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					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                       Insecticidal Ovicidal Killing
 Ingredient    Form    Name      Activity Activity Time

 pyrethrin /         RID                           10-23
  piperonyl shampoo A-200         100%      70-80% min
  butoxide          Pronto
             Cream
 permethrin Rinse    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)

				
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posted:4/29/2010
language:English
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