Diagnostic Findings [Last Modified: ]
Ascariasis
[Ascaris lumbricoides]
Causal Agent Life Cycle Geographic Distribution Clinical Features Laboratory Diagnosis Treatment

Microscopy
 

Fertilized and unfertilized Ascaris lumbricoides eggs are passed in 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.  Complete development of the larva requires 18 days under favorable conditions (moist, warm, shaded soil).  However, eggs of Ascaris lumbricoides may continue to develop and are infectious even when preserved in formalin.

A. lumbricoides unfertilized egg Ascaris lumbricoides unfertilized decorticated egg
A B

A: Unfertilized egg of A. lumbricoides in an untained wet mount, 200 magnification.
B: Unfertilized, decorticated egg of A. lumbricoides in an unstained wet mount. 
Image courtesy of The Leiden University Medical Center, The Netherlands.

A. lumbricoides fertilized egg with embryo development A. lumbricoides fertilized egg with embryo development
C D

C: A. lumbricoides fertilized egg with embryo in the early stage of development, in a wet mount.  Image taken at 200 magnification.
D: A. lumbricoides fertilized eggs in a wet mount, 200 magnification.  A larva is visible in the egg.

A. lumbricoides fertilized, decorticated egg A. lumbricoides fertilized egg
E F

E: Decorticated, fertile egg of A. lumbricoides in an unstained wet mount, 200 magnification.
F: Fertilized egg of A. lumbricoides.

A. lumbricoides with larva inside the egg A. lumbricoides larva hatching from an egg
G H

G: Egg of A. lumbricoides with larva inside.
H: Larva of A, lumbricoides hatching from an egg.

Macroscopic (Gross) Observations

Adult A. lumbricoides worm Ascaris lumbricoides mouthparts
I J

I: An adult Ascaris lumbricoides worm.  Diagnostic characteristics include tapered ends and size (length 15 to 35 cm; the females tend to be larger).  This worm is a female, as evidenced by the size and genital girdle (the dark circular groove at bottom area of image).
J:
Close-up of the anterior end of an adult A. lumbricoides.  Note the three 'lips.'  Image courtesy of the Orange County Public Health Laboratory, Santa Ana, CA.

 

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