Editing Toxocariasis (section)

==Signs and symptoms==
Physiological reactions to ''Toxocara'' infection depend on the host's immune response and the parasitic load.<ref name="Huh, Sun, Sooung">{{EMedicine|article|229855|Toxocariasis}}</ref> Most cases of ''Toxocara'' infection are [[asymptomatic]], especially in adults.<ref name="Huh, Sun, Sooung"/><ref name="CDC3">{{cite web | publisher = Centers for Disease Control and Prevention | work = Division of Parasitic diseases. | title = Fact Sheet: Toxocariasis. | date = November 2007 | url = https://www.cdc.gov/ncidod/dpd/parasites/toxocara/factsht_toxocara.htm |access-date=2017-09-17 |url-status=live |archive-url=https://web.archive.org/web/20110327164211/http://www.cdc.gov/ncidod/dpd/parasites/toxocara/factsht_toxocara.htm |archive-date=2011-03-27 }}</ref><ref name="CDC2">{{cite web | publisher = Centers for Disease Control and Prevention. | work = Division of Parasitic diseases | title = New CDC study results show Toxocara infection more common than previously thought. | date = 19 January 2009 | url = https://www.cdc.gov/ncidod/dpd/parasites/toxocara/Toxocara_announcement.pdf |access-date=2017-09-17 |url-status=live |archive-url=https://web.archive.org/web/20100310231042/http://www.cdc.gov/ncidod/dpd/parasites/toxocara/Toxocara_announcement.pdf |archive-date=2010-03-10 }}</ref> When symptoms do occur, they are the result of migration of second stage ''Toxocara'' larvae through the body.<ref name="Markell_2006"/>

Covert toxocariasis is the least serious of the three syndromes and is believed to be due to chronic exposure. <ref>{{cite journal | vauthors = Sariego I, Kanobana K, Rojas L, Speybroeck N, Polman K, Núñez FA | title = Toxocariasis in Cuba: a literature review | journal = PLOS Neglected Tropical Diseases | volume = 6 | issue = 2 | pages = e1382 | date = 2012-02-28 | pmid = 22389726 | pmc = 3289590 | doi = 10.1371/journal.pntd.0001382 | veditors = Carabin H }}</ref> Signs and symptoms of covert toxocariasis are coughing, fever, abdominal pain, headaches, and changes in behavior and ability to sleep.<ref name="Huh, Sun, Sooung"/><ref name="Holland_2006"/> Upon medical examination, wheezing, [[hepatomegaly]], and [[lymphadenitis]] are often noted.<ref name="Huh, Sun, Sooung"/>

High parasitic loads or repeated infection can lead to visceral larva migrans (VLM).<ref name="CDC3"/> VLM is primarily diagnosed in young children, because they are more prone to exposure and ingestion of infective eggs.<ref name="Markell_2006"/> ''Toxocara'' infection commonly resolves itself within weeks, but chronic [[eosinophilia]] may result.<ref name="Huh, Sun, Sooung"/>  In VLM, larvae migration incites inflammation of internal organs and sometimes the central nervous system.<ref name="Huh, Sun, Sooung"/><ref name="CDC3"/> Symptoms depend on the organ(s) affected.<ref name="Huh, Sun, Sooung"/> Patients can present with pallor, fatigue, weight loss, anorexia, fever, headache, skin rash, cough, asthma, chest tightness, increased irritability, abdominal pain, nausea, and vomiting.<ref name="Markell_2006"/><ref name="Huh, Sun, Sooung"/> Sometimes the subcutaneous migration tracks of the larvae can be seen.<ref name="Markell_2006"/> Patients are commonly diagnosed with [[pneumonia]], [[bronchospasms]], [[chronic pulmonary inflammation]], [[hypereosinophilia]], [[hepatomegaly]], [[hypergammaglobulinaemia]] (IgM, IgG, and IgE classes), [[leukocytosis]], and elevated anti-A and anti-B isohaemagglutinins.<ref name="Markell_2006"/><ref name="Despommier"/><ref name="CDC3"/><ref name="Holland_2006"/> Severe cases have occurred in people who are hypersensitive to allergens; in rare cases, [[epilepsy]], [[inflammation of the heart]], [[pleural effusion]], respiratory failure, and death have resulted from VLM.<ref name="Huh, Sun, Sooung"/><ref name="Holland_2006"/>

