A 26-year-old man came to a dentist complaining of facial asymmetry that developed because of a painful swelling in the left parotid area that appeared 3 days ago. His body temperature is 37.2°C. Two weeks ago he had a case of acute respiratory disease. Objectively, in the left parotid area there is a dense round infiltration up to 2 cm in size that is slightly mobile and moderately painful. The excretory duct of the parotid gland produces clear transparent saliva. Make the provisional diagnosis: