Parasitic infections are exceedingly rare in industrialized nations and are mostly found in third world countries that lack clean water, sterile food, etc. Therefore, if you reside in an industrialized nation, there is no clinical indication for prophylactic treatment of parasites.
There are many classes of parasites. For the purpose of your question, we will simplify them into: 1) those that infect the intestinal tract (round worms, tape worms, etc), 2) those that infect the blood (malaria), 3) those that infect the genitourinary tract (schistosomes and trichomonas), and 4) those that infect the brain (naegleria).
For intestinal parasites, your doctor can run a simple stool test for ova and parasites if you experience symptoms such as diarrhea, weight loss, vitamin deficiencies, etc. The treatment for most intestinal worm infections is one to two doses of albendazole or mebendazole.
For infections of the blood with parasites such as malaria, your doctor can obtain a blood smear to look for malaria if you experience symptoms such as cyclical fevers. Malaria can be prevented by prophylactic drugs prior to travel to an endemic area but can also be treated once contracted and is rarely deadly once treatment is initiated.
Genitourinary infections with schistosomes would produce bloody urine and trichomonas a frothy discharge. Both of these can be tested for by your doctor if you have symptoms and both are readily treatable.
Infections by naegleria fowleri are exceedingly rare but also rapidly fatal. These infections primary occur in people swimming in warm, freshwater lakes where the parasite invades the human via the nasal canal. There are a few treatment regimens available (such as amphotericin B) but the majority of infections lead to death. There is no prophylaxis for this parasite.
In summary, there is no reason for prophylactic treatment of parasites for individual without risk factors or exposure. If any symptoms arise, your doctor can readily test for parasites and offer the appropriate treatment. Furthermore, there exists no one way to “cleanse” your body of parasites as each class of parasite affects different organisms and the treatment regimen is unique for each parasite. And regarding those online “detoxes” or “cleanses” that promises to rid your body of parasites, there does not appear to be any medical evidence or legitimacy to support those claims.