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Ascariasis
[Ascaris lumbricoides]

Fertilized and unfertilized Ascaris lumbricoides eggs are passed in the stool of the infected host.  Fertilized eggs are are rounded and have a thick shell with an external mammillated layer that is often stained brown by bile.  In some cases, the outer layer is absent (known as decorticated eggs).  Fertile eggs range from 45 to 75 m in length.  Unfertilized eggs are elongated and larger than fertile eggs (up to 90 m in length).  Their shell is thinner and their mammillated layer is more variable, either with large protuberances or practically none.  Unfertile eggs contain mainly a mass of refractile granules.

Ascaris lumbricoides unfertilized egg Ascaris lumbricoides unfertilized egg
A B

A: Unfertilized egg of A. lumbricoides.  Note the prominent mammillations on the outer layer.
B: Unfertilized egg of A. lumbricoides in an unstained wet mount, 200 magnification.

Ascaris lumbricoides unfertilized egg Ascaris lumbricoides unfertilized decorticated egg
C D

C: Unfertilized egg of A. lumbricoides in an unstained wet mount of stool.
D: Unfertilized egg of A. lumbricoides in a wet mount of stool.  Note this specimen lacks the mammillated layer (decorticated).

Ascaris lumbricoides unfertilized decorticated egg Ascaris lumbricoides unfertilized decorticated egg
E F

E, F: Infertile, decorticated eggs of Ascaris lumbricoides.  Images courtesy of The Leiden University Medical Center, The Netherlands.

 

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