In July of last year, researchers in France described a rather disturbing example of what could happen if you’re not careful about cleaning your contact lenses. A 17-year-old patient had been wearing monthly lenses well past their expiration date, and rinsing them with a cleaning solution she’d diluted with tap water. The end result was an eye infection. Luckily, a bit of care managed to clear it up.
In the meantime, the people who treated her dumped some of the solution out of her contact lens case and started trying to culture any parasites that would grow out of it. In the end, they got an entire ecosystem—all contained inside a single strain of amoeba. Among the parasites-within-parasites were a giant virus, a virus that infects that virus, and a mobile piece of DNA that can end up inserting into either of them.