Costs, control and management of infestations

Public Health Significance of Urban Pests 455

13.7. Public health impact

In Canada and the United States, local governments, physicians and others typically report cases of rodent-related illness to provincial or state public health officials who monitor the incidences of some of these diseases and report them periodically to agen- cies at the national level. In the United States, the CDC is responsible for the national surveillance of reportable diseases, which includes a few of the rodent- or rabbit-related diseases given in Table 13.2 Hopkins et al., 2005. Unfortunately, incidence data for many of the remaining diseases associated with these animals are unavailable, making it diffi- cult to assess their impact on human populations. Similar data also appear to be unavai- lable for Europe.

13.8. Costs, control and management of infestations

Although a few rodent- or lagomorph-related diseases, such as LB, are viewed as signi- ficant health problems, many others rarely come to the attention of people living in a par- ticular area, which typically results in their believing that these diseases have little impact on their health or economic well-being. Such perceptions are often shared by policy- makers who see few reasons to use limited resources to prevent or control these often rare diseases or the rodent or lagomorph infestations associated with them. However, when Non-commensal rodents and lagomorphs 454 cialized and are completely dependent on a very restricted range of environmental condi- tions for their survival. However, many other rodent species can be classified as genera- lists and are quite adaptable, being able to survive in isolated patches of remaining habi- tat or in disturbed areas. In still other instances, landscape disturbances might actually provide new habitats for opportunistic rodent species. Such a process has been observed over the past 3–4 decades in plague-endemic regions of the south-western United States Barnes, 1982; Gage, Ostfeld Olson, 1995; Gage, 1998; Gage et al., 2000. Much of the development that has occurred in this area has involved the conversion of ranches and forests into semi-rural or suburban areas dotted with new home sites. Despite encroaching urbanization, these sites often retain significant amounts of native vegetation and thus remain attractive to a variety of non-commensal rodent spe- cies, including rock squirrels, which are important hosts and sources of Y. pestis infection for the flea species O. montana that is the primary vector of human plague in the United States. Building rock walls around properties or piling rocks or other debris near new home sites further increases rock squirrel populations Barnes, 1982. Problems with perido- mestic rock squirrel populations are complicated further by residents who improperly dispose of garbage or allow these rodents to have access to spilled pet foods, seeds at bird feeders or other edible items. The risk of LB in peridomestic environments also can be affected by landscaping choices intended to make backyards or other sites more attrac- tive Maupin et al., 1991; Piesman, 2002. Abandonment of agricultural lands in the north-eastern United States has resulted in landscapes characterized by various stages of succession. Initially, weeds and other inva- sive species colonize sites, but eventually other types of vegetation come to predominate, including the native tree species found in the climax forests of this region. Although aban- doned agricultural lands might eventually return to a fully forested state, such sites are often converted to low-density housing, creating semi-rural or suburban environments that offer an excellent mosaic of habitats for non-commensal rodents and their ectopa- rasites. This abandonment and redevelopment of farm lands in the north-eastern United States has also been accompanied by recolonization of the region by white-tailed deer, which act as hosts for the adult stages of the deer tick vector of LB Piesman, 2002. As tick-infested deer help to re-establish the deer tick populations in this region, local popu- lations of white-footed mice and certain other species are able to act as competent reser- voirs for infecting immature deer ticks with the agent that causes LB B. burgdorferi. Although evidence suggests that B. burgdorferi has been present in this region for at least many decades, the landscape changes noted above have resulted, over the past 20 years, in the emergence of Lyme disease as the most commonly reported vector-borne disease in the United States. Recreational use of highly heterogeneous woodlands also is repor- ted to be associated with an increased risk of LB in Europe Gray, 1999. Many of these sites are secondary growth woodlands, and people have altered these environments exten- sively. Table 13.2. Incidence of nationally reportable rodent- or lagomorph-associated diseases in the United States Disease Incidence 1993–2003 Years for which incidence per 100 000 population a data were available in the interval 1993–2003 HGA HGE 0.14 1998–2003 Encephalitismeningitis: arboviral, California serogroup 0.04 1995–2003 primarily La Crosse virus infections Powassan viral encephalitis 0.01 2002–2003 Giardiasis 7.45 2002–2003 HPS 0.01 2000–2003 Leptospirosis 0.02 1993–1994 Lyme disease 5.86 1993–2003 Plague 0.01 1993–2003 RMSF 0.24 1993–2003 Tularaemia 0.05 1993–1994; 2000–2003 a Average for years in which data were available. Note. HGA: human granulocytic anaplasmosis; HGE: human granulocytic ehrlichiosis; HPS: hantaviral pulmonary syndrome; RMSF: Rocky Mountain spotted fever. Source: Hopkins et al. 2005. Public Health Significance of Urban Pests 457

13.9. Control and management of non-commensal rodents and rodent-related diseases