Diagnosic Dilemma No. 6 

Contributor: Emeritus Professor John Goldsmid, University of Tasmania

 
This 3 year old child was noticed by his mother to be passing motile flat “things” about 10mm long in his faeces. The child was eating well and showed no signs of ill health. The mother said she had noticed that the “things” were passed every couple of days, either one or two each time. A stool specimen was collected from the child. The faecal specimen was soft but formed. No abnormalities could be seen on macroscopic examination, but microscopic examination by a direct faecal smear in saline revealed the parasite seen in Fig. 6.1
Parasite found in the faece
Fig. 6.1 Parasite (approx. 250x150 um) found in the faeces of the child on microscopic examination

What is your diagnosis?



 


The child is infected with the dog tapeworm, Dipylidium caninum. What was seen on microscopic examination, were the characteristic egg capsules of the cestode. If the “things” seen by the mother were examined microscopically, especially if mounted on a microslide and stained, the characteristic morphology of the proglottid (segment) would be clearly visible, showing that each proglottid had two sets of reproductive organs and two genital pores – one on each side. It is from this feature that D. caninum gets the name of the “double-pored tapeworm” (Fig. 6.2).
 
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Fig. 6.2 - Gravid proglottid of Dipylidium caninum (approx.3 mm in width) showing two sets of reproductive organs and two genital pores.
 
D. caninum is found virtually world-wide as a parasite of dogs. The tapeworm segments pass out of the final host, releasing the egg capsules. The eggs are ingested by larvae of the dog flea, Ctenocephalides canis which serves as the intermediate host. Within the flea larva, the larval tapeworm, or cysticercoid, develops. This passes to the flea pupa when the flea larva moults and then to the adult flea. When the flea is ingested by the dog, the life cycle of the cestode is completed. Humans, especially children, become infected by accidental ingestion of dog fleas or through ingestion of cysticercoids deposited on the mouth after being licked by a dog that has been ‘fleaing’ itself. Human cases have been widely, but sporadically, reported from many parts of the world (Goldsmid, 1965).
 
References:
Chin, J (2000) Control of Communicable Diseases Manual. 17th edit. APHA. Washington.
Goldsmid, J.M. (1966) Human infection with Dipylidium caninum. Linnaeus (Platyhelminthes: Cestoda) in Rhodesia. S.Afr.Med.J. 39: 333-334.



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