Multiple parasite phenomona

Can anyone explain the phenomena of having multiple parasites?

Is it that people who get parasites get infected with more than one since already having a type of parasite makes people more susceptible to have more or could it be that most people have some parasites and once immune system is compromised or people start parasite treatments, the signs of them start showing?


It seems like we can mostly speculate on this issue but does anyone have any idea?

For example imagine if one thousand random people in the U.S. or somewhere else where given anti parasite herbs it would be interesting to see how many people had a response in their system from them showing that they likely have parasites.

It would be an interesting experiment and could break down some of the walls in the U.S. medical system about their knowledge on parasites since these things seem to be masters at avoiding detection.

Also in this case by parasites, meaning helminths and protozoas, etc.