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fabric fibres Nuttall, 1917. The length of time required for eggs to hatch has never
satisfactorily been determined and the only study of body lice Leeson, 1941 sho-
wed that hatching was achieved between 6 and 11 days at temperatures likely to be
encountered under clothing 29–37°C.
After emerging from the egg, lice go through three nymphal stages, each of
which takes about three days to complete development Nuttall, 1917; Lang, 1975.
The final moult from the third nymphal stage gives rise to the adult louse Fig. 9.2.
Male lice often develop more rapidly than their female counterparts. Lang 1975
also observed that females mature for about one day after the final moult before they are able to lay eggs.
In all stages of development, lice feed at regular intervals throughout the day, with the youngest nymphs requiring more frequent blood-meals than third instar nymphs and
adults Lang, 1975, presumably due to their smaller size. All lice produce dry faecal mat- ter that may accumulate in clothing or hair; this dry matter is the vehicle for transmitting
the infective disease organisms for which lice may be vectors.
All bionomic studies of lice are inadequate. Theoretical estimates of the growth of louse populations for example, Evans Smith, 1952 are based on limited data and appear to
overestimate the rate of increase, by not addressing juvenile mortality, migration and des- truction by the host. In some cases, destruction by the host appears to account for more
than 50 of juveniles, so that some people who have never knowingly had an infestation can be found with long hatched nits empty eggshells. If populations grew as fast as esti-
mated, the numbers of insects would soon become apparent to the host; however, expe- rience indicates the contrary, in that infestations may go undetected for weeks or even
months.
When deprived of access to food, body lice survive longer than other species of human lice, presumably due to their larger body mass and to the historical selection of insects
more capable of resisting the dehydration that results from starvation induced by their host removing their clothing. Buxton 1947 reported survival for up to 10 days at 15°C,
with shorter survival at higher and lower temperatures, ranging from 7 days at 10°C to 2 days at 36°C.
All three species of human lice are distributed throughout human populations, and it is likely that they affect all communities to some extent. However, the increase of affluence
in Europe and North America over the past 50 years has relegated body louse infesta- tions to vagrants, the homeless and, in recent conflicts, refugees Gratz, 1985. Head lice
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9.1. Introduction
Human lice are host-specific, haematophagous, obligate ectoparasites that live their whole lives on their hosts. Few studies of their biology or physiology have been conducted
Burgess, 2004, and most of them were conducted in the first half of the 20
th
century, primarily and were focused on body or clothing lice Pediculus humanus. That species
constituted a major health risk as a vector of transmissible disease, especially during the First World War in Europe, the depression of the 1930s, and around 19421943 in parts
of North Africa and southern Europe Soper et al., 1945, 1947.
Environmental health practitioners who had responsibility for lice in most countries until the 1970s considered human lice of all three species – body lice P. humanus, head lice
Pediculus capitis and crab lice Phthirus pubis – as pests. Subsequently, rationalization of health and environmental services has transferred responsibility for control of lice to
other services or to parent carers, as in the case head lice. Should the need arise, legisla- tion that still exists in many countries could be used to control these insects – for exam-
ple, in an arthropod-borne outbreak of disease. Thus, environmental health officers, say in the United Kingdom, can address verminous conditions – that is, people infested with
parasites, such as body lice – by using Section 85 of the Public H ealth Act of 1936. However, such legislation requires a foreknowledge of the existence of an infestation,
which limits its effectiveness.
Body lice, although relatively uncommon now in most high- and medium-income coun- tries, do still constitute a health risk. Many of the services that formerly were in place to
deal with these infestations no longer exist and, for the most part, the comparatively small numbers of indivi-
duals affected can obtain relief from a variety of volun- tary agencies. Recently recognized changes in disease
demography, however, suggest that body lice may still constitute a small risk of disease to people Raoult
Roux, 1999.
T his chapter concentrates on body lice as an environ- mental health problem. Head lice and crab lice, although
essentially similar in physiology and behaviour, constitute specific clinical hazards for which the remedy is found in
the clinical medical context rather than the environmen- tal health context. Therefore, these two species are out-
side the scope of this report and are mentioned less exten- sively.
