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rat-bite fever in the United States are due to infection with S. moniliformis. The name of the disease is derived from the fact that infection usually develops after a person is bitten
or scratched by an infected rat. Other rodents, such as mice, squirrels and gerbils, may also spread the infection to people. Sometimes, infection can result from handling infec-
ted rats, with no reported bite or scratch. Infections also result from ingesting food or drink such as milk or water contaminated with rodent excrement.
13.4.3. Major rodent- and lagomorph-related parasitic agents
The following subsections discuss the major rodent- and lagomorph-related parasitic agents that are believed to cause illness in people in Europe or North America.
13.4.3.1. Toxoplasma
Toxoplasmosis is caused by the protozoan parasite T. gondii. The definitive host of T. gondii
is the domestic cat, but non-commensal rodents, other mammals and some birds play important roles as intermediate hosts for this parasite Marquardt, Demaree
Grieve, 2000. Cats can become infected with Toxoplasma through consumption of infec- ted intermediate hosts, especially rodents. People typically become infected through
contact with infectious oocysts shed in cat faeces, an event that can occur while cleaning cat litter boxes. Infections also occasionally arise from eating raw or undercooked meat,
particularly mutton or pork, that contains infectious cysts. Pregnant women who become infected can pass T. gondii to their developing fetus, an event that can lead to the death
of the fetus or other severe consequences, including brain damage with intracerebral cal- cification, microcephaly, hydrocephaly, jaundice and convulsions at birth Marquardt,
Demaree Grieve, 2000; Heymann, 2004. Infections of children and adults are often asymptomatic, but can appear acute with lymphadenopathy. In some instances T. gondii
infections resemble mononucleosis, with lymphadenopathy, fever and lymphocytosis.
13.4.3.2. Toxocara
Infestation with larval forms of Toxocara spp. can cause a chronic but usually mild dis- ease in people. Infestations are most common in children, but adults also can become
infested. People acquire infestations by ingesting worm eggs contained in faecal-conta- minated materials, particularly those shed by dogs or cats, which are definitive hosts of
Toxocara canis
and T. cati, respectively. Rodents become infested by ingesting eggs contai- ning infective larvae. Once infected, these rodents can act as transport hosts, maintaining
the larval worms in their tissues for long periods. If an appropriate definitive host eats an infested transport host, the worms can mature and complete their life-cycle. Dubinsky
and colleagues 1995 found anti-Toxocara antibodies in 30.4 and 25.0 of striped field mice and harvest mice Micromys minutus, respectively, in Slovakia, demonstrating that
small mammals can play a role in maintaining toxocariasis foci in urban biotopes.
13.4.3.3. Babesiae
Rodent-related B. microti and other highly similar agents cause a rare, but potentially severe and even fatal illness in people who live in Europe and North America Goethert
Telford, 2003b; Meer-Scherrer et al., 2004; Telford Goethert, 2004. The disease is likely to be severe in immunocompromised individuals, such as those who have under-
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444
13.4.2.6. Leptospirae
Leptospirosis is an important zoonosis worldwide and is well known in rural and urban settings in Europe Rosicky Sebek, 1974; Daiter et al., 1993; Handysides, 1999; Perra et
al., 2002. The infection causes a systemic illness that often leads to renal and hepatic dys- function Levett, 2001. Urban dwellers are at increased risk because of sporadic expo-
sures to rat urine as inner cities deteriorate. Reportedly, the incidence of leptospirosis is increasing in urban children, but most cases occur in adults and are acquired as a result
of occupational exposures. The causative agent, Leptospira interrogans, is subdivided into numerous serovars that can differ by geographic location and primary host. Most lep-
tospiral serovars have their primary reservoir in mammals, which can result in continual re-infection of commensal and non-commensal rodent populations in urban settings
Daiter et al., 1993. At least 12 species of small mammals, predominantly those rodents that live in highly moist environments, are known to carry Leptospira. Reported sero-
prevalences in small mammals were 3–12 in water voles, 11 in muskrats and 5 in Microtus
voles Tokarevich et al., 2002. The most common serogroups of Leptospira found in wild rodents were grippotyphosa 65, javanica 21, and pomona 12.