Ocular larva migrans (OLM) is rare compared with VLM.<ref name="Markell_2006"/><ref name="merckvetmanual">{{cite book | title = The Merck Veterinary Manual | chapter = Roundworm | date = January 2008 | url = http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/23505.htm | archive-url = https://web.archive.org/web/20110526143628/http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm%2Fbc%2F23505.htm | archive-date=2011-05-26 }}</ref> A light ''Toxocara'' burden is thought to induce a low immune response, allowing a larva to enter the host's eye.<ref name="Holland_2006"/> Although there have been cases of concurrent OLM and VLM, these are extremely exceptional.<ref name="Holland_2006"/> OLM often occurs in just one eye and from a single larva migrating into and encysting within the orbit.<ref name="Markell_2006"/><ref name="ocular larva migrans">{{cite book | title = Review of Optometry Online: Handbook of Ocular Disease Management. | chapter = Toxocariasis: Ocular Larva Migrans | date = January 2009 | url = http://cms.revoptom.com/handbook/oct02_sec5_4.htm |access-date=2011-07-03 |url-status=live |archive-url=https://web.archive.org/web/20111119012641/http://cms.revoptom.com/handbook/oct02_sec5_4.htm |archive-date=2011-11-19 }}</ref> Loss of vision occurs over days or weeks.<ref name="Holland_2006"/> Other signs and symptoms are red eye, [[white pupil]], fixed pupil, [[retinal fibrosis]], [[retinal detachment]], inflammation of the eye tissues, retinal [[granulomas]], and [[strabismus]].<ref name="Markell_2006"/><ref name="Holland_2006"/><ref name="ocular larva migrans"/><ref name="pmid16340531">{{cite journal | vauthors = Stewart JM, Cubillan LD, Cunningham ET | s2cid = 8659870 | title = Prevalence, clinical features, and causes of vision loss among patients with ocular toxocariasis | journal = Retina (Philadelphia, Pa.) | volume = 25 | issue = 8 | pages = 1005–13 | date = December 2005 | pmid = 16340531 | doi = 10.1097/00006982-200512000-00009 }}</ref> Ocular granulomas resulting from OLM are frequently misdiagnosed as [[retinoblastoma]]s.<ref name="Markell_2006"/> ''Toxocara'' damage in the eye is permanent and can result in blindness.<ref name="Huh, Sun, Sooung"/><ref name="CDC3"/><ref name="ocular larva migrans"/>

A case study published in 2008 supported the hypothesis that eosinophilic cellulitis may also be caused by infection with ''Toxocara''.  In this study, the adult patient presented with [[eosinophilic cellulitis]], [[hepatosplenomegaly]], [[anemia]], and a positive [[ELISA]] for ''T. cani''s.<ref name="pmid19038064">{{cite journal | vauthors = Bassukas ID, Gaitanis G, Zioga A, Boboyianni C, Stergiopoulou C | title = Febrile "migrating" eosinophilic cellulitis with hepatosplenomegaly: adult toxocariasis - a case report | journal = Cases Journal | volume = 1 | issue = 1 | pages = 356 | date = November 2008 | pmid = 19038064 | pmc = 2621125 | doi = 10.1186/1757-1626-1-356 }}</ref>

