Pediculus Humanus
Human head, body and pubic lice
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Genus: Pediculus humanus (capitis or corporis)
&
Genus: Phthirus Pubis (pubis)
Head lice are parasites (living off a human host) with all peoples of the world potentially susceptible to infestation with either.
Pediculus Humanus exists as:
• Capitis - (head louse) normally inhabits the scalp regions and occasionally the body.
• Corporis - (body louse) may differ anatomically from the head louse from which it may have evolved. It rarely inhabits the scalp.
Pediculus Humanus
Wingless six legged creatures measuring 1.0 to 4.0 mm.
Adults are greyish-white/brown in colour, nymphs (hatched larvae) become blood red from feeding. They may inhabit and infest the entire scalp, but are initially found near the hairline at the lower occipital and auricular margins.
They require a source of human blood to survive acquired by puncturing the skin. This invasion injects insect's saliva, causing pruritis (variable levels) and excoriations, which in sensitive patients may lead to secondary infection.
The female louse may produce a total of 300 ova in a lifetime (9 -12 per day).
The louse possesses a flattened jointed body with jointed limbs ( Arthropoda ); each leg is equipped with a claw by which it clings to hair-shafts. It has two antennae.
Infestations occur without regard to social status or levels of personal cleanliness. Long-haired Caucasoid female children from crowded environments are at greatest risk. Fastidiously clean hair provides no immunity to infestation. Adults are significantly less vulnerable to infestation.
Transmission is mainly by direct contact - head to head, sharing headwear, combs and brushes. Head lice survive on combs brushes, chair backs, hats, and scarves for up to 48 hours. As they do not survive off-host beyond this period, fumigation or spraying premises is probably unnecessary.
The Pediculus 'welds' its Ova (egg or 'nit') onto the hair shaft approx. 2-4 mm above scalp level. Ova hatch at temperatures of above 21 ° C. within 5-8 days. The vacated 'shell' remains attached to the hair shaft and becomes increasingly distanced from scalp level due to hair growth at the nominal 1-2 cm per month.
Ova are note removed by shampooing, but may sometimes be combed off the hairshaft at its distal end.
Symptoms: irritation scratching and possible secondary bacterial infection.
Pubic Lice - Genus: Phthirus Pubis, or crab louse -
Its name is synonymous with its distinctive shape. It measures approx. 2.cm in width and length (Herms & James 1961).
The insect is slow moving and may remain in situ for lengthy periods.
Of its three pairs of legs, the two hind pairs possess claws.
Ova incubation is approx. seven days. Infestations primarily involve the pubic region in adults, but these lice may be located anywhere on the body.
In post natal infants the eyebrows and lashes may be inculcated.
Treatments currently available for lice (not always satisfactory)
There are different classes of parasiticides which act on the central nervous system of the louse. Infestation may respond to chemical treatments formulated either as creams, shampoos, or lotions.
Over the counter medicines may not provide long-term satisfaction (e.g. the Permethrin based products).
A lice repellent containing Piperonal 2% (Rappell) is available.
An electric combing device which delivers small shock waves has been heralded as a satisfactory means for killing the insects in some persons. However the ova are usually unaffected.
A silicone based treatment marketed as Hedrin ( a cutaneous solution containing 4% Dimeticone w/w.) suffocates the louse and she 'explodes'
Take advice regarding such local treatment from a registered pharmacy/trichologist/health centre/.
All chemicals must be used with care, as they can be inherently toxic to humans.
Consult a doctor before using these medicines on infants or during pregnancy.
Medication -free treatment for headlice infestations: Daily applications of heavy creamy conditioners and thorough (30 minute) combings with a fine tooth-comb to dislodge the creatures preferably over a basin.
As re-infestation requires just one hidden egg to hatch, continue this procedure with diminishing frequency for several weeks after the last creature has been thus removed.
Treatment of an infested person should involve the removal of all clothing, and treating the person with the parasiticide.
All family members may be treated on the same day and subsequently as recommended to control any lice hatching.
Clothes and bedclothes should be isolated in plastic bags for 14 days, then dry cleaned.
Alternative : Place items in a freezer. Freezing for a minimum period of six hours is lethal to ova and lice.
Very short hair reduces the probability of infestation/re-infestation.
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