the plants should be destroyed there is no way you can get rid of the virus. I would take out the plants that show signs of the disease before they spread to the other plants. Sucking insects are the main carrier.

Thanks for the followup; even though it's not the answer I was hoping for. I actually tried spraying them with Immunex and they do look a little perkier, but maybe that's because it killed the insects that brought the virus in the first place. Unfortunately it's too late in the season to find healthy impatiens to replace them around here. I guess I'll just pull the bad ones and try to get the good ones to grow large enough to fill in the gaps. Thanks again!

I agree, any plants showing symptoms should be destroyed. It affects many different plants, not just impatiens; in the Smithsonian's research greenhouses it spread to nearly the entire collection of Gesneriaceae.

That said, I assume that in zone 4 you are growing impatiens strictly as annuals. The virus will not overwinter in the soil, and as far as I know it is not transmitted through seeds; you can start with fresh plants next year. But I would suggest trying a different source for your plants, and in the meantime, there is the risk of it being transmitted to some of your perennials...