9.2. Biological factors
Using glue-like secretions from glands attached to the oviduct, all human lice fix their eggs Fig. 9.1 to hairs or
Fig. 9.2. Young adult body lice on cloth
Source: Photo by E. Kidman, Medical Entomology Centre.
Fig. 9.1. Louse egg, showing the cap and micropyles breathing pores
Source: Scanning electron micrograph
by J. Maunder, Medical Entomology Centre.
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293
confirm this British Department of Health and Social Security, 1987; Lindsay, 1993. However, the appearance of resistance to the most commonly used insecticides is belie-
ved to have had an impact on the number of children infested in most communities in high- and middle-income countries Burgess Brown, 1999; Downs, Harvey Kennedy,
1999; Meinking, 1999. The studies by Lindsay 1993 and Willems and colleagues 2005 showed that socioeconomic factors influence both the risk of infestation and the ability
to cure it, indicating a broader spectrum of social and environmental health problems associated with louse infestations.
The burden of crab lice infestation is largely unknown. Anecdotal evidence suggests that infestations diminished significantly in the 1980s, but no epidemiological studies have
been performed in any large population group. More recently, Meinking 1999 sugges- ted that the levels of infestation have recovered.
9.4. Implications for public health
In general, low-grade morbidity is the principal effect of louse infestations on public health. Constant infestation affects general well-being through disturbed sleep, diminis-
hed concentration and itching that results in excoriation. Body lice have a greater impact on infested individuals whose skin is not only excoriated, but is also thickened and dis-
coloured over time through constant exposure to louse bites. Other pathological effects seen in some people with longer-term infestations include lymphadenopathy and impe-
tigo due to S. aureus and Group A S. pyogenes Taplin Meinking, 1988, with a poten- tial reduction of their immune status rendering them more susceptible to other infec-
tions.
Body lice are primary vectors for: classical typhus, caused by Rickettsia prowazekii; trench fever, caused by B. quintana; and louse-borne relapsing fever LBRF, caused by Borrelia
recurrentis . They are also secondary vectors for murine typhus, caused by Rickettsia moo-
seri . Endemics of these diseases were still found throughout Europe and parts of North
America in the early 20th century, resulting in considerable mortality and morbidity during and immediately following the two world wars Soper et al., 1945, 1947; Jackson
Spach, 1996. For centuries, these diseases followed warfare, social disruptions and natural disasters. Surprisingly, no typhus outbreak was identified after the conflicts in
the Balkans the region in Europe where typhus had most recently been endemic in the 1990s or after the 1991 Gulf War, when large numbers of prisoners of war became lousy
in temporary camps.
Typhus disappeared from high- and middle-income countries with the recession of body louse infestations during the late 20th century. The current endemic zones are primarily
limited to a few tropical regions, mostly in upland areas of Ethiopia, parts of Somalia and southern Sudan, Rwanda and Burundi, and to parts of the high Andes and Himalayas,
where the combination of poverty and colder climate makes laundering or complete changes of clothing impractical or impossible. Small outbreaks occur in other regions,
and it is suspected that some occurrences are underreported or under-diagnosed Gratz,
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have remained primarily an infestation of children. In communities where reasonably effective methods of treatment are available, adults are normally only affected by head lice
through contact with infested children in their care. Crab or pubic lice mostly affect sexually active adults, although they may be passed to children and others by close non-
sexual physical contact. Few studies have investigated the epidemiology of this louse. One study, however, showed that they were more common on females between the ages of 15
and 19 years and on males more than 20 years of age Fisher Morton, 1970.
In high- and medium-income countries, body lice are more common in urban environ- ments; that is because the majority of people prevented from laundering or changing clo-
thing, due to poverty, congregate in urban environments. In the past, the prevalence of head lice Mellanby, 1941, 1943, and of infestations with lice lousiness in general
Lindsay, 1993, was also greatest in urban industrial slums and communities that were in close proximity. However, in the United Kingdom, increased mobility of populations
during the latter half of the 20th century led to a more even spread of infestations, with only small differences between rural and urban areas and between different regional
communities Downs, Harvey Kennedy, 1999; Smith et al., 2003.
9.3. Louse infestation in Europe and North America
