CootiesAll About Head Lice

LT Greg Gorman, MC, USNRCamp 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

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

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 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)