Recent serological surveys of leptospirosis in animals in Croatia indicated that 13 of small rodents were seropositive Cvetnic et al., 2003. In this study, antibodies to diffe-
rent serovars of leptospires were identified in 15 of field voles, 11 of yellow-necked mice, 9 of bank voles and 7 of wood mice.
13.4.2.7. Bartonellae
With the recognition of several novel or re-emerging diseases caused by Bartonella spp., interest in bacteria of this genus has been increasing Boulouis et al., 2005. The distri-
bution of certain Bartonella spp. appears to be closely linked to the distribution patterns of their hosts or arthropod vectors. Bartonella elizabethae was isolated originally from a
patient with endocarditis in Massachusetts. Subsequently, identical or similar organisms were found in rats in America, Asia and Europe. It is possible that B. elizabethae first
spread from Asia, because most Rattusspp. probably originated there, and only later were carried to other continents with the dispersal of two domestic Rattusspp. Two other puta-
tive human pathogens, Bartonella washoensis and Bartonella vinsonii subsp. arupensis, are thought to be associated with American rodents ground squirrels Spermophilus spp.
and deer mice and their allies Peromyscus spp., respectively Welch et al., 1999; Kosoy et al., 2003. Bartonella vinsonii subsp. arupensis also has been reported for a human case
of endocarditis in a French hospital Fenollar, Sire Raoult, 2005. Although this bacte- rium has been associated with non-commensal rodents, the patient was an urban dwel-
ler and had no obvious rodent exposures. T hree other species, Bartonella grahamii, Bartonella taylorii,
and Bartonella doshiae, circulate in woodland rodent communities in Europe. Bartonella grahamii infection has been associated with neuroretinitis in Europe
Kerkhoff et al., 1999; Rothova et al., 1999.
13.4.2.8. Rat-bite fever agents
Rat-bite fever is an illness caused by either of two bacteria, Streptobacillus moniliformis and Spirillum minusalso called Spirillum minor Heymann, 2004. The disease is thought
to be relatively rare in Europe and North America. However, since reporting this dis- ease is not mandatory, reliable estimates of case numbers are not available. Most cases of
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447
tant for people residing in the areas affected. A number of cities in central Colorado and nearby Cheyenne, Wyoming, also have experienced occasional plague epizootics among
fox squirrel populations that live in the urban deciduous forests found in these cities, and a single human plague case was associated with these animals in Denver, Colorado
Hudson et al., 1971. It is believed that fox squirrels, which are not native to the region, acquire plague bacteria from rock squirrels or other native species that are common hosts
of plague in this region. In another report, a gray squirrel kept as a pet was implicated as the source of an infectious bite that resulted in a human tularaemia case in Arkansas
Magee et al., 1989. Acute T. gondii infections have caused fatalities among gray squir- rels, but the epidemiological significance of this observation is unknown Roher et al.,
1981. Gray squirrels also were found naturally infected with LB spirochetes in the United Kingdom Craine et al., 1997. Another report suggested that five patients in
Kentucky had contracted spongiform encephalopathy as a result of eating the brains of tree squirrels species not given that perhaps contained a prion-like agent Berger,
Weisman Weisman, 1997. American red squirrels in western North America have been implicated as important hosts for a soft tick O. hermsi that transmits relapsing
fever spirochetes B. hermsii to people. These same squirrels also are susceptible to infec- tion with B. hermsii and are thought to be sources of infection for feeding O. hermsi
Burgdorfer Mavros 1970; Burgdorfer 1976. Although rarely reported in rodents, a case of rabies was identified in a fox squirrel Cappucci, Emmons Sampson, 1972.
13.4.4.2. Flying squirrels
