Star Surgeon Book

I read this SF book when I was about 9, and I forgot most of it pretty quickly, but there was one subplot I've often wondered about. The heroes are space doctors who go around the galaxy doing heroic medical stuff (the author was himself a medical doctor). They land on a planet where the monkey-like inhabitants are suffering from a weird virus infection, and they do their best to cure them. It doesn't work: every time a native looks like he's virus-free, he turns into a babbling idiot. In the end, the hero has an epiphany. They've got the wrong patient! The intelligent species isn't the monkeys, it's the viruses. They've been doing their best to kill the people who needed their help.

It works okay as a metaphor for various kinds of misguided interventionist foreign policy, which of course I completely missed as a 9-year-old. But that isn't the thing I wondered about; I was more curious to know whether it was in principle possible to have an intelligent virus. In the book, they were supposed to have some kind of hive mind, but this struck me even then as nonsense and still does. I couldn't really have said why at the time, but now I think I can voice my objections coherently: a virus contains too little information to encode any kind of intelligent behavior. It doesn't matter how many bodies you spread it over.

Or is it so obvious? Maybe there's a flaw in my reasoning... what do other people think?