Question
In a corner of my (Michigan) back bed (lightly wooded) I have worked hard over fifteen years to eradicate some poisonous plants that have caused me many painful allergic reactions.  I thought I had gotten them all, but yesterday I noticed a ground-rooting vine that has crept out of the woods with symmetrical clumps of five leaves.  The leaf shape and color look like poison ivy, so I am suspicious but don't recognize five leaves.

Answer
You likely have Virginia Creeper, Parthenocissus quinquefolia. It looks a lot like Poison Ivy, but with five toothed leaflets arranged like the fingers of a hand. Each leaflet often has a red stem. Sometimes the same vine will have smaller clumps of leaflets with only 3 in a clump. Poison Ivy is closely related but when it climbs it uses hairy, brown rootlets. Virginia creeper uses tendrils with tiny suction cups on the ends.

While Virginia Creeper does not have the same oils as Poison Ivy and does not cause the same rash, many people are sensitive to it and find they get a burning/itching rash, especially if they have been pulling it out and thus getting exposed to the sap.

Virginia Creeper has attractive fall color and is less likely than many wild vines to completely choke out your bushes and shrubs, but if it giving you a rash, by all means get rid of it.

It is relatively easy to eradicate by pulling (wear gloves and perhaps long sleeves). It will re-sprout from roots left in the ground, but not aggressively so. It fruits in the fall, and birds will eat the fruits, so be certain to get it out before then. But, because birds like it, they will tend to re-seed it (by pooping) from other people's yards to yours, particularly under their favorite perches (fences, branches of trees#. So you will tend to see new plants every year.

Round Up works nicely on Poison Ivy, I imagine it would work on Virginia Creeper as well, if you would rather use a pesticide. Best applied in the fall before the leaves change, as the plant is storing up food to make it through the winter.

To deal with the rash, first prevent contact by wearing gloves, long sleeves, long pants, socks (ever so much fun in summer, I know). Be conscious of not touching your face (wiping sweat away, for example) while weeding.  As soon as you are done, wash all exposed skin with soapy water. Some people like Technu for removing plant oils (I find it irritating). An alcohol-based cleanser like Purell might help if water is not available, particularly if you wipe the skin off with a clean cloth before the Purell evaporates.

Once you have the rash, I have found antihistamine creams and steroid creams help with some rashes. Oatmeal soaks, calamine, Aveeno and Aquaphor are other possibilities, but I am not a doctor. If you get generalized swelling, especially on your face or neck, you should call a doctor right away.