human louse / lice

see also:

• insect bites and stings
• bed bugs

• the human louse has been a long standing pest for humans and can carry a range of pathogenic organisms

• Pediculus humanus capitis (head lice / nits)
  • a common problem amongst school children aged 3-11yrs due to close play
  • nits are the small, yellow-white, oval-shaped eggs of head lice that stick tightly to hair shafts near the scalp
  • spread only by crawling from head-to-head contact; they cannot fly or jump
  • cannot survive for more than 2 days off the human head - thus no need to treat bedding or clothes
  • Rx involves wet combing with conditioner or using medicated lotions/sprays (eg. dimeticone) to kill lice and remove eggs
    • treat all household members at same time
• Pediculus humanus (human louse), diverged from lice infecting other primates around 13 million years ago and infested hominins
  • body lice diverged from head lice between 83,000 and 170,000 years ago, with some studies suggesting a divergence as recent as 70,000 years ago and others as early as 190,000 years ago, and this appears to be an indicator of when early humans began wearing clothing as body lice require clothing to live and breed, unlike head lice, which live on scalp hair.
• pubic lice (Pthirus pubis) are a separate species from head and body lice
  • their closest relatives are lice that parasitize gorillas, indicating a host switch event which occurred 3.3 million years ago when hominids were in close contact with gorillas, and is thought to be associated with the loss of body hair in hominids while retaining a similar hair characteristic in pubic hair as with gorilla hair

• louse-borne relapsing fever - Borrelia recurrentis
• epidemic typhus - Rickettsia prowazekii
• trench fever - Bartonella quintana
• bubonic plague (caused by Yersinia pestis) can be spread by human body lice under certain conditions, though fleas remain the primary vector for plague