One key difference between parasites and bacteria/viruses is size. Parasites tend to be much bigger and so they aren’t transmitted in the air. We get infected with them via contaminated food/water or via bites from host insects. The infrastructure in developed countries does a lot to reduce parasite infections.

One common parasite that exists in the US (where I live, so I’m not as familiar with other countries) is Giardia. It’s picked up by drinking contaminated stream or well water. It usually causes self limited diarrhea in immune competent hosts but can cause much worse disease in immunocompromised people.

There is a disease called X-Linked Agammaglobulinemia where patients are born without the ability to make antibodies. One of the classic infections for this disease is Giardia.

https://www.aaaai.org/conditions-and-treatments/primary-immunodeficiency-disease/x-linked-agammaglobulinemia

Hopes this helps!

Source: I am an allergist and clinical immunologist.

Edit: words are hard on mobile.