Different virus may or may not be transmitted by water droplets, hands, knives, clippers, mealy bugs, scale, aphids... and touching one plant to another. Smokers have tobacco mosaic virus on their hands (and in their lungs) and TMV does infect orchids.

A poorly growing plant might or might not have virus infection. A vigorous plant might or might not have virus infection. It's impossible to tell without testing, and even then we can only test for 2 out of very many viruses. A negative virus test for one of those two doesn't mean negative for other virus.

If a plant is growing and flowering well in good conditions, it doesn't make sense to me as a hobbyist to worry about something I can't detect.

Does anyone know how the heritage plants work?

There are lots of very old plants that have historical significance and may be a hundred or more years old. Many of these plants have viruses and yet are still grown and traded, hopefully with full openess of the condition. Clearly these plants continue to survive and bloom so do people just keep them spearated from unvirused plants? How do they not eventually die? In those cases it must be the 'HIV' situation that MateoinLosAngeles mentioned, right?

As for me, i live in ignorant bliss, and even though i am pretty attached to my 30- 40 plants i dont really worry about viruses. I havent reached the maturity level with most of them to start sharing divisions so perhaps when i do ill get some tests...

I do not test my orchids. It does not make sense for me. My orchids are not valuable or rare, I am not going to do any crosses, I am not planning to sell orchids, I grow orchids to enjoy the flowers and I want collecting plants to be fun and not stressful. If an orchid is healthy and hits all the milestones for growing and blooming...it is either free of virus or resistant to virus and either one is good enough for me. I would rather not be paranoid about virus...I was years ago and it nearly killed my love of growing orchids.

I grow other plants that may or may not have virus and I really value these plants so...it is what it is.

If one notes that all or most of their orchids seem to be failing to thrive and grow and keep having issues with fungus and bacteria and one rules out Calcium deficiency, then one might want to do either some tossing or some testing. But, remember, plant virus is everywhere in our environment...it could be in any plant matter...the fruit and vegetables we buy, the plants outside, trees, nuts, other houseplants, in the mouths of bugs and even on our skin after we have been outside (mosaic virus is easily spread). I sometimes wonder how we can trust it is not in bark or moss used as a medium for plants.

When I had the one Cattleya that I quarantined due to knowing it had been exposed to virus, it missed all the milestones in growth...a complete loss of vigor. It had always put out growths like clockwork twice a year and I saw that the new growths did not begin at the usual time. When it did put out new growths, they grew much more slowly. When it finally bloomed, there was obvious color-break. I was pretty sad but I tossed it.

Just a note...when I added orchids to my plant collection in the 1990's, there were plants that one could use as virus indicator plants. You would nick your plant, take a little sap from it and introduce it to a cut on the indicator plant. The other plant would very quickly begin to express signs of the virus. Funny enough, all those plants are now resistant to virus expression and no longer show any effects so they can no longer be used to test other plants for virus. Some were purposely bred to be resistant and others naturally gained the ability to resist. Maybe orchids will one day also be resistant to virus...maybe some already are.