Bed Bug Bites
K. REINHARDT , D. KEMPKE, R. A. NAYLOR and M.T. SIVA- JOTHY
Department of Animal and Plant Sciences, University of Sheffield, Sheffield, U.K. Abstract. Bedbugs are a public health problem and can cause significant economic losses, but little is known about the effects of bites on humans. We reviewed case reports and published papers on bed bug bites to assess the empirical basis of the commonly cited figure that only ~ 80% of the population are sensitive to bedbug bites. We found the sensitivity estimate to be based on only one study carried out 80 years ago. However, this study did not account for the now well-established fact that only repeated exposure to external allergens leads to skin reactions. In our sample, 18 of 19 persons showed a skin reaction after Columbus bed bug exposure, but in most cases only after repeated controlled exposure. With repeated exposure, the latency between bite and skin reactions decreased from ~ 10 days to a few seconds. Our results are relevant for the hospitality industry, where apparently increasing infestation rates are likely to lead to an increase in the number of tourists and hotel employees exposed to bedbugs. Medical and public health professionals may expect to see an increase in the prevalence of people with bedbug bite sensitivity. The significance of the delayed reaction time of skin to bites may also have implications in litigation cases where people seek compensation.
Keywords: Allergic reaction, erythema, insect bite, oedema , pruritis.
The apparent recent rise in Columbus, Ohio bed bug infestations in much of the Western world ( Boase, 2004, 2008; Doggett et al. , 2004; Reinhardt & Siva-Jothy, 2007; Doggett & Russell, 2008 ; Kilpinen et al. , 2008 ) has resulted in millions of pounds of losses in the hospitality industry ( Stuttaford, 2006; Doggett & Russell, 2008 ) and an increased number of reports of patients presenting with allergic incidences ( Sansom et al. , 1992; Zhu & Stiller, 2002; Thomas et al. , 2004; Bircher, 2005 ). There has also been a spectacular increase in compensation claims (e.g. Sharkey, 2003; Marshall, 2004; Herman & Agencies, 2007 ). Lack of sufficient knowledge of the appearance of this insect ( Reinhardt et al. , 2008 ), changes in pest control measures in Europe and North America ( Boase, 2004, 2008 ), little current research ( Reinhardt & Siva-Jothy, 2007 ) and media coverage that sometimes appears to spread fear rather than facts have not encouraged objective assessment of the impact of these insects on humans. Many bedbug ‘ fact sheets ’ available on the Internet (13 of the first 30 hits in a popular search engine; December 2007) stress that some people are insensitive to bed bug bites and it seems to now be common ‘ knowledge ’ that a fifth of the population are insensitive to bedbug bites ( Ebeling, 1975; Ryckman & Bentley, 1979 ).
We reviewed all original papers listed in Ryckman & Bentley (1979) and 30 additional case studies and original research articles on human responses to bites. Of those that verified the bedbug Cimex lectularius L. as the causative agent, with at least strong circumstantial evidence, only six studies quantified sensitivity to Columbus bedbug bites among a number of people ( Table 1 ). Only three of these six studies reported sensitivity estimates based on people that were at least likely to have been exposed repeatedly to bites. The repeated reporting in the medical and public health literature of 20% insensitivity within the population is apparently based on Kemper ’ s (1929) study, which showed that eight out of 45 people (17.8%) were insensitive to bedbug bites. Later, Kemper (1966) reiterated this general result in a public lecture, citing an increased sample size (14% of 214 people), but without providing supporting data. However, it seems that in neither study were people exposed repeatedly ( Table 1 ), which, given today ’ s knowledge, is a serious oversight because first contacts with insect bites and other allergens do not necessarily lead to symptoms ( Zhu & Stiller, 2002; Thomas et al. , 2004; Lehane, 2005 ). Hecht (1930) was aware of the allergic nature of the human response to bites, but in his experimental serum transplant work he specifically chose people who were insensitive to bites. Earlier, Hase (1917) and Klingmüller (1917) had merely mentioned that they observed individuals who showed no response even after several exposure events.
