Microbiology Case Study: A 22 Year Old Female with Recent Travel

Case History

A 22 year old female with recent travel to Nicaragua noted passage of a 10-12 cm long worm in her stool. She also noted some intermittent hematochezia over the past several days and had developed an itchy eczematous rash on her extremities.

Laboratory Diagnosis

Stool sample was submitted for ova and parasite exam. Stool sediment exam showed the presence of multiple fertilized eggs measuring 50 microns (Image 1). Based on the size of the egg, and the presence of the thick and yellow mammelated coat, she was diagnosed with an Ascaris lumbricoides infection.


Image 1.


Ascaris is the largest of the common nematode parasites of humans with females measuring 20-35 cm long and males measuring 15-31 cm. Notably, males have a curved posterior end. Infection is acquired through ingestion of the embryonated eggs from contaminated soil. In the larval migration phase of infection, diagnosis can be made by finding the larvae in sputum or in gastric washings. One female worm can lay up to 20,000 eggs, therefore enumeration of eggs does not correlate with worm burden. Both fertilized and unfertilized eggs can be easily be recovered using the sedimentation concentration from a fecal sample. It is estimated that 25% of the world population is infected with Ascaris and since transmission depends on fecal contamination of the soil, in areas where infection rates are high, mass population treatment plans with Abendazole have been successful.


-Agnes Balla, MD is a 3rd year anatomic and clinical pathology resident at the University of Vermont Medical Center.


Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.

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