Friday, 24 April 2015

LICE STORY

LICE



Lice are small bloodsucking insects that live on the skin of mammals and birds.
Three species of lice have adapted themselves to humans: the head louse (Pediculus
humanus capitis), the body louse (Pediculus humanus) and the crab or pubic louse
(Pthirus pubis) . All three species occur worldwide. Lice infestations can
cause severe irritation and itching. In addition the body louse can transmit typhus fever, relapsing fever and trench fever. Outbreaks of louse-borne typhus fever,
sometimes claiming thousands of lives, have occurred in colder areas where people
live in poor, crowded conditions, especially in some highland areas of Africa, Asia
and Latin America.

Biology




The three species live only on humans (not normally on animals) and feed on
human blood; the life cycle has three stages: egg, nymph and adult .
Development from egg to adult takes about two weeks. The white eggs (called
nits) are glued to a hair or, in the case of the body louse, to fine threads on clothes.
The nymphs are similar to the adults but much smaller. Fully grown lice are up to
4.5 mm long and feed by sucking blood. Feeding occurs several times a day. Lice
can only develop in a warm environment close to human skin, and die within a
few days if they lose contact with the human body. They are normally spread
by contact, e.g. in overcrowded sleeping quarters and other crowded living
conditions.
The three species of human lice are found on different parts of the body:
• the head louse occurs on the scalp and is most common in children on the
back of the head and behind the ears;
• the pubic louse or crab louse is mainly found on hair in the pubic region but
it may spread to other hairy areas of the body and, rarely, the head;
• the body louse occurs in clothing where it makes direct contact with the
body; it is similar to the head louse but slightly bigger.

Body lice
Body lice are most commonly found in clothing, especially where it is in direct
contact with the body, as in underwear, the crotch or fork of trousers, armpits,
waistline, collar and shoulders. They attach themselves to body hair only when
feeding. The eggs are attached to thin threads of clothing. Body lice are most
common in colder areas where people do not frequently wash or change clothes.
Body lice are spread by close contact between people. They are most commonly
found, therefore, on people living in overcrowded, unhygienic conditions,
as in poorly maintained jails, refugee camps and in trenches during war. They also
spread by direct contact between people in crowded transport vehicles and markets.
Body louse infestations may also be acquired through sharing bedding, towels
and clothing or by sitting on infested seats, chair covers or cushions. Body lice (Pediculus humanus corporis) are normally associated with crowded and unhygienic living
conditions but are also transmitted through any close contact with an affected person.
Body lice are similar to head lice but the region of occurrence is important in their
identification. They are found mainly in clothing, often in the seams, but also on the body surface,
especially the armpits and around the waist. In Australia, they are less common than headlice or
pubic lice.
Body lice are flat wingless insects with six legs ending in a claw. They may be greyish or brown in
colour and range in size from 2 – 5 mm. They feed on human blood and their bites can cause
irritation. Secondary infections can occur if louse faeces are introduced into the skin by the affected
person scratching.

Transmission
Body lice can be transmitted in clothing and bedding as well as by close physical contact.

Head lice
The head louse is the most common louse species in humans. It lives only in the
hair on the head and is most often found on children. The eggs (or nits) are firmly
glued to the base of hairs of the head, especially on the back of the head and behind
the ears. Because the hairs grow about a centimeter a month
it is possible to estimate the duration of an infestation by taking the distance
between the scalp and the furthest egg on a hair. Infested persons usually harbour
10–20 adult head lice. The females lay 6–8 eggs per day. Head lice are spread by
close contact between people, such as children at play or sleeping in the same bed.
Head lice are also spread by the use of other people’s combs that carry hairs with
eggs or lice attached. Headlice (Pediculus humanus capitis) are a social pest and are rarely a threat to health however their
presence can have social, economic, psychological and educational repercussions. Correct
information, treatment and monitoring should ensure they are controlled with minimum impact on
individuals and communities.

Transmission
Headlice are mainly transmitted by head-to-head contact with an infested person.
Children are more susceptible because they are more likely to have close contact with other children
and adults in homes, playgrounds, schools, kindergartens and childcare centres. Adults and older
children may become desensitized to headlice bites, thereby delaying treatment and becoming a
source of infestation to others.
Headlice will dehydrate quickly once removed from the head. In humid conditions they may survive
for more than 24 hours off the head, however they are unlikely to be able to reinfest another person. In
the early stages of dehydration, lice will continue to move or crawl but are unable to feed or lay eggs
(nits). For this reason, items such as brushes, headgear, bedclothes and towels are less likely to
transmit headlice than close contact although transmission may occur if these items are used
immediately following use by an infested person.


Crab or pubic lice
Crab lice, also called pubic lice, are greyish-white and crab-like in appearance.
They are most often found on hair in the pubic region, and eggs are laid at the base of the pubic hair. Heavy infestations may spread to other hairy areas of the body,
such as the chest, thighs, armpits, eyelashes, eyebrows and beard. Crab lice are
mainly spread through sexual or other close personal contact, and are most
common in young, sexually active adults. Pubic lice (Phthirus pubis) are not associated with the spread of disease but their bites can cause
irritation. Scratching of the irritation may lead to localized infection.
The pubic (crab) louse (refer to Figure 3) is a small 1-2 mm, light brown, round, flat, six-legged insect
that clings to the pubic hairs, sucks blood for nourishment, and fixes its eggs (nits) to the pubic hairs.
As its name suggests it looks very much like a tiny crab. The life cycle lasts about two to three weeks.
Small red sores and itching may occur as a reaction to the injection of saliva from the louse. They are
mainly found in the pubic hair but may also be found on other hairy parts of the body e.g. eyebrows or
armpits.
Transmission
Pubic lice are transmitted mainly by close body contact, including sexual activity and, occasionally,
by clothing, bedding or towels recently used by an infested person.


