Editing Ascaris lumbricoides

{{Short description|One of several species of Ascaris}}
{{About|the organism|the disease|Ascariasis}}
{{Use dmy dates|date=September 2018}}
{{Speciesbox
| image = Ascaris_lumbricoides.jpeg
| image_caption = An adult female ''Ascaris'' worm
| taxon = Ascaris lumbricoides
| authority = [[Carl Linnaeus|Linnaeus]], [[10th edition of Systema Naturae|1758]]
}}

'''''Ascaris lumbricoides''''' is a large [[parasitic worm|parasitic]] [[Nematoda|roundworm]] of the genus ''[[Ascaris]].'' It is the most common parasitic worm in humans.<ref name="titleeMedicine - Ascaris Lumbricoides: Article by Aaron Laskey">{{cite web|url=http://www.emedicine.com/EMERG/topic840.htm|title=eMedicine - Ascaris Lumbricoides: Article by Aaron Laskey|access-date=2008-02-03|archive-url=https://web.archive.org/web/20080127165320/http://www.emedicine.com/EMERG/topic840.htm|archive-date= 27 January 2008}}</ref> An estimated 807 million–1.2 billion people are infected with ''Ascaris lumbricoides'' worldwide.<ref name=CDC>{{cite web|url=https://www.cdc.gov/parasites/ascariasis/|access-date=14 February 2024|title=Parasites - Ascariasis|date=13 June 2023 |publisher=U.S. Centers for Disease Control and Prevention}}</ref> People living in [[tropics|tropical]] and [[subtropics|subtropical]] countries are at greater risk of infection. Infection by ''Ascaris lumbricoides'' is known as [[ascariasis]].<ref name=CDCEpi>{{cite web|url=https://www.cdc.gov/parasites/ascariasis/epi.html|access-date=3 March 2016|title=Ascariasis, Epidemiology & Risk Factors|publisher=U.S. Centers for Disease Control and Prevention}}</ref>

It has been proposed that ''Ascaris lumbricoides'' and ''[[Ascaris suum]]'' (pig roundworm) are the same species.<ref>{{cite journal|last1=Leles|first1=Daniela|last2=Gardner|first2=Scott L.|last3=Reinhard|first3=Karl|last4=Iñiguez|first4=Alena|last5=Araujo|first5=Adauto|date=20 February 2012|title=Are Ascaris lumbricoides and Ascaris suum a single species?|journal=Parasites & Vectors|volume=5|pages=42|doi=10.1186/1756-3305-5-42|pmid=22348306|pmc=3293767|issn=1756-3305|doi-access=free}}</ref>

==Life cycle==
[[File:Ascaris lumbricoides life cycle.tif|thumb|Image showing life cycle inside and outside of the human body of one fairly well described helminth: ''A. lumbricoides'']]
''Ascaris lumbricoides'', a roundworm, infects humans via the fecal-oral route. Eggs released by adult females are shed in feces. Unfertilized eggs are often observed in fecal samples but never become infective. Fertilized eggs embryonate and become infectious after 18 days to several weeks in soil, depending on the environmental conditions (optimum: moist, warm, shaded soil).<ref name=CDC2018>Parasites - Ascariasis. (14 February 2018). Retrieved from https://www.cdc.gov/parasites/ascariasis/biology.html</ref>

Infection occurs when a human swallows water or food contaminated with embryonated eggs. In the [[duodenum]], a single rhabditiform larva hatches from each of the ingested eggs. The larvae then penetrate the [[mucous membrane|mucosa]] and [[submucosa]] and enter the [[venule]]s or [[lymphatic vessel]]s. From there, the larvae then pass through the heart to enter the [[pulmonary circulation]]. The larvae then break through the walls of the pulmonary [[capillary|capillaries]] to enter the [[pulmonary alveolus|alveoli]].<ref name="Murray">Murray, Patrick R.; Rosenthal, Ken S.; Pfaller, Michael A. ''Medical Microbiology'', Fifth Edition. United States: Elsevier Mosby, 2005{{page needed|date=August 2015}}</ref><ref name=Read1995>{{cite journal |last1=Read |first1=A. F. |last2=Sharping |first2=A. |title=The evolution of tissue migration by parasitic nematode larvae |journal=Parasitology |volume=111 |issue=3 |pages=359–71 |year=1995 |pmid=7567104 |doi=10.1017/S0031182000081919 |s2cid=30723471 }}</ref> The juvenile worms then migrate from the alveoli, through the [[bronchiole]]s and [[bronchus|bronchi]], and into the [[trachea]]. An acute [[Inflammation|inflammatory reaction]] can occur if some of the worms get lost during this migration process and accumulate in other organs of the body.<ref name=Read1995/>

