The pinworm (

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

''Enterobius vermicularis''), also known as threadworm (in the United Kingdom, Australia and New Zealand) or seatworm, is a

parasitic worm Parasitic worms, also known as helminths, are a polyphyletic group of large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other par ...

. It is a

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

(roundworm) and a common

intestinal parasite An intestinal parasite infection is a condition in which a parasite infects the gastro-intestinal tract of humans and other animals. Such parasites can live anywhere in the body, but most prefer the intestinal wall. Routes of exposure and inf ...

or helminth, especially in humans.

Encyclopædia Britannica The is a general knowledge, general-knowledge English-language encyclopaedia. It has been published by Encyclopædia Britannica, Inc. since 1768, although the company has changed ownership seven times. The 2010 version of the 15th edition, ...

. The medical condition associated with pinworm infestation is known as pinworm infection (

enterobiasis Pinworm infection (threadworm infection in the UK), also known as enterobiasis, is a human parasitic disease caused by the pinworm (parasite), pinworm, ''Enterobius vermicularis''. The most common symptom is pruritus ani, or itching in the Human ...

) Merriam-Webster: Enterobiasis (a type of

helminthiasis Helminthiasis, also known as worm infection, is any macroparasite, macroparasitic disease of humans and other animals in which a part of the body is infected with parasitism, parasitic worms, known as helminths. There are numerous species of the ...

) or less precisely as oxyuriasis in reference to the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Oxyuridae. Merriam-Webster: Oxyuriasis Other than human, ''Enterobius vermicularis'' were reported from

bonnet macaque The bonnet macaque (''Macaca radiata''), also known as zati,Chambers English Dictionary is a species of macaque endemism, endemic to southern India. Its distribution is limited by the Indian Ocean on three sides and the Godavari River, Godavari a ...

. Other species seen in

primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...

s include ''Enterobius buckleyi'' in

Orangutan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus ...

and ''Enterobius anthropopitheci'' in

chimpanzee The chimpanzee (; ''Pan troglodytes''), also simply known as the chimp, is a species of Hominidae, great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close rel ...

. ''Enterobius vermicularis'' is common in human children and transmitted via the faecal-oral route. Humans are the only natural host of ''Enterobius vermicularis''. ''Enterobius gregorii'', another human species is morphologically indistinguishable from ''Enterobius vermicularis'' except the spicule size. Throughout this article, the word "pinworm" refers to ''Enterobius''. In British usage, however, pinworm refers to '' Strongyloides'', while ''Enterobius'' is called threadworm.

Classification

The pinworm (genus ''Enterobius'') is a type of roundworm (nematode), and three species of pinworm have been identified with certainty. NCBI taxonomy database 2009 Humans are hosts only to ''Enterobius vermicularis'' (formerly ''Oxyurias vermicularis''). dpdx 2009

Chimpanzee The chimpanzee (; ''Pan troglodytes''), also simply known as the chimp, is a species of Hominidae, great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close rel ...

s are host to ''Enterobius anthropopitheci'', which is morphologically distinguishable from the human pinworm. Hasegawa et al. 2006 Hugot (1983) claims another species affects humans, ''Enterobius gregorii'', which is supposedly a

sister species In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

of ''E. vermicularis'', and has a slightly smaller spicule (i.e., sexual organ). Hugot 1983 Its existence is controversial, however; Totkova et al. (2003) consider the evidence to be insufficient, Totkova et al. 2003 and Hasegawa et al. (2006) contend that ''E. gregorii'' is a younger stage of ''E. vermicularis''. Hasegawa et al. 1998 Regardless of its status as a distinct species, ''E. gregorii'' is considered clinically identical to ''E. vermicularis''.

