Borrelia burgdorferi s.l. Tick-borne relapsing fever borreliae

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.

LB is the most commonly reported vector-borne illness in the United States, with about 20 000 cases reported annually during recent years Bacon et al., 2004; Hopkins et al., 2005; Jajosky et al., 2006, and some have stressed the threat this disease poses to people who live in urban areas Steere, 1994; Junttilla et al., 1999. Forms of LB also are common in Europe, and Randolph 2001 has noted that populations of castor bean ticks, the vec- tor of LB, have increased in Europe as a result of human impacts on landscapes, which suggests that the risk is likely to remain high on this continent for the foreseeable future. Although LB is covered more thoroughly in Chapter 10, on tick-borne diseases, a brief mention should be made of the essential role rodents play in the maintenance of this dis- ease, by acting as tick hosts and as sources for infecting vector ticks with different geno- types of B. burgdorferi s.l. in European and American foci of infection Kurtenbach et al., 2002. Indeed, the presence of non-commensal rodents has been considered a prere- quisite for LB in an area of endemicity Junttilla et al., 1999. In Europe, voles and non- commensal mice, including yellow-necked mice, wood mice and bank voles, act as impor- tant hosts of different genotypes of LB spirochetes, serving as sources of infection for feeding castor bean ticks and as hosts for immature ticks. White-footed mice and eastern chipmunks play similar roles in various regions of the major LB foci found in the north- eastern and upper Midwestern United States, as do dusky-footed wood rats Neotoma fuscipes in California foci Piesman, 2002.

13.4.2.3. Tick-borne relapsing fever borreliae

Certain spirochetes, including Borrelia hermsii, B. turicatae and B. parkeri cause relapsing fevers in western North America. All are transmitted by species of Ornithodoros ticks that feed primarily on rodents. Some of these rodent hosts develop high levels of spirochete- mias and can serve as sources for infecting vector ticks Burgdorfer Mavros, 1970; Burgdorfer, 1976. The vectors of B. turicatae and B. parkeri the ticks O. turicata and O. parkeri , respectively feed primarily on burrow-dwelling rodents and other rodents that occur most often in highly rural areas and rarely come in close contact with people Burgdorfer, 1976; Gage et al., 2001. However, the tick O. hermsi, the vector of B. herm- sii , frequently feeds on American red squirrels and chipmunks, both of which can invade homes and build tick-containing nests in attics and wall spaces Thompson et al., 1969; Trevejo et al., 1998; Schwan et al., 2003. If the hosts of these ticks die, they are likely to leave these nests to find other hosts, which can result in people being bitten by B. herm- sii -infected ticks.

13.4.2.4. Rickettsiae