Rats

RATS, mammals, species of the genus Mus (Epimys), family Muridae, order of rodents (see). The most common in the USSR is the gray, or brown, rat, or sewer rat [Epimys (Rattus) norvegicus, which is also known under the old name Mus decumanus]; the black rat [Epimys (Rattus) rattus, or Mus rattus] is found only in certain places: in the North-West, North-East and in the center of the RSFSR, in Ukraine and Transcaucasia. In colloquial speech, rats are also incorrectly applied to other rodents, such as the Central Asian nesokia (Nesokia), the water rat (Arvicola terrestris L.), the hamster (Cricetus cricetus) and others.-Sewer rat. The fur is stiff, on the back brownish- or reddish-gray, on the belly dirty light-gray. The tail is somewhat shorter than the body with the head. The ear, folded forward, does not reach the eye. At the base of the fingers there are small webs. Sewer rats live in dwellings, service buildings, warehouses, garbage pits, in sewer pipes, in manure, in vegetable gardens and fields. They burrow holes in the ground or nest under floors, in cellars, in walls, in the rooms themselves, in warehouses of bags, etc. They arrange nests from rags, paper, tow, wool and other materials. They climb well, jump and swim. They usually come out of their holes at night. They eat the most diverse plant and animal food, preferring grain. They devour sick or old and weak fellows, as well as other small animals. They gnaw various inedible objects-lead pipes, books, clothing, linen, fabrics, etc. There are known cases of sewer rats biting off the tails of horses and gnawing to death pigs and people. They begin to reproduce at 3-4 months and even earlier. After a 3-week pregnancy, females give birth to 7-8 or more young. There can be up to six litters per year. Reproduction is timed mainly to the warm season of the year. In Transbaikalia and the former Irkutsk province lives the Transbaikal gray rat-Rattus norvegicus caraco, which inhabits not only buildings but also far from dwellings, in the open nature (in thickets along river banks and other biotopes).-Black rat. The back is of a dark, almost black color. The tail is longer than the body and head. The ear folded forward reaches the eye or comes just short of it. The muzzle is sharper than that of the sewer rat. The latter displaces the black rat, which is much more numerous in southern countries than in the USSR. Varieties of the black rat are the Alexandrian, or Egyptian rat (Rattus rattus alexandrinus) and the Indian (Rattus rattus rufescens). In Rattus rattus alexandrinus the back is brown or reddish-brown, the belly is white, in some-with a reddish sheen; in Rattus rattus rufescens the back is brick-colored, the color of the fur on the belly gradually lightens. They often live on steamships, with which they are transported from distant ports. During the plague of 1902 in Odessa, the following proportions of various forms among the rat population (in percent) were established (according to Belilovsky, Burda and Gamalei; 1904). Rats Barges | In port | In the city Sewer rat...... Alexandrian rat..... Black rat . . Brown rat . . 2.8 63 33.1 0.6 69.8 27.7 1.9 59.8 27.6 12.5 0.1 1.3 0.5 0.1 Rats have now spread throughout the world due to the improvement of communication routes and the transportation of food products. In particular, the sewer rat apparently spread from Eastern Asia, where it lives wild in uninhabited places. The spread of the sewer rat over land was slow (to Eastern Siberia). On ships, the sewer rat was transported to European ports, from where it advanced into the interior of the continent. The rapid spread of the sewer rat was facilitated by the transport of food cargo by river routes; railways played the same role. Kachenko asserts that Western Siberia was almost entirely free of sewer rats earlier. The first specimens of this species were obtained by him from Omsk in 1907, i.e., after the construction of the Siberian Railway. An important auxiliary factor in the spread of the sewer rat was the Russo-Japanese War. By 1912, the entire Trans-Siberian route was inhabited by the sewer rat, which now encircles the globe with its zone of distribution. In Central Asia lives Rattus turkestanicus (the distribution of which has been studied insufficiently). This rat was considered by some a subspecies of Rattus rattus; however, it is a well-defined species, although close to the black rat. Rattus turkestanicus probably penetrated into Central Asia from Kashmir via the Pamir.-Platyodont rodents, or ground rats (Nesokia) replace the sewer rat and black rat in the south of Central Asia, to which they are very similar in external appearance, differing at the same time in some essential features: the molars of nesokia consist of parallel transverse plates. In the former Syr-Darya and Fergana regions lives Nesokia huttoni, in the Merv oasis-Nesokia satunini and near Chardjuyu-Nesokia boettgeri. The species Nesokia bythiana is also indicated for Samarkand. These species have been little studied. They live in human dwellings, in warehouses, as well as in vegetable gardens and fields. They burrow into the banks of irrigation canals, dams and thereby cause very great harm (leakage of water, flooding). The water rat is exclusively an agricultural pest. The damage caused by rats. Due to the intensity of reproduction, rats can multiply in countless numbers. One pair of rats, with abundant food, can produce 1,130 offspring in a year (if we assume only four generations per year), and in four years 10,934,690 individuals. A rat eats 60 g of grain per day, and 22 kg per year. The annual offspring of a pair of rats destroys about 41¹/₂ tons of wheat in the next six months. However, the economic harmfulness of rats is determined not only by the amount of food eaten, but also by the number of spoiled objects. Rats contaminate flour, grain, bread and other products with urine and excrement; rats gnaw and spoil fabrics, clothing, leather goods and other items. Due to the gnawing of rats on the insulation of wires, fires occur, etc. If all the damage from rats is calculated, enormous figures are obtained: in Denmark they are estimated at 15 million francs, in France-200 million francs, in Germany-200 million marks, in England-15 million pounds sterling, in the USA-200 million dollars, in the USSR-over 500 million rubles (in gold currency). In reality, the material damage is even greater, especially if we also consider the indirect harm caused by rats in terms of spreading parasites and transmitting various diseases to humans.-Rats play a very important role in the spread of plague (see) due to the transportation of rats from plague-infested ports. In this connection, the study of the flea fauna (see) parasitic on rats acquires significant importance. Besides rat fleas, other species of fleas can be found on rats, up to chicken and human ones. Strickland and Merriman in West Suffolk (England) identified 3,293 fleas from 822 rats; a total of 15 species of fleas were found; Ceratophyllus fasciatus (60%) and Ctenophthalmus agyrtes (38%) were the most numerous; the remaining two percent of fleas accounted for Ceratophyllus mustelae (17 fleas), Ceratophyllus walkeri (8 fleas), Archaeopsylla erinacei (7 hedgehog fleas), Ctenophthalmus pentacanthus (three fleas), Ctenopsylla musculi (three mouse fleas), Pulex irritans (two human fleas), Histrichopsylla talpae (two mole fleas), Ctenocephalus canis (2 dog fleas), Ctenophthalmus bisoctodentatus (two fleas) and one specimen each of Ceratophyllus gallinae (chicken flea), Ceratophyllus hirundinis, Palaeopsylla soricis and Palaeopsylla minor. The number of rat fleas Ctenophthalmus agyrtes and Ceratophyllus fasciatus on rats and the number of rats infected with these species decrease with the onset of colder weather. The first species of flea is predominantly 'domestic', while the second is 'field'.-The flea fauna on rats in Liverpool and on ships in the port is different; only 5 species were found: Xenopsylla cheopis (Indian rat flea, which plays an important role in the transmission of plague), Ceratophyllus fasciatus, Leptopsylla musculi, Ceratophyllus londinensis and Ctenocephalus canis. During the 10 months of research, Xenopsylla cheopis was found in abundance on ship rats in docks, port warehouses, while in the city it was rarely encountered. Ceratophyllus fasciatus greatly predominated over all other species of fleas. The frequency of finding Ceratophyllus fasciatus on rats in the port and in the city was not the same. In summer, the number of fleas on rats is maximum. Along with the spread of rats, their fleas also spread. Thus, the Indian rat flea Xenopsylla cheopis was introduced to Odessa, Batumi, Leningrad, Saratov and even to the mouth of the Volga (found near the village of Yandyki of the Astrakhan district). Rat fleas-Ceratophyllus fasciatus and Xenopsylla cheopis-are intermediate hosts of the rat tapeworm (Hymenolepis diminuta), which also occurs as a parasite in humans. Infection occurs by swallowing fleas with cysticercoids of the worm. Cats play an auxiliary role in human infection with this rat parasite. When cats eat caught rats (or mice), fleas of the latter pass to them. Of other pathogenic bacteria for humans, rats contribute to the spread of paratyphus A and B bacteria, as well as bacilli of the Gartner group. Paratyphoid bacteria are pathogenic for rats only when administered subcutaneously or intravenously.

