Bjørn Arne Rukke

Head lice prevalence among households in Norway: importance of spatial variables and individual and household characteristics

SUMMARY Head lice prevalence varies greatly between and within countries, and more knowledge is needed to approach causes of this variation. In the present study, we investigated head lice prevalence among elementary school students and their households in relation to individual and household characteristics as well as spatial variables. The investigation included households from 5 geographically separated municipalities. Present infestations among household members as well as previous infestations in the household were reported in a questionnaire. In elementary school students prevalence was low (1·63%), but more than one-third of the households (36·43%) had previously experienced pediculosis. Prevalence was higher in elementary school students than in other household members, and highest in third-grade children. Prevalence was also influenced by the school attended, which suggested that interactions between children in the same school are important for head lice transmission. Previous occurrence of head lice in homes also increased the risk of present infestation. Prevalence of previous infestations was higher in households with more children and in more densely populated municipalities, indicating that the density of hosts or groups of hosts influences transmission rates. These results demonstrate that information of hosts’ spatial distribution as well as household and individual characteristics is needed to better understand head lice population dynamics.

Questing activity in bed bug populations: male and female responses to host signals.

A large‐arena bioassay is used to examine sex differences in spatiotemporal patterns of bed bug Cimex lectularius L. behavioural responses to either a human host or CO2 gas. After release in the centre of the arena, 90% of newly‐fed bed bugs move to hiding places in the corners within 24 h. They require 3 days to settle down completely in the arena, with generally low activity levels and the absence of responses to human stimuli for 5 days. After 8–9 days, persistent responses can be recorded. Sex differences are observed, in which females are more active during establishment, respond faster after feeding, expose themselves more than males during the daytime, and respond more strongly to the host signal. The number of bed bugs that rest in harbourages is found to vary significantly according to light setting and sex. Both sexes stay inside harbourages more in daylight compared with night, and males hide more than females during the daytime but not during the night. The spatial distribution of the bed bugs is also found to change with the presence of CO2, and peak aggregation around the odour source is observed after 24 min. Both male and female bed bugs move from hiding places or the border of the arena toward the centre where CO2 is released. Peak responses are always highest during the night. Bed bug behaviour and behaviour‐regulating features are discussed in the context of control methods.

Mortality, temporary sterilization, and maternal effects of sublethal heat in bed bugs.

Adult bed bugs were exposed to the sublethal temperatures 34.0°C, 35.5°C, 37.0°C, 38.5°C, or 40.0°C for 3, 6, or 9 days. The two uppermost temperatures induced 100% mortality within 9 and 2 days, respectively, whereas 34.0°C had no observable effect. The intermediate temperatures interacted with time to induce a limited level of mortality but had distinct effects on fecundity, reflected by decreases in the number of eggs produced and hatching success. Adult fecundity remained low for up to 40 days after heat exposure, and the time until fertility was restored correlated with the temperature-sum experienced during heat exposure. Three or 6 days of parental exposure to 38.5°C significantly lowered their offspring’s feeding and moulting ability, which consequently led to a failure to continue beyond the third instar. Eggs that were deposited at 22.0°C before being exposed to 37.0°C for 3 or 6 days died, whereas eggs that were exposed to lower temperatures were not significantly affected. Eggs that were deposited during heat treatment exhibited high levels of mortality also at 34.0°C and 35.5°C. The observed negative effects of temperatures between 34.0°C and 40.0°C may be utilized in pest management, and sublethal temperature exposure ought to be further investigated as an additional tool to decimate or potentially eradicate bed bug populations. The effect of parental heat exposure on progeny demonstrates the importance of including maternal considerations when studying bed bug environmental stress reactions.

