Parasites infecting the human body can range in size from longer than a shoe string to very few microns in diameter.
Here are 26 parasites:
Ancylostomids, Ascaris lumbricoides, Trichuris trichiura,
Enterobius vermicularis, Strongyloides stercoralis,
Trichostrongylus spp., Fasciala spp., Schistosona spp.,
Dicrocoelium spp., Opisthorchiformes, Paragonimus spp.,
Taenia spp., Diphyllobothrium spp., Hymenolepis spp.,
Acanthocephala, Entamoeba spp., Giardia duodenalis,
Chilomastix mesnili, Cyclospora cayetanenis, Cystoisospora_belli,
Isospora belli, Sarcocystis hominis, Echinoccus granulosus,
Trichinella spiralis, Dracunculus medinensis, Filarial worm
These names are two-part names each naming a specific species. When using a search engine to get information about any one of these, most often you will find articles about the class of parasite that has the first of the two names. The number of species associated with such a name is typically many. Here is an example for Cryptosporidium:
Cryptosporidium hominis Cryptosporidium marcopodum
Cryptosporidium parvum size = 4–6 microns
At least seven of the 26 classifications contain species that are very small. Below, the size range is noted after each of the following seven links to articles about them:
Size = 10 to 20 microns
Size = 10 microns
Size = 8.5 microns × 7.5 microns
Size = 8–10 microns
Size is between 20 and 33 microns.
Isospora belli size = 12-17 microns.
Average size = 9.3 by 14.7 microns
If the method chosen to help detect parasites is a standard MRI without extra attachments, ask whether such MRIs in that hospital are capable of detecting parasites smaller that 30 microns. If you are cleared by an MRI machine not able to see smaller parasites, your insurance will probably not cover the use of Ivermectin, which treats parasites regardless of size.
This article provides insights relating to parasites: Radiologists seldom encounter parasitic diseases in their daily practice . . .