Morphology

The adult female has a sharply pointed posterior end, is 8 to 13 mm long, and 0.5 mm thick. Gutiérrez 2005, p. 354. The adult male is considerably smaller, measuring 2 to 5 mm long and 0.2 mm thick, and has a curved posterior end. The eggs are

translucent In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable light scattering by particles, scattering of light. On a macroscopic scale ...

and have a surface that adheres to objects. The eggs measure 50 to 60 μm by 20 to 30 μm, and have a thick shell flattened on one side. The small size and colourlessness of the eggs make them invisible to the naked eye, except in barely visible clumps of thousands of eggs. Eggs may contain a developing

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

or a fully developed pinworm

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

. The larvae grow to 140–150 μm in length. Cook 1994, p. 1159 Image:Pinworms in the Appendix (1).jpg, Pinworms are sometimes diagnosed incidentally by

pathology Pathology is the study of disease. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in the context of modern medical treatme ...

Micrograph A micrograph is an image, captured photographically or digitally, taken through a microscope or similar device to show a magnify, magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken ...

of pinworms in the appendix,

H&E stain Hematoxylin and eosin stain ( or haematoxylin and eosin stain or hematoxylin–eosin stain; often abbreviated as H&E stain or HE stain) is one of the principal tissue stains used in histology. It is the most widely used stain in medical diag ...

Image:Pinworms in the Appendix (3).jpg, High magnification

micrograph A micrograph is an image, captured photographically or digitally, taken through a microscope or similar device to show a magnify, magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken ...

of a pinworm in cross section in the appendix,

File:Enterobius vermicularis - intermediate magnification.jpg, Partially longitudinal cross-section of ''Enterobius vermicularis'',

File:Enterobius vermicularis egg.jpg, Cross-section of early ''E. vermicularis'' egg,

File:Histopathology of enterobius vermicularis eggs, HE stain.jpg, Later ''E. vermicularis'' eggs, of the same size as early eggs but having undergone more mitoses.

Image:Evermicularis worm4 HB.jpg, Pinworms are sometimes diagnosed incidentally by

of male pinworm in cross section, alae (blue arrow),

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. T ...

(red arrow) and

testis A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is Homology (biology), homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of Androgen, androgens, p ...

(black arrow),

Image:Enterobius vermicularis (01).tif, Pinworm eggs are easily seen under a

microscope A microscope () is a laboratory equipment, laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic ...

. Image:Head of Enterobius vermicularis human pinworm 5230 lores.jpg, This micrograph reveals the cephalic alae in the head region of'' E. vermicularis''. Image:Enterobius vermicularis-1.jpg, ''E. vermicularis''

Life cycle

The entire life cycle, from egg to adult, takes place in the

human gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system ...

of a single host, from about 2–4 weeks Cook et al. 2009, p. 1516 or about 4–8 weeks. ''E. vermicularis'' molts four times; the first two within the egg before hatching and two before becoming an adult worm. Although infection often occurs via

ingestion Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms, inge ...

of embryonated eggs by inadequate hand washing or nail biting, inhalation followed by swallowing of airborne eggs may occur rarely. The eggs hatch in the

duodenum The duodenum is the first section of the small intestine in most vertebrates, including mammals, reptiles, and birds. In mammals, it may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest p ...

(i.e., first part of the

small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...

). The emerging pinworm

e grow rapidly to a size of 140 to 150 μm, and migrate through the small intestine towards the colon. During this migration, they

moult In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...

twice and become adults. Females survive for 5 to 13 weeks, and males about 7 weeks. The male and female pinworms mate in the

ileum The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may ...

(i.e., last part of the small intestine), whereafter the male pinworms usually die, Garcia 1999, p. 246 and are passed out with stool. Caldwell 1982, p. 307. The gravid female pinworms settle in the

caecum The cecum ( caecum, ; plural ceca or caeca, ) is a pouch within the peritoneum that is considered to be the beginning of the large intestine. It is typically located on the right side of the body (the same side of the body as the appendix, ...

(i.e., beginning of the

large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the Digestion, digestive system in tetrapods. Water is absorbed here and the remaining waste material is stored in the rectum as feces befor ...

