How many diseases are known to be spread by rats

The retina is poorly developed at birth, equivalent to a human fetus of 4—5 months. The eyelids open at about 14—17 days of age, although the retina does not fully mature until 30—40 days of age, and the final components in the angle of the anterior chamber are not fully formed until 60 days of age Weisse, Some hairs may be present on the trunk at birth, usually associated with touch domes, indicating that they are guard hairs English and Munger, Pups are considered fully haired at about 7—10 days of age.

Maternal antibody is transferred passively across the yolk sac in utero Laliberte et al. Antibody can also be transferred across the intestinal mucosa from maternal colostrum and milk in the suckling rat. This transfer occurs at low rates shortly after birth, reaches maximal rates at day 14, and ceases by the 21 days, when gut closure is said to be complete Martin et al. Sex is readily determined in mature rats by direct observation of the perineal region.

Males have a distinct scrotum located between the anus and the preputial opening. The penis is often visible and is larger than the urethral papilla of the female. In addition the distance between the anus and the genital opening, called the anogenital distance, is greater in the male than in the female. Sex discrimination is more difficult in prepubertal rats but is possible even in neonates.

Comparative evaluation will reveal that neonatal males have a greater anogenital distance than their female littermates, although the distinction is more subtle than in adults.

More recently, a technique for sex determination of preblastocyst embryos has been described Utsumi et al. Male embryos ceased development in the presence of antibody to the HY antigen, and resumed development only after the antibody was washed off. Rats are weaned at 20—21 days of age, although they may be weaned successfully as early as 17 days. Prior to 17 days, the pups may not be fully capable of urination without maternal stimulation, and weaning may result in obstructive urinary tract disease.

Although synchronization of estrus may be useful in the production of large numbers of timed pregnant rats, use of the impedance meter, as described above, may be more practical in most circumstances.

More recently, synchronization of estrus to prepare recipients in embryo transfer has been reported. Five days later estrus was confirmed by vaginal cytology. Artificial insemination AI in rats is complicated by the rapid coagulation of semen, especially when the semen is obtained by electroejaculation, due to the contributions of the coagulating glands and seminal vesicles Bennett and Vickery, These glands may be surgically removed without compromising fertility rates from AI.

Alternatively, sperm may also be collected by stripping directly from the epididymis, although probably not more than twice from each male rat. Sperm from the proximal portion of the cauda epididymidis are reported to have greater fertility than sperm for the middle or caudal portions Moore and Akhondi, Once collected, sperm may be surgically introduced directly into the uterus of estrous females Orihuela et al.

An essential step in assuring the success of AI is the induction of pseudopregnancy in the recipient female by prior mating with a vasectomized male, by mechanical stimulation of the vagina, or by electrical stimulation of the cervix Bennett and Vickery, ; Rouleau et al. Embryo transfer in rats is becoming more widely used as an alternative to cesarean rederivation in order to eliminate pathogens from breeding lines.

Embryo transfer can also be used to investigate whether specific characteristics are due to, or modified by, the uterine environment, in contrast to being solely determined by genetic factors Kubisch and Gomez-Sanchez, ; Rouleau et al.

Additionally, embryo collection is the first step in cryopreservation. In embryo transfer, embryos are collected 2—4 days after the females are bred. Embryos are usually washed in phosphate-buffered saline PBS and bovine serum albumin BSA , with or without added trypsin.

Trypsin may more effectively remove pathogens than PBS alone. Embryos are then suspended in PBS with BSA and fetal calf serum and surgically transferred into the uterus or oviduct of the pseudopregnant recipient Kubisch and Gomez-Sanchez, ; Rouleau et al.

Nonsurgical implantation of embryos through the cervix, using an otoscope, has also been reported Bennett and Vickery, but has not found wide use. In vitro fertilization IVF is performed in the rat but is used primarily as a research tool for events in fertilization and early development rather than as a colony management tool Gaddum-Rosse et al.

One form of IVF, the microinjection of spermatids into individual oocytes, is, however, used in mice to rescue or maintain strains that do not produce motile spermatozoa Tanemura et al. The same techniques will probably become more common in rats. Cryopreservation has not been performed in rats as often as it has in mice, but the technique is becoming more widespread, for the same reasons that it is used widely in mice Tada et al.

