Diagnosic Dilemma No. 16 


Contributors: Emeritus Professor John Goldsmid and Dr Richard Bradbury, University of Tasmania

 
This “parasite/worm” was brought to a GP by a 54 year old lady who found it in her toilet bowl after passing a motion. She was concerned that it might have been passed by herself or one of her family. The GP queried whether it might have been passed by the lady or whether it was living in the toilet bowl. The specimen was black in colour and was about 1cm in length.
On arriving at the Pathology laboratory, the specimen was histologically sectioned and a tentative identification of “Gnathostoma-like species” was suggested.

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Fig. 16.1 - Whole specimen in section (x40 magnification)
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Fig. 16.1 - Whole specimen in section (x40 magnification)
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Fig. 16.1 - Whole specimen in section (x40 magnification)

What is your diagnosis?



 


The section shows none of the characteristics of a trematode, a cestode or a nematode and the probable answer is that it is a fly maggot – suggested by the type of musculature and the spines on the cuticle.

The problem of intestinal myiasis in humans is an interesting one. The best summary of the situation is that of Kennedy (1973) in his monograph on Pathoparasitology. He states:
“ The possibility of a true intestinal myiasis ie the development of maggots of flies in the intestinal mucosa of man, has been discussed for decades. Intestinal myiasis does exist in animals eg Gastrophilus , a parasite of the alimentary canal of horses where larvae live until mature and ready for further development outside. Experimental intestinal myiasis seems to indicate that maggots of some species of flies, when swallowed, may survive the passage through the gastrointestinal tract of man, but do not establish themselves for any length of time in the mucosa and are immediately evacuated”

Thus the possibilities are:
a) A passage of ingested maggots through the gut of the patient.
b) A true intestinal myiasis with the maggots infecting the gastrointestinal tract of the patient
c) Maggots contaminating the toilet bowel

For a definitive confirmatory identification and an indication of the species, the whole specimen is required, it is a pity that this specimen was sectioned. Identification of maggots to species level may be performed by careful observation of the morphology of the posterior respiratory spiracles, posterior peritremes, cephalic cytoskepeton and the larval cuticle (Bradbury 2010).
One might request repeat specimens if they are passed and then send them in 70% alcohol, as 10% formalin results in shrinkage and deformity of the specimen (Bradbury 2010). Specimens should be preserved immediately upon passage to avoid spurious contamination with fly larvae.
When true intesinal myiasis does occur (very rarely), it is generally clinicaly innocuous, although mild diarrhoea, abdominal discomfort have been reported. The condition is however, psychologically disturbing for the patient, and they may require counselling with regard to the transient and clinically insignificant nature of the condition (brabduyr 2010).

The most likely answer is that this maggot was deposited directly into the toilet bowel by a fly, and was observed by the patient following passage of stool.
 
References:
Kennedy M. Pathoparasitology. Upjohn Co. Kalamazoo. 1973.
Bradbury RS. 2010. A Case of Intestinal Myiasis – Fact or Fiction?. Annals of the ACTM; 11:19-20.




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