Although a variety of infectious<unk> s existed in the<unk>  in pre-Columbian times, the limited size of the populations, smaller number of domesticated animals with zoonotic<unk> s, and limited interactions between those populations (as compared to areas of Europe and Asia) hampered the transmission of communicable<unk> s. One notable infectious<unk>  of<unk>  origin is syphilis. Aside from that, most of the major infectious<unk> s known today originated in the Old World (Africa, Asia, and Europe). The<unk>  era of limited infectious<unk>  ended with the arrival of Europeans in the<unk>  and the Columbian exchange of microorganisms, including those that cause human<unk> s. Eurasian infections and epidemics had major effects on<unk><unk>  life in the colonial period and nineteenth century, especially. Europe was a crossroads among many distant, different peoples separated by hundreds, if not thousands, of miles. But repeated warfare by invading populations spread infectious<unk>  throughout the continent, as did trade, including the Silk Road. For more than 1,000 years travelers brought goods and infectious<unk> s from the East, where some of the latter had jumped from animals to humans. As a result of chronic exposure, many infections became endemic within their societies over time, so that surviving Europeans gradually developed some acquired immunity, although they were still subject to pandemics and epidemics. Europeans carried such endemic<unk> s when they migrated and explored the New World.<unk><unk> s often contracted infectious<unk>  through trading and exploration contacts with Europeans, and these were transmitted far from the sources and colonial settlements, through exclusively<unk><unk>  trading transactions. Warfare and enslavement also contributed to<unk>  transmission. Because their populations had not been previously exposed to most of these infectious<unk> s, the indigenous people rarely had individual or population acquired immunity and consequently suffered very high mortality. The numerous deaths disrupted<unk><unk>  societies. This phenomenon is known as the virgin soil effect.
Native American disease and epidemics
Virgin soil epidemic
Cocoliztli epidemics
HIV/AIDS in North America
HIV/AIDS in Asia
Third plague pandemic
Hittite plague
Japan Air Lines food poisoning incident