Classification and Morphology of Oesophagostomum

Eggs and Adult Worms

Borrowed from

+Phylum: Nematoda
+Order: Strongylida
+Superfamily: Strongyloidea
+Family: Strongylidae
+Genus: Oesophagostomum
+Species: Bifurcum, Apiostomum, Colombianum, Radiatum, Dentatum, Brumpti.
The Worm, Magnified

Borrowed from Williams and Wilkins. Parasitic Disorders: Pathology, Diagnosis, and Management. Second Edition, 1999.

Background on the Phylum

There are over 16,000 species of nematodes (roundworms), 138 of which are well-characterized parasites of humans. The five orders that make up the phylum include Strongylida, Ascaridida, Oxyurida, Rhabditida, Spirurida, and Enoplida. Within the Strongylida order there are three superfamilies, namely Trichostrongyloidea, Strongyloidea, and Ancyclostomatoidea. Oesophagostomum are in the STRONGYLOIDEA superfamily however there is some controversy over which family they belong to. They are typically classified as either being in the Chabertidae family or in the Strongylidae family. As bursate nematodes, Oesophagostomum can potentially be classified into either family. This parasite resembles hookworms in both appearance and size. In fact, infection by Oesophagostomum cannot be distinguished from Necator americanus infection in most cases.

The classification of this parasite is useful in understanding its life cycle and clinical manifestations. As an intestinal nematode, it displays a typical life cycle and presentation of disease that is similar to other intestinal nematodes.


Distinct Anterior Cylindrical Morphology of Oesophagostomum bifurcum

Borrowed from

Because Oesophagostomum is a member of the Strongyloids, their morphology resembles that of other parasites found in this family. Adults are generally stout and white, with the male being smaller (6-16.6 mm) than the female (6.5-24 mm). The eggs are indistinguishable from hookworm eggs. They have a thin shell and range in size from 50 and 100 microns. The stage in which Oesophagostomum can be distinguished from hookworm is the L3 stage. Unlike hookworms, the Oesophagostomum males in L3 taper at the end, forming the posterior bursa. The anterior end of these parasites contains a striated cuticle located between the excretory pore and the mouth. The mouth is surrounded by oral papillae. The cylindrical buccal capsule, as depicted above, is surrounded by a protective "external leaf crown" that is called the corona radiata. Similar to other nematodes in this family, Oesophagostomum contains a well-developed, multi-nucleated digestive tract and an immature reproductive system.

Oesophagostomum Egg

Borrowed from Leoutsakos et al. "Rectal bleeding due to Oesophagostomum brumpti. Report of a Case." Disease of the Colon and the rectum. 20:632-634.

Life Cycle
Clinical Manifestations