), appendix and

ascending colon In the anatomy of humans and homologous primates, the ascending colon is the part of the colon located between the cecum and the transverse colon. Characteristics and structure The ascending colon is smaller in calibre than the cecum from wh ...

, where they attach themselves to the

mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It ...

and ingest colonic contents. Almost the entire body of a

gravid In biology and medicine, gravidity and parity are the number of times a female has been pregnant (gravidity) and carried the pregnancies to a viable gestational age (parity). These two terms are usually coupled, sometimes with additional terms, t ...

female becomes filled with eggs. The estimations of the number of eggs in a gravid female pinworm range from about 11,000 to 16,000. The egg-laying process begins about five weeks after initial ingestion of pinworm eggs by the human host. The gravid female pinworms migrate through the colon towards the

rectum The rectum (: rectums or recta) is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. Before expulsion through the anus or cloaca, the rectum stores the feces temporarily. The adult ...

at a rate of 12 to 14 cm per hour. They emerge from the

anus In mammals, invertebrates and most fish, the anus (: anuses or ani; from Latin, 'ring' or 'circle') is the external body orifice at the ''exit'' end of the digestive tract (bowel), i.e. the opposite end from the mouth. Its function is to facil ...

, and while moving on the skin near the anus, the female pinworms 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 female emerges from the anus to obtain the oxygen necessary for the maturation of the eggs.

Infection

''E. vermicularis'' causes the medical condition pinworm infection also known as ''enterobiasis'', whose primary symptom is

itching An itch (also known as pruritus) is a sensation that causes a strong desire or reflex to scratch. Itches have resisted many attempts to be classified as any one type of sensory experience. Itches have many similarities to pain, and while both ...

in the anal area. Extraintestinal disease is rare and most commonly involves the female reproductive tract, but spleen abscess has also been reported. Enterobius vermicularis infections are found to be correlated with stunting and lower mean I.Q. among prepubescent children.

Distribution

The pinworm has a worldwide distribution, Gutiérrez 2005, p. 355. and is the cause of the most common

(

infection) in the United States, western Europe, and Oceania. Burkhart & burkhart 2005, p. 837 In the United States, a study by the Center of Disease Control reported an overall

incidence rate In epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and Risk factor (epidemiology), determinants of health and disease conditions in a defined population, and application of this knowl ...

of 11.4% among children. Pinworms are particularly common in children, with prevalence rates in this age group having been reported as high as 61% in India, 50% in England, 39% in Thailand, 37% in Sweden, and 29% in Denmark. Finger sucking has been shown to increase both incidence and relapse rates, and

nail biting Nail biting, also known as onychophagy or onychophagia, is an oral compulsive habit of biting one's fingernails. It is sometimes described as a parafunctional activity, the use of the mouth for an activity other than speaking, eating, or drink ...

has been similarly associated. Cook 1994, p. 1160 Because it spreads from host to host through

contamination Contamination is the presence of a constituent, impurity, or some other undesirable element that renders something unsuitable, unfit or harmful for the physical body, natural environment, workplace, etc. Types of contamination Within the scien ...

, pinworms are common among people living in close contact, and tends to occur in all people within a household. The prevalence of pinworms is not associated with gender, nor with any particular social class, race, or culture. Pinworms are an exception to the tenet that intestinal parasites are uncommon in affluent communities. A fossilized nematode egg was detected in 240 million-year-old fossil dung, showing that parasitic pinworms already infested pre-mammalian

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

s. The earliest known instance of the pinworms associated with humans is evidenced by pinworm eggs found in human

coprolites A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name i ...

carbon dated to 7837 BC found in western

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

Notes

References

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External links

Enterobius vermicularis image library at DPD
{{Taxonbar, from=Q213912 Oxyuridomorpha Parasitic nematodes of humans Parasitic nematodes of mammals Parasites of equines Parasites of primates Colorectal surgery