Failures in the treatment of head lice can be due to four
causes.
By approaching the problem systematically, you can usually work out which aspects are significant in a particular case. Each case is different.
Cause 1. Inadequate
application of product.
In this problem the chemical does not come into contact with the lice for long enough at a high enough concentration. This is usually due to failure to cover all hairs adequately with the chemical. Cover from roots to tip. This problem occurs most commonly in treating pediculosis in long hair. One way of ensuring that coverage is adequate is to comb the product in with a normal comb. The end result is a head with every hair coated from root to tip, and lying parallel with its neighbours. The "parallel" aspect ensures that the product has been combed through and makes subsequent use of a fine tooth comb easier.
The product should be on the hair for 20 minutes.
Check how you are applying the product. If you meet the above criteria, then application is not a problem.
Cause 2. Lice are
resistant to the insecticide used.
Head lice can become resistant to insecticide. Some strains appear to be resistant to at least two insecticides simultaneously. Insecticide resistance in lice can not be predicted before exposing them to insecticide. Resistant lice look just the same as sensitive lice. One can roughly assess insecticide resistance by treating the head adequately as described in Point 1, leaving the product on for at least 20 minutes, and then checking for live lice. Use a fine tooth comb, and after every stroke from roots to tip wipe the combings onto paper tissue. Look for movement. If the lice are active and walking around, you have a strain resistant to the insecticide in that product. If they are all dead or imobile, the lice are sensitive to the insecticide.
If lice are resistant, change to a product containing a different insecticide. Look at the section, "If lice aren't killed, what should I do?". Keys points: note the active ingredient, not the product name. If the lice are resistant, swap to another active ingredient.
Cause 3. Failure to retreat
to kill nymphs newly emerged from eggs.
No product kills 100% of eggs even if the strain of lice is sensitive to the active ingredient. Eggs take 7 days to hatch. Therefore, starting from 1 day after treatment to about 7 days, nymphs may be hatching to come back onto the hair. Retreatment at 7 days is a mandatory part of the initial treatment regime. At this treatment if things are going well, you should expect to find nymphs, but no adults. At 14 days you should recheck the hair, or if necessary, retreat a third time. Whether you retreat, depends on your philosophy. If you want to make 100% sure the lice are eradicated, you retreat using the same product. If you just want to check, use conditioner to do so or a mechanical technique like the LiceMeister comb, and retreat only if you find nymphs. Technique using conditioner is given on http://www.jcu.edu.au/dept/PHTM/hlice/hldetkit.htm.
Reinfection can complicate treatment of head lice. This occurs usually from head to head contact with an infected child. Reinfection from the environment is very rare.
Reinfection is hard to detect. Suspect it if you have a sensitive strain as shown by testing as described in Point 3, and are treating it correctly (Cause 1 and Cause 2), but you unexpectedly find adult lice in the hair. Check the hair weekly by using the conditioner technique, or a good metal comb like the LiceMeister comb. If the hair is clear one week, and lice are present the next, reinfection is highly likely. However, don't blame reinfection for persistence of pediculosis until you have ruled out the other causes (Causes 1 to 3).
If you suspect reinfection, ask your child who she has head to head contact with and see if they can be checked. Being in the same room with an infected person, does not transmit head lice. Head to head contact is needed. The potential sources of reinfection for your child may come down to just a few children even in a class with a number of children with pediculosis since your child will probably only have head to head contact with a few of them. Don't just concentrate on the classroom; look at head to head contact opportunities at play and in the family.
Protocol for failed treatments
To manage treatment failures in pediculosis systematically look at the potential causes of failed treatment. Use the following check list in a step-wise fashion.
Treatment failures can be due to several causes, but the ones lower down the sequence can't be accurately identified until the ones higher up have been corrected.
Be systematic. Don't expect a cure in less than 1 week. Keep a balanced view; pediculosis is a minor disease, so do not use measures that put your child's health at a greater risk.
Assoc Prof Rick Speare
School of Public Health and Tropical Medicine
James Cook University
Townsville 4811
AUSTRALIA
richard.speare@jcu.edu.au