, steppes of the Volga region; Citellus fulvus - sandy ground squirrel; Citellus citillus - European ground squirrel, etc.; the North American species (Citellus mollis) is infected with Bact. tularense and can therefore spread tularemia. b) Marmot (see), or souslik, or tarbagan [Arctomys (Marmota) bobac], plays an analogous role in the spread of plague (see). c) The common squirrel (Sciurus vulgaris) can be infected with the vesicular stage of echinococcus. 2. Dipodidae - jerboa family (southern and south-eastern USSR, Central Asia). Dipodipus sagitta - the ground hare (Kazakh steppes) can be infected with plague and be a transmitter of it through fleas. 3. Muridae - mouse family, which splits into several subfamilies, a) Murinae (mouse subfamily), to which mice and rats belong, with species: Mus decumanus = Rattus norvegicus - the brown rat, or house rat, which has almost completely displaced (in Europe) Mus rattus - the black rat. They are pests of human stores and dwellings and a source of plague infection. They are a reservoir for: Spirillum morsus muris (disease from rat bite, or "sodoku"), Leptospira icterohaemorrhagiae, disseminated with rat urine (see Botkin-Weil disease). The brown rat also has Mycobacterium leprae-murinum (leprosy of rats) and Treponema crocidurae, pathogenic for man. Both species of rats have worms: Hymenolepis (see) diminuta - rat tapeworm, Clonorchis sinensis, Trichinella spiralis - trichina and Moniliformis moniliformis - thorny-headed worm, which can also parasitize in man. Besides fleas, rats can also feed on ticks of various species Ornithodorus (Ixodoidea) - carriers of relapsing fever (see). In addition, rat Gamasidae (see Mites) can transfer to man. There are indications that the black rat suffers from amebic dysentery, caused probably by Entamoeba histolytica. Mus musculus (house mouse) - a pest of stores. It can contract and infect man with plague. The above-mentioned spirilla are also found in mice. Known cases of human infection with scabies from mice (pathogen Achorion quinckeanum) exist. Diplococcus pneumoniae can also be found in mice. In the muscles of mice, sarcosporidia - Sarcocystis muris parasitize. Besides trichina and rat tapeworm, nematodes Syphacia obvelata parasitize in mice, which can be a guest parasite (see) of man. The field mouse (M. agrarius) attacks fields and stacks of grain and causes great losses in case of mass reproduction ("mouse plague"), b) Subfamily Cricetinae, Cricetus cricetus (common hamster) can contract plague. Cricetus griseus (North China and Mongolia) is susceptible to experimental infection with Leishmania Donovani. It is possible that this rodent is the natural reservoir of the kala-azar virus in China, c) Subfamily Microtinae - voles. Microtus arvalis - the common vole, can be infected with Spirillum morsus muris. Among voles and steppe jerboas (Lagurus lagurus) there are plague epizootics. Sometimes it multiplies in extraordinary quantities and causes enormous damage to agriculture ("mouse plague"), d) Water vole - Arvicola amphibius is in the Astrakhan, Ryazan provinces and Ural region a source of infection of man with a tularemia-like disease. Infection occurs when stripping the skin. It is possible that the virus is also spread through the ectoparasites of water voles. Young guinea pigs, white and domestic mice proved susceptible to laboratory infection with the microbe of Russian tularemia. White rats and ground squirrels either did not get infected at all or recovered and could not be used to maintain the virus, e) Subfamily Gerbillinae. Gerbillus meridianus (the midday gerbil and other species) is subject to plague epizootics. 4. Family Castoridae - beavers. 5. Family Caviidae - capybaras. Cavia cobaya (guinea pig), an important laboratory animal (see), as well as white rats and white mice. 6. Family Leporidae - rabbits. The rabbit (Lepus timidus) can contract plague. It is a host of liver flukes (Fasciola hepatica and Dicrocoelium lanceolatum), the vesicular stage of echinococcus, and the larvae of Linguatula serrata. The rabbit - Oryctolagus cuniculus. It can contract plague. It is a host of the spirochete Treponema cuniculi, the microsporidia Encephalitozoon cuniculi, the coccidia Eimeria Stiedai, the vesicular forms of echinococcus, Diphyllobothrium Mansoni and Linguatula serrata, as well as adult worms of the liver fluke, Dicrocoelium lanceolatum and the schistosome Schistosoma japonicum. The rabbit represents an important laboratory animal (inoculations against rabies, etc.).