<unk>  life cycle. The cause of a<unk>  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<unk>  spreads through human-to-human transmission, by swallowing<unk> s<unk>  eggs. The eggs are hardy and can remain<unk> s 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<unk> s do not strictly multiply inside the body of their human host, some of the<unk>  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<unk>  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<unk> s, autoinfection<unk>  from the original host to itself), either through the anus-to-mouth route or through retroinfection, causes the<unk> s to inhabit the same host indefinitely. Life cycle The life cycle begins with eggs being ingested. The eggs hatch in the duodenum (first part of the small intestine). The emerging<unk>  larvae grow rapidly to a size of 140 to 150 micrometres, and migrate through the small intestine towards the colon. During this migration they moult twice and become adults. Females survive for 5 to 13 weeks, and males about 7 weeks. The male and female<unk> s mate in the ileum (last part of the small intestine), whereafter the male<unk> s usually die, and are passed out with stool. The gravid female<unk> s settle in the ileum, caecum (beginning of the large intestine), appendix and ascending colon, where they attach themselves to the mucosa and ingest colonic contents. Almost the entire body of a gravid female becomes filled with eggs. The estimations of the number of eggs in a gravid female<unk>  ranges from about 11,000 to 16,000. The egg-laying process begins approximately five weeks after initial ingestion of<unk>  eggs by the human host. The gravid female<unk> s migrate through the colon towards the rectum at a rate of 12 to 14 centimetres per hour. They emerge from the anus, and while moving on the skin near the anus, the female<unk> s deposit eggs either through (1) contracting and expelling the eggs, (2) dying and then disintegrating, or (3) bodily rupture due to the host scratching the worm. After depositing the eggs, the female becomes opaque and dies. The reason the female emerges from the anus is to obtain the oxygen necessary for the maturation of the eggs.
Pinworm infection
Hookworm infection
Tick infestation
Soil-transmitted helminthiasis
Intestinal parasite infection
Arthropod bites and stings
Myiasis
Dental plaque