Their presence in the intestine of rats is not accompanied by symptoms of paratyphoid; therefore, rats must be considered as bacillus carriers. Young rats are susceptible to infection from Gartner's bacilli, even with significant mortality. Older rats gradually acquire immunity and, upon infection per os, actually become carriers. These circumstances have important epidemiological consequences: rats contaminate various products (carcasses of meat, etc.) with their excrement, thereby contributing to the spread and maintenance of certain intestinal infections. In various countries, 'wild' rats are carriers of Spirochaeta ictero-haemorrhagica to a certain percentage, which they disseminate with saliva and urine, contributing to human infection with infectious jaundice (see Botkin-Weil disease). For other spirochaetoses spread by rats, see Sodoku, Relapsing fever. For the possibility of transferring leprosy from rats to humans, see Leprosy. Certain species of mites (see) live on rats. The role of rats in the spread of trichinosis - see Trichinosis. Among tapeworms, the parasitism of Echinococcus granulosus in rats is important. The fungus Achorion quinckeanum, the cause of rat favus, can affect some domestic animals and humans. Rats are susceptible to rabies poison, but epizootics of rabies among them have not been observed. Natural enemies of rats are cats, dogs (pinchers, dachshunds, shepherds, mongrels), ferret (Putorius foetidus), pigs, and various birds (buzzard, or mouse hawk - Buteo vulpinus, common buzzard - Buteo vulgaris, barn owl - Strix flammea, long-eared owl, etc.). The fight against rats is a difficult sanitary task; methods of this fight - see Deratization. The white rat is an important laboratory animal. Of its anatomical features, the following details deserve attention: the right lung is four-lobed, the left is without lobes; the cecum is 6-8 cm in length, while the appendix reaches only a few mm in length; the liver is lobulated; there is no gallbladder; the hepatic ducts join into a common bile duct, which pierces the pancreas and opens into the duodenum 2-4 cm from the pyloric opening of the stomach. A periodic descensus testiculorum is observed. The accessory sex glands are strongly developed. The young are born blind and gain sight by the 13th-16th day of life. They suckle for 4-5 weeks. They are capable of reproduction from the 3rd month, but at this time they produce only 3-4 young. (See also Laboratory animals.)

E. Pavlovsky