Short answers, pulled from the story.
The Plague of Cyprian was a pandemic that afflicted the Roman Empire from approximately AD 249 to 262, with some accounts extending the timeline to 270. It caused widespread deaths across the empire and severely weakened Rome during the Crisis of the Third Century.
The cause remains debated. Suspects include smallpox, measles, and viral hemorrhagic fever such as Ebola. Historian Kyle Harper argues the recorded symptoms, including conjunctival bleeding, intestinal destruction, and limb putrefaction, better match a hemorrhagic fever than smallpox. Historian William Hardy McNeill proposed the Plague of Cyprian was one of two first transfers from animal hosts to humans, either smallpox or measles.
Cyprian described fever, continuous vomiting, diarrhea, a swollen throat, deafness, blindness, conjunctival bleeding (blood filling the eyes), and paralysis of the legs and feet. In severe cases, diseased putrefaction took off feet and parts of limbs. Most victims died.
Cyprian was the bishop of Carthage and an early Christian writer who witnessed the plague firsthand and described it in his treatise De mortalitate (On the Plague). The plague bears his name because his account is the most detailed surviving description of the disease and its symptoms.
No account comprehensive enough to estimate total deaths survives. At the height of the outbreak, 5,000 people a day were said to be dying in Rome alone. One historian calculated that Alexandria's population dropped from 500,000 to 190,000 during the plague years, though some of that decline may have come from people fleeing the city.
The plague created conditions favorable to Christian conversion. Bishop Cyprian urged his congregation to care for the sick and poor rather than flee, setting Christian communities apart from the widespread abandonment of plague victims. The Church's promise of afterlife offered comfort to the dying, and the conviction of Christian clergy in the face of mass death won many converts during the years of the outbreak.