Our 'perfect' spring is good for all kinds of things, even poison ivy. It's easy to miss the plants when they are small so they can become established before you realize you have an infestation. Since the seeds are a favorite food for birds, they will be planted all over the place. I find it easy to pull the vines before the leaves come out (I'll be totally covered with long sleeves and gloves etc) There are some brush killer that are supposed to work but I find the pulling method more certain. (Technu from the pharmacy is effective to wash yourself with when you're done)

You've been getting presents from your bird friends. They perch on the fence and provide each seed they pass along with a little packet of fertilizer.
Eternal vigilance is the price of liberty. Roundup will work but may need repeated applications. I don't 'get it' but still exercise caution and use heavy gloves when pulling it out from among cherished plants.

My arms are so broken out that I'm on the way to my doctor for a Medrol pack. Once my face started itching I knew it was time for an appointment. All this despite an immediate scrubbing in the shower and a slathering of Ivy Dry.

Damn birds.

To quote the Wicked Witch of the West, "I'll get you my pretty, just you wait, Ahhhh-ha-ha-ha!"

Dian,
I mentioned above but again, the best thing to use after exposure and even after you 'get' it, is Technu. It's a soap often used by telephone pole repair people (you often see p'ivy climbing to poles) It debonds the oil from your skin and is good even after the itching starts, washing with other things including soap just spreads the oil over a larger area.

Don't forget about jewel weed - it generally grows close by and I have found that it is also effective - crush the plant and rub the juices on your hands and arms. Then, later when you come inside, use a little Technu.

I second the Tucnu cream. Other products treat the itch, but Tecnu is a soap that disolves the oils and washes them away.

I do a spraying of Brush Be Gone in June when the plants are young. If I miss a year, they are out of control! Holy moly, I will never miss it again! lol. I do it on a calm, cool morning, with rubber gloves, pants, and long sleeves.