Editing Toxocariasis (section)

==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" />