''Ascaris'' is a genus of

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 ...

worms known as the "small intestinal roundworms", which is a type of parasitic worm. One species, ''

Ascaris lumbricoides ''Ascaris lumbricoides'' is a large parasitic worm that causes ascariasis in humans. A Nematoda, roundworm of genus ''Ascaris'', it is the most common parasitic worm in humans. An estimated one-sixth of the human population is at some point infe ...

'', affects humans and causes the disease

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 ...

. Another species, ''

Ascaris suum ''Ascaris suum'', also known as the large roundworm of pig, is a parasitic nematode that causes ascariasis in pigs. While roundworms in pigs and humans are today considered as two species (''A. suum'' and '' A. lumbricoides'') with different host ...

'', typically infects

pigs 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 ...

. ''

Parascaris equorum ''Parascaris equorum'' is a species of ascarid that is the equine roundworm. Amongst horse owners, the parasites are colloquially called "Ascarids". This is a host-specific helminth intestinal parasite that can infect horses, donkeys, and zeb ...

'', the equine roundworm, is also commonly called an "ascarid". Their eggs are deposited in feces and soil. Plants with the eggs on them infect any organism that consumes them. ''A. lumbricoides'' is the largest intestinal roundworm and is the most common

helminth Parasitic worms, also known as helminths, are 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 parasitic worms such as schi ...

infection of humans worldwide. Infestation can cause morbidity by compromising nutritional status, affecting cognitive processes, inducing tissue reactions such as granuloma to larval stages, and by causing intestinal obstruction, which can be fatal.

Morphology

* Adult: cylindrical shape, creamy white or pinkish in color * Male: average 15–30 cm (6–12 inches); more slender than the female * Female: average 20–35 cm (8–14 inches) The body is long, cylindrical, and fusiform (pointed at both the ends). The body wall is composed of

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 ...

, epidermis and musculature. There is a

pseudocoelom A body cavity is any space or compartment, or potential space, in an animal body. Cavities accommodate organs and other structures; cavities as potential spaces contain fluid. The two largest human body cavities are the ventral body cavity, and ...

Respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellula ...

is by simple diffusion. The nervous system consists of a

nerve ring A circumesophageal or circumpharyngeal nerve ring is an arrangement of nerve ganglia around the esophagus/ pharynx of an animal. It is a common feature of nematodes, molluscs, and many other invertebrate animals, though it is absent in all vertebra ...

and many longitudinal nerve cords. Reproduction is exclusively sexual, and males are usually shorter than females.

Defense mechanism

As part of the parasite defense strategy, ''Ascaris'' roundworms secrete a series of inhibitors to target digestive and immune-related host

proteases A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...

, which include

pepsin Pepsin is an endopeptidase that breaks down proteins into smaller peptides. It is produced in the gastric chief cells of the stomach lining and is one of the main digestive enzymes in the digestive systems of humans and many other animals, w ...

trypsin Trypsin is an enzyme in the first section of the small intestine that starts the digestion of protein molecules by cutting these long chains of amino acids into smaller pieces. It is a serine protease from the PA clan superfamily, found in the dig ...

chymotrypsin Chymotrypsin (, chymotrypsins A and B, alpha-chymar ophth, avazyme, chymar, chymotest, enzeon, quimar, quimotrase, alpha-chymar, alpha-chymotrypsin A, alpha-chymotrypsin) is a digestive enzyme component of pancreatic juice acting in the duodenu ...

elastase In molecular biology, elastase is an enzyme from the class of ''proteases (peptidases)'' that break down proteins. In particular, it is a serine protease. Forms and classification Eight human genes exist for elastase: Some bacteria (includin ...

cathepsin Cathepsins (Ancient Greek ''kata-'' "down" and ''hepsein'' "boil"; abbreviated CTS) are proteases ( enzymes that degrade proteins) found in all animals as well as other organisms. There are approximately a dozen members of this family, which are d ...

s, and

metallocarboxypeptidase A metalloexopeptidase is a type of enzyme that acts as a metalloproteinase exopeptidase. These enzymes have a catalytic mechanism involving a metal, often zinc. They function in molecular biology as agents that cut the terminal (or penultimate) p ...

s (MCPs). ''Ascaris'' species inhibit MCPs by releasing an enzyme known as ''Ascaris''

carboxypeptidase inhibitor A carboxypeptidase ( EC number 3.4.16 - 3.4.18) is a protease enzyme that hydrolyzes (cleaves) a peptide bond at the carboxy-terminal (C-terminal) end of a protein or peptide. This is in contrast to an aminopeptidases, which cleave peptide bonds a ...

(ACI). This enzyme binds to the active site of MCP and blocks the cleavage of its own proteins by the host MCP. Similarly, they inhibit trypsin by releasing the protein Ascaris Trypsin Inhibitor
pdb 1ATA
.

History

''Ascaris'' has been present in humans for at least several thousand years, as evidenced by ''Ascaris'' eggs found in

paleofeces Paleofeces (or palaeofaeces in British English) are ancient human feces, often found as part of archaeological excavations or surveys. The term coprolite is often used interchangeably, although coprolite can also refer to fossilized animal fe ...

and in the intestines of mummified humans. ''A. lumbricoides'' was originally called ''Lumbricus teres'' and was first described in detail by

Edward Tyson Edward Tyson (20 January 1651 – 1 August 1708) was an English scientist and physician. He is commonly regarded as the founder of modern comparative anatomy, which compares the anatomy between species. Biography Tyson was born the son of Edward ...

in 1683. The genus ''Ascaris'' was originally described as the genus for ''Ascaris lumbricoides'' by

Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...

in 1758. The morphologically similar ''Ascaris suum'' was described from pigs by

Johann August Ephraim Goeze Johann August Ephraim Goeze (; 28 May 1731 – 27 June 1793) was a German zoologist, born in Aschersleben. He is known for the discovery of tardigrades, also called water bears. He was the son of Johann Heinrich and Catherine Margarete (née Kirc ...

in 1782.

Gallery

Image:Ascarisesophagus.jpg, Esophagus of an ''Ascaris'' worm Image:Ascariscs40x1.jpg, ''Ascaris'' cross section 40× Image:Ascariscs40x3.jpg, ''Ascaris'' cross section 40× Image:Ascariscs400x1.jpg, ''Ascaris'' cross section 400×

References

{{Taxonbar, from=Q310838 Ascaridida Nematode genera Taxa named by Carl Linnaeus

Morphology

Defense mechanism

History

Gallery

See also

References