Lice

Lice (singular: louse), also known as fly babies, is the common name for over 3000 species of wingless insects of the order Phthiraptera; three of which are classified as human disease agents. They are obligate ectoparasites of every avian and mammalian order except for Monotremes (the platypus and echidnas), bats, whales, dolphins, porpoises and pangolins.

Most lice are scavengers, feeding on skin and other debris found on the host's body, but some species feed on sebaceous secretions and blood. Most are found only on specific types of animal, and, in some cases, only to a particular part of the body; some animals are known to host up to fifteen different species, although one to three is typical for mammals, and two to six for birds. For example, in humans, different species of louse inhabit the scalp and pubic hair. Lice generally cannot survive for long if removed from their host.

A louse's color varies from pale beige to dark gray; however, if feeding on blood, it may become considerably darker. Female lice are usually more common than the males, and some species are even known to be parthenogenetic. A louse's egg is commonly called a nit. Many lice attach their eggs to their host's hair with specialized saliva; the saliva/hair bond is very difficult to sever without specialized products. Lice inhabiting birds, however, may simply leave their eggs in parts of the body inaccessible to preening, such as the interior of feather shafts. Living lice eggs tend to be pale white. Dead lice eggs are more yellow.

Lice are exopterygotes, being born as miniature versions of the adult, known as nymphs. The young moult three times before reaching the final adult form, which they usually reach within a month of hatching.

Classification

The order has traditionally been divided into two suborders, the sucking lice (Anoplura) and the chewing lice (Mallophaga); however, recent classifications suggest that the Mallophaga are paraphyletic and four suborders are now recognised:

• Anoplura: sucking lice, including head and pubic lice (see also Pediculosis or Head lice)
• Rhyncophthirina: parasites of elephants and warthogs
• Ischnocera: avian lice
• Amblycera: chewing lice, a primitive suborder of lice

It has been suggested that the order is contained by the Troctomorpha suborder of Psocoptera.

Lice and humans

Humans host three different kinds of lice: head lice, body lice (which live mainly in clothing), and pubic lice. The DNA differences between head lice and body lice provide corroborating evidence that humans started wearing clothes about 72,000 years ago, give or take 42,000 years.

Recent DNA evidence suggests that pubic lice spread to humans approximately 3,000,000 years ago from the ancestors of humans by sharing the same bed or other communal areas with them, and are more closely related to lice endemic to gorillas than to other lice species which infest humans.

Adult and nymphal lice can survive on sheep-shearers' moccasins for up to 10 days, but microwaving the footwear for five minutes in a plastic bag will kill the lice.

Symptoms

Recognising an infestation

Head lice are tiny (pin-head sized) grey-brown, wingless insects that live by sucking blood from the scalp. Their eggs, which look like tiny white specks, are known as nits and are glued to the hairs. A mild infestation may result in no symptoms at all but as time passes it will become more severe.

A severe infestation will result in:

• Itching of the head and neck

The saliva of head lice is irritating on the skin, and itching is often worse behind the ears or at the back of the neck.

• Lack of sleep

Persistent irritation and itching can disturb concentration and disrupt sleep

• Black louse droppings.

Look out for black lice droppings, which can be easily spotted on blond hair but if your child has dark hair check their pillow where it can sometimes be seen.

• Nits.

Lice lay eggs in the hair but are really tricky to spot. When they are hatched you will find it easier to look for the nits. Nits are simply the empty egg shells which are recognisable from scalp fragments by the fact of being glued on. Where dandruff will fall from a shaken hair a nit will remain attached.

• A general non-specific malaise.

Whether from lack of sleep or continual irritation an infestation can lead to feeling "lousy" which is possibly how the word came into being.

Treatment

General recommendations for treatment

Because eggs hatch 6–9 days after oviposition, if a pediculicide is used, treatment is recommended to be repeated at least once and this after 10 days, when all lice have hatched from the eggs. Between the two treatments, i.e., days 2–9, the person will still be infested with lice, which hatch from eggs not killed by the anti-louse product. Therefore, with some products a third treatment on day 5 is recommended. Between the treatments, it is advised to wet the hair and comb daily with a louse-comb to remove the hatching lice.

The instructions for use should be read carefully before using any anti-louse product. During the treatment, it is particularly important to note the starting time and to treat the hair for the exact period specified in the instructions.

Contact of the product with the eyes of the infested person should be avoided by holding a towel over the face, and eyes should be rinsed well with water if the product does get in contact.

After the treatment and while the hair is still wet after rinsing with water, hair should be combed for 3–4 minutes with a louse comb to remove lice and eggs.

One to three days after the last treatment, i.e., days 11, 12 and 13, hair should be checked with a louse comb. If no living lice are found, the treatment was successful, even if nits/eggs are visible on the hair. If living lice are still present, the treatment should be repeated using an anti-louse product with a different active ingredient. Prophylactic treatment with pediculicides is not recommended. Itching may persist for up to a week after head lice eradication.

Chemical treatments

Today, insecticides used for the treatment of head lice include organochlorines (lindane), organophosphates (malathion), carbamates (carbaryl), pyrethrins (pyrethrum), and pyrethroids (permethrin, phenothrin, bio-allethrin). Laboratory and clinical studies found that many of the pediculicides in the market are either not fully effective or are ineffective when they are used according to the instructions.

Pediculicides may rapidly lose their efficacy because of the development of resistance. Resistance of head lice to insecticides such as lindane, malathion, phenothrin and permethrin has been reported.

