Pinworm infection (threadworm infection in the UK), also known as enterobiasis, is a human parasitic disease caused by the pinworm, Enterobius vermicularis. The most common symptom is pruritus ani, or itching in the anal area. The period of time from swallowing eggs to the appearance of new eggs around the anus is 4 to 8 weeks. Some people who are infected do not have symptoms. The disease is spread between people by pinworm eggs. The eggs initially occur around the anus, and can survive for up to three weeks in the environment. They may be swallowed following contamination of the hands, food, or other articles. Those at risk are those who go to school, live in a health care institution or prison, or take care of people who are infected. Other animals do not spread the disease. Diagnosis is by seeing the worms which are about one centimetre long or the eggs under a microscope. Treatment is typically with two doses of the medications mebendazole, pyrantel pamoate, or albendazole two weeks apart. Everyone who lives with or takes care of an infected person should be treated at the same time. Washing personal items in hot water after each dose of medication is recommended. Good handwashing, daily bathing in the morning, and daily changing of underwear can help prevent reinfection. Pinworm infections commonly occur in all parts of the world. They are the most common type of worm infection in Western Europe, Northern Europe and the United States. School-aged children are the most commonly infected. In the United States about 20% of children will develop pinworm at some point. Infection rates among high-risk groups may be as high as 50%. It is not considered a serious disease. Pinworms are believed to have affected humans throughout history.
Signs and symptoms
One-third of individuals with pinworm infection are totally asymptomatic. The main symptoms are itching in and around the anus and perineum. The itching occurs mainly during the night, and is caused by the female pinworms migrating to lay eggs around the anus. Both the migrating females and the clumps of eggs are irritating, as well as the sticky substance that is produced by the worms when the eggs are laid. The intensity of the itching varies, and it can be described as tickling, crawling sensations, or even acute pain. The itching leads to continuously scratching the area around the anus, which can further result in tearing of the skin and complications such as secondary bacterial infections, including bacterial skin inflammation, and hair follicle inflammation. General symptoms are trouble sleeping, and restlessness. A considerable proportion of children experience loss of appetite, weight loss, irritability, emotional instability, and bed wetting. Pinworms cannot damage the skin, and they do not normally migrate through tissues. However, they may move onto the vulva and into the vagina, from there moving to the external orifice of the uterus, and onwards to the uterine cavity, fallopian tubes, ovaries, and peritoneal cavity. This can cause inflammation of the vulva and vagina. This causes vaginal discharge and itchiness of the vulva. The pinworms can also enter the urethra, and presumably, they carry intestinal bacteria with them. According to Gutierrez (2000), a statistically significant correlation between pinworm infection and urinary tract infections has been shown; however, Burkhart & Burkhart (2005) maintain that the incidence of pinworms as a cause of urinary tract infections remains unknown. One report indicated that 36% of young girls with a urinary tract infection also had pinworms. Painful urination has been associated with pinworm infection. Sometimes, pinworms can be stopped before reaching the vaginal area. The relationship between pinworm infestation and appendicitis (a condition in which the appendix becomes inflamed and filled with pus, causing pain) has been researched, but there is a lack of clear consensus on the matter: While Gutiérrez maintains that there exists a consensus that pinworms do not produce the inflammatory reaction, Cook (1994) states that it is controversial whether pinworms are causatively related to acute appendicitis, and Burkhart & Burkhart (2004) state that pinworm infection causes symptoms of appendicitis to surface.
Cause
The cause of a pinworm infection is the worm Enterobius vermicularis. The entire lifecycle – from egg to adult – takes place in the human gastrointestinal tract of a single human host. This process is two to eight weeks.
Spread Pinworm infection spreads through human-to-human transmission, by swallowing infectious pinworm eggs. The eggs are hardy and can remain infectious in a moist environment for up to three weeks, though in a warm dry environment they usually last only 1–2 days. They do not tolerate heat well, but can survive in low temperatures: at −8 degrees Celsius (18 °F), two-thirds of the eggs are still viable after 18 hours. After the eggs have been initially deposited near the anus, they are readily transmitted to other surfaces through contamination. The surface of the eggs is sticky when laid, and the eggs are readily transmitted from their initial deposit near the anus to fingernails, hands, night-clothing and bed linen. From here, eggs are further transmitted to food, water, furniture, toys, bathroom fixtures and other objects. Household pets often carry the eggs in their fur, while not actually being infected. Dust containing eggs can become airborne and widely dispersed when dislodged from surfaces, for instance when shaking out bed clothes and linen. Consequently, the eggs can enter the mouth and nose through inhalation, and be swallowed later. Although pinworms do not strictly multiply inside the body of their human host, some of the pinworm larvae may hatch on the anal mucosa, and migrate up the bowel and back into the gastrointestinal tract of the original host. This process is called retroinfection. According to Burkhart (2005), when this retroinfection occurs, it leads to a heavy parasitic load and ensures that the pinworm infestation continues. This statement is contradictory to a statement by Caldwell, who contends that retroinfection is rare and not clinically significant. Despite the limited, 13-week lifespan of individual pinworms, autoinfection (infection from the original host to itself), either through the anus-to-mouth route or through retroinfection, causes the pinworms to inhabit the same host indefinitely.
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