View source for Toxocariasis

{{about|the infection|the organism|Toxocara}}
{{short description|Illness of humans caused by larvae of the dog, the cat or the fox roundworm}}
{{Infobox medical condition (new)
| name            = Toxocariasis
| synonyms        = [[roundworm]]
| image           = Canine roundworm 1.JPG
| caption         = ''Toxocara canis''
| pronounce       =
| field           = [[Infectious disease (speciality)|Infectious disease]]
| symptoms        =
| complications   =
| onset           =
| duration        =
| types           =
| causes          =
| risks           =
| diagnosis       =
| differential    = [[filariasis]]
| prevention      =
| treatment       =
| medication     = [[ivermectin]]
| prognosis       =
| frequency       =
| deaths          =
}}
'''Toxocariasis''' is an illness of humans caused by [[larvae]] (immature worms) of either the dog [[roundworm]] (''[[Toxocara canis]]''), the cat roundworm (''[[Toxocara cati]]'') or the fox roundworm (''[[Toxocara canis]]'').<ref name = "Wu_2020" /> Toxocariasis is often called [[visceral larva migrans]] (VLM). Depending on geographic location, degree of [[eosinophilia]], eye and/or pulmonary signs, the terms [[human eye|ocular]] larva migrans (OLM), [[Weingarten's disease]], [[Frimodt-Møller]]'s syndrome, and eosinophilic pseudoleukemia<ref name="afip.org">{{cite book | last = Marty | first = Aileen | chapter = Toxocariasis Chapter 27 | pages = 411–421 | veditors = Meyers WM, Neafie RC, Marty AM, Wear DJ | title = Pathology of Infectious Diseases | volume = I: Helminthiases | publisher = Armed Forces Institute of Pathology | location = Washington DC | date = 2000 | url= http://www.afip.org/cgi-bin/description.cgi?item=FS28  |access-date=2014-11-20 |url-status=dead |archive-url= https://web.archive.org/web/20101227085414/http://www.afip.org/cgi-bin/description.cgi?item=FS28 |archive-date=2010-12-27 }}</ref> are applied to toxocariasis. Other terms sometimes or rarely used include nematode ophthalmitis, toxocaral disease, toxocarose, and covert toxocariasis.<ref name="Markell_2006"/>  This [[zoonotic]], [[helminth]]ic infection is a rare cause of blindness and may provoke [[rheumatic]], [[neurologic]], or [[asthmatic]] symptoms.<ref>{{cite journal | vauthors = Schantz PM | title = Of worms, dogs, and human hosts: continuing challenges for veterinarians in prevention of human disease | journal = Journal of the American Veterinary Medical Association | volume = 204 | issue = 7 | pages = 1023–8 | date = April 1994 | pmid = 8045801 }}</ref>  Humans normally become infected by ingestion of embryonated eggs (each containing a fully developed second stage [[larva]], L2) from contaminated sources (soil, undercooked meat, fresh or unwashed vegetables).<ref name="afip.org"/>

''[[Toxocara canis]]'' and ''[[Toxocara cati]]'' are perhaps the most [[ubiquitous]] [[gastrointestinal]] worms ([[helminth]]s) of domestic dogs, cats, coyotes, wolves and foxes.<ref name = "Wu_2020">{{cite journal | vauthors = Wu T, Bowman DD | title = Visceral larval migrans of Toxocara canis and Toxocara cati in non-canid and non-felid hosts | journal = Advances in Parasitology | volume = 109 | pages = 63–88 | date = 2020 | pmid = 32381221 | doi = 10.1016/bs.apar.2020.02.001 | publisher = Elsevier | isbn = 978-0-12-820958-5 }}</ref> There are many 'accidental' or [[paratenic]] hosts including humans, birds, pigs, rodents, goats, monkeys, and rabbits.<ref name="afip.org"/> In paratenic hosts, the larvae never mature and remain at the L2 stage.<ref name="Markell_2006">{{cite book | last1 = Markell | first1 = Edward K. | first2 = Marietta | last2 = Voge | name-list-style = vanc | title = Markell and Voge's Medical Parasitology. | edition = 9th | location = St. Louis | publisher = Saunders Elsevier | date = 2006 }}</ref>

