Ascaris lumbricoides
Encyclopedia
Ascaris lumbricoides is the giant roundworm of humans, belonging to the phylum
Nematoda. An ascarid nematode
, it is responsible for the disease ascariasis
in humans, and it is the largest and most common parasitic worm
in humans. One-sixth of the human population is estimated to be infected by this parasite. Ascariasis
is prevalent worldwide and more so in tropical and subtropical countries.
It can reach a length of up to 35 cm.
that penetrates the wall of the duodenum
and enters the blood stream. From here, it is carried to the liver
and heart
, and enters pulmonary circulation
to break free in the alveoli
, where it grows and molts. In 3 weeks, the larva
e pass from the respiratory system
to be coughed up, swallowed, and thus returned to the small intestine
, where they mature to adult male and female worms. Fertilization can now occur and the female produces as many as 200,000 eggs per day for a year. These fertilized eggs become infectious after 2 weeks in soil; they can persist in soil for 10 years or more.
The eggs have a lipid
layer, that makes them resistant to the effects of acid
s and alkali
s as well as other chemicals. This resilience helps to explain why this nematode
is such a ubiquitous parasite.
Ascaris lumbricoides is characterized by its great size. Males are 2–4 mm in diameter and 15–31 cm long. The males' posterior end is curved ventrally and has a bluntly pointed tail. Females are 3–6 mm wide and 20–49 cm long. The vulva
is located in the anterior end and accounts for about a third of its body length. Uteri
may contain up to 27 million eggs at a time with 200,000 being laid per day. Fertilized eggs are oval to round in shape and are 45-75 micrometer
s long and 35-50 micrometer
s wide with a thick outer shell. Unfertilized eggs measure 88-94 micrometer
s long and 44 micrometer
s wide.
, and low temperatures. The eggs can remain viable in the soil for several months or even years.
Eggs of A. lumbricoides have been identified in archeological coprolite
s in the Americas, Europe, Africa, the Middle East, and New Zealand, the oldest ones being more than 24,000 years old.
are used as fertilizer.
requires educated hygienic habits/culture and fecal treatment systems once a year. This is particularly important with ascaris
because its eggs are usually the most difficult pathogen to kill (besides prion
s), and the eggs commonly survive 1-3 years. Ascaris lives in the intestine
where it lays eggs. Infection occurs when the eggs, too small to be seen by the unaided eye, are eaten. The eggs may get onto vegetables when improperly processed human feces
of infected people, are used as fertilizer
for food crops. Infection may occur when food is handled without removing or killing the eggs on the hands, clothes, hair, raw vegetables/fruit, or cooked food that is (re)infected by handlers, containers, etc. Bleach will not (necessarily) kill Ascaris eggs but it will remove their sticky film, to allow the eggs to be rinsed away. Ascaris eggs can be reduced by most composting, but to completely kill them may require rubbing alcohol
, iodine
, specialized chemicals, cooking
heat, or "unusually" hot composting (for example, over 120 degrees Fahrenheit for 24 hours http://weblife.org/humanure/chapter8_7.html).
s. The juvenile
s hatch in the duodenum
(1st section of small intestine). They then penetrate the mucosa and submucosa
and enter venule
s or lymphatics. Next they pass through the right heart
and into pulmonary circulation
. They then break out of the capillaries and enter the air spaces. Acute tissue reaction occurs when several worms
get lost during this migration and accumulate in other organs of the body. The juveniles migrate from the lung up the respiratory tract
to the pharynx
where they are swallowed. They begin producing eggs within 60–65 days of being swallowed. These are produced within the small intestine
where the juvenile
s mature. It might seem odd that the worms
end up in the same place where they began. One hypothesis
to account for this behavior is that the migration mimic
s an intermediate host, which would be required for juvenile
s of an ancestral form to develop to the third stage. Another possibility is that tissue migration enables faster growth and larger size, which increases reproductive capacity.
are made by identifying the appearance of the worm
or eggs in feces
. Due to the large quantity of eggs laid, physicians can diagnose using only one or two fecal smears.
Infections can be treated with drugs called ascaricide
s. The treatment of choice is Mebendazole
. The drug functions by binding to tubulin
in the worms' intestinal cells and body-wall muscles. Nitazoxanide
and ivermectin can also be used.
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
Nematoda. An ascarid nematode
Ascaridida
The order Ascaridida includes several families of parasitic roundworms with three "lips" on the anterior end. They were formerly placed in the subclass Rhabditia by some, but morphological and DNA sequence data rather unequivocally assigns them to the Spiruria...
