Post on 15-Dec-2015
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
This determines treatment, how to interpret findings and how to combat parental/school myths and phobias
Egg NymphAdult
Lice Eggs
Several embryos in one eggIncomplete nervous system (not affected by drugs)Need heat to hatch, so always 1-3 mm from scalpGlued to hair shaft with chitinHave an “operculum” at top for air and humidity
“Live” eggs are hard to seeclose to scalp and translucent
Empty eggs (“nits”) are easier to seefurther from scalp as hair growsinside of egg is reflective
Hatches after 7-12 days
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 typicalOf 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
ActiveIngredient Form Name
InsecticidalActivity
OvicidalActivity
KillingTime
pyrethrin /piperonylbutoxide
shampooRID
A-200Pronto
100% 70-80%10-23min
permethrinCreamRinse Nix 97% 70-80% Not
Reported
lindane shampoo generic 67% 45% 3 hr
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)