Cryopreservation can be an efficient method of maintaining the potential of raising live mice of the thousands of genetically modified genotypes currently available Songsasen and Leibo, It can serve as a fail-safe measure, should a strain become genetically contaminated. In addition to being used for murine reproductive purposes, frozen embryos are also used to test culture reagents and environments for human IVF Meyer et al. Although embryos, two-cell through morula, are most frequently cryopreserved, the techniques for cryopreservation of mouse sperm have recently been developed Songsasen and Leibo, ; Tanemura et al.

Cryopreservation of sperm has not yet been reported for rats. Relatively little space in many laboratory animal medicine texts, including the previous edition of this volume, has been devoted to the behavior of laboratory rats, especially as it relates to experimental design or disease status. Although this unfortunate, perhaps unavoidable, lack may lead some readers to conclude that rat behavior is not an important aspect of laboratory animal science, quite the contrary is actually true.

Many aspects of the rat's normal behavior may affect scientific use of rats in biomedical research and should be investigated by researchers prior to initiating studies in those specific areas.

Aspects of rat behavior relevant to experimental design and disease status may be considered in two broad and overlapping categories: normal behavior, and stressors and stress responses. Only a few examples will be cited here. Laboratory rats of all stocks and strains have been selected for many years for a variety of traits, among which is docility.

Nonetheless, strain differences exist. Frequent gentle handling will increase docility, whereas infrequent or rough handling will evoke fear responses.

Gentle handling not only reduces the likelihood of occupational injury for animal workers but also avoids stress for the rats.

Handling-induced stress can lead to altered responses in behavioral studies Hirsjarvi and Valiaho, ; Shalev et al. Handling also leads to vocalization, much of which is ultrasonic, in the range of 22 kHz Brudzynski et al. Stress-induced vocalization can make handling more difficult for other rats within hearing range.

An additional interesting fact regarding rat vocalization, illustrative of its importance in rat behavior, is that rat pups vocalize in the ultrasonic range, probably to signal their mothers, even before their ears are sufficiently developed for them to be capable of hearing Feldman, Rats are most active at night but will also move and feed some during the day; they are also more active in the mornings than in afternoons Saibaba et al.

This circadian rhythm is relevant to a broad range of behavioral measurements. For example, pain threshold is often determined in a tail flick test. Female rats have shorter tail flick response times in the middle of the dark period, as well as during estrus and metestrus Martinez-Gomez et al.

Rats, as are other rodents, are coprophagic and vary considerably between individuals in the percentage of feces consumed. This may be of significance when measuring fecal output volume or intestinal absorption of some agents. However, it appears to have no effect on iron absorption Tidehag et al. Rats may be housed singly or in groups. In general, males are less likely to fight when housed together than are male mice, but they also do well when housed singly, as is the norm in many toxicology and safety assessment studies.

Temporary single housing of female Wistar: Han rats accustomed to group housing resulted in elevated glucose levels, although the same was not observed in males Perez et al. It is not clear if the change in glucose levels was due to stress of being alone, was just a generic response to any change in environment, or was a result of the higher food consumption recorded in the singly housed females.

Also, given a report that transportation stress reduced blood glucose in Wistar:WU rats Van Ruiven et al. When afforded the choice, rats have shown preferences for solid flooring, bedding consisting of large particles of aspen wood chips, and nest boxes Manser et al. When provided with objects as part of an environmental enrichment program, rats will chew on inanimate objects such as wooden blocks and nylon bones and balls Watson, ; Chmiel and Noonan, No deleterious effects of these objects have been found; neither have benefits been measured.

Streptococcosis is disease caused by infection with Streptococcus spp: Several species of Streptococcus are opportunistic pathogens in rats i. In addition, Enterococcus spp. Pneumonia caused by S. However, because the term streptococcosis could be used to describe any streptococcal infection, it is inherently nonspecific and should be avoided.

Streptococcus pneumoniae is rarely present today in commercially obtained rats and is now considered to be a pathogen of low significance in laboratory animals National Research Council, Humans are the natural host of S. Streptococcus pneumoniae is transmitted primarily via aerosol, although fomites may play a minor role. Disease due to S. In asymptomatic rats the organism colonizes the nasopharynx.

Numerous serotypes of S. Infection in rats resembles that in both human and nonhuman primates, characterized by suppurative inflammation in the upper respiratory tract, which spreads to the lung to cause bronchopneumonia Kohn and Barthold, and sometimes fibrinosuppurative pleuritis. Affected rats may become bacteremic and may develop fibrinopurulent inflammation of other serous surfaces e. Monitoring for S. Differentiation of S. Optochin inhibition is greater for most S.