There are three [[Portal:Main|main]] syndromes: ''[[visceral larva migrans]]'' (VLM), which encompasses diseases associated with major organs; ''[[covert toxocariasis]]'', which is a milder version of VLM; and ''ocular larva migrans'' (OLM), in which pathological effects on the host are restricted to the eye and the [[optic nerve]].<ref name=Despommier>{{cite journal | vauthors = Despommier D | title = Toxocariasis: clinical aspects, epidemiology, medical ecology, and molecular aspects | journal = Clinical Microbiology Reviews | volume = 16 | issue = 2 | pages = 265–72 | date = April 2003 | pmid = 12692098 | pmc = 153144 | doi = 10.1128/CMR.16.2.265-272.2003 }}</ref>

==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"/>

==Diagnosis==
Finding ''Toxocara'' larvae within a patient is the only definitive diagnosis for toxocariasis; however, biopsies to look for second stage larvae in humans are generally not very effective.<ref name="Huh, Sun, Sooung"/><ref name="Holland_2006"/>  [[PCR]], [[ELISA]], and [[serological testing]] are more commonly used to diagnose ''Toxocara'' infection.<ref name="Huh, Sun, Sooung"/><ref name="Holland_2006"/>  Serological tests are dependent on the number of larvae within the patient, and are unfortunately not very specific.<ref name="Holland_2006"/> ELISAs are much more reliable and currently have a 78% sensitivity and a 90% specificity.<ref name="Auweerter">{{cite book | last = Auweerter | first = Paul | name-list-style = vanc | publisher = Johns Hopkins | title = Point-of-Care Information Technology Center: ABX Guide. | chapter = Toxocariasis | date = 8 January 2008 | chapter-url = http://prod.hopkins-abxguide.org/pathogens/parasites/toxocariasis.html?contentInstanceId=425999&siteId=153 }}</ref> A 2007 study announced an ELISA specific to ''Toxocara canis'', which will minimize false positives from cross reactions with similar roundworms and will help distinguish if a patient is infected with ''T. canis'' or ''T. cati''.<ref name="pmid17374974">{{cite journal | vauthors = Iddawela RD, Rajapakse RP, Perera NA, Agatsuma T | title = Characterization of a Toxocara canis species-specific excretory-secretory antigen (TcES-57) and development of a double sandwich ELISA for diagnosis of visceral larva migrans | journal = The Korean Journal of Parasitology | volume = 45 | issue = 1 | pages = 19–26 | date = March 2007 | pmid = 17374974 | pmc = 2526337 | doi = 10.3347/kjp.2007.45.1.19 }}</ref> [[Ocular larva migrans|OLM]] is often diagnosed after a clinical examination.<ref name="Auweerter"/> Granulomas can be found throughout the body and can be visualized using ultrasound, MRI, and CT technologies.<ref name="Holland_2006"/>

==Preventions==
Actively involving veterinarians and pet owners is important for controlling the transmission of ''Toxocara'' from pets to humans. A group very actively involved in promoting a reduction of infections in dogs in the United States is the [[Companion Animal Parasite Council|Companion Animal Parasite Council -- CAPC]].  Since pregnant or lactating dogs and cats and their offspring have the highest, active parasitic load, these animals should be placed on a deworming program.<ref name="CDC3"/><ref name="Holland_2006"/><ref name="CDC1"/> Pet feces should be picked up and disposed of or buried, as they may contain ''Toxocara'' eggs.<ref name="CDC3"/> Practicing this measure in public areas, such as parks and beaches, is especially essential for decreasing transmission.<ref name="Markell_2006"/><ref name="Despommier"/> Up to 20% of soil samples of U.S. playgrounds have found roundworm eggs.<ref name="Cheprasov">{{cite journal | first = Artem | last = Cheprasov | name-list-style = vanc | date = 2012 | title = Death at the Playground | journal = Guru Magazine | volume = 11 | pages = 59–61 }}</ref> Also, sandboxes should be covered when not in use to prevent cats from using them as litter boxes.  Hand washing before eating and after playing with pets, as well as after handling dirt will reduce the chances of ingesting ''Toxocara'' eggs.<ref name="Markell_2006"/><ref name="CDC3"/><ref name="Holland_2006"/> Washing all fruits and vegetables, keeping pets out of gardens and thoroughly cooking meats can also prevent transmission.<ref name="Holland_2006"/> Finally, teaching children not to place nonfood items, especially dirt, in their mouths will drastically reduce the chances of infection.<ref name="CDC3"/>

