Toxocara

Life cycle of the nematode (roundworm) Toxocara canis, the most common cause of Toxocariasis in humansToxocara canis completes its life cycle in dogs, with humans acquiring the infection as accidental hosts. Unembryonated eggs are shed in the feces of the definitive host (1). Eggs embryonate and become infective in the environment (2). Following ingestion by dogs (3), the infective eggs hatch and larvae penetrate the gut wall. In younger dogs, the larvae migrate through the lungs, bronchial tree, and esophagus; adult worms develop and oviposit in the small intestine (4). In older dogs, patent infections can also occur, but larval encystment in tissues is more common (an infection is "patent" when direct evidence of the organism can be detected, e.g., in the patient’s feces or blood, regardless of whether symptoms have appeared). Encysted stages are reactivated in female dogs during late pregnancy and infect by the transplacental and transmammary routes the puppies (5), in whose small intestine adult worms become established (6). Puppies are a major source of environmental egg contamination. Toxocara canis can also be transmitted through ingestion of paratenic hosts ("transport hosts"): eggs ingested by small mammals (e.g. rabbits) hatch and larvae penetrate the gut wall and migrate into various tissues where they encyst (7). The life cycle is completed when dogs eat these hosts (8) and the larvae develop into egg-laying adult worms in the small intestine. Humans are accidental hosts who become infected by ingesting infective eggs in contaminated soil (9) or infected paratenic hosts (10). After ingestion, the eggs hatch and larvae penetrate the intestinal wall and are carried by the circulation to a wide variety of tissues (liver, heart, lungs, brain, muscle, eyes) (11). While the larvae do not undergo any further development in these sites, they can cause severe local reactions that are the basis of toxocariasis. The two main clinical presentations of toxocariasis are visceral larva migrans and ocular larva migrans. Diagnosis is usually made by serology or the finding of larvae in biopsy or autopsy specimens.From Centers for Disease Control Parasites and Health website.

This is an illustration of the life cycle of Toxocara canis and Toxocara cati, the causal agents of Toxocariasis.Created: 2002

Description: English: Toxocara canis eggs (close-up, Numarski contrast). Undeveloped eggs were isolated from uteri of adult female worms. Photo taken through a microscope at 400x. Čeština: Vajíčka Toxocara canis. Foceno pod mikroskopem, Numarskiho kontrastem, při zvětšení 400x. Nevyvinutá vajíčka byla izolována z děloh dospělých samic T. canis. Date: 12 December 2007. Source: Own work. Author: Flukeman.

Description: Toxocara canis - adult worms isolated from dog's feces. Date: 27 December 2007. Source: Own work. Author: Flukeman.

Description: Photo of a dog pooping at Cadogan Street Temporary Garden, Kennedy Town, Hong Kong. Date: 1 September 2007. Source: Own work. Author: Minghong. Camera location22° 16′ 57.35″ N, 114° 07′ 33.17″ E View all coordinates using: OpenStreetMap 22.282598; 114.125880.

Description: Toxocara canis (canine roundworm) from a puppy. Date: 19 January 2006 (cropped on 2006-06-25). Source: Own work. Author: Joel Mills.

Description: English: Scanning electron micrograph of the mouth of Toxocara canis, a parasitic roundworm of dogs that can be transmitted to humans, extracted from a dingo (Canis dingo). Date: 13 December 2017. Source: Own work. Author: Ben Liffner.

Description: English: Ocular larva migrans granuloma via toxocara canis infection from newborn puppies, onset date 1976. Date: 2006. Source: photo of uploader's right eye taken during eye exam; photo belongs to uploader. Author: user: enableuser. Permission (Reusing this file): this work is not published elsewhere. Licensing[edit] I, the copyright holder of this work, hereby publish it under the following licenses: : Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License.http://www.gnu.org/copyleft/fdl.htmlGFDLGNU Free Documentation Licensetruetrue. : This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.:.. This licensing tag was added to this file as part of the GFDL licensing update.http://creativecommons.org/licenses/by-sa/3.0/CC-BY-SA-3.0Creative Commons Attribution-Share Alike 3.0truetrue. : Copyleft: This work of art is free; you can redistribute it and/or modify it according to terms of the Free Art License. You will find a specimen of this license on the Copyleft Attitude site as well as on other sites. http://artlibre.org/licence/lal/enFALFree Art Licensefalsetrue. You may select the license of your choice.

Description: Toxocara canis embryonated eggs. Photo taken through a microscope at 400x. On the left side: T. canis egg containig morula, On the right side: T. canis egg containing fully developed infectious larva L3 Česky: Vyvinutá vajíčka T. canis. Foceno pod mikroskopem při zvětšení 400x. vlevo: vajíčko obsahující mourulu, vpravo: vajíčko obsahující plně vyvinutou larvu L3. Date: 12 December 2007. Source: Own work. Author: Flukeman.

Description: Toxocara canis eggs. Undeveloped eggs were isolated from uteri of adult female worms. Date: 12.12.07. Source: Own work. Author: Flukeman.

Description: English: Toxocara canis (canine roundworm) from a puppy. Čeština: Dospělá škrkavka Toxocara canis izolovaná ze štěněte. Date: 1 March 2008 (upload date). Source: compiled from Image:Canine roundworm 1.JPG. Author: Joel Mills (scale bar added by Flukeman).

Description: The life cycle of Toxocara canis. Source: http://www.dpd.cdc.gov/dpdx/HTML/ImageLibrary/Toxocariasis_il.htm. Author: This file is lacking author information.

Description: English: Toxocara canis adult nematode worms of dog. Date: 10 April 2012. Source: Own work. Author: Alan R Walker.

Description: Toxocara canis egg with fully devoloped larva L3 (Numarski contrast). Date: 12 December 2007. Source: Own work. Author: Flukeman.

Description: Čeština: Přední část těla dospělé samičky škrkavky Toxocara canis z tenkého střeva psa (Canis lupus familiaris). Ústní otvor je lemován třemi výraznými pysky, které jsou pro škrkavky typické. Kolorovaný snímek pochází ze skenovacího elektronového mikroskopu SEM JEOL 6380 LV umístěného na PřF UK. Date: 27 April 2018. Source: Own work. Author: Jana Bulantová.

Description: English: Toxocara canis - adult worms isolated from dog's feces. Diameter of 5 Czech Crown coin is 23 mm. Date: 11 February 2008 (upload date). Source: Own work. Author: Flukeman.

Description: A canine roundworm (Toxocara canis) egg. Photo taken through a microscope at 400x. Date: 17 August 2006 (cropped on 2006-08-17). Source: Own work. Author: Joel Mills.

Description: A feline roundworm (Toxocara cati) egg. Photo taken through a microscope at 400x. Date: 29 July 2006 (cropped on 2006-07-31). Source: Own work. Author: Joel Mills.

Description: Toxocara cati, Glista kocia, Białowieża, Polska. Date: January 2008. Source: Own work. Author: Beentree.