However, because of the occurrence of nonpathogenic isolates Fallon et al. Action to eliminate S. Infrequently, they may be isolated from abscesses, but exclusion from most colonies is neither necessary nor practical, for humans are often carriers.

Streptococcal enteropathy is a disease that affects only suckling rats, not postweaning animals. Affected litters develop diarrhea or soft stool, with bright yellow pasty feces. Mortality can be high. Microscopically, the villi of the small intestine are carpeted with gram-positive cocci.

Disease is clearly associated with some strains of enterococci and not with others, but the factors determining the pathogenic potential have not been elucidated. They may, however, involve the ability of pathogenic isolates to adhere to the surface of the microvilli.

Control of Streptococcus spp. Some Enterococcus spp. Streptococci can be excluded by aseptic microisolator technique or by use of isolators Pleasants, , yet the low incidence of disease may not warrant the additional time, expense, or other resources that such housing techniques would require.

Pseudotuberculosis is caused by Corynebacterium kutscheri, which can infect rats, mice, guinea pigs, and hamsters, although in the last two there is only bacteriological evidence. Infections with C. Nonspecific clinical signs may be observed, such as ruffled fur, hunched posture, dyspnea and rales, porphyria, mucopurulent ocular and nasal discharges, lethargy, and lameness.

These are usually followed by death in 1 to 7 days. In infected colonies, C. Latent infections may be triggered to become clinical by a variety of stressors that can cause immunosuppression in the host. These include poor husbandry, overcrowding, shipping, malnutrition, intercurrent infections, irradiation, and treatment with immunosuppressive drugs Barthold and Brownstein, As with other persistent infections, such as mycoplasmosis, disease is more frequent in older animals. Transmission is probably through direct contact or oronasal exposure.

Lesions are due to septic emboli becoming trapped in organs or tissues with an extensive capillary network, such as lung, liver, kidney, and synovium. Although any organs and tissues may be involved, the lung is the organ most frequently involved in the rat.

Gross lesions of C. Suppurative inflammation may also be found in the preputial gland and tympanic bullae. Histopathologically, the lesions are generally as expected from the gross findings. Interstitial inflammation in the lung is due to the hematogenous seeding of the lung with bacteria, although bronchi and bronchioles may also contain suppurative exudate.

Caseous necrosis is often prominent, and epithelioid macrophages and multinucleated giant cells may be present in areas of abscessation. Large areas of caseous necrosis may also be present in the liver.

Septic embolic glomerulitis may be present in the kidneys, as may abscesses with or without pyelonephritis. Abscesses and caseous necrosis may also be observed in virtually any tissue. Definitive diagnosis is accomplished by bacteriologic culture Fox et al. The best site, other than lesions, to culture is probably the submandibular cervical lymph nodes.

The oral cavity, cecum, colon, and rectum may also harbor the organism. Microscopic evaluation may reveal the characteristic irregularly branching arrays of gram-positive rods in tissue sections Brown and Brenn stain or impression smears Gram stain. However, if possible, histopathology should always be confirmed by bacteriology. Disease provocation tests, often called stress tests, have also been employed to activate latent infections with C.

Adequate culture techniques should obviate the need for stress tests. Serology has also been widely employed for detection of C. As with other serologic assays, especially serologic assays for agents more antigenically complex than viruses, false positives and false negatives occasionally occur, so positive results should always be confirmed by culture.

Differential diagnosis for the presence of multiple abscesses in rats should include streptococcosis, streptobacillosis, mycoplasmosis pulmonary abscesses , CAR bacillus infection pulmonary abscesses , or other miscellaneous bacteria.

Of these, only mycoplasmosis and CAR bacillus infection would be found predominantly in older animals. Tyzzer's disease, first discovered by Tyzzer in Japanese Waltzing mice Tyzzer, , is caused by Clostridium piliforme Duncan et al. The host range is protean among mammals, including numerous rodent species, rabbits, carnivores, horses, and both nonhuman and human primates DeLong and Manning, ; Skelton et al. Clostridium piliforme infection is usually clinically silent Motzel and Riley, ; Hansen et al.

Overt disease in rats, as in other species, is most likely to be observed in young, recently weaned animals. In these, the clinical signs are nonspecific anorexia, lethargy, emaciation, ruffled fur and may include acute death without clinical signs.

