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

Public Health Significance of Urban Pests 457

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

A variety of approaches can be used to prevent rodent-related illnesses. Obviously, cost- effective and reliable surveillance methods must be developed, so that threatening situa- tions can be identified quickly and appropriate preventive measures taken Gage, Ostfeld Olson, 1995; Glass et al., 1997; Trevejo et al., 1998; Gage, 1999; Hopkins et al., 2002; Douglas et al., 2003; Hayes Piesman, 2003. Although the types of preventive measu- res used will vary from one situation to another, certain steps are likely to be appropriate in nearly all instances. Clearly, residents of the areas affected by threatening situations should be made aware of the risks and be educated about the best means of protecting themselves and their families. This includes taking certain precautions, such as avoiding sick or dead animals, using insect repellents, performing so-called tick checks, wearing protective clothing or gloves, or treating clothing with appropriate pesticides Gage, Ostfeld Olson, 1995; Hayes Piesman, 2003. The intentional feeding of seeds or other foods to rodents and lagomorphs is to be discouraged, as it is likely to increase the risk of people coming in contact with infected animals or their ectoparasites. Residents of the areas affected also should be advised that pets can become infected after contact with non- commensal rodents or lagomorphs and can spread these infections to their owners. Pets also can carry infected vectors into homes. Applications of rodenticides, insecticides or acaricides in rodent habitats is sometimes warranted as a means of quickly reducing the risk of transmission, but such treatments are best done by pest control specialists. Although proper use of pesticides can often provide rapid reductions in the risk of dis- ease, they should not be used solely for long-term management of problems posed by non-commensal rodents or lagomorphs. Whenever possible, rodent-related disease problems should be addressed by a combina- tion of personal protective measures, treatment and restraint of pets, limited applications of pesticides, reductions of rodent food and harbourage in or near people’s homes, and modification of rodent habitats, so that people will be less likely to come in contact with infected rodents Childs et al., 1995; Gage, Ostfeld Olson, 1995; Gage et al., 2000; Mills et al., 2002. The last two measures reductions of rodent food and harbourage and mana- gement of rodent habitats are likely to represent the most sustainable and effective approach to reducing widespread threats posed by non-commensal rodents Gage, Ostfeld Olson, 1995; Levy Gage, 1999; Glass et al., 1997; H opkins et al., 2002; Douglass et al., 2003. Temporary reductions in rodent numbers are of minimal use and might even be harm- ful. Douglass and colleagues 2003 reported that removal of deer mice from buildings actually resulted in an increased number of mice entering these structures, leading these authors to speculate that mouse removal in the absence of rodent-proofing is likely to increase the risk of human hantavirus. The importation and ownership of exotic rodents, such as prairie dogs, as pets also should be discouraged, because this practice could result in direct human exposures to various pathogens. A remote possibility also exists that these animals might escape and spread Non-commensal rodents and lagomorphs 456 the negative health and economic effects caused by non-commensal rodents and lago- morphs are considered as a single, combined problem, their impact is likely to be signi- ficant and easier to recognize. Addressing rodent- or lagomorph-related issues in this way should be justifiable from a planning and policy perspective, because in many instan- ces the measures used to prevent and control the various rodent- or lagomorph-associa- ted pathogens are quite similar. The control measures recommended to reduce rodent or lagomorph infestations in homes or other sites also, are often nearly identical, although in some instances a specific technique must be employed for a particular species. Another advantage that is likely to result from treating rodent- or lagomorph-associated issues as a single problem is that programme duplication can be minimized, resulting in more suc- cessful, cost-effective programmes that can maximize the use of limited resources. Unfortunately, estimating the costs of rodent-related diseases is difficult, and few publi- cations have addressed this issue. An early evaluation of plague control in California campgrounds determined that control was economically beneficial compared with other options, including surveillance-only and no-programme alternatives Kimsey et al., 1985. Similar estimates were not made, however, for benefits derived from plague control pro- grammes targeted at peridomestic environments. More recently, a number of authors have attempted to estimate the costs associated with LB. Maes, Lecomte Ray 1998 estimated that the total economic burden for this illness in the United States was US2.5billion 1996 US over a five-year period. These costs are likely to have increa- sed dramatically as a result of the general inflation of health care costs in the United States, as well as actual increases in the number of LB cases reported. In a later study, the mean cost per case of LB in the United States was estimated to be US4466 1996 US Meltzer, Dennis Orloski, 1999. A more recent study estimated the annual costs for LB in Scotland to be £331 000 Joss et al., 2003. Carabin and colleagues 2005 described methods for assessing the economic burden of echinococcosis in people, which they defined as involving infestations with either E. mul- tilocularis , the agent of alveolar echinococcosis, or E. granulosus, which causes cystic echi- nococcosis. Although E. granulosus is not associated with rodents, E. multilocularis utili- zes rodents as intermediate hosts see section 13.4. According to the methods described by Carabin and colleagues, a case of echinococcosis in the United Kingdom costs about US 10 215 2005US. Although no estimate of costs for treating hantaviral cases was found, Hopkins and col- leagues 2002 reported that inexpensive rodent proofing less than US 500 per house- hold in 2002 was effective in reducing the intensity of rodent intrusions in homes, a method that should prove cost effective and result in the decreased risk of SNV infec- tion among the people living in these homes. Public Health Significance of Urban Pests 459 cations intended to reduce the attractiveness of sites for rodents, removal of sources of rodent food and shelter provided by people, and construction of barriers to exclude poten- tially infected animals from people’s homes, recreation areas or work sites. Provide, in emergency situations, for selective and limited use of pesticides to rapidly reduce the risk of disease or to protect property. Develop a comprehensive plan for monitoring and controlling rodent- and lagomorph- related diseases. This plan should include provisions for increased disease surveillance that will provide a more comprehensive assessment of the risk of people being exposed to these diseases in sites undergoing urbanization. Such information is currently lacking for most rodent- or lagomorph-related diseases in Europe and North America, making it difficult to determine the true health and economic burdens posed by these diseases. The plan also should integrate all surveillance, prevention and control efforts for these diseases into a single programme for each region. A single integrated programme for addressing these diseases should be highly effective, because the techniques, equipment and trained personnel required to prevent or control many of them are quite similar. Combining all prevention and control activities into one programme also will reduce duplication of effort and will better utilize scarce resources and personnel, making these efforts more cost effective and easier to justify to programme managers, politicians and the general public. Non-commensal rodents and lagomorphs 458 pathogens to native rodent species, leading to the establishment of enzootic cycles of these agents in various rodent species. These issues were well illustrated by the recent identi- fication of tularaemia bacteria in prairie dogs that were shipped from an exotic-pet faci- lity in the United States to other sites in the United States and Europe Avashia et al., 2004; Petersen et al., 2004. At least one animal handler at the exotic-pet facility was thought to have acquired tularaemia from handling these infected prairie dogs. In ano- ther incident in the United States, black-tailed prairie dogs became infected with mon- keypox virus at an exotic-pet facility after being exposed to infected Gambian giant pou- ched rats imported from Africa. Following infection, the prairie dogs were shipped to pet stores in the Midwestern states, which resulted in numerous human monkeypox infections among people who handled these animals Kile et al., 2005.

13.10. Conclusions