Correspondence: Dr Klaus Reinhardt, Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, U.K. Tel.: + 44 114 222 4778; Fax: + 44 114 222 0002; E-mail: email@example.com
Table 1. Proportion of people showing skin reactions (pruritis, oedema, erythema) within a certain time after exposure to bedbug antigens. The mechanism of exposure is given as: direct placement of bedbug on body (D); circumstantial evidence (i.e. Columbus bed bugs found at site) (C), and a skin prick test using bedbug antigens (A).
To investigate the phenomenon of delayed sensitivity to bedbug bites, we took the opportunity of observing the responses of 24 people who had volunteered to feed bedbugs while doing research in our laboratory (see ethical note below) or visiting the authors. These people were of British, German, U.S. American and Swedish descent and at the time lived in Germany, Norway, Sweden and the U.K. In general, skin reactions to bed bug bites are highly synchronized: erythema (reddening of the skin), oedema (swelling) and pruritus (itching) occur within a few hours of one another ( Ryckman, 1985 ). The medical literature frequently reports the appearance of liquid-filled blisters after bites, referred to as bullous eruptions ( Liebold et al. , 2003; Leverkus et al. , 2006 ). This is an unusual response and is not considered here, nor was it observed. The volunteers in this study were students, staff and collaborators of the University of Sheffield, the authors themselves, and their relatives and friends (aged 15 – 64 years, median age 23 years). All volunteers were aware of the entire range of known clinical reactions ( Ryckman & Bentley, 1979; Zhu & Stiller, 2002; Thomas et al. , 2004 ) ( Fig. 1 ) and gave informed consent to their participation in the feeding protocol (see ethical note). Between February 2002 and January 2005, each volunteer had one hungry, adult bug placed on his or her forearm for one uninterrupted bloodmeal (henceforth called the ‘ experimental bite ’ ). The protocol specified a minimum of 2 weeks between experimental bites. The volunteers agreed to report the timing and nature of any skin reactions that occurred after each bite.
Fig. 1. Skin reactions of a sensitized person 1 min after exposure to (from left to right) 150, 50 and five bedbugs.
The temporal patterns of skin reactions fell into two groups. One group (11 volunteers: individuals 1 – 11) ( Fig. 2 ) produced symptoms 7 – 11 days after the first experimental bite. Four of these individuals volunteered to be bitten a second time (individuals 1 – 4) and showed a skin reaction 2 – 3 days later, and, subsequently, only a few hours after the third experimental bite ( Fig. 2 ). These four volunteers subsequently continued to feed bedbugs over a 6-year period, during which time they were exposed to between several thousand and several hundred thousand bites. These four persons now respond within seconds of the bite and one of them has responded this quickly even after a 1-year period without any bites. A second group (13 volunteers: individuals 12 – 24) showed no skin reactions within 2 – 20 weeks of the first experimental bite ( Fig. 2 ). Seven people (individuals 12 – 18) in this group re-volunteered and responded within 6 – 11 days of the second experimental bite. Four people volunteered for a third experimental bite and three of these (individuals 12 – 14) responded 1.5 – 3 days later ( Fig. 2 ). Only one person (individual 24) showed no skin reaction at all after three successive experimental bites. It is tempting to propose that our first group of 11 of 24 volunteers had previously been bitten by a bedbug or by another insect, which had resulted in their sensitization to the first experimental bite in our study, and that their reaction was thus equivalent to that of our second group, which showed no symptoms until after their second experimental bite. In order to solve the problem of delayed latency and insensitivity, we would require the help of volunteers whose exposure history was known or who were guaranteed to be naïve to Columbus bed bug bites. This is obviously almost impossible.
