Not virus. (For one thing, virus doesn't hit "all" the plants at the same time. Instead, it's more like one or two among at a time.

Beyond that, we need a few clues. What have you done with the plants and are doing now? Planting mix? Soil? Fert? Lighting? & number of hours? of light? Sprays? Anything else?

i did not use any spray. for germination i have used a gardening soil recommended by the gardening store. when i came home i have seen that it had fertilizer already in it. (usually I use soil without fertilizer). Also I have a little green house window where the seedling stay during the night and bad weather. when the weather is good (sunny and at least around 60-74F) I put them outside (most of the days). they get direct sun for approximately 5-6 hours. Maybe over watering is the issue? The seeds come from the same vendor - Baker Creek Heirloom Seeds. I had no problem with their seeds before so I think the problem might be on my side. Could I still use these plants?

I just moved from Europe to CA and everything is new for me. I had a garden in Europe and never had problems with seedlings. Thanx for helping me.