Babesiae Leptospirae Major rodent- and lagomorph-related parasitic agents

Public Health Significance of Urban Pests 445 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- Non-commensal rodents and lagomorphs 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