Diarrhea may be noted and may contain mucus and blood. Particularly in the rat, a distended abdomen has been observed in weanlings with Tyzzer's disease, albeit at a very low incidence Hansen et al.

Clostridium piliforme is transmitted horizontally in rats by spores through fecal—oral contamination. The spores are highly resistant to desiccation and some disinfectants Ganaway, The delicate vegetative form, however, survives only inside of cells. After being ingested, C. Multiple, pale foci, pinpoint or larger, of necrosis are often visible on the surface of and within the liver.

Megaloileitis—a greatly dilated, flaccid, and hyperemic ileum—may be present Fig. Hyperemia, edema, hemorrhage, and ulceration may affect any part of the intestine, especially the terminal ileum, cecum, and colon. Secondary to intestinal involvement, mesenteric lymph nodes may be enlarged, hyperemic, and edematous. In the heart, pale circumscribed areas may be visible on the epicardium. Myocardial necrosis due to Tyzzer's disease may also appear as pale linear streaks or areas in the heart, especially near the apex.

Tyzzer's disease in an adolescent rat with the skin reflected. Note enlargement of ileal loops in situ. Histopathologically, characteristic lesions may be observed in the liver, ileum, cecum, and colon, and, less frequently, the heart.

In the intestinal tract, there may be necrotizing enteritis, typhlitis, and colitis. Coagulative necrosis in the liver is the hallmark lesion and is often accompanied by a moderate leukocytic infiltrate, usually neutrophils and mononuclear cells, at the periphery of the lesions.

Acute lesions may be hemorrhagic, and mineralization may occur with time. In the heart, myocardial degeneration and necrosis occurs in a minority of cases, often with a mixed leukocytic infiltrate and dystrophic calcification.

Histopathologic evaluation is diagnostic if the characteristic bacilli are observed Tyzzer, ; Duncan et al. Bacilli are intracellular, are often numerous, and may appear as either a jumbled array pickup stick or parallel arrangement, as dictated by the shape of the cell. The vegetative form may rarely be visible in hepatocytes in tissue sections stained with hematoxylin and eosin, but usually special stains are necessary, including Warthin—Starry silver best , Giemsa, and methylene blue stains.

Although gram-negative, C. In the liver, the organisms are most often observed in surviving hepatocytes at the periphery or within lesions. In the intestine, normal gut flora within mucosal crypts and superimposed upon the mucosal epithelial cells may complicate evaluation. Organisms may also occasionally be observed in cardiac myocytes or myocytes of the tunica muscularis of the intestine. Tyzzer's disease in rat ileum. Clostridium piliforme in villous submucosa at base of crypt.

Giemsa stain. Magnification: X Differential diagnoses for necrotizing hepatitis in the rat should include other bacterial septicemias, such as Corynebacterium kutscheri, as well as infection with rat virus. Diagnosis of clinical disease depends on demonstration of the organism in tissue. Tissue smears may facilitate rapid diagnosis; Giemsa-stained smears of suspicious liver lesions are especially useful Percy and Barthold, a. Colony screening for latent infection is problematic.

Serologic screening is rapid and technically simple Motzel and Riley, but is subject to false positives, yielding results that can be difficult to put into context. Disease provocation tests, or stress tests, to exacerbate latent infections are widely used and are recommended as a follow-up test when serologic positive results are obtained. However, there is some doubt as to efficacy of stress tests that rely on chemical immunosuppression, usually with cyclophosphamide Boivin et al.

The doubt arises because test animals may have already cleared the C. Alternatively, sentinel animals can be placed on soiled bedding, but this may require sentinels to be of the same species to avoid species specificity's causing false negatives , for not even gerbils are susceptible to all strains of C.

Interference of Clostridium piliforme with research has primarily been attributed to the morbidity and mortality, although effects on coagulation and leukokines have also been reported Van Andel et al.

Pasteurella pneumotropica is a gram-negative coccobacillus. It grows aerobically on sheep blood agar without producing hemolysis, but producing smooth, gray translucent colonies Carter, It has been isolated from numerous mammalian species, including humans, and is generally considered to be of low significance in immunocompetent rats National Research Council, d.

