I thought Jewish dietary laws were designed to prevent this.
Warning! This is a high-volume ping list.
Some more "shit" to blame the Jews for
Not sure about the "designed" to prevent -- more like "God said so" and the answer is "Yes, sir, how high?" --- but to those that try to guess the mind of God, parasites is really good rationale.
Regardless, there are a lot more IP that one can still get from kosher animals (and, even more likely in that day, drinking water).
There were also almost always non-Jews that lived among the Jews who would not have been subject to the Laws of Moses.
In some follow up, I'm not at all sure the Essenes kept Kosher, or at least Kosher in the way we think of it today. I really don't know anything about them.
Also, there is a current school of though that a fair number of the Rabbinical Kosher requirements were developed out of the "I might be accidently sinning" school of thought. (The most common argument being related to milk/meat -- although I am not sure I buy that, as I think it has more to do with deeper thought as to the basis for the requirements.)
Anyway, according to this school of thought, what-we-think-of-today as kosher developed more as the Romans crushed and occupied Israel --- kind of a response to "why is this happening to us."
That said, pork would have been always off the list, which is high on the IP culprits.
And washing hands before you eat would have been on the list, too.