===Incubation period===
<!-- Image with unknown copyright status removed: [[File:Embryonated egg.jpg|thumb|right|''Toxocara canis'' embryonated egg]] -->
The incubation period for ''Toxocara canis'' and ''cati'' eggs depends on temperature and humidity.<ref name="Markell_2006"/><ref name="CDC1"/> ''T. canis'' females, specifically, are capable of producing up to 200,000 eggs a day that require '''2–6 weeks''' minimum up to a couple months before full development into the infectious stage.<ref>{{cite journal | vauthors = Azam D, Ukpai OM, Said A, Abd-Allah GA, Morgan ER | s2cid = 10075744 | title = Temperature and the development and survival of infective Toxocara canis larvae | journal = Parasitology Research | volume = 110 | issue = 2 | pages = 649–56 | date = February 2012 | pmid = 21779864 | doi = 10.1007/s00436-011-2536-8 }}</ref> Under ideal '''summer conditions''', eggs can mature to the infective stage after two weeks outside of a host.<ref name="Huh, Sun, Sooung"/><ref name="Holland_2006"/><ref name="CDC1"/> Provided sufficient oxygen and moisture availability, ''Toxocara'' eggs can remain infectious for years, as their resistant outer shell enables the protection from most environmental threats.<ref name="search.proquest.com">{{cite journal | vauthors = Gamboa MI | title = Effects of temperature and humidity on the development of eggs of Toxocara canis under laboratory conditions | journal = Journal of Helminthology | volume = 79 | issue = 4 | pages = 327–31 | date = December 2005 | pmid = 16336716 | doi = 10.1079/JOH2005287 | s2cid = 30220871 | id = {{ProQuest|213503935}} }}</ref><ref name="Huh, Sun, Sooung"/><ref name="Harris Linton"/><ref name="Soskolne">{{cite web | last = Soskolne | first = Gayle | name-list-style = vanc | publisher = The University of Michigan Museum of Zoology: Animal Diversity Web. | title = Toxocara cati | date = January 2001 | url = http://animaldiversity.ummz.umich.edu/site/accounts/information/Toxocara_cati.html |access-date=2010-01-17 |url-status=live |archive-url=https://web.archive.org/web/20110605072955/http://animaldiversity.ummz.umich.edu/site/accounts/information/Toxocara_cati.html |archive-date=2011-06-05 }}</ref> However, as identified in a case study presented within the journal of helminthology, the second stage of larvae development poses strict vulnerabilities to certain environmental elements.<ref name="search.proquest.com"/> High temperatures and low moisture levels will quickly '''degrade''' the larvae during this stage of growth.<ref name="search.proquest.com"/>
{{Automatic taxobox
| taxon = Toxocara
| subdivision_ranks = [[Species]]
| subdivision =
Species include:<ref>{{cite book | last = Johnstone | first = Colin | name-list-style = vanc | publisher = University of Pennsylvania | title = The Nematodes | date = January 2000 | url = http://cal.vet.upenn.edu/projects/merial/Nematodes/nems_top.htm |chapter = Nems-topics |access-date=2009-02-23 |url-status=live |archive-url=https://web.archive.org/web/20090216095731/http://cal.vet.upenn.edu/projects/merial/Nematodes/nems_top.htm |archive-date=2009-02-16 }}</ref>
* ''[[Toxocara canis]]''
* ''[[Toxocara cati]]''<ref name="Harris Linton">{{cite web | last = Harris-Linton | first = Megan | name-list-style = vanc | publisher = The University of Michigan Museum of Zoology: Animal Diversity Web. | title = Toxocara canis | date = January 2001 | url = http://animaldiversity.ummz.umich.edu/site/accounts/information/Toxocara_canis.html  |access-date=2009-02-23 |url-status=live |archive-url=https://web.archive.org/web/20100501134950/http://animaldiversity.ummz.umich.edu/site/accounts/information/Toxocara_canis.html |archive-date=2010-05-01 }}</ref>
* ''[[Toxocara malaysiensis]]''<ref name="NCBI">{{cite web|url=https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Tree&id=6264&lvl=3&p=mapview&p=has_linkout&p=blast_url&p=genome_blast&keep=1&srchmode=1&unlock|title=Taxonomy Browser|website=www.ncbi.nlm.nih.gov|access-date=14 January 2019}}</ref>
* ''[[Toxocara tanuki]]''<ref name="NCBI" />
* ''[[Toxocara vitulorum]]''<ref name="NCBI" />
}}

===Transmission===
Transmission of ''Toxocara'' to humans is usually through ingestion of infective eggs.<ref name="CDC3"/><ref name="CDC1">{{cite web | publisher = Centers for Disease Control and Prevention.| work = Division of Parasitic diseases. | title = Guidelines for Veterinarians: Prevention of Zoonotic Transmission of Ascarids and Hookworms of Dogs and Cats. | date = 27 September 2004 | url = https://www.cdc.gov/ncidod/dpd/parasites/ascaris/prevention.htm |access-date=2017-09-17 |url-status=live |archive-url=https://web.archive.org/web/20100821105900/http://www.cdc.gov/NCIDOD/DPD/PARASITES/ascaris/prevention.htm |archive-date=2010-08-21 }}</ref> ''T. canis'' can lay around 200,000 eggs per day.<ref name="Cheprasov"/>  These eggs are passed in cat or dog feces, but the defecation habits of dogs cause ''T. canis'' transmission to be more common than that of ''T. cati''.<ref name="Markell_2006"/><ref name="CDC1"/> Both ''Toxocara canis'' and ''Toxocara cati'' eggs require a several week incubation period in moist, humid, weather, outside a host before becoming infective, so fresh eggs cannot cause toxocariasis.<ref name="Markell_2006"/><ref name="Huh, Sun, Sooung"/><ref name="CDC1"/><ref name="Cheprasov"/>

