Where Do Lice Come From?

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Epidermal parasitic skin diseases (EPSD) are well known since ancient times. It is a heterogeneous group of infectious illnesses characterized by the parasite effect limited to the upper layer of the skin. Among the most important EPSD is pediculosis: head, ward and pubic. The name of this parasitic disease comes from the Latin word “pediculus” – in English “louse.” CDC reports about more than 12 million lice invasions annually in the US.

What is lice?

A louse is a small, wingless, parasitic insect that lives on the hair. It feeds human blood, and the structure of its legs allows it to easily cling and move through the hair. Without food, the louse perishes within 24 hours. There are numerous types of lice – only in mammals, there are more than 500 species. However, only two types parasitize on a human – the head louse (Pediculus humanus) and the pubic louse (Pthirus pubis).

  • The head louse, according to its name, settles in the head hair. The length of ander is 2-3 mm, female – 4 mm.
  • The body louse can be found in underwear. It is believed that the body louse evolved from the head lice when the person developed the habit of constantly walking dressed. The length of the male is 2-3.5 mm, the female is about 2-4.5 mm.
  • The pubic louse lives in the pubic hair, genitals, anus, in the armpits, on the chest and even on the lashes.

Female grown up lice lays approximately six eggs onto the stem of a hair per day. The eggs should be glued less than 6 mm from the scalp to survive. It takes a week to produce a nymph and they need to go through three growth cycles to reach adult size.

Where do lice come from?

Human lice do not live on the body of other mammals. So, only people can carry and pass on the insects. The main way of infection is contact; the person gets contaminated with lice only from another person. The insects do not pass on with food, water, and blood.

There are a lot of myths about where does lice come from:

  • The carriers are those who rarely shower and do not observe the rules of hygiene.
  • A person cannot get infected swimming in a pool or pond.
  • Insects do not pass on from animals, cats and dogs included.
  • Stress cannot be the cause of pediculosis.

How do people get lice?

Pediculosis is transmitted in several ways:

  • The insects creep from the head of an infected person. It happens with those who share one bed, in joint games, during hugs and kisses.
  • Head lice are carried through everyday items – hairbrushes, towels, hair binders.
  • Lice also spread through clothing. For head lice, hats, kerchiefs, and hoodies are most relevant.
  • In very rare cases parasites fall on bed linens and pillows, and from there they transfer to the head of the other person.
  • Body lice pass on from clothing.
  • Crab lice spread during sexual contact, from toilet seats or bed.

Societal consequences

Louse-transmitted illnesses are not common in the US. Lice spread on typhus, epidemic relapsing fever, and Werner-His disease. Lice cause much discomfort due to their irritating bites, causing insomnia. Scratching results in bacterial inflammation.

How does lice start?

With the help of proboscis insects prick the skin and suck blood. Their secret comes into the skin and irritates it. Foci of a dense inflammatory infiltrate spring up on the site of the bites. The inflammatory process manifests with the extension of the blood vessels and the development of skin edema. Intense itching results in local scratching that leads to pyogenic dermatitis and eczematization. Itching disturbs sleep and causes neurotic conditions, especially in children.

Signs of pediculosis

Head lice settle on the scalp mainly in the cervical and temporal area. The manifestation of pediculosis varies from the severity of the parasitism. With a small number of parasites and low sensitivity of the skin, a person can have no complaints for a long time. The main subjective symptom of pediculosis is itching. Impetiginous foci covered with yellow crust are found. Hair can be tangled and stuck together with pus.

Body lice bite skin on neck, shoulders, upper back, abdomen, waist, inguinal-femoral region. The signs are characterized by intense skin itch and multiple linear brushes. The development of the process is accompanied by the formation of a distinct brownish pigmentation and defurfuration.

Pubic lice are bordered with the site of ​​the thighs and abdomen. Insects move to the skin of the chest, underarm, on the mustache and beard, the brows and lashes. Bites live round pale blue spots. When eyelashes are infected, edema and inflammation of the lids occur.

How to confirm lice?

Diagnosis of pediculosis is based on the anamnesis, and careful examination:

  • Head lice are found during combing (preferably over a sheet of white paper).
  • Insects are easily detected in the pleats of underwear or clothes that contact with the skin.
  • Pubic lice are seen as grayish-brown dots at the hair roots.
  • People with phthiriasis ought to be examined for the STD (detected in 30% of patients).

What should be done?

  • People with pediculosis should wash scrupulously.
  • To relieve the itching, 1% hydrocortisone cream is recommend
  • All clothes and bed linen should be washed in hot water.
  • To kill head lice use 1% lotion of permethrin.
  • Use permethrin lotion again after 7 days to kill nits.

References:

  • Smith, Vincent S. “The Chewing Lice: World Checklist and Biological Overview.—RD Price, RA Hellenthal, RL Palma, KP Johnson, DH Clayton. 2003. Illinois Natural History Survey Special Publication 24. x+ 501 pp. ISBN 1–882932–08–0. $35.00 (hard cover).” (2004): 666-668.
  • Frankowski, Barbara L., et al. “Head lice.” Pediatrics 110.3 (2002): 638-643.
  • Maganga, Gaël D., et al. “Ebola virus disease in the Democratic Republic of Congo.” New England Journal of Medicine 371.22 (2014): 2083-2091.

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