Sunday, March 3, 2013

Answer to Case 248

Answer:  Eggs of Macracanthorhynchus sp., one of the "thorny-headed" worms causing human acanthocephaliasis. 

The main Macracanthorhynchus species that infects humans is M. hirudinaceous, although a second species, M. ingens, can also rarely infect humans (there have been a few case reports), and the eggs of the two cannot be differentiated microscopically

Humans typically become infected following ingestion of larvae in the intermediate insect host - usually hydrophilid or scarabaeoid beetles for M. hirudinaceous and milipedes for M. ingens.  I tend to agree with Anonymous that the child was more likely to eat a beetle than a miilipede, but you never know with kids! Humans are accidental hosts, while the definitive hosts in nature are pigs for M. hirudinaceous and carnivores such as raccoons, dogs, and foxes for M. ingens. Following ingestion, the larvae may mature, mate, and produce eggs, although maturation in humans does not always occur.

Eggs may also been seen in human fecal specimens if the child has ingested dirt containing the eggs (i.e. pica).  This does not represent true infection, but rather spurious passage of eggs.

The eggs are easily recognized by their large size and coarsely textured, thick-walled brown-yellow eggs:

And now, believe it or not, Blaine has managed a poem for us!

Macracanthorhynchus hirudinaceous
It’s appetite for pig intestine is quite voracious
It digs those hooks in
much to Porky’s chagrin
The excruciating pain must be quite hellacious

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