Tracing the origins of viruses is difficult because they don’t leave fossils and because of the tricks they use to make copies of themselves within the cells they’ve invaded. Some viruses even have the ability to stitch their own genes into those of the cells they infect, which means studying their ancestry requires untangling it from the history of their hosts and other organisms. What makes the process even more complicated is that viruses don’t just infect humans; they can infect basically any organism—from bacteria to horses; seaweed to people.
The U.S. continues to dominate as the main source of the world’s viruses, producing 15.9 per cent of all viruses. It is followed closely by Brazil, which produces 14.5 per cent (similar levels to last month’s 14.1 per cent).
Brazil continues to be the biggest source of spam, producing 11.6 per cent of all spam, followed by the US at 8.6 per cent and South Korea at 7.2 per cent.South Korea remains the biggest source of intrusion attacks, at 17.3 per cent.
The fact that viruses like the deadly Ebola and Marburg viruses, as well as the distantly related viruses that cause measles and rabies, are only found in a limited number of species suggests that those viruses are relatively new—after all, those organisms came along somewhat recently in evolutionary time. Many of these “new” viruses likely originated in insects many million years ago and at some point in evolution developed the ability to infect other species—probably as insects interacted with or fed from them.
In the second half of the Twentieth Century, buoyed up by post-war optimism and the accelerating pace of scientific and technological advancement, many believed that the battle against bacteria and viruses was over. Even the US Surgeon General William H. Stewart remarked in 1967 “It’s time to close the book on infectious diseases and pay more attention to chronic ailments such as cancer and heart disease…the war against infectious diseases has been won.” 1 Some went even further: “The most likely forecast about the future of infectious disease is that it will be very dull. There may be some wholly unexpected emergence of a new and dangerous infectious disease, but nothing of the sort that has marked the past fifty years,” wrote the eminent Australian virologist and Nobel Prize winner Macfarlane Burnet in a medical textbook in the early 1970s.
Unfortunately history has proved them both wrong. Since those bold claims were made more than twenty novel diseases, including the worst pandemic humans have ever faced, AIDS, have emerged onto the world stage and, globally, infectious diseases now account for over 25% of the fifty-seven million annual deaths worldwide 3. But what are the origins of these new threats, and what provokes their appearance in the first place?
The biggest viral threats come from man-made super-viruses. To prevent lethal global epidemics, scientists must trade experimental research for tighter safety measures.
If asked to name the world’s most dangerous virus, many people would cite Ebola viruses, which cause gory, often fatal, hemorrhagic illness; or perhaps H5N1 avian influenza, which kills 60 percent of its victims. These highly lethal viruses present great danger to those they infect, justifying elaborate biosafety precautions taken to avoid exposure. However, their ability to spread from person to person is limited, so the danger they pose is thankfully local rather than global – limited to those directly exposed and perhaps a few close contacts. Indeed, the fact that hundreds of people have suffered infection from Ebola and from “wild-type” or natural H5N1 avian flu, yet these have not spread to become a global pandemic, is the best evidence that such viruses at present cannot sustain large-scale human-to-human transmission.