section_path: Impact/Introduced diseases
section_name: Introduced diseases
paragraph_text: Introduced diseases
  
  Encounters between explorers and populations in the rest of the world often introduced new diseases, which sometimes caused local epidemics of extraordinary virulence. For example, smallpox, measles, malaria, yellow fever, and others were unknown in pre-Columbian America.
  
  Half the native population of Hispaniola in 1518 was killed by smallpox. Smallpox also ravaged Mexico in the 1520s, killing 150,000 in Tenochtitlan alone, including the emperor, and Peru in the 1530s, aiding the European conquerors. Measles killed a further two million Mexican natives in the 17th century. In 1618–1619, smallpox wiped out 90% of the Massachusetts Bay Native Americans. Smallpox epidemics in 1780–1782 and 1837–1838 brought devastation and drastic depopulation among the Plains Indians. Some believe that the death of up to 95% of the Native American population of the New World was caused by Old World diseases. Over the centuries, the Europeans had developed high degrees of immunity to these diseases, while the indigenous peoples had no time to build such immunity.
  
  Smallpox decimated the native population of Australia, killing around 50% of indigenous Australians in the early years of British colonisation. It also killed many New Zealand Māori. As late as 1848–49, as many as 40,000 out of 150,000 Hawaiians are estimated to have died of measles, whooping cough and influenza. Introduced diseases, notably smallpox, nearly wiped out the native population of Easter Island. In 1875, measles killed over 40,000 Fijians, approximately one-third of the population. The Ainu population decreased drastically in the 19th century, due in large partto infectious diseases brought by Japanese settlers pouring into Hokkaido.
  
  Conversely, researchers have hypothesised that a precursor to syphilis may have been carried from the New World to Europe after Columbus 's voyages. The findings suggested Europeans could have carried the nonvenereal tropical bacteria home, where the organisms may have mutated into a more deadly form in the different conditions of Europe. The disease was more frequently fatal than it is today; syphilis was a major killer in Europe during the Renaissance. The first cholera pandemic began in Bengal, then spread across India by 1820. Ten thousand British troops and countless Indians died during this pandemic. Between 1736 and 1834 only some 10% of East India Company 's officers survived to take the final voyage home. Waldemar Haffkine, who mainly worked in India, who developed and used vaccines against cholera and bubonic plague in the 1890s, is considered the first microbiologist.
  
  According to a 2021 study by Jörg Baten and Laura Maravall on the anthropometric influence of colonialism on Africans, the average height of Africans decreased by 1.1 centimetres upon colonization and later recovered and increased overall during colonial rule. The authors attributed the decrease to diseases, such as malaria and sleeping sickness, forced labor during the early decades of colonial rule, conflicts, land grabbing, and widespread cattle deaths from the rinderpest viral disease.