Enterobius Vermicularis And Strongyloides Stercoralis: Symptoms, Diagnosis And Identification

Enterobius vermicularis

Clinical Manifestations

Pinworm infection is the most common helminth infection within the United States and Western Europe; prevalence rates in some areas may be as high as 30 to 50%. The most striking symptom of this infection is pruritus, which is caused by the migration of the female worms from the anus onto the perianal skin before egg deposition. The sometimes intense itching results in scratching and occasional scarification. In most infected people, this may be the only symptom, and many individuals remain asymptomatic.

Diagnosis and Identification

A diagnosis of a pinworm infection is made by finding the female worm or the eggs. To find a female worm, examine the area around an infected person's anus at night with a flashlight. The person should be sleeping for at least an hour before inspection. The white, hair-thin female worm is only about 10 mm long (males average 3 mm), but it wriggles and is clearly visible to the eye without a microscope. Any worms that are discovered should be placed in alcohol or vinegar and taken to the clinic or doctor for diagnosis.

Another method of diagnosis involves the use of a piece of sticky tape (cellulose tape) to pick up any eggs or worms that may be around the anal area in the morning before washing or a bowel movement. Pat the folds of skin around the anus with the sticky side of the tape. Then fold the tape on itself, sticky side down, and take it to the doctor. The tape is transferred to a glass slide and examined under the microscope for the presence of eggs or adult worms. Pinworms can also sometimes be seen in stool samples.

The cellulose tape (Scotch tape) preparation is recommended as the diagnostic test of choice (a minimum of four to six consecutive negative tapes is required to rule out the infection). Commercial paddles or other collection devices are also acceptable. Although the paraffin swab is also an option, this method is seldom used.

Adult worms may be found on or under the surface of the stool specimen, particularly in children. The adult worms can also be found on the tapes. Eggs are occasionally recovered in stool, but this is an incidental finding and not the specimen of choice.

Strongyloides stercoralis

Clinical Manifestations

The symptomatic spectrum of Strongyloides ranges from subclinical in acute and chronic infection to severe and fatal in hyper-infection syndrome and disseminated strongyloidiasis, which have case-fatality rates that approach 90%. In either case, patients’ symptoms are a result of the parasite’s larval form migrating through various organs of the body.

Diagnosis and Identification

The gold standard for the diagnosis of Strongyloides is serial stool examination. However, traditional stool examinations are insensitive and require up to seven stool exams to reach a sensitivity of 100%. Specialized stool exams include Baermann concentration, Horadi-Mori filter paper culture, quantitative acetate concentration technique, and nutrient agar plate cultures. Duodenal aspirate is more sensitive than stool examination, and duodenal biopsy may reveal parasites in the gastric crypts, in the duodenal glands, or eosinophilic infiltration in the lamina propria. Frequently, larvae can be seen by a simple wet-mount in fluid from a bronchoalveolar lavage (BAL).