, it is responsible for the disease ascariasis
Ascariasis
Ascariasis is a human disease caused by the parasitic roundworm Ascaris lumbricoides. Perhaps as many as one quarter of the world's people are infected, with rates of 45% in Latin America and 95% in parts of Africa. Ascariasis is particularly prevalent in tropical regions and in areas of poor...
in humans, and it is the largest and most common parasitic worm
Parasitic worm
Parasitic worms or helminths are a division of eukaryoticparasites that, unlike external parasites such as lice and fleas, live inside their host. They are worm-like organisms that live and feed off living hosts, receiving nourishment and protection while disrupting their hosts' nutrient...
in humans. One-sixth of the human population is estimated to be infected by this parasite. Ascariasis
Ascariasis
Ascariasis is a human disease caused by the parasitic roundworm Ascaris lumbricoides. Perhaps as many as one quarter of the world's people are infected, with rates of 45% in Latin America and 95% in parts of Africa. Ascariasis is particularly prevalent in tropical regions and in areas of poor...
is prevalent worldwide and more so in tropical and subtropical countries.
It can reach a length of up to 35 cm.
Life cycle
Ascaris lumbricoides, or "roundworm", infections in humans occur when an ingested infective egg releases a larval wormLarva
A larva 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...
that penetrates the wall of the duodenum
Duodenum
The duodenum is the first 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 anterior intestine or proximal intestine may be used instead of duodenum...
and enters the blood stream. From here, it is carried to the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
and heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
, and enters pulmonary circulation
Pulmonary circulation
Pulmonary circulation is the half portion of the cardiovascular system which carries Oxygen-depleted Blood away from the heart, to the Lungs, and returns oxygenated blood back to the heart. Encyclopedic description and discovery of the pulmonary circulation is widely attributed to Doctor Ibn...
to break free in the alveoli
Pulmonary alveolus
An alveolus is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well...
, where it grows and molts. In 3 weeks, the larva
Larva
A larva 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...
e pass from the respiratory system
Respiratory system
The respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles...
to be coughed up, swallowed, and thus returned to the small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
, where they mature to adult male and female worms. Fertilization can now occur and the female produces as many as 200,000 eggs per day for a year. These fertilized eggs become infectious after 2 weeks in soil; they can persist in soil for 10 years or more.
The eggs have a lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
layer, that makes them resistant to the effects of acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
s and alkali
Alkali
In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
s as well as other chemicals. This resilience helps to explain why this nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
is such a ubiquitous parasite.
Morphology
Vulva
The vulva consists of the external genital organs of the female mammal. This article deals with the vulva of the human being, although the structures are similar for other mammals....
is located in the anterior end and accounts for about a third of its body length. Uteri
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
may contain up to 27 million eggs at a time with 200,000 being laid per day. Fertilized eggs are oval to round in shape and are 45-75 micrometer
Micrometer
A micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
s long and 35-50 micrometer
Micrometer
A micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
s wide with a thick outer shell. Unfertilized eggs measure 88-94 micrometer
Micrometer
A micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
s long and 44 micrometer
Micrometer
A micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
s wide.
Epidemiology
More than 1 billion people are affected by this infection. In the United States there is a reported prevalence of 0.8% of the total population as of 1987. Ascaris lumbricoides eggs are extremely resistant to strong chemicals, desiccationDesiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
, and low temperatures. The eggs can remain viable in the soil for several months or even years.
Eggs of A. lumbricoides have been identified in archeological coprolite
Coprolite
A coprolite is fossilized animal dung. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour rather than morphology. The name is derived from the Greek words κοπρος / kopros meaning 'dung' and λιθος / lithos meaning 'stone'. They...
s in the Americas, Europe, Africa, the Middle East, and New Zealand, the oldest ones being more than 24,000 years old.
Infections
Infections with these parasites are more common where sanitation is poor and raw human fecesHuman feces
Human feces , also known as a stool, is the waste product of the human digestive system including bacteria. It varies significantly in appearance, according to the state of the digestive system, diet and general health....
are used as fertilizer.
Prevention
Preventing any fecal-borne diseaseFecal-oral route
The fecal-oral route, or alternatively, the oral-fecal route or orofecal route is a route of transmission of diseases, in which they are passed when pathogens in fecal particles from one host are introduced into the oral cavity of another potential host.There are usually intermediate steps,...
requires educated hygienic habits/culture and fecal treatment systems once a year. This is particularly important with ascaris
Ascaris
Ascaris is a genus of parasitic nematode worms known as the "giant intestinal roundworms". One species, A. suum, typically infects pigs, while another, A. lumbricoides, affects human populations, typically in sub-tropical and tropical areas with poor sanitation. A...
because its eggs are usually the most difficult pathogen to kill (besides prion
Prion
A prion is an infectious agent composed of protein in a misfolded form. This is in contrast to all other known infectious agents which must contain nucleic acids . The word prion, coined in 1982 by Stanley B. Prusiner, is a portmanteau derived from the words protein and infection...