Pasteurella pneumotropica has a high prevalence in infected colonies and is most often isolated from the nasopharynx, cecum, vagina, uterus, and conjunctiva during routine monitoring National Research Council, The vast majority of animals are asymptomatic, with only rare instances of conjunctivitis, metritis, and mastitis Percy and Barthold, b.

Histologically, lesions are characterized by necrotizing, suppurative inflammation. Control of the agent may not be necessary in immunocompetent animals, because of the rarity of P. However, treatment with enrofloxacin has been described Goelz et al. Rederivation by either cesarean section or embryo transfer will also eliminate the agent SultanDosa et al.

Antibiotic treatment of infected dams prior to cesarean section has been recommended by at least one major rodent vendor C. Clifford, unpublished observations, , because P.

The probability of successful elimination of P. Offspring should also be held in strict isolation—i. Pasteurella pneumotropica is not transmitted to a significant degree by fomites, does not persist or multiply in the environment, and only rarely colonizes humans. Therefore, once a colony is free of the agent, there is relatively little risk of reinfection except through introduction or incursion of infected animals.

Salmonellosis is the disease caused by bacteria of the genus Salmonella. The taxonomic classification and subdivision of the genus are controversial and, like much taxonomy, subject to change see Chapter 3.

However, for clarity in communication, it is useful to refer to all salmonellas that one is likely to encounter in rats as belonging to S. Salmonella enteritidis is composed of more than serovars. These vary greatly in pathogenicity and geographic distribution, which makes serovar classification of epizootiologic significance. However, this discussion will treat S. Salmonellosis may be virtually nonexistent in laboratory rats in the United States, but because infection is thought to be prevalent among many other species of vertebrates, including wild rodents, the potential for introduction remains.

In rats, as in most species, clinical signs of infection with S. Salmonella enteritidis is transmitted by ingestion of contaminated materials, including feed, bedding, or water. Incursion of wild or feral rodents into a laboratory facility poses a further risk. In addition, salmonellosis is an anthropozoonosis Wray, ; humans not only are at risk of infection from rodents but also may serve as a source of the agent.

In rats with subclinical infections, gross and microscopic lesions will usually be absent. Rats with clinical disease may have evidence of gastrointestinal involvement and septicemia, including mural thickening and mucosal ulcers in the cecum and ileum, as well as splenomegaly. Microscopically, enteric lesions are characterized by edema of the lamina propria, leukocyte infiltration in areas of ulceration, and reactive hyperplasia of crypt epithelial cells. Lymphoid hyperplasia, with focal necrosis and neutrophil infiltration, may be observed in Peyer's patches, as well as in the spleen and mesenteric lymph nodes.

Septicemic rats will have necrosis in the spleen and liver, with emboli composed of fibrin, bacteria, and debris present in liver, spleen, and lymph nodes Percy and Barthold, b. Salmonellosis is most often diagnosed by culture of feces, mesenteric lymph nodes, liver, spleen, or blood. Material is placed in enrichment broth and then inoculated onto selective growth medium. Detection of S. Salmonellosis is prevented by rigorous pest control and by ensuring that food and bedding are not contaminated.

Good personal hygiene of employees will prevent them from serving as a source of Salmonella or other enteric pathogens to the colony. Once S. Strict quarantine of a small group of animals may be practical in some situations, prior to rederivation by embryo transfer or cesarian section. This may be most feasible in a flexible film or semirigid isolator. Treatment is not recommended, because a chronic carrier state may result and there is the potential for zoonotic disease.

Rats infected with S. Research complications from salmonellosis have primarily been reported in mice National Research Council, c.

Pseudomoniasis refers to clinical disease caused by Pseudomonas aeruginosa, a gram-negative bacillus of the order Eubacteriales, family Pseudomonadaceae. Pseudomonas aeruginosa is motile, aerobic, oxidase-positive, and widely distributed in water, soil, sewage, and the skin and gastrointestinal tract of many animals. It is considered as part of the common commensal flora of humans, domestic animals, and laboratory rodents and is more frequently isolated from animals and humans receiving antibiotics Kiska and Gilligan, Rats of the genus Rattus are reservoir hosts for pathogenic Bartonella species: an Old World origin for a New World disease?

J Infect Dis. Global parasite and Rattus rodent invasions: the consequences for rodent-borne diseases. Integr Zool. Migration of Norway rats resulted in the worldwide distribution of Seoul hantavirus today. J Virol. Natural history of plague: perspectives from more than a century of research. Annu Rev Entomol. The importance of parasite geography and spillover effects for global patterns of host—parasite associations in two invasive species.