Head Lice in Norwegian Households: Actions Taken, Costs and Knowledge

Introduction Head lice infestations cause distress in many families. A well-founded strategy to reduce head lice prevalence must shorten the infectious period of individual hosts. To develop such a strategy, information about the actions taken (inspection, treatment and informing others about own infestations), level of knowledge and costs is needed. The present study is the first to consider all these elements combined. Materials and Methods A questionnaire was answered by 6203 households from five geographically separated municipalities in Norway. Results 94% of the households treated members with pediculicides when head lice were discovered. Nearly half of the households checked biannually or not at all. Previous occurrence of head lice and multiple children in a household improved both checking frequency and method. More than 90% of the households informed close contacts about their own pediculosis. Direct costs of pediculosis were low (less than €6.25 yearly) for 70% of the households, but the ability to pay for pediculicides decreased with the number of head lice infestations experienced. One in three households kept children from school because of pediculosis. Other widespread misconceptions, such as that excessive cleaning is necessary to fight head lice, may also add unnecessary burden to households. School affiliation had a significant effect on checking frequency and method, knowledge and willingness to inform others about own pediculosis. Conclusions Increased checking frequencies appear to be the most important element to reduce head lice prevalence in Norway and should be a primary focus of future strategies. National campaigns directed through schools to individual households, might be an important tool to achieve this goal. In addition to improving actions taken, such campaigns should also provide accurate information to reduce costs and enhance the level of knowledge about head lice in households.

Head lice predictors and infestation dynamics among primary school children in Norway

Background. Health providers need to know which measures to take and children to prioritize in order to decrease costs associated with head lice infestations. Objective. Our aim was to determine the most important predictors for head lice and identify the major drivers of an infestation outbreak in a low-prevalence area. Methods. The study was based on three datasets of head lice prevalence (retrospective, point prevalence and prospective approach) from primary school children (ages 6–12) at 12 schools in Oslo, Norway. The tested predictors were siblings with lice, individual and household characteristics as well as class and school affiliation. Self-reported monthly incidences (prospective approach) of head lice were used to evaluate infestation dynamics. Results. Infested siblings strongly increased the odds of head lice infestation of school children (odds ratio 36, 26 and 7 in the three datasets) whereas having short hair halved the odds. Household characteristics were of minor importance, and class affiliation proved more important than school affiliation. Having head lice in one school term increased the odds of an infestation in the next, but this effect diminished over time. About 97% of all self-reported infestations were noted in two consecutive months or less. Conclusions. With the exception of hair length, we have found that individual and household characteristics are of minor importance to predict head lice infestations in a low-prevalence country and that unnoticed transmissions in school classes and families are likely to be the major driver upon outbreaks.

Confirming Hypoderma tarandi (Diptera: Oestridae) human ophthalmomyiasis by larval DNA barcoding

DNA barcoding is a practical tool for species identification, when morphological classification of an organism is difficult. Herein we describe the utilisation of this technique in a case of ophthalmomyiasis interna. A 12-year-old boy was infested during a summer holiday in northern Norway, while visiting an area populated with reindeer. Following medical examination, a Diptera larva was surgically removed from the boy’s eye and tentatively identified from its morphological traits as Hypoderma tarandi (L.) (Diptera: Oestridae). Ultimately, DNA barcoding confirmed this impression. The larval cytochrome c oxidase subunit 1 (COI) DNA sequence was matched with both profiles of five adult H. tarandi from the same region where the boy was infested, and other established profiles of H. tarandi in the Barcode of Life Data Systems (BOLD) identification engine.

Mortality, fecundity and development among bed bugs (Cimex lectularius) exposed to prolonged, intermediate cold stress

