Clinical Parasitology
This list captures a typical top ten common enteric parasites of medical importance, though the order of importance will vary around Australia. Information on Entamoeba histolytica is given, as this species is a common reason for a test request even if a positive result is relatively uncommon. The pathogenic role of several of the other parasite species is debatable, and detection may be more useful as an indication of poor hygiene, recent international travel or immune compromise. Further details at the CDC.
| Species | Diagnostic stage | Size | Key features |
| Blastocystis hominis | round-oval form | 6-40um | Large central vacuole surrounded by small nuclei |
| Cryptosporidium parvum | oocyst | 4-5um | Round, pink on modified acid-fast stain |
| Endolimax nana | cyst & trophozoite | Cyst, 5-10m; troph, 6-12um | Oval cyst – 4 nuclei; troph variable chromatin |
| Entamoeba coli | cyst & trophozoite | Cyst, 10-35um; troph, 15- 50um | Cyst – 8-16 nuclei; troph – uneven periph chromatin, large karyosome |
| Entamoeba histolytica | cyst & trophozoite | Cyst, 10-20um; troph, 16- 20um | Cyst – 4 nuclei; troph – even periph chromatin, central karyosome, may have ingested erythrocytes |
| Enterobius vermicularis | egg | 50-60um long, 20-40um wide | Flattened on one side, colourless |
| Giardia lamblia | Cyst & trophozoite | Cyst, 8-19um long; troph, 10-20um | Oval or round cyst; troph pear-shaped, 2 nuclei, flagellate |
| Hymenolepis nana | egg | 30-45um | 6-hook oncosphere at centre of thin walled egg |
| Iodamoeba butschlii | cyst & trophozoite | Cyst, 5-20um; troph, 8- 20um | cyst – large glycogen vacuole; troph – large karyosome |
| Schistosoma spp. | egg | S.mansoni egg = 115- 175um long; S.haematobium egg = 112-170um long | S.mansoni egg, prominent lateral spine; S.haematobium egg , terminal spine |
| Strongyloides stercoralis | first stage larva | 180-380um long | Short buccal cavity, mid-body genital primordium |
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