VETERINARY PARASITOLOGY VPTH603
LABORATORY 
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last updated:  08/16/2005

           

                Laboratory #4 

Ascarids, Oxyuris, Trichocephalids

Objective: The egg deposited in the feces is the usual diagnostic stage for the worms considered in this laboratory.  Therefore, you should be able to identify the eggs of these worms. Sometimes you or your client will notice adult worms in feces or vomitus of infected animals and, therefore, you should be able to identify the adults of these nematodes (most can easily be recognized by size and characteristic morphology). Trichinella spiralis is exceptional in that it does not have eggs or larvae occurring in the feces. For this species the L1 in the muscles is the diagnostic stage.

 

Ascaridoidea

The ascarids are large nematodes that usually live in the small intestine. All ascarids have three lips around the mouth opening and have no buccal capsule. Species occurring in cats and dogs have prominent cervical alae. Eggs are thick-shelled and unsegmented when passed. They embryonate in feces or fecally contaminated soil. Infection is by ingestion of the embryonated egg, by ingestion of a larva in a paratenic host, or may occur by vertical transmission (in utero or via the milk).  Vertical transmission is particularly important among the ascarids of dogs (prenatal) and cats (transmammary).

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 ascaridchart.jpg (67148 bytes)

Pig

Ascaris suum - largest nematode of the pig, up to 40 cm long.

a. Demonstrations of Adults

b. Eggs - bottle #59 (60 x 45 µm, pg. 143 Foreyt)

Ascaris suum:

Anterior end.  Like all the ascarids, this adult worm has 3 lips.  The dorsal lip (#2) is out of focus in this picture.

 asuumlips.jpg (30777 bytes)
Ascaris suum adults from the small intestine of a pig.  They can be up to 40 cm long. asuum.jpg (60143 bytes)
 

Ascaris suum eggs in a fecal float.  The eggs measure 60 x 45 µm

 asuumeggs.jpg (37811 bytes)

c. Slide #SSB25 is a hematoxylin and eosin-stained section from the lung of a guinea pig, showing migrating Ascaris suum larvae. The guinea pig had been experimentally infected 6 days previously. There is little histopathology associated with a primary infection; subsequent infections elicit a strong host response with marked cellular infiltration and granuloma formation around the killed larvae. A similar reaction in the liver produces "milk spots", the gross lesions visible on the liver’s surface as white spots.

        Slide #SSB25

Ascaris suum larva in the lung.

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Horse

Parascaris equorum - largest nematode of the horse (up to 40 cm long), similar to A. suum in appearance.

a. Demonstration of Adults (These will be seen in the feces of successfully treated horses).

b. Eggs - bottle #19 (90 to 100 µm, pg. 129 Foreyt)

Parascaris equorum - largest nematode of the horse (up to 40 cm long), similar to A. suum in appearance.  This picture shows the lips around the mouth. parascarisant.jpg (55539 bytes)
Parascaris equorum egg from a fecal float.  It measures 90 to 100 µm in diameter. parascarisegg.jpg (19775 bytes)

 

Continued on the next page

 

Copyright University of Pennsylvania 2005

         Comments or Questions contact  Dr. Thomas Nolan at