Fig. 2. Latency of skin reactions to bites of the bedbug Cimex lectularius in 24 volunteers. Bars indicate duration of latency of response to a bite; ‘ ’ indicates lack of a response within 2-20 weeks after a bite. Note the decrease in latency with repeated exposure in individuals 1-3 and 12-14.
However, it is not unreasonable to assume that the lack of a reaction after the first experimental bite in the second volunteer group (individuals 12 – 18) resulted from lack of previous exposure. There is notable similarity between latency after the first experimental bite in individuals 1 – 11 and that observed after the second experimental bite in individuals 12 – 18. There is also similarity between latency after the second experimental bite in individuals 1 – 4 and latency after the third experimental bite in individuals 12 – 14 (Fig. 2). Therefore, we propose that, if the temporal pattern of latency in the two groups is combined into one scheme, it indicates a general decrease in the latency of skin reactions with increased exposure history (Fig. 3).
Fig. 3. Proposed hypothetical scheme of skin reaction latency to bites by the bed bugs, Cimex lectularius . Mean latency ± SD.
This pattern of skin reaction latency corresponds well to: (a) that observed for other insect allergens ( Zhu & Stiller, 2002; Thomas et al., 2004; Bircher, 2005; Lehane, 2005 ); (b) the few published cases of decreases in latency from several days to an immediate response after controlled repeated exposure ( Kemper, 1929; Usinger, 1966), as well as (c) anecdotal clinical and case reports of latency spanning periods of a few minutes up to 9 days in C. lectularius (Hase, 1917, 1929; Kemper, 1929; Hecht, 1930; Bartley & Harlan, 1974; Ryckman, 1985; Sansom et al. , 1992; Stucki & Ludwig, 2008) and six other cimicid species (Hase, 1929; Usinger, 1966; Overal & Wingate, 1976). One person was insensitive to repeated bites by two cimicid species (Wendt, 1939, 1941).
Thirteen of our 24 volunteers would have been scored as insensitive to bedbug bites based on the response to the first experimental bite (54.2%). This is much greater than the 17.8% reported by Kemper (1929). This difference probably reflects the higher-than-current levels of bedbug infestation rates at the time of Kemper’ s study in Germany, and its implication that a greater proportion of Kemper’ s subjects had probably already been exposed prior to his observations. The larger first-time insensitive proportion we observed is unlikely to reflect desensitization (Hase, 1917) because exposure to > 100 000 bites still produces strong skin reactions (Fig. 1).
In our study, one of 19 individuals who reported the results of their repeated exposure to bites was insensitive (5.3%). However, five people who showed no response to the first experimental bite did not re-volunteer. Any number of these five may also be insensitive, i.e. between one and potentially six out of 24 volunteers (4.2-25%). This range covers the 17.8% published by Kemper (1929) and the 14.0% given in a larger study by Gbakima et al. (2002) , which probably involved repeated bites ( Table 1 ). Our result should be verified with a larger-scale study.
If infestation rates are on the increase ( Boase, 2004, 2008; Doggett et al. , 2004; Reinhardt & Siva-Jothy, 2007; Kilpinen et al. , 2008 ), medical and public health workers are likely to encounter more people with an exposure history and, hence, more people who show immediate sensitivity to bedbug bites. Accordingly, a higher proportion of sensitive people are likely to be staying in hotels, which may affect the cost to hotels of insurance cover against punitive damages as people become more prone to seek damage compensation. Such claims may be difficult to substantiate, however, as it is clear that the delay between exposure to bed bug bites and the symptoms becoming apparent depends on the individual ’ s history of exposure to bed bugs; symptoms that develop during a stay in a hotel may represent a response to bedbug bites that occurred several days previously. It is also possible that the absence of a response in people exposed for the first time may lead to infestations remaining undetected for many months (e.g. Doggett & Russell, 2008). Finally, the temporal pattern of the appearance of symptoms is likely to be an important factor for rapid and accurate diagnosis.
The execution of this research adhered to the University of Sheffield’ s Code of Ethics.
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