Not being a virologist, I have to wonder. Usually, they are just a genetic core of DNA or RNA covered by a capsid of glycoprotein. They might be able to persist indefinitely. The only thing they have to do is reproduce. That's why they hijack their host's genetic "machinery." They don't need energy to do any cellular housework of their own.
Thanks,you know plenty, so it’s likely not an obvious answer.
“Instead, two unknown forms were identified, which are older and differ from the modern pathogens found in Africa, America, the Middle East, and the former Soviet Union regions”
Yikes - Bioweapons from the past!