Many objects and surfaces can become contaminated with infectious ''Toxocara'' eggs.  Flies that feed on feces can spread ''Toxocara'' eggs to surfaces or foods.<ref name="Holland_2006"/> Young children who put contaminated objects in their mouths or eat dirt ([[Pica (disorder)|pica]]) are at risk of developing symptoms.<ref name="Markell_2006"/><ref name="Despommier"/><ref name="Holland_2006"/> Humans can also contaminate foods by not washing their hands before eating.<ref name="Huh, Sun, Sooung"/><ref name="CDC3"/>

Humans are not the only accidental hosts of ''Toxocara''.<ref name="Fan_2015">{{cite journal | vauthors = Fan CK, Holland CV, Loxton K, Barghouth U | title = Cerebral Toxocariasis: Silent Progression to Neurodegenerative Disorders? | journal = Clinical Microbiology Reviews | volume = 28 | issue = 3 | pages = 663–86 | date = July 2015 | pmid = 26062575 | pmc = 4462679 | doi = 10.1128/CMR.00106-14 }}</ref>  Eating undercooked rabbit, chicken, or sheep can lead to infection; encysted larvae in the meat can become reactivated and migrate through a human host, causing toxocariasis.<ref name="Fan_2015" />  Special attention should be paid to thoroughly cooking giblets and liver to avoid transmission.<ref name="Markell_2006"/><ref name="Holland_2006"/>

===Reservoir===
[[Image:2009-08-16 Puppy at Duke East 1.jpg|thumb|270px|Puppies are the major source of environmental contamination with roundworm eggs]]
Dogs and foxes are the reservoir for ''Toxocara canis'', but puppies and cubs pose the greatest risk of spreading the infection to humans.<ref name="Huh, Sun, Sooung"/><ref name="CDC3"/> Infection in most adult dogs is characterized by encysted second stage larvae.  However, these larvae can become reactivated in pregnant females and cross the placental barrier to infect the pups.  Vertical transmission can also occur through breastmilk.<ref name="Markell_2006"/><ref name="CDC1"/><ref name="CDC4">{{cite web | publisher = Centers for Disease Control and Prevention. | work = DPDx: Parasites and Health. | title = Toxocariasis | date = 19 January 2009 | url = http://www.dpd.cdc.gov/dpdx/HTML/Toxocariasis.htm |access-date=2006-03-07 |url-status=live |archive-url=https://web.archive.org/web/20060513184653/http://www.dpd.cdc.gov/dpdx/HTML/Toxocariasis.htm |archive-date=2006-05-13 }}</ref> Infectious mothers, and puppies under five weeks old, pass eggs in their feces.<ref name="CDC1"/><ref name="CDC4"/> Approximately 50% of puppies and 20% of adult dogs are infected with ''T. canis''.<ref name="Markell_2006"/>

Cats are the reservoir for ''Toxocara cati''.<ref name="Huh, Sun, Sooung"/><ref name="CDC3"/> As with ''T. canis'', encysted second stage larvae in pregnant or lactating cats become reactivated.  However, vertical transmission can only occur through breastfeeding.<ref name="CDC1"/>

Flies can act as mechanical vectors for ''Toxocara'', but most infections occur without a vector.<ref name="Holland_2006"/> Most incidents with Toxocariasis result from prokaryotic expression vectors and their transmission through direct physical contact with feces that results in the contraction of the illness.<ref>{{cite journal | vauthors = Mohamad S, Azmi NC, Noordin R | title = Development and evaluation of a sensitive and specific assay for diagnosis of human toxocariasis by use of three recombinant antigens (TES-26, TES-30USM, and TES-120) | journal = Journal of Clinical Microbiology | volume = 47 | issue = 6 | pages = 1712–7 | date = June 2009 | pmid = 19369434 | pmc = 2691092 | doi = 10.1128/JCM.00001-09 }}</ref>

