Answer to Case 430

Answer: Sarcoptes scabei, the scabies or human itch mite. The presence of thick skin crusts is consistent with crusted or 'Norwegian' scabies.

This case demonstrates adult mites (with 8 legs) and nymphs and larvae (with 6 legs). Eggs with clearly-visible internal larvae are also seen:

Here are some fun facts about Sarcoptes scabei. They are arachnids, rather than insects (related to ticks and spiders). Also they undergo incomplete metamorphosis between life cycle stages (i.e. they are hemimetabolus). That means that the immature forms such as larvae and nymphs look very similar to the adults. That is quite different from holometabolus arthropods where the larvae look completely different from the adult (a good example is the flea which has a worm-like larval stage).

Here is a fun little poem from Florida Fan to go with this case:

Itchy, itchy little buggy.

Wherever cramped and unsanitary

You spread, from one fellow inmate than another,

You itch, I scratch then the bacteria follow to bother.

From the spaces between the knuckles,

To where there is a skin fold you dwell

For the poor souls, you terrorize you inflict just hell.

Itchy, itchy little buggy,

Sarcoptes scabiei you're not funny.