An interview with urban pest management expert Clive Boase

Clive Boase, in an expansive discussion via email, generously allowed us to pick his brain on the bed bug resurgence and what it will take to eradicate bed bugs from our cities.

Clive Boase is the principal consultant entomologist with the Pest Management Consultancy (Haverhill, UK). He is the author of two essential articles (PDF) about the bed bug resurgence.

New York vs Bed Bugs: What is the present situation in the UK at what must be nearly a decade if not more since the beginning of the bed bug resurgence? We understand the London School of Hygiene & Tropical Medicine was working on an infestations forecasting model. Is there any effort at a coordinated response to the spread of infestations? Is the UK working on formulating best practices in the manner of the Australian Code of Practice? And are there perhaps other countries in Europe that have undertaken such an effort?

Clive Boase: Yes, it was almost a decade ago that the first signs of an increase in bedbug infestations and treatments became apparent. In the years since then we have seen substantial increases in infestation levels. A retrospective survey was carried out by a student at the London School of Hygiene and Tropical Medicine of the number of requests from residents for bedbug treatment received by the pest control teams in several London boroughs over the period 2000-2006. Results showed a c. 25% annual increase. However, across the UK, the absolute level of infestation varies very considerably from region to region. London and the south-east of the UK appear the most affected, while there are other substantial urban areas where infestation, although rising significantly, is at a much lower level.

In the hospitality sector some improvements are already taking place. The gloomy perception held by many a few years ago was that there was an almost unstoppable flux of bedbugs into hotels, and this was responsible for maintaining high infestations levels. However, it is now becoming clear that infestations in hotels persist mainly because of failure to achieve eradication, not because of repeated re-invasion on guests etc. There have now been pilot studies in which hotels that had had deeply entrenched bedbug infestations, have had their bedbugs completely eradicated by thorough treatment. In these hotels, once complete eradication has been achieved, then even at 15 months later, and after almost 100k guests have passed through the hotels, then repeated inspection of every room continues to show a complete absence of infestation. Clearly re-infestation does not take place as rapidly as some believe.

Here in the UK, although the bedbug upsurge is widely recognised, we do not have a nationally co-coordinated response to the problem. In terms of the debate about the causes of the outbreak, there is still a popular and widespread view that it is partly caused by overcrowding, human migration, travel etc., and while such views are widely held, then there is also a feeling that although pest control measures may be improved, the real cause of the problem cannot be easily addressed. There has been interest in the Australian Code of Practice, and in the San Francisco by-laws. However, the differences in the range of insecticides available, in the performance of laundry equipment, and in legislation regarding rights of access to residential properties, means that it is inappropriate to adopt the guidelines as they stand. In addition, there is some concern that the guidelines and Codes of Practice have not yet been fully ‘road-tested’. To be worth adopting, a CoP needs not just a lot of thought put into it, but there needs to be good evidence to show that it actually gives results. Having said that, I understand that Italy has adopted the Australian Code of Practice.

Nonetheless, a bedbug strategy for London is under development. This includes a range of initiatives aimed at: pest control staff, residents, landlords, healthcare professionals, and legislators etc. Where possible the strategy is evidence-based, i.e., it proposes changes that have been shown to have an effect in practice. The intention is that the strategy will be evaluated to ensure that it is not just hopeful thinking, but that it actually delivers a result.

New York vs Bed Bugs: By the way, in your susceptibility evaluations, have you by chance also tested DDT?

Clive Boase: No we have not looked at DDT susceptibility.

However, regarding DDT, this is often claimed as being responsible for the demise of the bed bug in the late 1940s and 50s. However, here in the UK, bedbug infestation levels were declining fast in the late 1930s, some years before DDT was introduced. This decline coincided with the introduction of the Public Health Act 1936, which gave local authorities (i.e., local government organisations) powers and responsibilities to deal with vermin, including bedbugs. To me this suggests that effective bedbug control is as much about organisation and management, as it is about using high performance insecticides, although of course they help.

New York vs Bed Bugs: What are your current thoughts about how and why bed bugs spread within structures?

Clive Boase: Regarding spread of bedbugs within buildings, I now regard this as the norm. An isolated complaint of bedbug infestation from a unit (i.e., apartment, or hotel room) within a building will often turn out be part of a cluster of infested units within that building. We would now say that when inspecting/investigating a complaint of bedbug infestation, that several units to the left and right of the complainant should automatically be inspected, if access is possible.

The dispersion routes seem to vary from building to building, depending on construction. For example, we see some evidence of dispersion from one floor to another mainly in older buildings, where the barrier between floors is not so good. In buildings constructed in recent decades, then the fire-barrier between floors appears good at preventing vertical bedbug movement. However, lateral/horizontal movement between rooms is common, especially where plumbing or other services run from room to room. In such places bedbug infestations will normally appear as strings of infested rooms (sometimes with rooms that appear to have been ‘skipped’) along one side of the corridor. Looking inside pipe conduits etc., we sometimes see bedbugs, or exuviae. Having said that, there are buildings where the construction detail is good, and infestations occur in individual units only, with no discernible dispersion. In some hotels where the dirty linen is removed from the room and deposited temporarily on the floor in the corridor, then the pattern of infestation shows a spread of bedbugs across the corridor as well.

