The good news about head lice is that they carry no human diseases—they just create a major annoyance.
No mother wants to see her child crammed into an overcrowded classroom, where she can experience the joys of head lice.
The one that drives most families over the edge is head lice.
"parasitic insect infecting human hair and skin," Old English lus, from Proto-Germanic *lus (cf. Old Norse lus, Middle Dutch luus, Dutch luis, Old High German lus, German Laus), from PIE *lus- "louse" (cf. Welsh lleuen "louse"). Slang meaning "obnoxious person" is from 1630s. The plural lice (Old English lys) shows effects of i-mutation. The verb meaning "to clear of lice" is from late 14c.; to louse up "ruin, botch" first attested 1934, from the literal sense (of bedding), from 1931.
n. pl. lice (līs)
Any of numerous small, flat-bodied, wingless biting or sucking insects of the orders Mallophaga or Anoplura, many of which are external parasites on humans.