''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 ha ...
nematode worms known as the "small intestinal roundworms", which is a type of parasitic worm. One species, ''
Ascaris lumbricoides'', affects humans and causes the disease
ascariasis. 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 hos ...
'', 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 ...
. ''
Parascaris equorum'', 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 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, epidermis and musculature. There is a
pseudocoelom.
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 cellul ...
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,
chymotrypsin/
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 di ...
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 (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 and in the intestines of
mummified humans.
''A. lumbricoides'' was originally called ''Lumbricus teres'' and was first described in detail by
Edward Tyson 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 Nobility#Ennoblement, ennoblement in 1761 as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalise ...
in 1758.
The morphologically similar ''Ascaris suum'' was described from pigs by
Johann August Ephraim Goeze 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×
See also
*
List of parasites (human)
References
{{Taxonbar, from=Q310838
Ascaridida
Nematode genera
Taxa named by Carl Linnaeus