Pediculosis

The piojo of the human scalp, Pediculus humanus capitis.

Pediculosis is a contagious ectoparasitosis (external parasitosis) caused by infestation by lice (order Phthiraptera). The condition can appear in almost any species of warm-blooded animals (mammals and birds), although in particular the term usually refers to infestation by Pediculus humanus capitis, which is mainly located on the scalp. human.

Other human head lice are corporeal (infestation by Pediculus humanus humanus = Pediculus humanus corporis) and pubic (infestation by crabs, Pthirus pubis).

Life Cycle

Main article: Phthiraptera (piojos), Pediculus humanus capitis (human scalp stick)

Lice are hemimetabolous insects. This means that its development consists of 3 phases: egg (in lice called nit), nymph and adult.

The female secrets a glue that quickly cements in the form of a pod that firmly attaches the handre to the hair, and surrounds the entire egg except the respiratory operculus at the opposite end of the pod.

Ninfa and adult have the ends of the legs in claw which allows them to climb and cling heavily to the hair.

• Liendre: The hats are the eggs of the lice. The female deposits them in the hair near the root, where they remain firmly cemented. The hats need the heat and atmosphere of the head at a certain distance from the root to survive. They are visible to the naked eye during the inspection of the head, and can be confused with dandruff or other compounds that are differentiated because they are not easily removed from the hair. They have an oval shape and their color is yellowish to white. It takes six to eight days to bleach, but the outer shell or corion ("the empty handre") stays attached to the hair until it is removed mechanically.

• Ninfa: The animal emerges from the handre in the form of a small piojo called ninfa. It looks very similar to that of an adult piojo, it feeds, but is smaller, and its reproductive organs are not yet mature. The nymphs take about 7 or 10 days to move to the adult state. Pyojo's nymph feeds in the same way as the adult.

• Adult: The adult piojo measures 1 or 2 to 4 mm, and can already be reproduced. Like every bug has six legs. The females are the ones who ovipose and cement the hats to the hair and are usually bigger than the males. The lice feed in blood up to five times a day, squeezing the host's skin with its small, pungent mouthpieces. As they feed they excrete an anticoagulant and vasodilating saliva that irritates the skin and causes itching. The adult can live about 30 days, in that period every adult female can put about 50 or 100 eggs at a rate of about 6 per day. The lice migrate with overcrowding, so a head perhaps has about a dozen lice, but hundreds of hats in incubation. If the piojo falls out of the person or emigrates and cannot climb to another, it will live up to 2 days or perhaps 4 without feeding, then it will starve. The lice of the human scalp do not survive either in other animals such as dogs or cats. They move quickly moving up to 23 cm per minute. In the abdomen there are six holes called spies, which communicate the respiratory trachea system with the outside environment. Such openings can voluntarily close what allows them to float in the water and survive up to 36 hours, even in chlorinated water and also protect the parasite from the action of certain toxic substances.

Females cement nits to the hair more easily on clean, washed hair.

Forms of contagion

Lice do not fly and cannot jump. The common form of transmission is direct contact, or by sharing contaminated clothing or other objects. Lice live from a few hours to two or four days off a host, depending on conditions environmental conditions, after which they starve. Contact with infested objects can be:

1. When you wear infected clothes (used recently by people with lice) such as hats, scarves, coats, sports uniforms, hair ribbons, etc.
2. When using combs, hair brushes or towels Infested.
3. When using a bed, mattress, clothes, pillow, carpet or a teddy who has recently been in contact with an infected person.
4. Areneros, swimming pools.

Nits are not spread, because if a nit breaks free from the hair, it has no way of climbing onto another head, and the nits have to be a certain distance from the scalp to get the warmth and moisture from the scalp. to mature, so when you remove them they will no longer survive. Therefore, to be infected by the forms indicated above, it is necessary that these (hats, combs...) have lice (nymphs or adults), because if they only have nits, contagion will not be possible.

Clinical picture and diagnosis

Characteristic symptoms:

1. Pruritus (picture) on the scalp. The bites are very small and generally cannot be seen in an inspection of the scalp naked eye.
2. Eccemas (lesions on the scalp) caused by scratching. These injuries can be infected by increasing irritation.

There is no proven transmission of disease by human scalp lice at least in Europe. There may be complications such as bacterial superinfections or pediculide (a secondary papular reaction on the neck and back).

Lice and nits are visible on naked eye inspection of the scalp. Lice preferentially lodge in the areas behind the ears and on the nape of the neck. Nits are most common in those areas, visible on ocular inspection of the hair near the roots. Lice can cling to hair with their clawed feet and are rarely found on other parts of the body or on clothing. To make the diagnosis, live lice must be found in the nymph or adult phase, it is not enough to find nits, of which only the empty chorion may have remained or the embryo inside it could be dead. The most effective way to check a head is to pass a fine comb through all the hair from the hairline to the ends, and the teeth of the fine comb should be checked for live lice after each pass.