Overall, I would say that surveys should normally include nearby units, although this raises the issue of access and powers of entry to owner-occupied and rented property.

Where horizontal pipework is present, then proofing around pipes is very important in preventing dispersion.

It has been suggested that dispersion is accentuated by the irritant effect of pyrethroid treatment (as has been shown with cockroaches). This may be true, but it is not only due to insecticide irritation—we have seen clusters of infestations in adjoining units in premises that are not recorded as being treated. Similarly, dispersion may be part of the reported tendency for adult females to seek more outlying harbourages.

New York vs Bed Bugs: How did we arrive at this juncture? Our reading has led us to understand that bed bugs have been present in low and occasionally rising numbers throughout the period they were thought to have been eradicated.  In the US there is a paucity of reliable data on the incidence of infestations at present; data about previous cycles is entirely non-existent and information has to be pieced together from news archives. In the UK, however, there is actual, if discontinuous, data available. For example, in the 1980s, bed bug infestations were noticeably high. What can we learn from these previous cycles? And what is your current opinion on the reasons for the bed bug resurgence now that we are several years into it? And, finally, what do you make of the chickens and DNA research that suggests bed bugs have subsisted on alternate hosts?

Clive Boase: Yes, in general, historical records of bedbug infestation are fragmented, and non-standardised, so it is far from easy to assemble these into a coherent story. Records from private pest control companies are seldom available, with the exception of Peter Cornwell’s records from Rentokil, published in 1974. Records from local authorities, where they exist, are potentially more useful since they cover a fixed geographical area. However, local authority records only show the infestations they dealt with, and do not include those treated by private companies. And other issues such as pricing or local policy will change the proportion of bedbug infestations dealt with by a local authority pest control section. Nonetheless, it would be churlish not to try to use the information we have got….

The more information that becomes available, the clearer it appears that bedbugs have a very patchy distribution, on whatever scale you look at them. Matheson in 1941 showed that bedbug infestation levels varied by up to 10x from one town to the next. In general, larger towns then had a higher proportion of infested homes, and seaports were more heavily infested than inland cities. More recently, records from the northwest of the UK in the 1970s-1990s, show a 60x variation in the number of bedbug treatments between similarly sized towns, with differences being maintained over 2 decades. Even now, when we talk in general terms of an upsurge in the UK, infestation rates outside London appear to be much lower, even in relatively large cities, than in the capital. Current information on infestation levels does not correlate well with city size, but there are some indications that correlations with socioeconomic factors work better.

One thing we have learnt from looking at these and other records is that in the UK (and the same appears true of other European countries where data is available, such as Denmark and Switzerland), bedbugs came nowhere near national eradication in the so-called recession period. We do not need to invoke importation or overseas travel to find a source of bedbugs that drove the resurgence of bedbugs in the last 10 years. They were here all the time.

Did bedbugs in poultry act as a reservoir that survived the ‘recession’ and then helped fuel the current upsurge? In some areas it may have done. However, here in the UK, bedbugs are not known as pests of poultry. We do not see bedbugs in poultry acting as a reservoir to fuel the upsurge. For us, bedbugs in localised areas of some larger cities would appear to have been a much more important reservoir.

So why are we here now? The growing feeling, contrary to what the media say, is that the current upsurge is much less about repeated and frequent reintroduction of bedbugs, and much more about failure to achieve eradication of identified infestations. If we can sort out the question of eradication, then the issue of re-importation will look after itself.

New York vs Bed Bugs: You have written about taking an epidemiological approach to bed bug infestations; can you describe why it is a sound approach? I am mindful that in 2001 you identified 3 critical needs: a monitoring tool to identify infestations rapidly, susceptibility research, and consolidated data collection. What is necessary today?

Clive Boase: Looked at from an epidemiological perspective, the more infestations there are, the more new ones will appear. A larger number of infestations will by itself give rise to an increased number of new infestations. We do not need to look for changes in human behaviour or movement to explain the increase. However, push the model the other way and completely close infestations down, then not only are we not having to play catch-up with infestations that weren’t quite eradicated, but also we are reducing the opportunity for new infestations to appear. We are putting this kind of thinking into practice at large numbers of linked accommodation facilities, to see if we can reverse upward trends in re-infestation rates, by introducing a systematic eradication process.

Components of eradication would include:

  • Early detection of infestations

This may mean proactive inspection in commercial or institutional premises. In addition, as mentioned previously, availability of effective bedbug monitors are also central to this. In residential premises, then public awareness is the issue.

