These diagnostic dilemmas relate to routine stool specimens received in hospital diagnostic laboratories, cases 1- 4 at Harare Central Hospital in Zimbabwe, and case 5 at the Royal Hobart Hospital in Tasmania.
The common theme is that all of these are pseudoparasites in human faeces:
- Case 1: Egg of an avian Hymenolepis. Note the extra egg membrane around the onchosphere.
- Case 2: Eggs of the rootknot nematode, Meloidogyne sp
- Case 3: Motile stage and egg of rotifers
- Case 4: Egg of an avian Capillaria.
- Case 5: Cyst of Entamoeba sp and a myxosporidean cyst
These spurious parasites (or pseudoparasites) are all examples of “transit” organisms in human faecal specimens ie they have been ingested and have passed through the human intestinal tract – often unharmed and motile (eg the rotifer and the mature Meloidogyne egg, in which the larva could be seen to be active within the egg).
The Hymenolepis egg and the Capillaria egg were probably ingested with bird meat; the Meloidogyne with root vegetables (eg carrots) and the rotifers with water. The myxosporidea were probably ingested with fish, being found as parasites in the tissues of a range of fish species.
Rotifers are small free-living invertebrates often encountered in water. In relation to rotifers encountered in human specimens, the reference by Kenny (1973) to the finding of rotifers attached to a gall bladder in an histology specimen is of interest. He believed the rotifers in his case may have represented contaminants in the processing of the specimen.
In these days of wide occurrence of HIV/AIDS when unusual infections may be encountered at any time, it is all too easy to label a recovered parasite as “spurious” if it does not correspond to what can be recognised as a human pathogen on morphological appearance or size. To check that an unrecognised parasite found in a patient’s faeces is spurious or not, a repeat stool specimen should be collected 7 – 10 days later, with the patient being kept on a controlled diet.
Kenny, M. (1973). Pathoparasitology. Upjohn. Kalamazoo.