Once in the trachea, the worms are coughed up into the [[pharynx]] and then swallowed again, after which they pass through the stomach and into the [[small intestine]], where they mature into adult worms.<ref name=CDC2018/><ref name=Read1995/> The adult worms begin producing [[Fertilisation|fertilized]] eggs within 60–65 days of being swallowed;<ref name=Read1995/> females produce as many as 200,000 eggs per day for 12–18 months. These fertilized eggs become infectious after two weeks in soil; they can persist in soil for 10 years or more.<ref name="Murray"/>

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 mimics an intermediate host, which would be required for juveniles 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.<ref name=Read1995/> The eggs have a [[lipid]] layer which makes them resistant to the effects of [[acid]]s and [[alkali]]s, as well as other chemicals.<ref>{{cite book|last=Piper|first=R|year=2007|title=Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals|publisher=Greenwood Press|isbn=978-0313339226}}{{page needed|date=August 2015}}</ref>

==Morphology and anatomy==
[[File:Ascaris lumbricoides4.jpg|right|thumb|Fertile egg as can be seen in a microscope]]
[[File:Ascaris lumbricoides.jpg|right|thumb|Fertile egg in human faeces (detail)]]
[[File:Ascaris lumbricoides non-fertile egg.jpg|right|thumb|Infertile egg]]
''Ascaris lumbricoides'' is characterized by its great size. Males are {{Convert|2|–|4|mm|in|abbr=on|sigfig=1}} in diameter and {{Convert|15|–|31|cm|in|abbr=on|sigfig=2}} long. The male's posterior end is curved ventrally and has a bluntly pointed tail. Females are {{Convert|3|–|6|mm|in|abbr=on|sigfig=1}} wide and {{Convert|20|–|49|cm|in|abbr=on|sigfig=2}} long. The [[vulva (disambiguation)|vulva]] is located in the anterior end and accounts for about one-third of its body length. [[uterus|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 {{Convert|45|–|75|μm|in|abbr=on}} long and {{Convert|35|–|50|μm|in|abbr=on}} wide with a thick outer shell. Unfertilized eggs measure {{Convert|88|–|94|μm|in|abbr=on}} long and {{Convert|44|μm|in|abbr=on}} wide.<ref name="Roberts">Roberts, Larry S.; Janovy, John Jr. ''Foundations of Parasitology'', Eighth Edition. United States: McGraw-Hill, 2009{{page needed|date=August 2015}}</ref>

Anatomically, the digestive tract is complete with prominent muscular [[pharynx]]. [[Respiration (physiology)|Respiration]] is by simple diffusion across body wall. The nervous system consists of a [[nerve ring]] and many longitudinal nerve cords. They are dioecious and have separate reproductive systems consisting of thread like gonads and genital ducts that open outside by apertures. Fertilization is internal and [[Embryo|development]] is mostly indirect. [[Sexual dimorphism]] is well marked. Externally, males are much shorter than females and males also have a curved posterior end, unlike females. Internally, in males, all the digestive, reproductive systems open in a common chamber- cloaca whereas in females, there is a separate anus for digestive tract and female genital pore for female reproductive system.{{fact|date=March 2025}}

==Epidemiology==
An estimated 807 million–1.2 billion people are infected with ''A. lumbricoides'' worldwide.<ref name=CDC/> While infection occurs throughout most of the world, ascariasis is most common in sub-Saharan Africa, the Americas, China, and east Asia.<ref name=Dold2010>{{cite journal|title=''Ascaris'' and ascariasis|author1=DoldC|author2=HollandCV|journal=Microbes and Infection|volume=13|issue=7|year=2011|pages=632–637|doi=10.1016/j.micinf.2010.09.012|pmid=20934531|hdl=2262/53278 |hdl-access=free }}</ref> Although the prevalence is low in the United States, ascariasis is still endemic in the southeastern United States due to the temperature and humid climate.<ref>{{cite journal|last1=Tietze|first1=PE|last2=Tietze|first2=PH|title=The roundworm, Ascaris lumbricoides|journal=Prim Care |year=1991 |volume=18 |issue=1 |pages=25–41 |doi=10.1016/S0095-4543(21)00914-3 |pmid=2011640 }}</ref>

''A. lumbricoides'' eggs are extremely resistant to strong chemicals, [[desiccation]], and low temperatures. The eggs can remain viable in soil for months or even years.<ref name="Roberts"/> Eggs of ''A. lumbricoides'' have been identified in [[coprolite]]s in the Americas, Europe, Africa, the Middle East, and New Zealand, the oldest ones being more than 24,000 years old.<ref>{{cite book|author=Dridelle R|title=Parasites. Tales of Humanity's Mostly Unwelcome Guests|publisher=Univ. of California, 2010|page=26|isbn=978-0-520-25938-6|year=2010 }}</ref>

