Parasites can, and do cause IBS symptoms [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5680167/].
If you have IBS symptoms, like diarrhoea, bloating and constipation, you could have a parasite. However, it’s equally likely that you don’t. There are many things that can cause IBS symptoms: a parasitic infection is just one of them.
That’s why a comprehensive stool analysis like a Healthpath Gut Health Test is a great idea: it gives you a window into the goings-on of your gut, and can reveal the root causes of your IBS symptoms.