Dobson's work has been pointed to as a possible turning point in thinking about disease. Even feeding birds in your garden can contribute to the problem, since the bird table provides a mixing bowl for droppings and food. Birds congregate at feeders in numbers and a mix of species that would never occur in the wild. According to MacKenzie, the growing popularity of bird-feeding may explain the worsening epidemics of Salmonella and E. coli that have killed thousands of songbirds, especially finches, in Europe and North America. One of the reasons wild animals are so much at risk from the diseases of domestic animals is simply unfamiliarity.
Humans react to new diseases the same way.
History teaches us, for example, that Native American populations were decimated by their new exposure to common European diseases, such as measles, flu, and smallpox, in the early years following the Spanish conquest. Some degree of immunity evolves over long association with a virus or other agent of disease. A population that has never encountered the disease before may have no defense against it. Animals, like humans, are exposed to more new diseases today than ever before. For one reason, animals and humans alike are much more readily transported across borders these days.