s), and the eggs commonly survive 1-3 years. Ascaris lives in the intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
where it lays eggs. Infection occurs when the eggs, too small to be seen by the unaided eye, are eaten. The eggs may get onto vegetables when improperly processed human feces
Human feces
Human feces , also known as a stool, is the waste product of the human digestive system including bacteria. It varies significantly in appearance, according to the state of the digestive system, diet and general health....
of infected people, are used as fertilizer
Fertilizer
Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
for food crops. Infection may occur when food is handled without removing or killing the eggs on the hands, clothes, hair, raw vegetables/fruit, or cooked food that is (re)infected by handlers, containers, etc. Bleach will not (necessarily) kill Ascaris eggs but it will remove their sticky film, to allow the eggs to be rinsed away. Ascaris eggs can be reduced by most composting, but to completely kill them may require rubbing alcohol
Rubbing alcohol
Rubbing alcohol, USP / B.P. is a liquid prepared and used primarily for topical application. It is prepared from a special denatured alcohol solution and contains 97.5-100% by volume of pure, concentrated ethanol or isopropyl alcohol...
, iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
, specialized chemicals, cooking
Cooking
Cooking is the process of preparing food by use of heat. Cooking techniques and ingredients vary widely across the world, reflecting unique environmental, economic, and cultural traditions. Cooks themselves also vary widely in skill and training...
heat, or "unusually" hot composting (for example, over 120 degrees Fahrenheit for 24 hours http://weblife.org/humanure/chapter8_7.html).
Details of infection process
Infections happen when a human swallows water or food contaminated with unhatched juvenileJuvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
s. The juvenile
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
s hatch in the duodenum
Duodenum
The duodenum is the first 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 anterior intestine or proximal intestine may be used instead of duodenum...
(1st section of small intestine). They then penetrate the mucosa and submucosa
Submucosa
In the gastrointestinal tract, the submucosa is the layer of dense irregular connective tissue or loose connective tissue that supports the mucosa, as well as joins the mucosa to the bulk of underlying smooth muscle .-Contents:Blood vessels, lymphatic vessels, and nerves will run through...
and enter venule
Venule
A venule is a very small blood vessel in the microcirculation that allows deoxygenated blood to return from the capillary beds to the larger blood vessels called veins. Venules range from 8 to 100μm in diameter and are formed when capillaries unite .Venules are blood vessels that drain blood...
s or lymphatics. Next they pass through the right heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
and into pulmonary circulation
Pulmonary circulation
Pulmonary circulation is the half portion of the cardiovascular system which carries Oxygen-depleted Blood away from the heart, to the Lungs, and returns oxygenated blood back to the heart. Encyclopedic description and discovery of the pulmonary circulation is widely attributed to Doctor Ibn...
. They then break out of the capillaries and enter the air spaces. Acute tissue reaction occurs when several worms
Worm
The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...
get lost during this migration and accumulate in other organs of the body. The juveniles migrate from the lung up the respiratory tract
Respiratory system
The respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles...
to the pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
where they are swallowed. They begin producing eggs within 60–65 days of being swallowed. These are produced within the small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
where the juvenile
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
s mature. It might seem odd that the worms
Worm
The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...
end up in the same place where they began. One hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
to account for this behavior is that the migration mimic
Mimic
In evolutionary biology, mimicry is the similarity of one species to another which protects one or both. This similarity can be in appearance, behaviour, sound, scent and even location, with the mimics found in similar places to their models....
s an intermediate host, which would be required for juvenile
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
s of an ancestral form to develop to the third stage. Another possibility is that tissue migration enables faster growth and larger size, which increases reproductive capacity.
Diagnosis and treatment
Most diagnosesDiagnosis
Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...
are made by identifying the appearance of the worm
Worm
The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...
or eggs in feces
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
. Due to the large quantity of eggs laid, physicians can diagnose using only one or two fecal smears.
Infections can be treated with drugs called ascaricide
Ascaricide
Ascaricides are drugs to treat ascariasis that is caused by infections with parasitic nematodes of the genus Ascaris...
s. The treatment of choice is Mebendazole
Mebendazole
Mebendazole or MBZ is a benzimidazole drug developed by Janssen Pharmaceutica and marketed as Vermox, Ovex, Antiox, and Pripsen...
. The drug functions by binding to tubulin
Tubulin
Tubulin is one of several members of a small family of globular proteins. The most common members of the tubulin family are α-tubulin and β-tubulin, the proteins that make up microtubules. Each has a molecular weight of approximately 55 kiloDaltons. Microtubules are assembled from dimers of α- and...
in the worms' intestinal cells and body-wall muscles. Nitazoxanide
Nitazoxanide
Nitazoxanide, also known by the brand names Alinia and Annita is a synthetic nitrothiazolyl-salicylamide derivative and an antiprotozoal agent.Nitazoxanide is a light yellow...
and ivermectin can also be used.