I am still experimenting and developing a testing regimen for mashua and I do not consider our varieties to be virus free, although I have eliminated some viruses from the collection. Mashua viruses are not well documented and many are not easy to test for. I suspect that most of our mashua varieties carry some sort of mild mosaic virus, as they show symptoms during warm weather and in the senescing leaves. It is possible that this is a physiological condition, but it looks more consistent with a viral disease to me. Whatever it is, it does not appear to impact yield as far as I can tell.
Currently, I test mashua for the Potyvirus group, which covers several common mashua viruses, and for Papaya Mosaic Virus. I once tested the collection for Potato Virus T, finding no positives. There are many more possible viruses in mashua and probably some that are not yet identified. As time and money allow, I will continue to test the mashua collection more broadly and eliminate or clean varieties that test positive for viruses.