Abstract BACKGROUND Bed bugs (Cimex lectularius L.) have returned as a nuisance pest worldwide. Their ability to withstand different types of environmental stress should be explored in order potentially to increase the efficiency of control methods. RESULTS Immediate and long‐term effects of exposure to temperatures from 0 to −10 °C for 1, 2 and 3 weeks are reported. Fifth‐instar nymphs and adults were exposed to constant or fluctuating temperatures. Increased cold and extended time yielded higher mortality; nymphs were more resilient than adults at the shorter durations of exposure. At intermediate temperatures, mortality was higher at constant compared with fluctuating temperatures, whereas all individuals died after 3 weeks of exposure to −7 °C. The success among survivors after cold treatment was also affected in terms of reduced egg production, hatching success and the ability of fifth‐instar nymphs to advance into the adult stage; however, nymphs produced after cold treatment developed normally. CONCLUSIONS Detrimental effects of prolonged exposure to low temperatures were seen in bed bugs both during and after cold treatment. The results suggest that temperatures below −7 °C can be applied by laymen to control this pest in small items if available treatment time is of less concern.

Mortality, fecundity and development amongbed bugs (Cimex lectularius) exposed toprolonged, intermediate cold stress

Abstract BACKGROUND Bed bugs (Cimex lectularius L.) have returned as a nuisance pest worldwide. Their ability to withstand different types of environmental stress should be explored in order potentially to increase the efficiency of control methods. RESULTS Immediate and long‐term effects of exposure to temperatures from 0 to −10 °C for 1, 2 and 3 weeks are reported. Fifth‐instar nymphs and adults were exposed to constant or fluctuating temperatures. Increased cold and extended time yielded higher mortality; nymphs were more resilient than adults at the shorter durations of exposure. At intermediate temperatures, mortality was higher at constant compared with fluctuating temperatures, whereas all individuals died after 3 weeks of exposure to −7 °C. The success among survivors after cold treatment was also affected in terms of reduced egg production, hatching success and the ability of fifth‐instar nymphs to advance into the adult stage; however, nymphs produced after cold treatment developed normally. CONCLUSIONS Detrimental effects of prolonged exposure to low temperatures were seen in bed bugs both during and after cold treatment. The results suggest that temperatures below −7 °C can be applied by laymen to control this pest in small items if available treatment time is of less concern.

Temperature stress deteriorates bed bug (Cimex lectularius) populations through decreased survival, fecundity and offspring success

Sublethal heat stress may weaken bed bug infestations to potentially ease control. In the present study, experimental populations exposed to 34, 36 or 38°C for 2 or 3 weeks suffered significant mortality during exposure. Among survivors, egg production, egg hatching, moulting success and offspring proliferation decreased significantly in the subsequent 7 week recovery period at 22°C. The overall population success was negatively impacted by increasing temperature and duration of the stress. Such heat stress is inadequate as a single tool for eradication, but may be included as a low cost part of an integrated pest management protocol. Depending on the time available and infestation conditions, the success of some treatments can improve if sublethal heat is implemented prior to the onset of more conventional pest control measures.

Insect pathogenic fungi and bed bugs: behaviour, horizontal transfer and the potential contribution to IPM solutions

The increasing problem of bed bugs requires the development of new control strategies, and insect pathogenic fungi can contribute towards management. We used laboratory bioassays with Isaria fumosoroseus, Lecanicillium muscarium and Beauveria bassiana to evaluate their virulence to the bed bug. Only B. bassiana significantly affected bed bug survival and was dependent on dose and formulation. A 2% B. bassiana oil formulation induced horizontal transfer to elevate mortality in a 10-day arena bioassay. Temporal distribution of contagious individuals and increasing the dose from 2 to 4% did not increase mortality. Horizontal transfer mainly occurred between adults, and only partly between adults and nymphs. Bed bugs showed activity peaks during the night, and activity was increased by elevated levels of CO2. Distribution between harbourages was not affected by CO2 activation, level of infection or the bio-pesticide, and horizontal transfer was not dependent on the degree of aggregation. Movement in the arenas negatively affected horizontal transfer when the number of susceptible individuals was large. Level of infection also influenced behaviour as the bed bug movement increased with elevated disease burden. The use of fungi as a part of an integrated pest management strategy seems to be an interesting option that should be investigated further. B. bassiana kills bed bugs and can be carried to harbourages to target hidden individuals.