Q. A 14-year-old male presents to the emergency department with a complaint of swelling and pain in his left cheek. The patient reports that the symptoms started 2 days ago and have been worsening since then. He also reports having a low-grade fever and difficulty opening his mouth. His past medical history is unremarkable and he takes no medications. The patient’s immunizations are up to date. He denies any known sick contacts or recent travel. On physical examination, the patient is afebrile. You detect significant swelling in his left parotid gland (see image), with associated moderate tenderness and mild erythema. Assessment of his neck demonstrates no masses or lymphadenopathy. No other significant findings are noted on his physical examination. You order blood work, which reveals an elevated white blood cell count. You order an ultrasound of the affected parotid gland. The ultrasound confirms a diagnosis of parotitis and shows diffuse swelling of the parotid gland with increased fluid in the gland. The patient is treated with antibiotics and anti inflammatories for pain management. He is also advised to increase his fluid intake and use warm compresses on the affected area. Based on the information you have at this point in time, which of the following is the LEAST likely underlying pathogen causing this patient’s symptoms?