Final answer:
Pertussis, also known as whooping cough, is a common viral infection that causes a brassy or seal bark cough. It is caused by the bacterium Bordetella pertussis and is highly communicable through droplet transmission.
Step-by-step explanation:
The common viral, low-grade fever that causes the patient to have a brassy or seal bark cough is pertussis, commonly known as whooping cough. Pertussis is caused by the bacterium Bordetella pertussis and is highly communicable through droplet transmission. The disease is characterized by mucus accumulation in the lungs, leading to severe bouts of coughing that sometimes produce a 'whoop' sound when air is inhaled.