Few creatures are as vile as the flea. These tiny, wingless, blood-sucking parasites are considered unsanitary for a reason: they spread disease. In fact, fleas were the vectors for one of the deadliest pandemics in history, the Black Death, also known as the bubonic plague.
Though the plague is uncommon today, it does still exist. Between 1,000 and 2,000 cases are reported each year worldwide.