I have heard of this working for chickens and people (I, myself don't know if I would want to eat them that way), but using raw pumpkin seeds (ah, the whole pumpkin, really) supposed to work well.
The shell of the seed is supposed to paralyze the worm, and the rest is roughage and helps it pass through, not to mention being very, very healthy. This is supposed to be done every 2 months.
I am not sure if guineas would eat the seeds, as we just brought some birds home yesterday, but I know that our chickens sure ate the seeds quickly. I am planning to keep my eyes open for unwanted pumpkins next year just for this purpose.
I remembered that something else that works is either cayenne pepper or crushed red pepper flakes. 1 tsp. to 1 Tbsp. in their water or feed, every 2 months. For chickens, anyway, it warms their insides, which is great in winter, and as a bonus, they will lay more eggs too. Don't know if this same positive side effect would show with guineas.
Last edited by niglefritz on Fri Mar 23, 2012 10:44 am; edited 2 times in total (Reason for editing : adding info)