All of the following are the diseases commonly transmitted by lice, EXCEPT:

Correct option is B

Giardiasis is a protozoal disease usually transmitted through contaminated water, not by lice. Lice are vectors for epidemic typhus, relapsing fever, and trench fever.
Explanation of options: (a) ✘ Lice transmit Rickettsia prowazekii, which causes epidemic typhus. (b) ✔ Giardiasis is caused by Giardia lamblia and spreads via fecal-oral route, not lice. (c) ✘ Relapsing fever is transmitted by lice (and ticks). (d) ✘ Trench fever is a louse-borne infection caused by Bartonella quintana.