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Macracanthorhynchus ingens Homepage

        Common name: Thorny headed worm

          Kingdom: Animalia

            Phylum: Acanthocephala

              Class: Acanthocephalae

                Order: Archiacanthocephala

                  Family: Oligacanthorhynchidae

                    Genus : Macracanthorhynchus

                      Species: ingens

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Adult Parasite:

The adult males are 10 cm and the females are up to 35 cm long.


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  • Raccoons, dogs, foxes (definitive).
  • Millipedes (intermediate).

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Life Cycle:

    The millipede ingests an egg. The egg hatches and the larva develops to the cystacanth stage. When the raccoon eats the infected millipede the larva is digested out and attaches to the wall of the small intestine and grow to the adult stage.

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Site in host where adult parasite is found:

  • Small intestine

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Diagnostic Stage:

Common Diagnostic Test

Clinical Signs:
  • Usually asymptomatic in the dog,
  • On rare occasions the worm may perforate the gut and peritonitis may result.


    Drug: Ivermectin

    • Ivermectin is an "extra label use".
    • 200 ug/kg, once a day for 7 days, removed M. hirudinaceus from pigs (Alva Valdes, et al., 1989.  Am. J. Vet. Res. 50:1392-1395).
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University of Pennsylvania  2004

Comments or Questions please contact:  Dr. Nolan at: