What does Preston say appears to be the cause of the emergence of AIDS, Ebola, and other dangerous agents?

In his description of the Kinshasa Highway, Preston presents human technology as another cause for the progression of disease. Since the paving of the road in the 1970s, travel through the middle of Africa became possible, which in turn allowed for a more efficient route for the AIDS virus. While Preston has spent the majority of the book on the filoviruses, he admits that AIDS poses a far greater threat to the human species. However, because the virus can be slow-moving with symptoms that are less dramatic than the filoviruses, it has not been viewed with the proper amount of concern.