This isn't true. Most studies of virgin soil epidemics have been in modern foragers and all of the "common" agents I could think of in a minute (Y. pestis, tuberculosis, smallpox, malaria...) evolved long before agriculture was invented.
>Since they lived in small groups and moved frequently, they had few problems with accumulating waste or contaminated water or food.
>The shift from the hunter-gather mode of living to an agricultural model provided a more secure supply of food and enabled expansion of the population. However, domesticated animals provided not only food and labor; they also carried diseases that could be transmitted to humans. People also began to rely heavily on one or two crops, so their diets were often lacking in protein, minerals, and vitamins
>Rodents and insect vectors were attracted to human settlements, providing a means of spreading disease.
That page is intended for a lay audience. I'm not sure a single sentence of the first paragraph is correct. Everything from the dates to the statements about mobility and nutrition are questionable or plainly incorrect.
Instead, here's Lifeways of Hunter-Gatherers. From the 2nd ed., p. 200 on disease:
> An important cause of childhood death in many forager societies are infectious and parasitic diseases, including respiratory tuberculosis (TB), influenza, pneumonia, bronchitis, and diarrheal diseases resulting in dehydration.
> Among the Dobe Ju/’hoansi, disease, especially TB and malaria, account for 85 percent of childhood deaths ... and violence for 8 percent.
> Infectious disease (with most deaths occurring among infants and juveniles) accounts for 85–95 percent of Agta deaths
One weakness of current literature is that the mechanism by which adults get sick (contact with other adults) is radically different for living foragers than our paleolithic ancestors. With that said, the fact that we still have these epidemic diseases with us today demonstrates that they were able to survive in ancient populations (excepting plague, which is resident in marmots and only "accidentally" infectious to humans). Perhaps larger regional group sizes and a functioning long-distance forager trade network helped these diseases to survive where they struggle today, but survive they clearly did.
