Theirs was a mysterious bacteria spreading at a time when people didn’t yet understand disease transmission; ours, a novel virus infiltrating a world that prides itself on its medical knowledge. But in both cases, the first instinct was to close borders to try to keep the disease at bay. When that didn’t work, officials called for strict rules — but only some people paid attention. All the while, there was a proliferation of conspiracy theories. Many tried to blame the disease on outsiders or minorities — in medieval Europe, often Jews.