Public health importance
Only the body louse is a vector of human diseases. It transmits typhus fever,
relapsing fever and trench fever.
Nuisance
Lice feed several times a day and heavy infestations can cause intense irritation and
severe itching. Toxic reactions to the saliva injected into the skin may lead to
weariness and a general feeling of illness.
Louse-borne typhus fever
This disease is caused by a microorganism, Rickettsia prowazekii, and is an acute,
highly infectious disease with headache, chills, fever and general pains as symptoms.
It may be fatal in 10–40% of untreated cases.
The disease has occurred on all continents except Australia. It is prevalent in
cool areas where heavy clothing is worn and where the vector is most common. In
the past the disease was most common during war and famine. Today, foci of
transmission are found in mountainous regions of South America, in Central and
East Africa and in the Himalayas.
Transmission
Body lice take the disease organisms up with the blood of an infected person
and then expel it with their faeces. Since louse faeces dry to form a fine black
powder they are easily blown about. The powder can infect small wounds, such as
those caused by scratching, or the mucous membranes of the nose and mouth.
Because the disease organism can remain alive for at least two months in dried
louse faeces, it is dangerous to handle the clothing or bedding of patients with
typhus.
Treatment
Effective treatment is possible with tetracycline, doxycycline or chloramphenicol.
Prevention and control
A vaccine has been prepared but is not yet commercially available. Infection can
be prevented by controlling the body lice. Epidemic outbreaks are controlled by
the application of a residual insecticide to the clothing of all persons in affected
areas.
Louse-borne relapsing fever
This disease is caused by a microorganism, Borrelia recurrentis. Infected people
suffer periods of fever lasting 2–9 days which alternate with periods of 2–4 days
without fever. Usually, about 2–10% of untreated persons die but the mortality
rate may be as high as 50% during epidemics. The disease occurs in limited areas
of Africa, Asia and South America.
Transmission
Louse-borne relapsing fever occurs under similar conditions to those of typhus
fever and the two diseases may appear together. Humans become infected by
crushing infected body lice between the fingernails or the teeth. The disease
organisms are thus released and can enter the body through abrasions, wounds or
the mucous membranes of the mouth.
Treatment
Treatment is possible with tetracycline.
Prevention and control
Prevention and control are as described for typhus fever; no vaccine is available.
Trench fever
This bacterial disease, caused by Rochalimaea quintana, involves intermittent fever,
aches and pains all over the body, and many relapses. Infection rarely results in
death.
The disease can probably be found wherever the human body louse exists.
Cases have been detected in Bolivia, Burundi, Ethiopia, Mexico, Poland, the
former USSR and North Africa. Epidemics occurred during the First and Second
World Wars among troops and prisoners living in crowded and dirty conditions,
hence the name “trench fever”.
Transmission
Transmission occurs through contact with infected louse faeces, as for typhus
fever.
Treatment
Tetracycline, chloramphenicol and doxycycline are probably effective but, as the
disease is rather mild, they have not been adequately tested.
Prevention and control
Prevention and control are as for typhus fever; no vaccine is available.

Control measures
The control methods used depend on the importance of the health problem.
Individual or group treatment may be carried out where lice are merely a nuisance.
Large-scale campaigns are recommended for the control of epidemic outbreaks of
disease.
Head lice
Hygienic measures
Regular washing with soap and warm water and regular combing may reduce the
numbers of nymphs and adults. However, washing will not remove the eggs, which
are firmly attached to the hair. A special louse comb with very closely set fine teeth
is effective in removing both adults and eggs . Shaving the head is
effective and this measure is sometimes adopted with young boys; however, it is
often objected to and should not be insisted on.
Insecticides
Insecticide applications to the hair give the most effective control . They
can be in the form of shampoos, lotions, emulsions or powders .
Some pyrethroids are the most recommended products, since
they do not cause the burning sensation of the scalp or other side-effects sometimes
associated with other insecticides, such as lindane . Powder or dust
formulations are usually less effective and less acceptable for use than lotions or
emulsions. A soap formulation containing 1% permethrin can be applied as a
shampoo .
How to make insecticidal dusts, shampoos and lotions
An insecticidal dust can be made by adding insecticide powder (wettable powder)
to talcum powder to obtain the recommended dosage of active ingredient (in
grams). An insecticidal shampoo is made similarly by adding insecticide powder or
emulsifiable concentrate to hair shampoo with a neutral pH. An insecticidal lotion
is made by mixing an emulsifiable concentrate with water or alcohol.

Crab or pubic lice
Shaving the infested pubic hairs from the body has been replaced by the application
of insecticidal formulations, as described for head louse control. In heavy

infestations all hairy areas of the body below the neck should be treated.



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