Yersiniae Major rodent- and lagomorph-related bacterial and rickettsial agents

Public Health Significance of Urban Pests 443 The most important and severe rickettsial disease in the United States is RMSF, which is caused by R. rickettsii Dumler, 1994; Sexton, 2001. This species of Rickettsia is trans- mitted primarily by the American dog tick D. variabilis in the eastern United States and by the Rocky Mountain wood tick in the central and northern Rocky Mountains of the United States and south-western Canada. Non-commensal rodents act as both tick hosts and sources of infection for the immature stages of the above two tick species. Serological evidence of human infection with A. phagocytophilum, the agent that causes HGA, has been identified in several European countries Strle, 2004. Non-commensal rodents act as reservoir hosts and sources for infecting ticks with A. phagocytophilum Parola Raoult, 2001; Strle, 2004; Parola, Davoust Raoult, 2005. The primary vector of this agent is the castor bean tick, which feeds heavily on non-commensal rodents, inclu- ding wood mice, yellow-necked mice and bank voles Panchola et al., 1995. The primary vector of HGA in the eastern United States is the deer tick, which feeds on rodents, birds and reptiles Piesman 2002. In the Pacific states, the primary vector is the western black- legged tick, which feeds during its immature stages on non-commensal rodents, birds and lizards Kramer et al., 1999; Piesman 2002 Additional information on tick-borne rickettsiae can be found in Chapter 10, on ticks and TBDs.

13.4.2.5. Yersiniae

Yersinia pseudotuberculosis causes intestinal illness and occasionally reactogenic arthritis in people. This bacterium is commonly identified in non-commensal rodents and has been implicated in numerous outbreaks that involve the consumption of raw vegetables conta- minated with rodent excreta Naktin Beavis, 1999; Chesnokova et al., 2003; Jalava et al., 2004. Recent outbreaks of Y. pseudotuberculosis infection have been reported from Finland and the Russian Federation. People who live in suburban areas and plant small vegetable gardens accessible to non-commensal rodents could be at risk for yersiniosis. Plague is a vector-borne rodent-related zoonosis caused by Y. pestis, a bacterium closely related to Y. pseudotuberculosis, but is able to cause much more severe illness in people than the latter agent Gage, Ostfeld Olson, 1995; Gage, 1998; Levy Gage, 1999; Gage et al., 2000; Gage Kosoy, 2005. The disease is maintained in nature through cycles that involve transmission between bacteraemic rodent hosts and their fleas. Most human cases are acquired through the bites of infectious rodent fleas, including not only those found on commensal rats, but also those found on non-commensal rodents. Additional cases have been acquired through handling infected animals, including non-commensal rodents and lagomorphs, as well as domestic cats and certain wild carnivores. Yersinia pestis probably first arose in central Asia, but has been dispersed along human trade rou- tes to many other parts of the world, including North America, which has extensive wild rodent foci in the western third of the United States, limited portions of south-western Canada and probably areas of northern Mexico Gage Kosoy, 2005. Although this organism was the cause of the Black Death in the Middle Ages, Y. pestis currently exists only in the extreme south-eastern portion of Europe near the Caspian Sea, where it occurs in enzootic foci that are of little epidemiological significance and rarely, if ever, serve as sources of human cases Tikhomirov, 1999. Non-commensal rodents and lagomorphs 442 the disease is underreported CDC, 2002.

13.4.2.2. Borrelia burgdorferi s.l.