Toxocariasis has been named one of the neglected diseases of U.S. poverty, because of its prevalence in Appalachia, the southern U.S., inner city settings, and minority populations.<ref name="Hotez">{{cite journal | vauthors = Hotez PJ | title = Neglected infections of poverty in the United States of America | journal = PLOS Neglected Tropical Diseases | volume = 2 | issue = 6 | pages = e256 | date = June 2008 | pmid = 18575621 | pmc = 2430531 | doi = 10.1371/journal.pntd.0000256 | veditors = Brooker S }}</ref> Unfortunately, there is currently no vaccine available or under development.<ref name="CDC2"/><ref name="Hotez"/> However, the mitochondrial genomes of both ''T. cati'' and ''T. canis'' have recently been sequenced, which could lead to breakthroughs in treatment and prevention.<ref name="pmid18482460">{{cite journal | vauthors = Li MW, Lin RQ, Song HQ, Wu XY, Zhu XQ | title = The complete mitochondrial genomes for three Toxocara species of human and animal health significance | journal = BMC Genomics | volume = 9 | pages = 224 | date = May 2008 | pmid = 18482460 | pmc = 2396643 | doi = 10.1186/1471-2164-9-224 }}</ref>

==Treatment==
Toxocariasis will often resolve itself, because the ''Toxocara'' larvae cannot mature within human hosts.<ref name="Markell_2006"/> Corticosteroids are prescribed in severe cases of VLM or if the patient is diagnosed with OLM.  Either albendazole (preferred) or mebendazole (“second line therapy”) may be prescribed.<ref name="Markell_2006"/><ref name="Huh, Sun, Sooung"/><ref name="ocular larva migrans"/><ref name="Auweerter"/> Granulomas can be surgically removed, or laser photocoagulation and cryoretinopexy can be used to destroy ocular granulomas.<ref name="Holland_2006"/><ref name="ocular larva migrans"/><ref name="Auweerter"/><ref>{{cite journal | vauthors = Werner JC, Ross RD, Green WR, Watts JC | title = Pars plana vitrectomy and subretinal surgery for ocular toxocariasis. | journal = Archives of Ophthalmology | date = April 1999 | volume = 117 | issue = 4 | pages = 532–4 | doi = 10.1001/archopht.117.4.532 | pmid = 10206586 | doi-access = free }}</ref>

Visceral toxocariasis in humans can be treated with antiparasitic drugs such as [[albendazole]] or [[mebendazole]], [[tiabendazole]] or [[diethylcarbamazine]] usually in combination with anti-inflammatory medications. Steroids have been utilized with some positive results. Anti-helminthic therapy is reserved for severe infections (lungs, brain) because therapy may induce, due to massive larval killing, a strong inflammatory response. Treatment of ocular toxocariasis is more difficult and usually consists of measures to prevent progressive damage to the eye.<ref>"Toxocariasis." Parasites. Centers for Disease Control and Prevention, 10 Jan. 2013. {{cite web |url=https://www.cdc.gov/parasites/toxocariasis/treatment.html |title=CDC - Toxocariasis - Treatment |access-date=2017-09-17 |url-status=live |archive-url=https://web.archive.org/web/20170906223048/https://www.cdc.gov/parasites/toxocariasis/treatment.html |archive-date=2017-09-06 |date=2017-05-02 }}. 22 Apr. 2014</ref>

==Epidemiology==
Humans are accidental hosts of ''Toxocara'', yet toxocariasis is seen throughout the world. Most cases of toxocariasis are seen in people under the age of twenty.<ref name="CDC2"/> Seroprevalence is higher in developing countries, but can be considerable in first world countries, as well.<ref name="Holland_2006"/> In Bali, St. Lucia, Nepal and other countries, seroprevalence is over fifty percent.<ref name="Holland_2006"/> Previous to 2007, the U.S. seroprevalence was thought to be around 5% in children.<ref name="Markell_2006"/> However, Won et al. discovered that U.S. seroprevalence is actually 14% for the population at large.<ref name="Huh, Sun, Sooung"/><ref name="CDC2"/> In many countries, toxocariasis is considered very rare. Approximately 10,000 clinical cases are seen a year in the U.S., with ten percent being OLM.<ref name="CDC2"/><ref name="ocular larva migrans"/> Permanent vision loss occurs in 700 of these cases.<ref name="ocular larva migrans"/>

