That is entirely possible. Loads of things like bacteria or viruses could have been frozen in the ice, lying dormant. I’m not sure how long a virus or bacterium can typically last for, but in theory it’s possible. They’ve done experiments where they bore holes into the ice to look at what the planet was like when the ice was formed – I know they were looking at carbon dioxide levels in the atmosphere thousands of years ago, but I don’t know if they found any new species. Think I’ll look into it.
Scientists have been able to revive microorganisms buried in Antarctic ice and permafrost for hundreds of thousands of years. I think this is pretty amazing. And even when frozen they found that biological processes are still going on – damage to DNA caused by UV radiation is still being repaired – this means that microbes can last longer than we thought in such extreme conditions.
This is important in the search for ancient life on Mars – if bacteria existed millions of years ago on Mars when the climate was more hospitable, they may still be alive today, but preserved in the frost and ice!
So back to your question: it is possible that some ancient disease we have no knowledge of, that might have wiped out the woolly mammoth or the sabre-toothed tiger, is still living in the ice waiting to be released and cause havoc with animals and humans today!