The Black Death was a bubonic and pneumonic plague pandemic that originated in Central Asia in the 1330s-1350s and spread along trade routes, eventually reaching Europe. It was carried by fleas on diseased rats and may have also spread through human-to-human contact. While Asia and the Islamic world limited its effects through medical advancements and sanitation, when it reached Europe, the Black Death devastated the population, killing between 1/4 to 1/2 of all Europeans - around 28 million people. The massive death toll led to widespread societal changes in Europe as it emerged from the aftermath of the pandemic.