A 33-year-old homeless woman comes to the emergency department because of an intense itch for the past 5 weeks. The itch is present mainly on her trunk, and is worse at night. She rarely has the opportunity to bathe or wash her clothes. She says she has occasionally seen ‘“small insects” in her clothing and denies fevers. She has no allergies and takes no medications. She has had unprotected sex with three men in the past year. She denies taking any form of illicit drug. She feels discomfort and is frequently scratching. Her vital signs show no abnormalities. There are small erythematous macules and excoriations primarily on her trunk, and there are some areas of skin thickening. There are no burrows in the web spaces between her fingers. Which of the following is the most likely diagnosis?