Early detection is likely to mean easier eradication, and importantly, less opportunity for dispersion to other premises before treatment.

  • Access to professional pest control services

Lower income communities may not have the resources to access professional pest control services. In these cases infestation may be ignored, or dealt with by an ad hoc and unsuccessful fashion by the resident. Some local authorities in the UK offer a free service for bedbugs (and some other pests), but this may be a controversial way forward for many. However, as previously, if we leave infestations ticking over in certain areas of our cities, then they may bounce back out again.

  • Access by pest control staff to infested areas

In many countries, there is no immediate right of access into rented or leased property. This can thwart block treatments or full inspections. The issues here are partly to do with legislation, and tenancy contracts. This is something we are trying to address in the UK.

  • Preparation of premises to be treated

This requires better communication to gain customer compliance. Some local authorities operate a ‘tough love’ approach, where treatments are not carried out if premises, bedrooms etc have not been properly prepared.

  • Treatments that actually eradicate infestation

Many treatments will reduce bedbug numbers and provide the illusion of eradication. However, bedbugs often re-appear in these previously treated premises after a period of a few months. This phenomenon is important, not just for the unhappy client, but because the infestation has then had the potential for onward dispersal to new sites all that time. So why does this occur? There are many possible explanations.

It may be that the treatment of the premises was fully effective, but that bedbugs re-invaded from adjoining but untreated premises. This raises the question of whether premises adjoining an infested premises should be treated as a matter of course. Given that we know that bedbugs are capable of local dispersion, and yet are difficult to detect in low numbers, then there is a case for this. In hotels it would be common practice to treat a block of rooms around known infested rooms, to be confident of treating all the bugs. Records show that such practice is more effective than just treating individual rooms. In residential property, then this practice is more contentious. In particular, who should pay for such treatment, and are such precautionary treatments allowed in law? However, there are precedents, as block treatments are accepted for other pests such as Pharaoh’s ants, cockroaches and mice.

Alternatively, even in sites where there are no bedbugs in nearby premises or rooms, then studies of records from treated premises, especially hotels, will show that bedbugs very often ‘re-appear’ in the very same rooms up to 18 months after treatment. There are probably a variety of reasons for this, but the important ones are likely to be a treatment that was not fully effective initially, coupled with a failure to carry out post-treatment follow-up inspections to ensure eradication had actually been achieved.

Achieving a positive result is partly about improved management of bedbug control work. I look back to the big reduction in bedbug levels in the UK in the late 1930s, following the introduction of the Public Health Act, and almost a decade before the introduction of effective synthetic insecticides such as DDT, as an example of what can be achieved by effective organisation.

Also, it’s about making better use of the pest control products we have. Even in the face of resistance, changes in application technique of conventional insecticides may improve impact. In the UK, two insect growth regulators (one juvenile hormone analogue, and one chitin synthesis inhibitor) are regularly used, but their efficacy against bedbugs is not yet fully understood. Desiccant dusts are also available, but again there is very little relevant public domain information on their efficacy, and the detail of their use is left to the individual pest control organisation. Similarly, we know that non-chemical techniques such as extremes of temperature will kill insects, but how best to integrate these into effective bedbug control? All this could of course be left to the initiative of individual organisations to resolve for themselves. However, in public sector pest control, where bedbugs represent a significant and growing challenge, then there is a case for public investment in evaluation and rationalisation of these approaches. We may already have all the tools we need, but just need to use them better.

And partly, of course, it is about new insecticides with alternative modes of action. However, this is a long-term way forward—we can’t wait for this.

Insecticide resistance is, of course, also part of this. Discovery of insecticide resistance is often accompanied by a period of denial. However, we are a mature industry, and resistance should not be a surprise. We should be able to discuss and address resistance issues in a practical way, and importantly should be developing ways to manage the use of insecticides to slow the onset of resistance before it appears. Resistance management techniques are reasonably well established and warrant open discussion with the key players in pest control.

  • Follow-up inspections to ensure eradication has actually been achieved

This is critical. We need to be able to demonstrate to our clients and ourselves that each infestation has actually been eliminated, and if not, then to take steps to complete the job. Good pest control is less about the work done, but much more about the results achieved. Knowing that we have the technology and management to take on infestations and eradicate them, is not only good for our clients, but gives us confidence. And if through timely eradication we are able to eliminate existing infestations faster than new ones are established, we will then reduce the total stock of infestations, which in turn will reduce the opportunity for new infestations to appear, and the upsurge itself will then turn into a decline.

(Ed. note. We could not find the Matheson article online. Matheson C. 1941. The distribution of Cimex lectularius in towns in England and Wales. Bulletin of Entomological Research. 32:165–71. The Peter Cornwell article is available from the Armed Forces Pest Management Board’s Literature Retrieval System. Enter accession:82952 as the search term. Cornwell PB. 1974. The incidence of fleas and bedbugs in Britain. International Pest Control 16:17–20.)

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