My point is at this stage there is no way of being 100% certain that you didn't already have the problem in your collection and by coincidence the outbreak has happened now. And if you have infected his collection is "there is nothing I could have done" good enough. If you said yes then you need to accept the same response from him. It is a horrible thing to happen and I know you need answers about where it came from but the simple truth is there is no way of really knowing and anything else is just speculation.