The scenario goes something like this if I remember correctly. Let's say that you wounded a duck that flew off some place and later on died. Along came an opportunistic coyote or skunk, found the duck, and ate it. Of course after a big meal, it had to go to the bathroom and its scat happened to fall into some shallow water. Later on some puddle ducks came along and were eating food in that area where the animal's feces had contaminated the water. The duck ingests the cysts (oocysts) and they get into the muscle structure. When the duck infested with the sarcocystis parasite is eaten by the animal talked about before, the parasite has gone full cycle. By the way, the parasite only lives within the intestinal tract of the animal.
As has already been talked about, meat infected with or infested with the parasite is not harmful to humans. However, I have never heard of anyone eating it when they knew that the bird had this condition. The infected bird is normally tossed.
If you look up rice breast or sarcocystis you will find some interesting reading and see the life cycle it needs.
Al