Enterobiasis: causes, symptoms, diagnosis, and treatment

Enterobiasis is a parasitic disease caused by enterobius vermicularis, also known as pinworm, parasitic in the human intestines, mostly in children, also in adults.


Causes

Adult pinworms are creamy white. Females are 8 - 13mm long, 0.3 - 0.5mm wide, with large middle, with thin tail. Males are 2 - 5mm long, 0.1 - 0.2mm wide, with tail curled toward the abdomen. Pinworm eggs are oblong, about 27μm × 56μm in size, asymmetrical, with slightly flat side. The egg shells are slightly thick, colorless, and transparent. The eggs are infective and with strong resistance outside the human body. The eggs can survive for 2 - 3 weeks in the humid environment, and can be eliminated in high temperature, 5% phenol, or 10% cresol soap solution.

Adult pinworms usually parasitize the cecum, colon, and lower ileum, and are adhered to the intestinal mucosa. The head pierces the superficial intestinal mucosa and absorbs nutrients, resulting in tiny ulcers. However, deep intestinal wall is not invaded. After copulation, the males die quickly and are excreted, and the uterus of the females is full of eggs. In the intestinal cavity temperature and low oxygen environment, the females generally do not ovulate or lay few eggs. When the host sleeps, the anal sphincter relaxes, and the females migrate down to outside the anus and lay eggs in the perianal and perineal skin folds. Each female lays more than 10,000 eggs, and the females die soon after ovulation. Eggs develop into embryos within 6 hours, forming infective eggs. The infective eggs can be scattered from the perianal skin to the clothes, sheets, bedclothes, dust, and air. After the eggs are ingested by humans, the eggs are hatched in the duodenum. The larvae migrate down to small intestine, where the larvae undergo 2 molts. The larvae migrate downward and parasitize the colon, where the larvae undergo 1 molt and develop into adults. The adults migrate downward and parasitize the ileocecum and large intestine, and the females have a lifespan of about 1 month. It takes about 15 - 28 days from the infective eggs being ingested to adults laying eggs.


Signs and Symptoms

About 1/3 of patients are completely asymptomatic.

Female pinworms crawl out of the anus at night to lay eggs, causing eczematous dermatitis on the anus, perineum, and vulvae or scrotum. Due to severe pruritus, the skin with eggs is often scratched, resulting in bleeding or secondary infection. There may be nightmares, insomnia, dysphoria, anorexia, bruxism, and night terrors.

Adult pinworms parasitize the cecum, colon, and lower ileum of the human body, and ingest intestinal epithelial cells, intestinal contents, and blood. The lesions in the intestinal mucosa can lead to chronic inflammation or tiny ulcers, forming granulomas. Intestinal symptoms are mostly not obvious, but enteritis and digestive tract dysfunction may occur. In severe infections, there may be diarrhea, bloody stools, and mucous stools.

There may be some symptoms caused by heterotopic parasitism of pinworms, such as vaginitis, salpingitis, endometritis, appendicitis, and peritonitis.


Diagnosis

If there are pinworm eggs found in the perianal and perineal skin folds of children, the disease can be diagnosed.


Treatment

The treatment regimen is mebendazole 100 mg orally or albendazole 400mg orally in a single dose, repeating in 2 weeks.