Transcript Cooties
Cooties All About Head Lice LT Greg Gorman, MC, USNR Camp Lejeune, NC Lice is a Big Deal Infests 6-12 million per year, mostly school-aged kids Does not carry disease, but carries huge social stigma Biggest problem: Parental Phobia School Hysteria Know Your Enemy Pediculus humanus var capitis A blood-sucking insect whose only environment is the human scalp (warm, vascular) East a blood meal every 4-6 hours If not on scalp, lice die within 24 hours Know Your Enemy’s Reproductive Cycle Egg Nymph Adult This determines treatment, how to interpret findings and how to combat parental/school myths and phobias Lice Eggs Several embryos in one egg Incomplete nervous system (not affected by drugs) Need heat to hatch, so always 1-3 mm from scalp Glued to hair shaft with chitin Have an “operculum” at top for air and humidity “Live” eggs are hard to see close to scalp and translucent Empty eggs (“nits”) are easier to see further from scalp as hair grows inside of egg is reflective Hatches after 7-12 days Lice Nymphs Smaller than adults Molts 3 times in 8-9 days Cannot reproduce Not easily transmitted Adult Lice Big as a sesame-seed; reddish-brown Cannot fly or hop Cling to hair shaft with 6 claws Claws evolved to conform to human scalp hair thickness Lay eggs 1-2 days after becoming adults Life-span is 30 days Host Factors Lice claws evolved to fit circumference of human hair Lice are less common in African-Americans, who have oval hair shaft Crowded living conditions Hair length is not a factor (just easier to see nits in longer hair) Personal hygiene does not play a role Kids are more susceptible 10% of school children have lice Have more physical contact with peers 10% of infestations occur at school Usually close friends transmit lice Girls > Boys (more close contact) Diagnosis of Lice (What to Do When the School Sends Your Kid Home) Look for a live louse on the scalp Hard to See 78% of infested kids had 1-10 lice 0.3% had more than 50 lice Use a comb with 0.3 mm teeth and use a magnifying glass for 5 minutes What if you Find Nits? Nits by themselves are not signs of infestation (especially after treatment) Could be hatched already or filled with dead embryos If nits are close to the scalp and treatment hasn’t been tried, it’s probably active Other Signs of Infestation • Soiled pillows (from lice feces) • Symptoms not typical Of 501 infested kids, 44% were asymptomatic 36% had pruritus • Itching usually requires sensitization thousands of bites (~ 3-8 months after infestations starts) Comparison of Head Lice Treatments Active Ingredient Insecticidal Ovicidal Killing Name Activity Activity Time pyrethrin / RID piperonyl shampoo A-200 butoxide Pronto Cream permethrin Rinse Nix 100% 10-23 70-80% min 97% 70-80% Not Reported 67% 45% 3 hr lindane Form shampoo generic Lindane • • • • • Oldest drug (Kwell) No longer on market Kills lice by interfering with their CNS Patients can sometimes feel lice convulsing Requires prescription since inappropriate use can cause seizures • Slower and less effective than other agents Pyrethrin & Permethrin • Derivatives of a natural insecticide derived from chrysantheums • Disrupt Na-channels in CNS • Very low systemic absorption with OTC preparations, but still classified as neurotoxic • Lasts long time by binding to hair, perhaps contributing to resistance How to Treat (Tricks of the Trade) • • • • Safety: Rinse in sink, not shower Apply to dry hair: the eggs close their operculum in water Repeat in 7-12 days After treatment, rinse with 1:1 vinegar:water mixture to dissolve glue and then remove eggs with 0.3 mm tooth comb with 1 1/2 inch teeth • Inspect scalp 48 hrs after treatment to determine what type of lice, if any, are present – A few large lice (maybe resistant) – Many sizes of lice (ineffective treatment) More Tricks of the Trade • Anti-histamines may be useful if itching is severe – Tell parents that itching may occur after treatment and that it is reaction to dead lice and is not a sign of re-infestation • Cleaning & washing inanimate objects – Probably plays no role in getting rid of lice, but if they must... • Drying clothes for 20 minutes before washing them • Seal clothing in bags for 14 days Questionable Folk Treatments • Kerosene: dangerous, ineffective • Smothering: layers of vaseline, olive oil, mayonnaise, or shower cap overnight. Probably not effective and not ovicidal Can Lice Be Resistant? • Incorrect use accounts for majority of treatment failures !!! However,... • Piperonyl-butoxide was added as an inhibitor of pyrethrin-inactivators • In UK, effective doses of drugs increased dramatically since 1948 – Lindane: up 200x (Burgess, Advan Parasit 36, 1995) – Permethrin: up 20x (Maunder, J R Soc Health 111, 1991) • In Israel, clinically significant resistance within 3 yrs of permethrin’s introduction (Mumcuoglu, Med Vet Entomol 9, 1995) • In Czech Republic, effective dose of permethrin rose 500x between 1981 and 1992 (Rupes, Cent Eur J Public Health 3, 1995)