Lice infestation is generally benign and has no manifestations other than itching and lesions on the scalp from scratching. However, in some rare cases it can cause some general involvement with iron deficiency anemia and eosinophilia.

Epidemiology and prevention

"Don't let the lice make you a MONO! If it's stingy, look for lice, if you find them, report it immediately!" Poster used in North America during World War II for the prevention of pedicule epidemics in men in service.

Due to their rapid development, population sizes increase rapidly if adequate measures are not taken, causing epidemics and causing them to be considered a pest insect. It is more common in school-age children, a presumably associated condition to crowding in schools.

If someone close to you is suspected of infesting lice, avoid direct contact with exposed hair (use a hat or cap), wash bedding, towels and personal clothing in 60º water or iron.

Avoid sharing clothing (such as hats, caps, or caps) with coworkers or class.

It has been recommended to use Quassia amara^{[citation needed]} balms or lotions or others that make it difficult for the nit to stick to the hair by the ovipositing female.^{[citation needed]}

In the case of wearing long hair, it is preventive to keep it tied up.

Treatment

The products that are usually used to combat lice are not effective in the nit phase, so successive applications must be made to ensure that all the nits present have passed to the nymph phase, more sensitive to treatments. Several of the treatments mentioned below can be combined.

Classic treatments

Fine comb (lendrera) for mechanical treatment of pediculosis.

Fine combs, combs with a very small gap between the teeth designed to trap nits in them (also called nit combs) that are sold in pharmacies, used methodically can be effective during treatment, especially at the time when the head is wet and with the application of rinse cream (hair conditioner), at which point lice and combs glide easily and the treatment damages the hair less. The fine side of a common comb during cream rinse application can work to slide lice (nymphs and adults).

There are electric fine combs to ensure the death of lice and nits.^{[citation needed]}

The use of kerosene and other solvents is not recommended due to their toxicity. Alcohol purchased at the pharmacy (ethanol) is toxic to lice and other arthropods and is not toxic to humans in a topical application. A mixture of alcohol with cream rinse (hair conditioner) causes lice to slip more easily. A combination of some insecticide, rinse cream and a fine comb can be very effective.

A common treatment is warm vinegar (no hotter than 50°C) on dry hair and an occlusive system (a plastic bag or cap) and a heat-sealing towel wrapped around the head for about 30 minutes, combined with the use of nits.^{[citation required]}

The hot air from a hair dryer seems effective against head lice.

An old treatment is shaving the head.

Drug treatments

Insecticides used to treat head lice include organochlorines such as lindane, organophosphates such as malathion, carbamates such as carbaryl, pyrethrins such as pyrethrum, and pyrethroids such as permethrin.

In Spain, the treatment of choice is 1% permethrin. It is applied to the hair and scalp, left to act for 10 minutes and then rinsed off. It has both pediculicidal and ovicidal action. It also has residual activity, that is, the remains of the product that remain in the hair after rinsing continue to have an action against new lice. For this reason, the use of a dryer after rinsing is not recommended, since the high temperature neutralizes its action. A single application is usually enough, but the process can be repeated after 10 days.

New treatments

One of the most effective, quick and effective ways to kill this parasite is through dehydration, although this type of treatment (carried out with a special device) can only be carried out by duly certified operators and in specialized centers. Approved by the FDA and with the seal of the Council of Europe.^{[citation needed]}

The FDA only has lindane and malathion approved for the treatment of head lice.

In some countries, the use of lindane is prohibited because it is considered toxic, and its manufacture and sale have been prohibited (Chile).

Clinical and laboratory studies ensure that many of the pediculicides on the market are not completely effective even when used according to their instructions.

Ivermectin is taken orally and has been shown to reduce head lice infestation. Ivermectin is not FDA-approved for the treatment of head lice, although it is approved for the treatment of onchocerciasis and head lice. strongyloidiasis.

Pediculicides can quickly lose their effectiveness due to the development of resistance. Lice resistance to products such as lindane, malathion, phenothrin and permethrin have been reported. The systematic use of insecticides is counterproductive if there is no infestation or real risk of contagion, since it helps to create new resistance.

The use of Quassia or other natural products to prevent pediculosis has demonstrated its effectiveness in a large part of the population due to its action on the scalp that changes the appropriate environment for the fixation and development of the louse.

New products have mixed the effectiveness of a chemical parasiticide (permethrin, deltamethrin) with substances that make it difficult for the parasite to attach itself, such as silicone or simethicone derivatives.

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