==Infections==
{{Main|Ascariasis}}
Infections with these parasites are more common where sanitation is poor,<ref name="titleDPDx - Ascariasis">{{cite web |url=http://www.dpd.cdc.gov/dpdx/html/Ascariasis.htm |title=DPDx - Ascariasis |access-date=2008-02-03 |archive-url=https://web.archive.org/web/20080224051907/http://www.dpd.cdc.gov/DPDx/HTML/Ascariasis.htm |archive-date=24 February 2008 |url-status=dead }}</ref> and raw human feces are used as [[nightsoil|fertilizer]].<ref>{{cite journal|last1=Dongjian|first1=Yang|last2=Ya|first2=Yang|last3=Yingjian|first3=Wang|last4=Yu|first4=Yang|last5=Shurong|first5=Dong|last6=Yue|first6=Chen|last7=Qingwu|first7=Jian|last8=Yibiao|first8=Zhou|title=Prevalence and Risk Factors of Ascaris lumbricoides, Trichuris trichiura and Cryptosporidium Infections in Elementary School Children in Southwestern China: A School-Based Cross-Sectional Study |journal=Int J Environ Res Public Health |date=22 August 2018|volume=15|issue=9|page=1809|doi=10.3390/ijerph15091809|pmid=30135364 |pmc=6165538 |doi-access=free }}</ref>

===Symptoms===
Often, no symptoms are presented with a minor ''A. lumbricoides'' infection, the inevitable consequence being the e.g. once a year passage of such clearly visible worm(s) on close inspection. In the case of bad infections symptoms commonly include bloody sputum, cough, fever, abdominal discomfort, intestinal ulcer(s), as well as a less commonly missed passing of the quite long worms.<ref>{{MedlinePlusEncyclopedia|000628|Ascariasis}}</ref><ref>{{Cite web|url=http://www.stanford.edu/group/parasites/ParaSites2005/Ascaris/JLora_ParaSite.htm#Symptoms|title=INTRODUCTION — Ascaris lumbricoides, an intestinal roundworm, is one of the most common helminthic human infections worldwide|access-date=7 May 2012|archive-date=4 November 2012|archive-url=https://web.archive.org/web/20121104151720/http://www.stanford.edu/group/parasites/ParaSites2005/Ascaris/JLora_ParaSite.htm#Symptoms|url-status=dead}}</ref> Ascariasis is the most common cause of [[Löffler's syndrome]] worldwide. Accompanying pathological symptoms include pulmonary infiltration, eosinophilia (symptoms of the overabundance of [[eosinophil]]s in the blood such as asthma and allergic reactions), and a diagnostic symptom is, aside from standard microscopy of stools, radiographic opacities.<ref>{{cite journal |last1=Löffler |first1=W |title=Transient Lung Infiltrations with Blood Eosinophilia|journal=International Archives of Allergy and Applied Immunology |volume=8 |issue=1–2|pages=54–9 |year=1956 |pmid=13331628 |doi=10.1159/000228268 }}</ref> One study has observed increases in fertility in infected women, in a similar vein to good diet and exercise, but with all of the pathological negatives and discomforts the disease carries with it, varying from host to host and again with diet.<ref>{{cite journal|doi=10.1126/science.aac7902|title=Helminth infection, fecundity, and age of first pregnancy in women|journal=Science|volume=350|issue=6263|pages=970–2|year=2015|last1=Blackwell|first1=A. D.|last2=Tamayo|first2=M. A.|last3=Beheim|first3=B.|last4=Trumble|first4=B. C.|last5=Stieglitz|first5=J.|last6=Hooper|first6=P. L.|last7=Martin|first7=M.|last8=Kaplan|first8=H.|last9=Gurven|first9=M.|pmid=26586763|pmc=5953513}}</ref>

===Distribution===
''Ascaris lumbricoides'' is primarily distributed in tropical and subtropical regions around the world, particularly in areas with poor sanitation and hygiene practices. It is most prevalent in sub-Saharan Africa, Southeast Asia (including countries like India, Bangladesh, and Indonesia), and parts of Latin America, where inadequate sanitation infrastructure and the use of human faeces as fertilizer contribute to its spread.<ref>{{cite journal | url=https://pubmed.ncbi.nlm.nih.gov/10696405/ | pmid=10696405 | date=1999 | last1=Hall | first1=A. | last2=Anwar | first2=K. S. | last3=Tomkins | first3=A. | last4=Rahman | first4=L. | title=The distribution of Ascaris lumbricoides in human hosts: A study of 1765 people in Bangladesh | journal=Transactions of the Royal Society of Tropical Medicine and Hygiene | volume=93 | issue=5 | pages=503–510 | doi=10.1016/s0035-9203(99)90351-6 }}</ref>

