Socioeconomic influences Conducive environmental conditions

Public Health Significance of Urban Pests 295 Over time, body lice have developed a greater body volume than head lice and, in turn, take larger blood-meals Busvine, 1978. They can tolerate longer periods of starvation and in most cases, can withstand being removed from their host for about 36 hours, but do not normally survive 48 hours McLeod Craufurd-Benson, 1941. They live in the folds and seams of clothing and use the fibres of cloth as a substrate for laying their eggs. All human lice attach their eggs to hairs or fibres in an area where the temperature is appropriate for incubation of the embryos and the local humidity is high enough to pro- tect the eggs from desiccation. Body lice only visit the body surface to feed, so after remo- val of clothing it is rare that lice are found on the skin. While not feeding, body lice of all stages are found alongside the eggs and empty eggshells in the clothing seams. In all cases, lice require optimum surface body temperature and humidity. In febrile individuals, lice move away from the skin and, given the opportunity, will move to another person Lloyd, 1919. 9.7. Louse management 9.7.1. Inspection and detection Discovering the presence of living adult or nymphal lice provides the only positive dia- gnosis. Body lice shelter in seams of clothing and a diagnosis of their presence is prima- rily based on inspection of these in pruritic people at risk. Small numbers of lice may be difficult to find, but indicators of infestation include excoriation of the skin in the proxi- mity of clothing seams and nits in the seams of clothing.

9.7.2. Physical removal

Physical methods for eliminating body lice are currently the norm for treating people and were the only method of treatment during the First World War, when most soldiers experienced infestation at some point Nuttall, 1918. Methods employed now include replacing all clothing and at the same time, killing the insects and their eggs, by using extreme environments – that is, various forms of application of heat or cold. Studies have shown that temperatures above 50°C sustained for more than 20 minutes are sufficient to kill all lice and their eggs Leeson, 1941; Buxton, 1947, so adequate control of infesta- tions can be achieved with limited equipment and normal domestic hot-water washing systems, by laundering clothes or exposing them to heat – for example, in a hot-air dryer. If desired, items of clothing that cannot be washed could be dry-cleaned, although cost may make this inappropriate in most circumstances.

9.7.2. Pesticides

In most high- and medium-income countries, neurotoxic pesticides have been the mains- tream method for eliminating louse infestations. In many cases, these have been used inappropriately, so that in the past lice have readily developed resistance. Resistance to pesticides is now potentially one of the main factors that govern approaches to louse Human body lice 294 1985. The distribution of LBRF is similar to that of typhus, but the number of cases is greater, particularly in East Africa Gratz, 1985. Recent serological investigations have shown that trench fever, thought to have died out in the 1940s, is still actively transmitted and more widespread than previously believed Jackson Spach, 1996; Raoult Roux, 1999. Although the infection may produce high fever and debilitation, such as in the million or so combatants infected during the First World War, many low-grade infections may have passed unnoticed –as influenza-like fever of unknown origin Jackson Spach, 1996; Fournier et al, 2002. Trench fever has not figured highly in the index of suspicion of physicians investigating such episodes, especially in the absence of lice. Trench fever now appears to be disseminated in the homeless of many nations and has probably spread into the wider population, as louse faeces are dispersed from the clothing of infested individuals and come into contact with mucosae of uninfested people Drancourt et al., 1995; Jackson Spach, 1996; Raoult Roux, 1999. Also, head lice may now be vectors of these infections, bringing with them the possibility that children could become infected Sasaki et al., 2006. So with increased human mobility and more-intense and longer-term infestations, there is a hypothetical risk of an increase in disease transmission in all geographical areas of high- and middle- income countries.

9.5. Socioeconomic influences

The general increase of affluence throughout Europe and North America has resulted in an overall decline in body louse infestations, as most people now have access to facilities to launder or change their clothing regularly. Data on the distribution of lice within and between communities are sparse, as is documentation on the impact of social welfare and economics on the prevalence of lice. This is an area of study that has been neglected due to difficulties in obtaining funding for studies that are large enough to be meaningful and due to the triumph of political correctness over common sense in fostering the pre- tence that socioeconomic status plays no role in either catching lice or the ability to eli- minate infestations. However, the study by Willems and colleagues 2005 gave the first clear indication of this link in modern times and confirms the retrospective analysis conducted by Lindsay 1993. The other evidence that exists suggests that the prevalence of all lice in many communities has increased since the beginning of the 1990s and shows no sign of abatement Downs, Harvey Kennedy, 1999; Meinking, 1999; Raoult Roux, 1999.

9.6. Conducive environmental conditions

Sucking lice are host-specific, obligate ectoparasites that depend on their hosts for food, water, warmth and habitat. Lice may accidentally leave their hosts on a temporary basis, but unless they are able to re-colonize within a short period they die from cumulative dehydration. They do not infest other mammals and there is no reservoir or long-term harbourage off the body where lice can hide. Public Health Significance of Urban Pests 297 to transmit disease. The widespread distribution of homeless people with positive sero- logy for trench fever indicates that this disease is probably transmitted regularly when lousy individuals come in contact with and are exposed to infected louse faeces Jackson Spach, 1996. This also indicates that infestation with body lice may be widespread and that, as there is no mechanism for monitoring the infestation due to the withdrawal of appropriate environmental health services, the level of lousiness in society may be consi- derably higher than previously thought. It is unlikely that epidemic typhus or LBRF could enter Europe or North America under current conditions, although individual cases, resulting from travel to endemic areas, could arise; in those circumstances, howe- ver, onward transmission would be highly unlikely. Unforeseen social disruptions in the future, however, could alter this position.

9.9. Conclusions