The correct option is A epidemic
When a disease affects an entire population at a particular time period, it is called an epidemic disease. Epidemic diseases can affect and kill a large number of people.
In other words, an epidemic is the rapid spread of an infectious disease to a large section of people in a given population, within a short period of time.
E.g., Black death was an epidemic in Europe and Asia in the mid 1300s. It killed around 20% of the population at that time.