Young children are at the greatest risk of infection because they play outside and tend to place contaminated objects and dirt in their mouths.<ref name="Markell_2006"/><ref name="Despommier"/><ref name="Holland_2006"/> Dog ownership is another known risk factor for transmission.<ref name="Despommier"/> There is also a significant correlation between high ''Toxocara'' antibody titers and epilepsy in children.<ref name="Markell_2006"/><ref name=":0">{{cite journal | vauthors = Luna J, Cicero CE, Rateau G, Quattrocchi G, Marin B, Bruno E, Dalmay F, Druet-Cabanac M, Nicoletti A, Preux PM | display-authors = 6 | title = Updated evidence of the association between toxocariasis and epilepsy: Systematic review and meta-analysis | journal = PLOS Neglected Tropical Diseases | volume = 12 | issue = 7 | pages = e0006665 | date = July 2018 | pmid = 30028858 | pmc = 6070292 | doi = 10.1371/journal.pntd.0006665 | veditors = Fleury A }}</ref>

Parasitic loads as high as 300 larvae in a single gram of liver have been noted in humans.<ref name="Holland_2006"/> The "excretory–secretory antigens of larvae ... released from their outer epicuticle coat [and] ... readily sloughed off when bound by specific antibodies" incite the host's immune response.<ref name="Huh, Sun, Sooung"/> The tipping point between development of VLM and OLM is believed to be between 100 and 200 larvae.<ref name="Holland_2006"/> The lighter infection in OLM is believed to stimulate a lower immune response and allow for migration of a larva into the eye. Larvae are thought to enter the eye through the optic nerve, central retinal artery, short posterior ciliary arteries, soft tissues, or cerebrospinal fluid.<ref name="Holland_2006"/><ref name="ocular larva migrans"/> Ocular granulomas that form around a larva typically are peripheral in the retina or optic disc.<ref name="ocular larva migrans"/>

Visceral larva migrans seems to affect children aged 1–4 more often while ocular larva migrans more frequently affects children aged 7–8. Between 4.6% and 23% of US children have been infected with the dog roundworm egg. This number is much higher in other parts of the world, in tropical countries there is seroprevalence of up to 80–90%, such as Colombia, where up to 81% of children have been infected, or Honduras where seroprevalence among school-age children was reported to be 88%.<ref name="Cheprasov" /><ref name=":0" /><ref name="Hernandez et al.">{{cite journal |last1=Hernandez |first1=S.A |title=An Integrated Study of Toxocara Infection in Honduran Children: Human Seroepidemiology and Environmental Contamination in a Coastal Community |journal=Trop Med Infect Dis . |date=August 2020 |volume=5 |issue=3 |page=135 |doi=10.3390/tropicalmed5030135 |pmid=32842560 |url=https://pubmed.ncbi.nlm.nih.gov/32842560/ |access-date=16 December 2020|pmc=7559065 }}</ref> In the western part of the world, seroprevalence is lower, around 35–42%.<ref name=":0" />

==History==
Werner described a parasitic nematode in dogs in 1782 which he named ''Ascaris canis''. Johnston determined that what Werner had described was actually a member of the genus ''Toxocara'' established by Stiles in 1905. Fülleborn speculated that ''T canis'' larvae might cause granulomatous nodules in humans. In 1947 Perlingiero and Gyorgy described the first case of what was probably toxocariasis.  Their patient was a 2-year-old boy from Florida who had classical symptoms and esoinophilic necrotizing granulomas.<ref name="afip.org" /> In 1950, Campbell-Wilder was the first to describe toxocariasis in humans; she published a paper describing ocular granulomas in patients with endophthalmitis, Coat's disease, or pseudoglioma. Two years later, Beaver et al. published the presence of ''Toxocara'' larvae in granulomas removed from patients with symptoms similar to those in Wilder's patients.<ref name="Holland_2006">{{cite book | veditors = Holland C, Smith HV | title = Toxocara: the enigmatic parasite. | location = Wallingford, UK and Cambridge, MA | publisher = CABI Publishing | year = 2006 | url = http://site.ebrary.com/lib/stanford/docDetail.action?docID=10157926 }}</ref><ref name="Despommier"/> The dangers of toxocariasis were first raised in Britain in the 1970s, leading to a public health scare.<ref>{{Cite web|url=https://blogs.kent.ac.uk/munitions-of-the-mind/2016/09/16/dog-dirt-disgust-and-1970s-british-health-propaganda/|title=Dog Dirt, Disgust and 1970s British Health Propaganda – Munitions of the Mind|first=Neil|last=Pemberton | name-list-style = vanc |website=blogs.kent.ac.uk}}</ref>

