A 5 Year Old Child With Anal Itching

A mother brings in her 5 year-old boy who has been suffering with anal itching.
On examination the physician finds several excoriations around the anus and suspects pin worms. The physician then applies scotch tape to the perianal area and places the tape on a glass slide. Review of the slide demonstrates adult worms and ova of Enterobius vermicularis (pinworms)

A magnified view of enterobius vermicularis worm (Pin worm)

The boy is treated with a single dose of chewable mebendazole and his symptoms resolove. His mother is advised to give the child mebendazole dose again in 2 weeks to increase the long-term
cure rate.
If the scotch tape test were negative, the physician could choose to treat empirically as mebendazole is a very safe medication. Another option is to test again having the parent apply the scotch tape to the boy’s perianal area first thing in the morning and bring that back to the office (the yield is higher in the morning).

Case Discussion:

Intestinal Parasites:
Intestinal parasites are most common in places with warmer temperatures and high humidity, poor sanitation and unclean water, and a large number of individuals (especially children) living in close proximity. In general, the parasites are either asymptomatic or cause symptoms related to their presence in the GI tract. Several migrate through the lungs and can also cause pulmonary symptoms during the migration.

Epidemiology: 
1. E. vermicularis (pinworm) is the most prevalent nematode in the United States. Populations at risk include preschool and school aged children, institutionalized persons, and household members of persons with pinworm infection.
2. Necator americanus (hookworm) is found predominately in the Americas and Australia, and is the second most common nematode identified in stool studies in the United States.
3. Ancylostoma duodenale (hookworm) is found mostly in southern Europe, North Africa, the Middle East, and Asia.
4. Ascaris lumbricoides is the largest and most common roundworm found in humans in the world; although less common in the United States, it is seen mostly in the rural southeast. It is found in tropical and subtropical areas, including the southeastern rural United States
5. Strongyloides stercoralis is seen mostly in tropical and subtropical areas, but can be found in temperate areas, including the southern United States
6. Cestodes (tapeworm) are a class in the phylum Platyhelminthes that contains Taenia solium and is found worldwide where pigs and humans live in close proximity.
7. Protozoa is the kingdom of one-celled organisms that includes Giardia
lamblia and Entamoeba histolytica. G. lamblia (Giardia intestinalis) is the most common parasite infection worldwide and the second most common in the United States (after pinworm), E. histolytica is seen worldwide, with higher incidence in developing countries.

Pathophysiology:
1. E. vermicularis (pinworm) is acquired through an oral route when hands that have contacted contaminated objects are placed in the mouth. Larvae hatch in the small intestine. Adults live in the cecum. The pregnant female goes to the perianal region at night to lay eggs.
2. N. americanus (hookworm) larvae penetrate the skin, travel through veins to the heart and then to the lungs, climb the bronchial tree to the pharynx, and then are swallowed and attach to intestine walls.
3. When fertilized eggs of A. lumbricoides are ingested, they hatch and the larvae enter the circulation through intestinal mucosa, travel to the lungs, climb to the pharynx, then are swallowed, and finally the adult Ascaris worms live in the small intestine.
4. S. stercoralis have both a free-living and parasitic cycle. In the parasitic cycle, larvae penetrate the skin, travel through the circulation to the lungs and are swallowed, and travel to the small intestine  to become adults. Adult females lay eggs, which become rhabditiform larvae, which can either become free living or can cause autoinfection by reentering the parasitic cycle or disseminating widely in the body.
5. Cestodes (tapeworms)—T. solium is acquired by ingesting undercooked contaminated pork.
6. G. lamblia cysts are ingested from contaminated water, food, or fomites and travel to the small intestine.
7.  E. histolytica cysts or trophozoites are ingested from fecally contaminated food, water, or hands or from fecal contact during sexual practices; these then travel to the large intestine, where these either remain or travel through the bloodstream to the brain, liver, or lungs.

Clinical Features: depends upon the infecting organisms:

• Perianal pruritus is the most common symptom of E. vermicularis (pinworm) infestation.
• N. americanus (hookworm)—Most commonly presents with iron deficiency anemia
• A. lumbricoides—Frequently asymptomatic; high numbers of worms can cause abdominal pain or intestinal obstruction. Cough, dyspnea, hemoptysis, or eosinophilic pneumonitis when in the lungs. Patients may cough up visible worms.
• T. solium—Frequently asymptomatic; risk of developing cysticercosis with symptoms based on location of cysts in brain (e.g., seizures, focal neurologic signs, and death), eyes, heart, or spine.
• G. lamblia—Diarrhea, nausea, emesis, abdominal bloating occurs 1 to 14 days after ingestion for up to 3 weeks, and can be asymptomatic.
• E. histolytica—Asymptomatic, intestinal symptoms (e.g., colitis and appendicitis), or extraintestinal (e.g., abscess in the liver or lungs, peritonitis, and skin or genital lesions).