Tanya, I haven't seen streaking like that on Oncidiums before. I've also never seen pictures of virused plants that looked quite like those, but I haven't seen very many pictures of them either, so my experience here is severely limited.
If it were me, I'd look to other causes first--nutrient deficiency maybe--before I'd move to viruses. There's going to be no real way to tell without testing, and even then, testing won't be 100 percent accurate either.
Did you do any cutting or something on the plant recently that makes you think it could have gotten virused?