Diversity Distrib. Epidemiological trends for human plague in Madagascar during the second half of the 20th century: a survey of 20, notified cases. Trop Med Int Health. Understanding the persistence of plague foci in Madagascar.

External Situation Report 12 ; November Lassa fever in West African sub-region: an overview. J Vector Borne Dis. Review of Lassa fever, an emerging old world haemorrhagic viral disease in sub-Saharan Africa. Afr J Clin Exp Microbiol. Mastomys natalensis and lassa fever, West Africa. Emerg Infect Dis. Urbanization and the ecology of wildlife diseases. Trends Ecol Evol. Effect of forest fragmentation on lyme disease risk. Conserv Biol. Comprehensive tables no 1. Aboriginal and invasive rats of genus Rattus as hosts of infectious agents.

Vector-Borne Zoonotic Dis. Changes in rodent communities according to the landscape structure in an urban ecosystem.

Landscape Urban Plann. Diseases of humans and their domestic mammals: pathogen characteristics, host range and the risk of emergence. Coxiella burnetii Q fever in Rattus norvegicus and Rattus rattus at livestock farms and urban locations in the Netherlands; could Rattus spp.

Prev Vet Med. Diversity of the human intestinal microbial flora. Environmental and behavioural determinants of leptospirosis transmission: a systematic review. Leptospirosis: a zoonotic disease of global importance. Lancet Infect Dis. Human leptospirosis: an emerging risk in Europe? Comp Immunol Microbiol Infect Dis. Leptospira exposure in the human environment in France: A survey in feral rodents and in fresh water.

Strikes, flooding, rats, and leptospirosis in Marseille, France. Inter J Infect Dis. Highly pathogenic leptospira found in urban brown rats Rattus norvegicus in the largest cities of Sweden. Vector Borne Zoonotic Dis.

Is it too cold for Leptospira interrrogans transmission on the Faroese Islands? Infect Dis Auckl. Modulation of innate immunity by Toxoplasma gondii virulence effectors. Nature Rev Microbiol. Species or local environment, what determines the infection of rodents by Toxoplasma gondii?

Human infection with Hymenolepis diminuta : case report from Spain. J Clin Microbiol. Analysis of a child infected with Hymenolepis diminuta in Poland.

Ann Agric Environ Med. Intestinal cestodes. Curr Opin Infect Dis. How much human helminthiasis is there in the world? J Parasitol. Hymenolepis diminuta infection in a child living in the urban area of Rome, Italy. Zoonotic helminths of urban brown rats Rattus norvegicus in the UK: neglected public health considerations? Zoonoses Public Health. An overview of the host spectrumand distribution of Calodium hepaticum syn.

Capillaria hepatica : part 1-Muroidea. Parasitol Res. Capillaria hepatica in man—an overview of hepatic capillariosis and spurious infections.

The atlas of european mammals. Skip to navigation Skip to main content Site map Accessibility Contact us. Search this site Search all sites Search. Go to whole of WA Government Search. Open search bar Open navigation Submit search. Safety and first aid. Facebook Youtube Twitter. Home Safety and first aid Protect your health — keep rats and mice under control. Protect your health — keep rats and mice under control Around the world, rats and mice are known to spread over 35 diseases.

Rats can be discouraged and controlled simply by denying them food and shelter. Why are rats and mice such a health risk to the community? Around the world, rats and mice are known to spread over 35 diseases that can infect both people and pets, including: plague salmonellosis leptospirosis tularemia.

These diseases can be passed on by: direct contact such as rat bites unsafe handling and disposal of infected dead rats eating food or drinking water contaminated with: rat urine faeces saliva hair breathing dust contaminated with the urine and faeces of infected rats. Through their natural behaviours, rats can weaken building structures by: gnawing through lead and aluminium sheeting chewing through electrical wiring, which can start fires by shorting-out appliances or lighting fixtures.

Rats do not transmit rabies, Corrigan notes. Plague is exceedingly rare, but is a bit more common in the Western United States than elsewhere in the country. Rats pick up viruses in the same way human beings do: with their fingers and mouths. Unsuspecting people then touch, inhale, and sometimes consume that urine and feces, allowing those germs into their bodies. And seal any gaps at least a half an inch wide under exterior doors, in your foundation, and around your roof, he advises.

You should also properly dispose of your trash.