Sunday, March 1, 2009

Answer to Case 59

Answer: Eggs of Dipylidium caninum, the double-pored dog tapeworm. This is the classic appearance of D. caninum eggs: multiple thin-shelled eggs with hooklets; the eggs being contained within packets or present singly. The packets typically contain 8-15 eggs; less eggs are present in the packets shown here and may reflect their premature extraction from the proglottid.

One hint regarding eggs that contain hooklets: these are likely to be cestode eggs. Eggs of nematodes and trematodes that infect humans do not not contain hooklets. The reverse is not true: not all cestodes capable of infecting humans have eggs with hooklets (e.g. eggs of the broad fish tapeworm, Diphyllobothrium latum).

D. caninum is typically found in children, and is acquired by ingestion of an infected flea such as the dog or cat flea (Ctenocephalides canis and Ctenocephalides felis, respectively).

A final note: one commenter suggested that these could represent eggs of a zoonotic cestode such as Inermicapsifer species which also has multiple eggs contained in a packet (referred to as an 'egg capsule'). Unlike D. caninum, the eggs of this organism cannot be seen easily while in the capsule. If the capsule is ruptured, 5 to 10 characteristic elongated eggs can be identified, which are recognizably different from the round eggs of D. caninum.

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