Natural products

Natural products tested clinically and found to be safe and effective could be very important in the control of head lice, as the complexity of the active ingredients may prevent the rapid development of resistance. They are more acceptable to some parents who are concerned with the use of chemical pediculicides. Several plant products such as aniseed, coconut, neem and tea tree oils offer promise for new compounds to treat head lice infestation. However, the number of clinical studies is very limited, and most have methodological problems such as lack of a comparison group.

Enzyme-based products

Certain protease enzymes can have insecticidal effects. This process works through using naturally occurring enzymes similar to those within the insects themselves. These protease enzymes cause the insect to hatch and molt prematurely, destroying the creature's exoskeleton. These enzymes are similar to those found in meat tenderizers and digestive aids. The benefits of this type of treatment is that the lice do not develop resistance and these products are less toxic.

Combs

For a treatment with the louse comb alone, it is recommended to comb the hair for 3–10 minutes (depending the length and type of the hair) daily or every second day for 14 days. Wetting the hair with water and especially with water and shampoo or conditioner will facilitate the combing and the removal of lice, eggs and nits.

Louse combs

A special finetooth comb that can pick out lice is used. The space between the teeth of the comb should be no more than 0.3 millimetres (0.012 in). Plastic combs are effective for very short-term use, but the spacing between the teeth will quickly spread out after repeated usage. Metal combs, being less flexible, are more effective for multiple uses.

Following are instructions for wet combing:

• First, comb through wet hair with an ordinary comb to relieve knots and tangles.
• Apply hair conditioner to make it easier to comb the hair with the fine-toothed comb.
• Comb through every bit of hair, pulling the comb from the scalp to the hair ends. After every comb-through, examine and rinse the comb. Use an old toothbrush to remove eggs and nits from the comb and flush the eggs down the sink. Comb through the entire head and scalp at least twice. Afterwards, rinse the conditioner out.
• Repeat the aforementioned steps every day or every second day to catch any new lice that have hatched since the previous combing.
• Repeat the aforementioned procedure until lice are not found for at least two treatments in a row. The Pharmaceutical Society of Australia recommends treating with comb and conditioner every two days until lice are not found for ten consecutive days.

Hot air

Several devices blowing hot air onto the scalp have been tested for their efficacy to kill lice and eggs. The most successful method, which used a custom-built machine called the LouseBuster, resulted in nearly 100% mortality of eggs and 80% mortality of hatched lice.

Silicone-based lotions

Dimethicone is a silicone oil, which coats and smothers the lice causing their death either by suffocation or dehydration. Most dimethicone lotions do not kill nits because the nits have only one breathing orifice, the operculum, so the dimethicone has less access there.

Accelerated Nano X-ray tomography of headlice treated with Silcap(4% dimethicone/96% mineral oil). After 15 min the lice and nits are suffocated and dry out. Courtesy of Oystershell NV & University of GhentTherefore most treatments should be repeated after 7–10 days to kill any lice that hatch from the eggs or to treat reinfection by family members or class mates. Combination lotions and foams exist (Silcap, Oystershell NV) that have an immediate effect on nits (15 min, 96% mortality) by combining the rather viscous dimethicone with penetrating excipients that increase the delivery through the abdominal spiracles of adults and the operculum of the nits.

Shaving the head

Shaving the head or cutting the hair extremely short can be used to control lice infestation. Short hair, baldness, or a shaven scalp are generally seen as a preventative measure against lice infestation. However, it is not recommended that children be suddenly shorn due to the psychological effects the child might experience. See the Treatment modalities not recommended section for more information.

Products in development

A number of promising compounds are currently in development for the treatment of head lice. Approval of any of these products may make it much easier to treat head lice in the future.

• Summers Laboratories is developing a non pesticide lice treatment that kills by asphyxiation (Summer's Non-pesticide Lice Asphyxiator). This product is a water-based, water-soluble gel, similar in consistency to a hair conditioner. It consists of a mixture of dermatological and cosmetic ingredients. The active ingredient is benzyl alcohol. The product was acquired by Sciele Pharma for distribution in the United States, Canada, and Mexico. The product was recently approved by the FDA and is being marketed under the brand name Ulesfia.
• ParaPRO is developing a crème rinse containing a novel biologically-derived pesticide, Spinosad. The product, tentatively branded NatrOVA, is currently being tested in FDA approved clinical trials.
• BTG (LSE: BGC) is developing a proprietary gel-based formulation for use as a topical treatment of head lice infestation. The product is a non-pesticide product derived from a natural source. In preliminary studies the product killed both lice and their eggs following very short treatment times.

Treatment modalities not recommended

Gasoline/kerosene

The use of kerosene or gasoline for prevention or treatment of lice is extremely dangerous due to the inherent fire hazard. Since 1989, there have been at least nine cases of children being severely burned during such attempts. These cases apparently occurred because, contrary to popular belief, it is the vapors of the gasoline, rather than the liquid itself, that are flammable. These vapors can ignite due to the presence of even a small spark or open flame – such as those caused by electrical appliances, lit cigarettes, or pilot lights in stoves and water heaters.

Before gasoline (Petrol) was used as fuel, it was sold in small bottles as a treatment against lice and their eggs. At that time, the word Petrol was a trade name.

The use of gasoline to treat lice also carries a high risk of dermatitis (i.e. irration of the scalp).

Shaving heads of children

It is not recommended that children's heads be shaved or even be given a short haircut for prevention or control of lice due to the psychological effects children might experience. Infestation with lice is not a disease and the medical symptoms are normally minimal. In any case, health providers and parents should try not to create emotional problems for children during examination and treatment.

Other non-recommended treatments

The use of oil and vinegar, hair bleaches and dyes, antibiotics or ivermectin, garlic and Vitamin B are also not recommended.