A 9-year-old girl presented to urgent care with acute painful irritation in her genital and anal area. She had been asleep for approximately two hours before awakening due to this sudden discomfort. Her parents reported that she had been scratching her vaginal area and walking with an altered gait over the previous three days. The patient reported that her vagina and anus had been painful and itchy at night during this time. Her medical history was only remarkable for intermittent constipation, and she did not have recent nausea, vomiting, or diarrhea. She had passed a formed bowel movement earlier that day. The patient was fully immunized and had no recent travel history.
Physical examination of the vagina revealed a live 1-cm, white worm wiggling in the introitus. Similar worms were observed in the anal area and moving along the intergluteal cleft (Figure 1). No blood or other abnormality was observed in the genital or anal area.
FIGURE 1
Question
Based on the patient's history and physical examination, which one of the following infections is the most likely diagnosis?
- A. Dientamoeba fragilis.
- B. Enterobius vermicularis (pinworm).
- C. Necator americanus (hookworm).
- D. Strongyloides stercoralis (threadworm).
- E. Trichuris trichiura (whipworm).
Discussion
The answer is B: Enterobius vermicularis, also known as pinworm. It is the most common helminth infection in the United States, especially in school-aged children. Humans are the only known host, and it infects 30% of children worldwide.1 Infection is fecal-oral through ingestion of eggs. Female worms, which are cylindrical and approximately 1 cm long, migrate at night from the anus to the perianal and perineal regions to deposit eggs.2 Patients experience pain and pruritus, which is worse at night. Scratching the area transfers eggs to hands, clothing, and bedding. Placing infected fingers into the mouth results in autoinoculation.2
Diagnosis is typically made by identifying eggs captured via the “cellophane tape test.” Pharmacotherapy is indicated for the entire family because the infection easily spreads to other family members. Hand hygiene is the best method of prevention. Laundering clothes and linens is sufficient for disinfection.2
Dientamoeba fragilis has a worldwide distribution and is the most common protozoan found in many industrialized countries. It is spread by fecal-oral transmission and is often associated with pruritus ani, diarrhea, abdominal pain, and nausea, among other symptoms.3 Diagnosis is typically made by examining stool for ova and parasites using microscopy.4
In its adult stage, Necator americanus, also known as hookworm, is a cylindrical, white, 1-cm intestinal nematode that does not migrate out of the anus.4 It is often found in conditions of poor sanitation and extreme poverty. Hook-worm causes hypochromic microcytic anemia, leading to malnutrition and developmental delays.5 Infection occurs when skin contacts the larval form in contaminated soil. Common entry points are the hands, buttocks, legs, and feet.4 Penetration is usually associated with intense pruritus referred to as “ground itch.”5 The larvae migrate to the lungs via venous circulation and are then coughed up and swallowed. They develop into the adult form in the small intestine. Eggs are passed in stools back into the soil.4
Strongyloides stercoralis, also known as threadworm, is a soil-transmitted helminth and is also found in conditions of poor sanitation.4 It penetrates the skin, enters the venous system, and travels to the lungs before it is coughed up and swallowed and reaches the small bowel.6 The eggs can be excreted back into the soil or transform into larvae that penetrate the small intestine or perianal skin, enter the venous system, and repeat the cycle, resulting in autoinfection. Common symptoms are abdominal pain, diarrhea, and larva currens (a pruritic creeping infection from larvae migrating under the skin, usually found near the buttocks).6
In its adult form, Trichuris trichiura, also known as whip-worm, is a cylindrical nematode that is 0.3 to 0.5 cm in length and inhabits the cecal area.2 Most cases are asymptomatic, but young children with intense infections may have abdominal pain, diarrhea, colitis, and dysentery. Finger clubbing, growth retardation, and prolapsed rectum with diarrhea are pathognomonic in endemic areas.4
SUMMARY TABLE
| Condition | Characteristics |
|---|---|
| Dientamoeba fragilis | Pruritus ani, diarrhea, abdominal pain, and nausea associated with microscopic protozoa; worldwide distribution |
| Enterobius vermicularis (pinworm) | Pruritus ani, which is worse at night during migration of 1-cm, white, cylindrical worms; worldwide distribution; common in school-aged children |
| Necator americanus (hookworm) | Intense pruritus at skin penetration point; leads to hypochromic microcytic anemia, malnutrition, and developmental delays; found in areas of poor sanitation and extreme poverty |
| Strongyloides stercoralis (threadworm) | Larva currens near skin penetration site, often near buttocks; associated with abdominal pain and diarrhea; found in areas of poor sanitation |
| Trichuris trichiura (whipworm) | Finger clubbing, growth retardation, and prolapsed rectum with diarrhea are pathognomonic; abdominal pain, diarrhea, colitis, and dysentery are also common; school-aged children have the most intense infections |
The opinions and assertions contained herein are those of the author and are not to be construed as official or as reflecting the views of the U.S. Navy Medical Department, the U.S. Navy at large, or the U.S. Department of Defense.
