Head lice. The email that sends a shudder down the spine of every parent with school age kids. Advice tends to vary on treatment for this bug and so what is best to treat this problem? Lets first understand bit about its lifestyle…
World wide there are more than 500 species of lice. Head lice are part of a subgroup of lice known as sucking lice of which there are three bad amigos:- head louse, body louse and crab louse. Head lice, Pediculus capitis are largely harmless, (other than their itch!) while body lice are implicated as the baddie in facilitating transmission of epidemic diseases such as typhus and crab louse, also known as pubic lice, don’t need any further explanation. As a point of interest you cannot get head lice from your pets- it is not a zoonosis, they have their own lice.
Not withstanding their relative innocence, head lice are very irritating and need to be treated- otherwise they spread like wildfire throughout elementary schools and within weeks the entire family can become afflicted. Head lice are thought to infest up to 13% of Australia’s population at any one time. Females are more prone to louse infestation than males, although it is still unknown if long hair is the significant variable here. What is known is that shaving your head makes no difference.
Lice are known as ‘obligate ectoparasites’. This means that they need a specific host in order to complete their life cycle and live on the outside of that host. Human head lice can only survive for 55 hours away from a human scalp before they die, hence the ‘obligate’ part. This is similar to scabies (see my article on sarcoptes here).
Adult lice are about 3mm in length, and grey in colour. They cling to the hair shafts with their claws and feed by sucking blood. Head lice infest the scalp of humans, laying their eggs (commonly called nits) on the hair shafts. One female louse will lay 4-5 eggs per day. After 7-13 days incubation a nymph, or immature louse, will emerge from the egg, this is when the itch will begin as the parasite begins sucking blood from its host in order to nourish itself. Lice reach maturity in 8 days and adult lice will live up to 27 days.
Transmission of head lice tends to be through direct person to person contact as lice can’t jump or fly. In experimental settings, objects such as hats or combs were also shown to be able to transmit lice. However real life studies looking at lice transmission suggest that objects may not be as important in transmission as was once thought. One Time magazine article was reporting a boom in head lice infestations due to the rise of the selfie with transmission occurring when heads are being crammed together in order to fit on a smart phone screen. While head to head contact is the best opportunity for transmission the selfie link may be tenuous at best, although I’m not volunteering to test it out!!.
They are only 3mm long and can’t drink that much blood, so why the itch? The itch from head lice is a form of allergic reaction to the saliva of the louse which contains special anticlotting proteins to maintain the flow of blood from the host while they feed. Over time the body becomes sensitized to the saliva. This means an initial infestation may take up to a month before the host will become sensitised to lice saliva and start itching. As such itch is not necessarily the first sign of an infestation and regular surveillance is necessary to prevent extensive infestation; itch is a late sign.
Live lice must be seen for complete diagnosis. Presence of eggs or itching active bites are suspicious but not does not definitely mean you have head lice. To visualise lice use wet combing:
- apply conditioner to a comb
- brush hair to remove tangles
- use a fine toothed comb, brushing from the crown to the ends of the hair
- comb entire head twice looking for lice after each stroke
- it may help to wipe the comb on a white tissue after each stroke to help see the insect.
Its important to use the conditioner as it stuns the lice and they stop crawling for twenty minutes so are easier to catch.
But what is the best way to treat head lice once they have been seen? Wet combing as above, repeated daily until lice are no longer found has a 40% success rate. Pros – no chemicals and straight lustrous locks; Cons – poor hit rate, difficult to get a three year old to sit still for two minutes let alone the 15 or so that this method will take each day.
Therapeutic guidelines currently recommend topical pediculicides when choosing an anti-louse medicated preparation. A medicated shampoo containing maldison 0.5% is recommended first line for individuals over the age of six months. Treatment involves application to the affected individuals scalp and it is then left in for eight hours before rinsing out. It is recommended to repeat treatment again in 1 week. Once again this is not to be used in children under the age of 6 months. Maldison is an organophosphate insecticide and will kill eggs as well as the louse. A stronger concentration of maldison 1% can be left in for 30 minutes and then repeated in 1 week. Pros – good eradication of the infestation as eggs as well as louse are killed. Cons – age limitations, time to administer treatment.
An alternative to the above is use of a permethrin 1% preparation. This is placed on the hair and scalp and are left in the hair for 10 minutes before rinsing out. Treatment is to be repeated on one week. Pros – less harsh of a chemical preparation, shorter treatment time. Cons – This is a synthetic pyrethroid so does not kill the eggs, followup treatment is one week is absolutely necessary to ensure adequate treatment.
When using medicated shampoos it is important to consider a number of tips in order to improve treatment success. Firstly never apply a conditioner before applying the shampoo, always follow the directions on the bottle closely. Think about rinsing hair over a bowl rather than in a shower as this is thought to reduce the risk of system wide absorption of the treatment chemical. In addition to treating the individuals, all pillow cases need to be washed on the hot cycle and hair brushes must also be washed in hot water. If one individual in a family is affected it is likely that you will need to treat the rest of the family so check and recheck hair of close contacts regularly. Finally, it is important to notify the child’s school if head lice are detected. The child can still attend school during their treatment but surveillance is key to early detection and treatment so let everyone know and the risks are reduced. (See uptodate.com for further information)
In some very rare situations topical treatments fail. In these situations the patient may need oral treatment and should see their GP to diagnose and discuss this further.
So if you have a child that likes instagram and scratches their hair a lot, might be time to check for the telltale lice.
GPearls on the GC
- head lice are largely harmless but irritating
- live lice need to be seen to back up a hunch of infestation
- Consider reducing your selfie time to reduce reinfection rates