[setrofim_]

Of course there are. The faecal matter (e.g. from egg shells, as described in the article) can be transferred onto hands, and from there onto clothing. The person then hops on a plane, flies to UK and goes for a stroll around British countryside, where they come into contact with some chickens.

This is contrived, admittedly, but not implausible. There are other scenarios as well. While they may all seem very unlikely, eventually contamination will occur, given how often people fly back and forth nowadays. If you keep rolling a thousand dice, eventually they will all come up sixes.

[lotharbot]

> "If you keep rolling a thousand dice, eventually they will all come up sixes"

A thousand sixes in a single simultaneous roll shouldn't happen in the entire lifetime of the universe. If your system is that safe, you're in pretty good shape. But rolling a thousand dice where you get to set aside each six you get, you should expect to get to all sixes in 30 or 40 rolls.

Whenever you're engineering a system for safety, the key is figuring out how much needs to go wrong for the system to fail, and how many opportunities you'll have for those things to go wrong. Diseases being carried from continent to continent is a fairly normal occurrence; contamination will happen fairly regularly, and the biggest protection against it becoming widespread is herd immunity.

[setrofim_]

Yes, true. My thousand dice comment was intended in vein of "if you put a thousand monkeys with typewriters in a room...". I did not mean to imply that the probability of rolling a thousand sixes is similar to the probability of contamination.