Which of the following is NOT a viral pathogen?

The correct choice, which identifies a non-viral pathogen, is Staphylococcus aureus. This organism is a type of bacteria, specifically a gram-positive cocci, and is known for causing various infections in humans, ranging from mild skin infections to more serious diseases like pneumonia and sepsis.

In contrast, the other options listed are all viruses. The Influenza virus is responsible for causing the flu, a contagious respiratory illness. The Measles virus causes measles, a highly contagious viral infection characterized by fever and a distinctive rash. The Mumps virus leads to mumps, which can cause swelling of the salivary glands. These distinctions between bacterial and viral pathogens are crucial in understanding infectious diseases and their treatment options.