Giant phages have been found in French lakes, baboons from Kenya, and the human mouth

From the article:

Though common, these big phages would have been completely missed by traditional lab techniques. It used to be that scientists could only discover viruses by first growing them—and they often filtered out anything above a certain size. In science, you tend to find what you look for. The huge phages don’t fit the standard conception of what a virus should be, so no one went looking for them. But Banfield used a different method, which she pioneered in the 1990s: Her team took environmental samples—scoops of soil or drops of water—and simply analyzed all the DNA within to see what popped out. And once Banfield realized that the huge phages existed, it wasn’t hard to find more.