What are the causes of Bell's palsy?

Bell’s palsy is associated with a viral infection, herpes simplex virus type 1.

It can occur after vaccination against the nasally (i.e. by the nose) given influenza (inactivated type) vaccine due to the enterotoxin component of the bacteria E. coli which is often added to the vaccine.

Bell’s Palsy: What is it?  How does it present?
What is the treatment of Bell’s palsy?