- FBNSV is one of several “multipartite viruses” that split their genes among different capsules. These oddballs were first discovered in the 1940s, and though they account for about 20 percent of known viral species, they’re still rather obscure. Blanc thinks that’s because they almost always infect plants and fungi, and only two have been found in animals—one in a moth and one in a mosquito. “I lecture on several virology courses, and even people in Ph.D. programs haven’t heard of them,” he laments. “They’re everywhere, but because they’re mainly on plants, no one cares.”
These viruses have always been baffling, even to virologists who knew about them. Everyone assumed that they could only reproduce if all the segments infected the same host cell. But the risk of losing a piece, and so dooming the others, skyrockets as the number of pieces goes up. In 2012, two researchers calculated that the odds of successfully getting every segment in the same cell become too low with anything more than three or four segments. FBNSV, with its eight segments, “should never have evolved,” Blanc says. Its mere existence suggests “that something must be wrong in the conceptual framework of virology.”
Perhaps, he realized, these viruses don’t actually need to unite their segments in the same host cell. “If theory was saying that this is impossible, maybe the viruses just don’t do it,” he says. “And once we had this stupid idea, testing it was very easy.”