I have never heard of a poisonous gourd, but even if it does exist it won't matter if you don't eat them. Also I have never in my life seen a gourd growing wild. If this gourd exists and you worry about it hybridizing with your pumpkins and making them inedible don't worry about it because it won't happen. While pumpkins and some gourds can hybridize the meat of the pumpkin won't contain any genetic material from this poison gourd, only the seeds will, so just buy new seeds every year if you are really worried.