===Morphology===
<!-- Image with unknown copyright status removed: [[File:Adulttoxocara.png|thumb|left]] -->
Both species produce eggs that are brown and pitted.<ref name="merckvetmanual" /><ref name="Harris Linton"/><ref name="Soskolne"/> ''T. canis'' eggs measure 75-90&nbsp;µm and are spherical in shape, whereas the eggs of ''T. cati'' are 65-70&nbsp;µm in diameter and oblong.<ref name="Markell_2006"/><ref name="Harris Linton"/><ref name="Soskolne"/> Second stage larvae hatch from these eggs and are approximately 0.5mm long and 0.02mm wide.<ref name="Huh, Sun, Sooung"/> Adults of both species have complete digestive systems and three lips, each composed of a dentigerous ridge.<ref name="Harris Linton"/><ref name="Soskolne"/>

Adult ''T. canis'' are found only within dogs and foxes and the males are 4–6&nbsp;cm in length, with a curved posterior end.<ref name="Despommier"/><ref name="Harris Linton"/> The males each have spicules and one “tubular testis.”<ref name="Harris Linton"/> Females can be as long as 15&nbsp;cm, with the vulva stretching one third of their bodylength.<ref name="Harris Linton"/> The females do not curve at the posterior end.<ref name="Despommier"/><ref name="Harris Linton"/>

''T. cati'' adult females are approximately 10&nbsp;cm long, while males are typically 6&nbsp;cm or less.  The ''T. cati'' adults only occur within cats, and male ''T. cati'' are curved at the posterior end.<ref name="Soskolne"/>

===Life cycle===
[[File:Toxocara canis LifeCycle.gif|thumb]]
Cats, dogs and foxes can become infected with ''Toxocara'' through the ingestion of eggs or by transmission of the larvae from a mother to her offspring.<ref name="CDC1"/><ref name="CDC4"/> Transmission to cats and dogs can also occur by ingestion of infected accidental hosts, such as earthworms, cockroaches, rodents, rabbits, chickens, or sheep.<ref name="Markell_2006"/><ref name="Holland_2006"/><ref name="Soskolne"/>

Eggs hatch as second stage larvae in the intestines of the cat, dog or fox host (for consistency, this article will assume that second stage larvae emerge from ''Toxocara'' eggs, although there is debate as to whether larvae are truly in their second or third stage of development).<ref name="Despommier"/><ref name="Holland_2006"/> Larvae enter the bloodstream and migrate to the lungs, where they are coughed up and swallowed.  The larvae mature into adults within the small intestine of a cat, dog or fox, where mating and egg laying occurs.<ref name="Holland_2006"/><ref name="ocular larva migrans"/><ref name="CDC1"/><ref name="Harris Linton"/> Eggs are passed in the feces and only become infective after three weeks outside of a host.<ref>{{Cite book|last=Becerril Flores | first = Marco Antonio | name-list-style = vanc |title=Parasitología médica| year = 2019 |isbn=978-1-4562-6784-1|edition=Quinta edición|location=México|oclc=1117384861}}</ref>  During this incubation period, molting from first to second (and possibly third) stage larva takes place within the egg.<ref name="Holland_2006"/><ref name="Soskolne"/> In most adult dogs, cats and foxes, the full lifecycle does not occur, but instead second stage larvae encyst after a period of migration through the body.  Reactivation of the larvae is common only in pregnant or lactating cats, dogs and foxes. The full lifecycle usually only occurs in these females and their offspring.<ref name="CDC1"/><ref name="CDC4"/>

Second stage larvae will also hatch in the small intestine of an accidental host, such as a human, after ingestion of infective eggs.<ref>{{cite journal | vauthors = Ahn SJ, Ryoo NK, Woo SJ | title = Ocular toxocariasis: clinical features, diagnosis, treatment, and prevention | journal = Asia Pacific Allergy | volume = 4 | issue = 3 | pages = 134–41 | date = July 2014 | pmid = 25097848 | pmc = 4116038 | doi = 10.5415/apallergy.2014.4.3.134 }}</ref> The larvae will then migrate through the organs and tissues of the accidental host, most commonly the lungs, liver, eyes, and brain.<ref>{{cite journal | vauthors = Lee RM, Moore LB, Bottazzi ME, Hotez PJ | title = Toxocariasis in North America: a systematic review | journal = PLOS Neglected Tropical Diseases | volume = 8 | issue = 8 | pages = e3116 | date = August 2014 | pmid = 25166906 | pmc = 4148222 | doi = 10.1371/journal.pntd.0003116 }}</ref>  Since L2 larvae cannot mature in accidental hosts, after this period of migration, ''Toxocara'' larvae will encyst as second stage larvae.<ref name="Markell_2006"/><ref name="Huh, Sun, Sooung"/><ref name="CDC1"/>