Lice are external parasites of warm-blooded animals
Head Lice are small blood-sucking, wingless insects found on the human scalp. They are six legged creatures with claws, which help them cling to and crawl through human hair. They live by feeding off a human host, piercing their scalp with their mouthpart to draw out the blood. Their survival needs necessitate spending their whole life cycle on a human host.
Head Lice origin dates back to the origin of human life. Humans are indispensable to their survival. Head lice are most commonly found in school children, with the most vulnerable age being 4-11 years old. They do not discriminate between rich or poor neither do they have any preference towards dirty or clean hair.
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Nature and Incidence of Head Lice
HEAD LICE also called, Pediculus Humanus Capitis are small blood-sucking, wingless insects found on the human scalp. They are approximately the size of a sesame seed (1) and cannot jump or fly. They are six legged creatures with claws, which help them cling to and crawl through human hair.
Head Lice origins date back to the origin of human life. Their survival needs necessitate spending their whole life cycle on a human host. They live by feeding off their human host by piercing their scalp with its mouthpart to draw out the blood.
Head to head contact with an infested person remains the most widely respected scientific view of how head lice are spread from one host to another. There are conflicting views amongst scientist as to whether lice can spread through sharing pillows, hats or combs.
Occurrence of Head Lice
Any person can be infested with head lice irrespective of age, gender or class. They are equally attracted to clean and dirty hair.
Head Lice are most commonly found in school children, the most vulnerable age for catching head lice infestation remains 4-11 years.
Life Cycle of a Head Louse
The life cycle of a head louse can be classified in three distinctive stages, egg, nymph and mature lice.
Louse eggs: This is the first stage in the life cycle of a head louse. Louse eggs are usually laid at the base of hairs, about ½ -inch from the scalp (2), where they hatch after 7-10 days. They can camouflage their presence by blending with the hair colour. A female louse can lay as many as five to six eggs each day. The eggs attach to the human hair with a material like super glue, which makes it difficult to remove these eggs.
Image: Viable egg on a hair shaft Source: MEC at Cambridge (6) |
The nymph: Lice eggs usually hatch within 7-10 days. Hatched eggs are called nymphs. They are similar to an adult louse in characteristics but they differ in size. Nymphs are much smaller than a mature louse. Nymphs moult three times before becoming a mature head louse. This process takes 9-12 days.
Mature head lice: An adult head louse is approximately the size of a sesame seed (1) and can lay as many as 50-100 eggs in its lifetime. Head Lice feed on human blood, making humans indispensable to their survival. Head Lice cannot survive for more than 2 days if they fall off their human host (3).
Image: Egg and Louse on A Hair Shaft Source: MEC at Cambridge (6) |
Nits: The empty egg-shell is called a nit and remains firmly glued to the hair. They are snowy white in colour. They cannot be easily brushed out and can sometimes be confused with dandruff (4).
Image: Nit on hair shaft Source: MEC at Cambridge (6) |
Detection of Head Lice
The presence of head lice can be signalled by itching in response to bites which instigates continuous head scratching that can be a symptom of head lice infestation.
Visual evidence can be through the presence of lice, eggs or nits (empty eggshells) in human hair. Behind the ears or at the nape of neck are the favourite places for head lice to appear.
‘Detection combing’ with a fine toothed plastic comb remains one of the most effective methods for detection of head lice. One detected, the comb can also be used for removal of lice. It remains extremely important to use a comb with optimum teeth spacing that allows no space for lice to escape and hence makes the detection and removal, a hassle free and quick process.
Treatment of Head Lice
The objective in treating a case of head louse infestation must be to free the host of eggs, nymphs and lice, as well as of nits or empty shells, for the continued presence of the latter can only serve to confuse later diagnosis. Further requirements are that the treatment be easy to carry out, be inexpensive, and that side effects be kept to a minimum.
The various options for treating head lice are:
Combing
Combing is an effective and safe way to eliminate head lice and eggs.
Use of a fine-toothed plastic comb can be extremely efficient for detection and removal of lice. However, a metal comb is more effective for removal of lice eggs and nits (empty eggshells). This is because; lice attach their eggs to hair with a material almost like superglue, making it necessary to use a metal pin comb.
To ensure fast and complete elimination from lice, selection of a good quality lice removal comb is important. The efficacy of a lice removal comb depends on various factors like spacing between its pins (or teeth), consistency in the spacing throughout the pin length and its make (plastic or metal) (5). A plastic comb is best used for detection and removal of lice. To get rid of lice eggs and nits, a metal pin comb should be used.
Proper cleaning of a lice removal comb can also help prevent any chances of re-infestation. A cleaning brush specially designed for cleaning between the comb pins can be used to get rid of any unwanted substances trapped between them.
Insecticidal Treatments
Insecticidal treatments are generally Pyrethroid or Malathion based. Pyrethroids block the respiratory pathway of the lice nerve cells leading to nervous hyper excitability and death. Malathion is an anticholinestrase that releases chlorine, which then kills head lice.
Other treatments
There are various other treatments available to treat head lice.
Dimeticone works by coating the lice which stops their ability to excrete surplus water.
Enzyme based treatments work by softening the glue attaching lice eggs and nits to hair. If the glue binding the egg to the hair is dissolved, the requirements placed on a comb for removal of the egg become less demanding.
Prevention of Head Lice
Prevention of head lice appears to be best achieved by being attentive to the problem of head lice. Regular combing can help early detection of head lice, hence ensuring proper treatment is taken to prevent an infestation. Use of an efficient detector comb, which can also remove lice, can help in minimising the probability of head lice infestation.
| Top Lice Myths and Facts There are abundant myths about head lice. These are our all time winners. Myth- Lice prefer long or dirty hair. Actual- Lice have no preference for hair length or cleanliness. Myth- Lice jump or fly from head to head. Actual- Lice are wingless, cannot jump and are transferred by head to head contact. Myth- Lice and nits are the same thing. Actual- Lice are small insects, nits are empty egg shells. Myth- Lice can be spread by pets Actual- Human lice only like and feed on human blood. Do you have another myth you want to share with us? Please email us on: - This e-mail address is being protected from spam bots, you need JavaScript enabled to view it |
References
1. Burkhart CN, Burkhart CG, 2006, ‘ Fomite Transmission in head lice’ Journal of the American Academy of Dermatology, Volume 56, Issue 6, Pages 1044-1047, Viewed 20 August 2007,
http://linkinghub.elsevier.com/retrieve/pii/S019096220604031X
2. Ogg B, 2006, ‘Managing Head Lice Safely’, University of Nebraska-Lincoln Extension in Lancaster County, Viewed 7 August 2007
http://lancaster.unl.edu/pest/lice/headlice018.shtml
3. Division of Parasitic Diseases 2005, ‘Head Lice Infestation Pediculosis ‘Available at World Wide Web at
http://www.cdc.gov/NCIDOD/DPD/parasites/lice/factsht_head_lice.htm
4. Head Lice and Nits, information on head lice, detection and various treatment options 2007, Patient UK, viewed 1 October 2007
http://www.patient.co.uk/showdoc/23068753/
5. Pollack R J, ‘Head Lice Information ‘, Harvard School of Public Health, Available at World Wide Web
http://www.hsph.harvard.edu/headlice.html#methods
6. We are greatful to the MET at Cambridge for use of these images