The point is: “dying en masse” aren’t words you want to hear in relation to tilapia.
With help from Eran Bacharach from Tel Aviv University, Eldar eventually discovered that the tilapia’s woes were caused by a brand new virus, which he called tilapia lake virus, or TiLV. When his team injected it into healthy fish, they reproduced the same symptoms seen in the dying ones: sluggish behavior, reddened skin, and inflamed eyes and brain. And when these infected fish shared water with healthy ones, they passed on their disease, killing off more than 80 percent of their neighbors in a few days.
The mystery may be solved, but the threat isn’t over. Even before anyone knew it existed, TiLV had already spread around the world, triggering similar tilapia die-offs in Ecuador and Colombia. It’s also utterly unlike any virus that we know of, hinting at an entire world of related viruses that could potentially harm our food supplies.
We should be deeply concerned about such threats, but we’re not. By contrast, diseases that affect us directly, such as swine flu, Ebola, and Zika, saturate our headlines, prompt panicked talks of pandemics, and intense quests to develop vaccines and cures. But diseases don’t need to infect humans to screw us over: They can also take out the plants and animals that we eat.
“It’s a matter of food security,” says Ian Lipkin from Columbia University, one of the world’s foremost virus-hunters. “There’s no major investment in the infectious diseases of fish, and that’s an error. The losses can be substantial.”
Lipkin helped Bacharach and Eldar to sequence the genetic material of their new virus, and what he found was very strange. The virus’s genome was split into ten different clusters, none of which matched any known viruses. “There really wasn’t anything that we could pinpoint that told us what this was,” he says. One small segment of the new virus, if you squint at it just right, looks a little like part of influenzavirus C, which causes cold-like symptoms in humans—but the resemblance is remote. “It’s like forcing a square peg into a round hole,” says Lipkin.
Don’t be surprised if other similar pegs start turning up. “Now, as people begin looking at possible infectious diseases, they’ll now be able to access sequences that weren’t available when we began looking,” says Lipkin. I’ll predict that we’ll find many more diseases due to viruses that look more similar to TiLV than to previously known viruses.”
This has happened to him once before. In 1990, he showed that a bizarre horse illness called borna disease was the work of a virus that, like TiLV, was totally unlike any other. Scientists have since found many members of this family—the bornaviruses—and all because of that initial study. Find one new trunk of the viral family tree, and suddenly a whole spray of branches comes into focus.