When the plague reached Europe, no-one knew it was upon them. Life continued as normal, those infected had no knowledge of the capacity of the plague, or its contagiousness, so families ate together, townspeople continued to interact with other townspeople, and all the while the disease traveled like wildfire. However, those who became infected would die within a week, so after the widespread death, it became apparent something was going on. The symptoms of the Black Death became very apparent as the disease continued to decimate insurmountable amounts of people.
Although death came quick to those infected by the Black Death, the week preceding the death would be nothing short of excruciating. Symptoms disguised the plague as the flu, as in the first few days after receiving the disease, high fevers, coughing up blood, nausea, vomiting, and headaches were typical. Although there were several symptoms involved with the Black Death, one in particular seemed to define its severity: large, pus and blood oozing "boils" called buboes (swelling of the lymph nodes) were characteristic of the disease. Numerous buboes would form on a victim's neck, groin region, and armpits - each being extremely sensitive.
While the plague was at its highest level of intensity, doctors and physicians were inept; nothing could be done for the ill. Individuals, including leaders of countries, offered the conclusion that the Black Death was God's punishment unto the world. During the winter, the plague would become dormant, only to revive itself in the spring; this flux would continue for centuries, killing millions upon millions.
Horrox, Rosemary. The Black Death. Manchester University Press, 1994.
Cantor, Norman F. In the Wake of the Plague: The Black Death and the World it Made. HarperCollins, 2002.