Future prospects Resurgence of bedbug populations in Europe and North America

Public Health Significance of Urban Pests 137

4.3.2. Potential as vectors of human pathogens

Common bedbugs have been found to naturally contain 28 human pathogens, but they have never been proven to transmit biologically or mechanically even one human patho- gen Usinger, 1966; Burton, 1968 – specifically hepatitis C Silverman et al., 2001 and HIV Webb et al., 1989. Nevertheless, shedding of viral DNA fragments in faecal mat- ter and transstadial across life stage transmission of hepatitis B virus seem to support the possibility of mechanical transmission by contaminated faeces, or when bugs are crus- hed during feeding onto abraded skin by a susceptible person Jupp et al., 1991; Blow et al., 2001. The study by Jupp and colleagues 1991 clearly indicated that common bed- bugs do not biologically transmit hepatitis B. Also, it is still unclear whether or not the reported induction of skin papillomas in the European rabbit Oryctolaguscuniculus sub- sequent to continuous exposure to bites of common bedbugs irradiated by gamma rays el-Mofty, Sakr Younis, 1989 is caused by a viral pathogen. One species of Cimicidae, the cliff swallow bug so far, found occurring naturally infec- ted, only in western North America, has been proven to transmit at least two identifia- ble virus entities in the western equine encephalitis complex: these are the Fort Morgan virus FMV and a distinct strain of FMV, called Buggy Creek virus Hayes et al., 1977; Calisher et al., 1980; Brown Brown, 2005. Transmission has thus far only been repor- ted to occur from infected swallow bugs, mainly adult bugs that usually live in or on the swallows’ nests over the winter until the next year’s susceptible hatchlings of cliff swal- lows. So far, no risk to people from this epizootic virus cycle has been established. The bugs are not very mobile and tend to stay at, on or in the swallow nests and do not rea- dily move to a different nest that is more than a short distance away Foster Olkowski, 1968. A few individual bedbugs of this species have been found very rarely in local small rodent nests and occasionally in a nearby nest of a European or barn swallow Hirundo rustica . This species has been reported to have fed on a person, and it readily feeds on mice in laboratories Usinger, 1966. Although some species of the Cimicidae that seek human beings over other animals have not been investigated very thoroughly, it is unli- kely that any of them pose a threat as a human pathogen vector. In Europe, infestations of human dwellings by the European swallow bug often occur, especially during the wintertime, when their normal hosts have migrated to Africa. Abandoned swallow nests may harbour hundreds of overwintering swallow bugs that search for blood hosts during warmer winter weather conditions. Within a radius of up to 5m, swallow bugs may infest buildings through any opening, and they feed readily on people. In an extensive study in Colorado, cliff swallows and house sparrows Passer domesticus , which live within the swallow nesting colonies, were the main vertebrate hosts for maintenance and amplification of FMV. However, the presence of fairly large populations of these bugs, and their transmission of FMV, reportedly had no significant impact on the health or reproduction of local populations of cliff swallows, house spar- rows or barn swallows in co-located or adjacent breeding sites Scott, Bowen Monath, 1984. Bedbugs 136 mentation of pest control measures. Although it is rare that they attack people, these spe- cies are noted because infestation of human dwellings may occur.

4.2.5. Future prospects

Under prevailing conditions, it seems inevitable that bedbugs will continue to spread and cause increased problems. Since 1970, in high- and middle-income countries, the loss of non-repellent and longer residual insecticides, through regulatory actions, has made their control much more difficult. In the United States, anecdotal reports from PMPs about currently labelled products are variable and hard to verify or compare objectively. Some have reported effective control, while others claim outright failure from the same pro- ducts. Also, screening for resistance to such products is rare. There are few published data or reports of screening for resistance on field populations of bedbugs, and no govern- ment or private agency is currently providing routine or even periodic screening of field populations of bedbugs in North America. A few laboratories in Europe and North America have only recently begun planning more extensive, controlled susceptibility resistance testing on bedbugs E. Snell, Snell Scientifics, Barnesville, GA, personal com- munication, May 2005; O. Kilpinen, Danish Pest Infestation Laboratory, Lyngby, Denmark, personal communication, August 2005. Fletcher Axtell 1993 published one of the most recent articles on the susceptibility of a population of lab-reared common bedbugs to several specific insecticide formulations, including some being used com- mercially at that time. At least five of the nine chemicals they tested, which include the active ingredients bendiocarb, carbaryl, dichlorvos, malathion and tetrachlorvinphos, have had their product labels changed, following the United States Food Quality Protection Act of 1996, and those products are no longer available for use in human dwel- lings. In addition to these factors, significant changes in application technologies against other household pests, such as cockroaches and ants, may also have unintentionally eased incidental control of bedbugs Potter, 2004; Gooch, 2005. 4.3. Implications for public health 4.3.1. Obligate blood feeders