''Ascaris suum'', also known as the large roundworm of pig, is a

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

that causes

ascariasis Ascariasis is a disease caused by the parasitic roundworm ''Ascaris lumbricoides''. Infections have no symptoms in more than 85% of cases, especially if the number of worms is small. Symptoms increase with the number of worms present and may in ...

pig The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus ...

s. While roundworms in pigs and humans are today considered as two species (''A. suum'' and '' A. lumbricoides'') with different hosts, cross-infection between humans and pigs is possible; some researchers have thus argued they are the same species. Ascariasis is associated with contact to pigs and pig manure in

Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Danish Realm, Kingdom of Denmark ...

. ''A. suum'' is distributed worldwide and grows up to in length. ''Ascaris'' infections are treated with

ascaricide Ascaricides are drugs to treat ascariasis that is caused by infections with parasitic nematodes (''roundworms'') of the genus ''Ascaris'' (''giant intestinal roundworms''). The large roundworm of pigs (''Ascaris suum'') typically infects pigs whil ...

s. ''A. suum'' is in the family

Ascarididae The Ascarididae are a family of the large intestinal nematoda, roundworms. Members of the family are intestinal parasites, infecting all class (biology), classes of vertebrates. It includes a number of genus, genera,Anderson RC (2000)''Nematode Pa ...

, and is one of the oldest associations to mankind.

Life cycle

Pigs get infected with ''A. suum'' by ingesting infectious parasite

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

s that are present in the environment. The

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e of Ascaris complete two moults within the egg; therefore, the larvae emerging from the egg is not a second-stage larva (L2) as was previously presumed, but rather a third stage larva (L3) covered by a loosened L2

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

. The larvae hatch from the egg inside the pig's

intestines 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 GI tract contains all the major organs of the digestive system, in humans ...

and subsequently start their migration through the body. First, they penetrate the intestinal wall at

caecum The cecum or caecum 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, to which it is joined). The wo ...

/ colon and use the mesenterial blood veins to migrate to the

liver The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...

. After burrowing their way through the liver tissue, they again use the efferent blood stream to carry them to the

lungs The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of th ...

. There, they get stuck in the

capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...

surrounding the lungs and they penetrate the lung

alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * ...

. It takes approximately 7 days to reach the lungs. Once the larvae are inside the lung, they migrate up the respiratory tree and are eventually

cough A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes. As a protective reflex, coughing can be repetitive with the cough reflex following three pha ...

ed up and swallowed by the host to reach the

small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...

again as soon as 10 days after infection. There, the larvae undergo their first molt inside the host to reach the L4 stage by day 14 post-infection. Around day 25 post infection, they develop into the L5 stage. Worms reach adulthood 6 weeks after infection, and when both female and male worms are present in the same host,

fertilized egg A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicellula ...

s are produced and secreted by the female worm. These eggs are then excreted together with the

faeces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

. After an incubation period, infective stage larvae develop in the eggs and are ready to cause infection in a new host.

Paratenic hosts In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' ( symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

ingest the eggs and the L3 larvae remain in the tissues of the paratenic host until a pig eats them. These may include

beetles Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

and

earthworms An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. Th ...

, as well as large to jumbo chicken eggs from at-risk

fowl Fowl are birds belonging to one of two biological orders, namely the gamefowl or landfowl (Galliformes) and the waterfowl (Anseriformes). Anatomical and molecular similarities suggest these two groups are close evolutionary relatives; together ...

Epidemiology

''Ascaris'' eggs can remain infective for years in the soil, even in a

temperate climate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...

. The migration of ''A. suum'' larvae through the lungs may cause secondary bacterial infections and result in acute respiratory symptoms in pigs.

Morphology

Males are about long, and wide. The posterior end is curved toward the

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...

side with a pointed tail. They have simple

spicules Spicules are any of various small needle-like anatomical structures occurring in organisms Spicule may also refer to: *Spicule (sponge), small skeletal elements of sea sponges *Spicule (nematode), reproductive structures found in male nematodes ( ...

that measure long. Females are larger than males, measuring long and in diameter. From the

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

end, the

vulva The vulva (plural: vulvas or vulvae; derived from Latin for wrapper or covering) consists of the external sex organ, female sex organs. The vulva includes the mons pubis (or mons veneris), labia majora, labia minora, clitoris, bulb of vestibu ...

occupies about one-third of the body length. In addition to their large size, these species also have the three prominent

lips The lips are the visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be ...

. Each lip contains a dentigerous ridge, and no interlabia or alae. Females can lay up to 200,000 eggs per day, and their

uteri The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uteru ...

can contain up to 27 million eggs at a time. Fertilized eggs are ovoid, ranging from 45 to 75 µm length and 35 to 50 µm in diameter. The uterine wall contributes to the lumpy and thick outer layer of the egg. The mammillated layer is stained golden-brown by the host's

bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bile ...

when the eggs are passed in faeces. Females can also deposit unfertilized eggs that are narrower and longer than normal fertilized eggs, ranging from 88 to 94 µm in length, and 44 µm diameter. Only the proteinaceous layer can be seen in unfertilized eggs, because after fertilization, the

vitelline Vitelline may refer to: Embryology * Vitelline arteries, arteries that bring blood to the yolk sac * Vitelline circulation, the system of blood flowing between an embryo and its yolk sac * Vitelline cyst, a developmental defect relating to the c ...

chitinous Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...

, and lipid layers form.

Incidents and outbreaks

In Canada in 1970, a postgraduate student tainted his roommates' food with ''A. suum''. Four of the victims became seriously ill; two of these suffered acute respiratory failure.

Genetics

A 273-megabase draft genome for ''A. suum'' was published in 2011.

References

* {{Taxonbar, from=Q2062253 Ascaridida Parasitic nematodes of mammals Swine diseases Veterinary helminthology Nematodes described in 1782 Taxa named by Johann August Ephraim Goeze