parasites such as roundworm are transmitted by fecal matter. i work a lot with people from central Africa who have a wonderful hospitable spirit, but like many from third world countries have not been taught basic sanitary measures. i ate. food from someone who apparently was infected and didn't wash their hands before cooking. of course, this can happen anywhere, including restaurants and in homes in developed countries.
i have been on a parasite protocol since april and have seen them come out both with and without enemas. they don't typically leave unless they are forced out ie by killing them.