I heard of rat bite fever...
...back in the '90s. I believe it was Bill Brant of Gourmet Rodents who got bitten by a rat and developed the infection. If I remember correctly, it was very serious and he was in the hospital. But he is the only person I personally know who suffered this disease.
However, it was really on my mind about a week or so ago, when I got my first "real" rat bite in all of the years I have been raising rats and mice (since the '70s). I have had little nips before, but this time a big, male rat really sank his teeth into my thumb. I put it (thumb, not rat!) under cold water and pushed hard on it to make it bleed as much as possible, then under water again, hoping to really clean it out. Sure did bleed A LOT!! Guess it worked, since it has been well over a week now and it pretty much healed up without any sign of infection.
I haven't looked up the disease, although I certainly would have been reading more about it if my thumb had shown any sign of infection. I am so sorry for the loss of the child. But if the animals looked healthy, I am not sure what the shop could have done. Unfortunately, people don't want to accept the fact that anything we do in life entails some risk. Do you really want to lock a kid away from EVERYTHING in order to TRY to keep him totally safe? Even that wouldn't work - he still has to eat, drink, and occasionally get in a car. That said, I can't even imagine how difficult it must be to endure the loss of a 10 year old child for a seemingly stupid reason. I can sympathize with them wanting to make "somebody" pay for it, even if there is no logical reason to do so.