RRM said ;
This is exactly why it is no surpise that many cell lines have become infected and there is also not much that can be done about this.
It is a surprise that this obvious danger was ignored for so long, though.
I don't know if it has been ignored. For instance, the Coffin/Stoye letter that was posted in JDJ's latest blog indicates that people were aware of the situation and dangers of these kinds of things.
The problem is: what are the alternatives? We could stop doing research using animals, but I think that would be a case of throwing out the baby (or rather, 100 babies) with the bath water. Alternatively, we could use animals that share less homology with humans, but this is a real Catch 22:
The more distant the animal, the harder it will be to propate human tissue (and thus the longer it will take and thus the more chance of chance recombinations to happen). Moreover, testing in these animals will be less valubale to understanding human disease. In the most extreme case, if macaques (ignoring ethical issues) were as easy to "breed" as mice it would from one standpoint be "great" to use them instead of mice: it would be relatively easy to propagate human tissue and test results would be more "refelictive" of human infection than mice experiments. On the other hand, it would be "very bad", because with macaques, you'd have the largest chances of "breeding" some lethal and horrific human pathogen.
In an extreme case from the other side, we could use spiders. On one hand, this again would be "great" because we wouldn't less chances of any of the spider viruses jumping into the human tissue and creating a real human pathogen, but from the other hand it would be "bad" because I guess it's very hard to propagate human tissue in non-mammals and even if we get some results in some experiments, it's not very likely that these results will be of use in the fight against human disease.