==Other animals==
===Cats===
Some treatments for infection with ''Toxocara cati'' include drugs designed to cause the adult worms to become partially anaesthetized and detach from the intestinal lining, allowing them to be excreted live in the feces.  Such medications include [[piperazine]] and [[pyrantel]].  These are frequently combined with the drug [[praziquantel]] which appears to cause the worm to lose its resistance to being digested by the host animal. Other effective treatments include [[ivermectin]], [[milbemycin]], and [[selamectin]].<ref name=fcp>{{Cite book|title=Feline clinical parasitology|last1=Bowman|first1=Dwight D.|last2=Hendrix|first2=Charles M.|last3=Lindsay|first3=David S.|last4=Barr|first4=Steven C. | name-list-style = vanc |edition=First|year=2002|page=275|publisher=Iowa State University|place=Ames, Iowa|url=https://books.google.com/books?id=mvpsA9dGdpAC&pg=PA278|isbn=978-0-8138-0333-3|url-status=live|archive-url=https://web.archive.org/web/20180426192104/https://books.google.com/books?id=mvpsA9dGdpAC&pg=PA278|archive-date=2018-04-26}}</ref> [[Dichlorvos]] has also been proven to be effective as a poison, though moves to ban it over concerns about its toxicity have made it unavailable in some areas.{{cn|date=May 2021}}

Treatment for wild felids, however, is difficult for this parasite, as detection is the best way to find which individuals have the parasite.  This can be difficult as infected species are hard to detect.  Once detected, the infected individuals would have to be removed from the population, in order to lower the risk of continual exposure to the parasites.A primary method that has been used to lower the amount of infection is removal through hunting.  Removal can also occur through landowners, as Dare and Watkins (2012) discovered through their research on cougars.  Both hunters and landowners can provide samples that can be used to detect the presence of feline roundworm in the area, as well as help remove it from the population.  This method is more practical than administering medications to wild populations, as wild animals, as mentioned before, are harder to find in order to administer medicinal care.{{citation needed|date=July 2020}}

Medicinal care, however, is also another method used in roundworm studies; such as the experiment on managing raccoon roundworm done by Smyser et al. (2013) in which they implemented medical baiting. However, medicine is often expensive and the success of the baiting depends on if the infected individuals consume the bait.  Additionally, it can be costly (in time and resources) to check on baited areas.  Removal by hunting allows agencies to reduce costs and gives agencies a more improved chance of removing infected individuals.{{citation needed|date=July 2020}}

== References ==
{{Reflist}}

== External links ==
* CDC information page on [http://www.dpd.cdc.gov/dpdx/HTML/Toxocariasis.htm toxocariasis].
* [http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=498 Roundworms: Cats and Kittens from The Pet Health Library]
* [http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=476 Roundworms: Dogs and Puppies from The Pet Health Library]
* {{cite journal | vauthors = Despommier D | title = Toxocariasis: clinical aspects, epidemiology, medical ecology, and molecular aspects | journal = Clinical Microbiology Reviews | volume = 16 | issue = 2 | pages = 265–72 | date = April 2003 | pmid = 12692098 | pmc = 153144 | doi = 10.1128/CMR.16.2.265-272.2003 }}
* [http://www.capvet.org/recommendations/ascarids.html CAPC Recommendations Ascarids]
{{Medical resources
|  DiseasesDB      = 29739
|  ICD10           = {{ICD10|B|83|0|b|65}} ([[ILDS]] B83.01)
|  ICD9            = {{ICD9|128.0 }}
|  ICDO            =
|  OMIM            =
|  MedlinePlus     =
|  eMedicineSubj   = med
|  eMedicineTopic  = 2293
|  eMedicine_mult  = {{eMedicine2|ped|2270}}
|  MeshID          = D014120
}}
{{Helminthiases}}
{{Use dmy dates|date=November 2020}}

[[Category:Helminthiases]]
[[Category:Dog diseases]]
[[Category:Cat diseases]]
[[Category:Neglected tropical diseases]]
[[Category:Tropical diseases]]
[[Category:Zoonoses]]