When European explorers and travelers spread out, they brought with them the germs that they had become essentially immune to, that they had learned how to tolerate over hundreds and hundreds of years, thousands of years, of living with domesticated animals who were the sources of those pathogens.
När europeiska upptäcktsresande for runt världen bar de med sig virus som de var i princip immuna mot, som de hade lärt sig att leva med under hundratals och åter hundratals, tusentals år, då de hade levt med de tamdjur som var källan till dessa smittoämnen.