The proportion of viral pathogen present in frozen permafrost should be relative to their hosts frozen in the same conditions. There is no question that amoebas or bacterias must be numerous in frozen ground and so are their viruses. But animals are quite rare, and humans even more, so one could expect a low risk of recovering an animal/primate pathogen. For example, the 1918 influenza strain was recovered from dead people burried in permafrost, because there is no trace of this virus in any "wild" permafrost of this time.

Still one should be cautious when digging out human or animal material frozen ages ago. For example variola has raged out in the past, and a contact with such a frozen virus could cause a pandemy since few people have immunity against this eradicated virus. Not to mention that poxviruses are able to endure numerous freeze/thaw cycles in labs and this can even enhance their infectivity.

I don't think that there is any model, and honestly I doubt that a model could be close to reality given the low amount of data we have today on this topic.

Philippe, thank you. Speaking about plant viruses I look at two facts: 1) current plant pathologic viruses like potyviruses evolved from non-specific strains just several thousands years ago, so strains existed 30,000 ago can be really very different from current populations; 2) large part of plants at Permanent frost area were frozen rapidly if not instantly, so, could preserve plant tissues with pathogens for long time.

Speaking about human/animals viruses - I remember that several Russian towns at those area were emptied by epidemics, and we know that mammoth flesh was so perfectly preserved (14,000 years old) that in one-two cases dogs were fed by it ( I am citing reports of expeditions of 1910-s).

Hey Alex, learning that towns have been emptied by epidemics is quite alarming indeed. The pandemic threat from permafrost frozen virus could be as high as ebolavirus threat in central Africa. It would certainly be worth investigating and documenting further this topic.

I remember that influenza human H1N1 disappeared in the 1950's, just to be back in 1975 with exactly the same genetic material. It's like this sequence jumped 25 years without genetic drift, which is unusual for flu. This virus has certainly been conserved either in a laboratory, or in frozen somewhere in nature.

Your point about potyvirus is quite interesting, maybe someone should investigate plant viruses sequence from old frozen materials, and estimate today's pathogenic potential!

Certainly, I did not say that it happened at 15-17 centuries - when at 1471 Moscow Duke Ivan III took Great Novgorod (trade town near modern St Petersburg, member of Hansa Union), some local people escaped and founded many new small towns along Northern and Siberian rivers - very few of them existed more than 50-100 years.