What symptom is commonly associated with lice infestation?

A persistent itch is commonly associated with lice infestation because the bites from lice cause an allergic reaction on the scalp or other affected areas of the skin. This reaction leads to intense itching as the body reacts to the saliva injected by the lice during feeding. The itching can become quite uncomfortable and is often one of the first noticeable symptoms of an infestation.

The other symptoms listed, such as severe headache, muscle pain, and fever, are not typical indicators of lice infestations. Severe headaches could be associated with other conditions, muscle pain might indicate physical stress or injury rather than lice, and fever is more indicative of an infection or systemic illness rather than an infestation of lice. Thus, persistent itch stands out as the primary and most characteristic symptom of lice.