Transcript Cooties

Lice
The good, the bad, and the ugly
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Objectives
• Understand the Life Cycle of the Louse
• Be able to identify Pediculosis humanus
• Know how to treat head lice
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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
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Know Your Enemy
Pediculus humanus var capitis
• A blood-sucking insect whose only
environment is the human scalp (warm,
vascular)
• Eats a blood meal every 4-6 hours
• If not on scalp, lice die within 24 hours
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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
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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
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Hatches after 7-12 days
Lice Nymphs
Smaller than adults
Molts 3 times in 8-9 days
Cannot reproduce
Not easily transmitted
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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
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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
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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)
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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
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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
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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)
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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
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Lindane – 2nd Line
•
•
•
•
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
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Pyrethrin & Permethrin – 1st Line
• 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
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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)
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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
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Questionable Treatments
• Kerosene: dangerous, ineffective
• Smothering: layers of vaseline, olive oil,
mayonnaise, or shower cap overnight.
Probably not effective and not ovicidal
• Hot air: can you stand the heat?
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Can Lice Be Resistant?
• Incorrect use accounts for majority of
treatment failures !!!
However,...
• Piperonyl-butoxide was added as an inhibitor of pyrethrininactivators
• 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)
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