===Prevention===
Preventing any [[fecal-oral route|fecal-borne disease]] requires educated hygienic habits/culture and effective fecal treatment systems. This is particularly important with ''A. lumbricoides'' because its eggs are one of the most difficult pathogens to kill (second only to [[prion]]s), and the eggs commonly survive 1–3 years. ''A. lumbricoides'' 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 does not readily kill ''A. lumbricoides'' eggs, but it will remove their sticky film, to allow the eggs to be rinsed away. ''A. lumbricoides'' eggs can be reduced by hot composting methods, but to completely kill them may require [[rubbing alcohol]], [[iodine]], specialized chemicals, cooking heat, or "unusually" hot [[composting]] (for example, over {{Convert|50|C|F}} for 24 hours).<ref>{{Cite book|isbn=978-0-9644258-3-5|chapter-url=http://weblife.org/humanure/chapter7_18.html|year=1999|title=The Humanure Handbook - A Guide to Composting Human Manure|edition= 2nd |chapter=Worms and Disease; Roundworms|first=Joseph|last=Jenkins|publisher=Joseph Jenkins, Incorporated }}</ref>

===Treatment===
{{Further|Ascariasis#Treatment}}
Control of roundworm infections is based on treatment with medication, improved sanitation and health education.<ref>{{cite web | url=https://patient.info/digestive-health/roundworms-leaflet |title=Roundworms: Symptoms and Treatment | date=10 February 2023 }}</ref> This usually takes around three days.<ref>{{cite web | url=https://my.clevelandclinic.org/health/diseases/15240-roundworms | title=Roundworms: Parasitic Infection, Pinworm Symptoms, Treatment }}</ref>

==History==
Giant intestinal roundworms have been known since antiquity. In 1758 [[Linnaeus]] named them ''Ascaris lumbricoides''. For many centuries, they were thought to arise by spontaneous generation. In 1855, ''Ascaris'' eggs were found in human faeces by [[Henry Ransom]] in England then this was described in the literature two years later by [[Casimir-Joseph Davaine]] in France.<ref>{{cite journal|last1=Grove|first1=David I|year=1986 |title=Who discovered that intestinal worm infections could be diagnosed by finding eggs in the faeces? |journal=Journal of the Royal Society of Medicine |volume=79|issue=11|pages=670–673|doi=10.1177/014107688607901118|pmc=1290536 |pmid=3540299 }}</ref> Attempts to infect animals by feeding them eggs were unsuccessful. In 1886, [[Salvatore Calandruccio]] in Italy successfully infected a boy to whom he had given 150 eggs. [[Battista Grassi]] published this information without giving any acknowledgement to Calandruccio.<ref>{{cite book |last=Grove |first=David I |date=2014 |title=Tapeworms, lice and prions: a compendium of unpleasant infections |location=Oxford |publisher=Oxford University Press |pages=1–602|isbn=978-0-19-964102-4 }}</ref> Development was thought to occur directly within the bowel lumen but [[Francis Stewart]] in Hong Kong in 1916 fed eggs to rats, then later mice, and found infective larvae in the faeces and in the lungs but no mature worms. In 1918, [[Sadao Yoshida]] ingested larvae recovered from the trachea of a guinea pig, then found eggs in his own stools 76 days later. In 1922, [[Shimesu Koino]] ingested 2,000 ''Ascaris lumbricoides'' eggs, found larvae in his sputum a few days later, then after 50 days took an [[anthelmintic]] and recovered 667 immature ''Ascaris lumbricoides'', thus confirming the life cycle.<ref>{{cite book |last=Grove |first=David I |date=1990 |title=A history of human helminthology|location=Wallingford |publisher=CAB International |pages=1–848 |isbn=0-85198-689-7 }}</ref>

==References==
{{Reflist}}

==External links==
* [https://web.archive.org/web/20120915095302/http://daveproject.org/duodenum-ascaris-lumbricoides/2004-05-10/ ''Ascaris lumbricoides'' Video - DAVE Project]
* [https://web.archive.org/web/20140811073350/http://ascarislumbricoides.org/ ''Ascaris lumbricoides'' Poll - Research]
* [https://web.archive.org/web/20131204001330/http://dpd.cdc.gov/dpdx/HTML/ImageLibrary/Ascariasis_il.htm Ascaris lumbricoides image library]

{{Helminthiases}}
{{Taxonbar|from=Q468771}}
{{Authority control}}

[[Category:Ascaridomorpha]]
[[Category:Parasitic nematodes of humans]]
[[Category:Nematodes described in 1758]]
[[Category:Taxa named by Carl Linnaeus]]