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.