Head lice infestation, also known as pediculosis capitis, is the infection of the head hair and scalp by the head louse (Pediculus humanus capitis). Itching from lice bites is common. During a person's first infection, the itch may not develop for up to six weeks. If a person is infected again, symptoms may begin much more quickly. The itch may cause problems with sleeping. Generally, however, it is not a serious condition. Although body lice are established vectors of several bacterial diseases, the role of head lice in disease transmission remains uncertain. Studies have detected bacterial pathogens in head lice, but detection alone does not prove that head lice can transmit infection to humans. Head lice are spread by direct contact with the hair of someone who is infected. The cause of head lice infestations in children is not related to cleanliness. Other animals, such as cats and dogs, do not play a role in transmission. Head lice feed only on human blood and are only able to survive on human head hair. When adults, they are about 2 to 3 mm long. When not attached to a human, they are unable to live beyond three days. Humans can also become infected with two other lice – the body louse and the crab louse. To make the diagnosis, live lice must be found. Using a comb can help with detection. Empty eggshells (known as nits) are not sufficient for the diagnosis. Possible treatments include combing the hair frequently with a fine-tooth comb or shaving the head completely. Several topical medications are also effective, including malathion, ivermectin, and dimethicone. Dimethicone, which is a silicone oil, is often preferred due to the low risk of side effects. Pyrethroids such as permethrin have been commonly used; however, they have become less effective due to increasing pesticide resistance. There is little evidence for alternative medicines. Head-lice infestations are common, especially in children. In Europe, they infect between 1 and 20% of different groups of people. In the United States, between 6 and 12 million children are infected each year. They occur more often in girls than boys. It has been suggested that historically, head lice infection was beneficial, as they protected against the more dangerous body louse. Infestations may cause stigmatization of the infected individual.
Signs and symptoms
Head lice are generally uncomfortable, but typically do not constitute a serious condition. The most common symptom is itching of the head, which normally worsens 3 to 4 weeks after the initial infestation. The bite reaction is very mild and can rarely be seen between the hairs. Bites can be seen, especially on the neck of long-haired individuals, when the hair is pushed aside. Swelling of the local lymph nodes and fever are rare. Itching may cause skin breakdown and uncommonly result in a bacterial infection. Many individuals do not experience symptoms. Itching may take 2–6 weeks to develop upon first infestation, and sooner in subsequent infestations.
Role as a disease vector Body lice are known to spread several bacterial diseases, including epidemic typhus, trench fever, and louse-borne relapsing fever. The role of head lice in disease transmission is less clear. Studies have detected bacterial pathogens in head lice, including Bartonella quintana, Borrelia recurrentis, Coxiella burnetii, Rickettsia prowazekii, Yersinia pestis, and several Acinetobacter species. These bacteria have been found in head lice collected from different populations, including schoolchildren, rural communities, refugees, people experiencing homelessness, and patients in areas where louse-borne diseases occur. However, finding bacteria in head lice does not prove that head lice can spread disease to humans. To be considered a disease vector, the louse would need to carry the pathogen and transmit it to a person under natural conditions. Current evidence suggests that head lice may have some vector potential, but further experimental and epidemiological studies are needed to determine whether they can actively transmit bacterial pathogens.
Transmission Head lice spread through direct contact of the head of an infested person with the head of a non-infested person. The presence of live lice indicates an active infestation, while the presence of nits indicates a past or currently inactive infection with the potential to become active. Head lice do not leap or spring as a means to transfer to their hosts; instead, they move by crawling. Transmission by indirect contact (e.g. sharing bedding, clothing, headwear, the same comb) is much less common. The cause of head lice infestations is not related to cleanliness. Neither hair length nor how often the hair is brushed affects the risk of infection. Pets are not vectors for head lice. Other lice that infest humans are the body louse and the crab louse (aka pubic lice). The claws of these three species are adapted to attach to specific hair diameters. Pubic lice are most often spread by sexual contact with an infested person. Body lice can be found on clothing and they are not known to burrow into the skin.
Diagnosis
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