An illness of humans caused by a larvae of either the dog roundworm (Toxocara canis) or the cat roundworm (Toxocara cati).

Also called visceral larva migrans.

A helminthic infection that is a major cause of blindness and may cause rheumatic, neurologic, or asthmatic symptoms.

Humans normally become infected by ingestion of embryonated eggs from contaminated soil, fresh or unwashed vegetables, or poorly cooked accidental hosts such s birds, pigs, goats and rabbits.

Toxocara canis and Toxocara cati are perhaps the most ubiquitous gastrointestinal worms of domestic dogs and cats.

There are three main illnesses are seen : 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 the illness is restricted to the eye and the optic nerve.

Most cases of Toxocara infection are asymptomatic, especially in adults.

When symptoms occur, they are the result of migration of second stage Toxocara larvae through the body.

Covert toxocariasis is the least serious of the three processes and is related to chronic exposure.

Covert toxocariasis symptoms include coughing, fever, abdominal pain, headaches, changes in behavior and insomnia and clinical findings include wheezing, hepatomegaly, and lymphadenitis.

VLM is associated with high parasitic loads or repeated infections.

Viceral larval migrans is primarily diagnosed in young children, as they are more prone to exposure and ingestion of eggs.

Toxocara infection commonly resolves itself within weeks, but chronic eosinophilia may result.

VLM associated with inflammation of internal organs and sometimes the central nervous system.

Patients may present with fatigue, weight loss, anorexia, nausea vomiting, fever, headache, rash, cough, asthma, chest tightness, irritability, and abdominal pain.

Subcutaneous migration tracks of the larvae can sometime be seen. pneumonia,

Patients may present with pulmonary symptoms such as bronchospasms, chronic pulmonary inflammation, eosinophilia, hepatomegaly, hypergammaglobulinaemia, leucocytosis, and have elevated anti-A and –B isohaemagglutinins.

Humans are accidental hosts of Toxocara,.

Seen throughout the world.

Rarely, patients have carditis, pleural effusion, respiratory failure seizures or death.

Ocular larva migrans is rare compared with visceral larval migrans.

Suspected a small Toxocara burden induces a low immune response, which allows a larva to enter the individual’s eye.

Rare for their to be concurrent ocular and VLM forms of the disease.

OLM often occurs in just one eye, with loss of vision occurring over days or weeks.

May manifest from a single larva migrating into and encysting within the orbit.

Eye involvement may manifest as eye inflammation, white pupil, fixed pupil, retinal detachment and fibrosis, retinal granulomas, and strabismus, and blindness.

Transmission is usually through ingestion of infective eggs passed in cat or dog feces.

Defecation habits of dogs cause T. canis transmission to be more common than that of T. cati.

Toxocara canis and Toxocara cati eggs require a several week incubation period outside of a host before becoming infective.

Many objects and surfaces can become contaminated with infectious Toxocara eggs.

Flies that feed on feces can spread Toxocara eggs to surfaces or foods, and foods can be contaminated by individuals not washing their hands before eating.

Children who put contaminated objects in their mouths or eat dirt are at risk of developing the illness.

Eating undercooked rabbit, chicken, or sheep can lead to infection as encysted larvae in the meat can become reactivated and migrate through a human host, causing toxocariasis.

Puppies pose the greatest risk of spreading the infection to humans.

Infection in most adult dogs is characterized by encysted second stage larvae.

Larvae can become reactivated in pregnant females and cross the placental barrier to infect the puppies, and vertical transmission can also occur through breastmilk.

Infected mothers, and puppies under five weeks old, pass eggs in their feces.

Approximately 50% of puppies and 20% of adult dogs are infected with T. canis.

Cats are the reservoir for Toxocara cati and encysted second stage larvae in pregnant or lactating cats become reactivated, and vertical transmission can only occur through breastfeeding.

The defecation habits of cats reduce the chances of human infection with T. cati.

While flies can act as mechanical vectors most infections occur without a vector.

The incubation period for Toxocara canis and cati to the infective stage after two weeks outside of a host.

Toxocara eggs can remain infectious for years, as they are very resistant to the effects of chemicals and temperature changes.

T. canis eggs measure 75-90 µm and are spherical in shape, while eggs of T. cati are 65-70 µm in diameter and oblong.

Second stage larvae hatch from these eggs, and adult roundworms have complete digestive systems and three lips, each composed of a dentigerous ridge.

Both cats and dogs can become infected with Toxocara through the ingestion of eggs or by transmission of the larvae from a mother to her offspring, and by ingestion of infected accidental hosts, such as earthworms, cockroaches, rodents, rabbits, chickens, or sheep.

Eggs hatch as second stage larvae in the intestines of the cat or dog host, and 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 or dog, where mating and egg laying occurs.

Eggs are passed in the feces and become infective after several weeks outside of a host.

In most adult dogs and cats the second stage larvae encyst after a period of migration through the body.

Reactivation of the larvae is common only in pregnant or lactating cats and dogs.

Second stage larvae hatch in the small intestine of an accidental host, such as a human, after ingestion of infective eggs andI then migrate through the organs and tissues of the accidental host, most commonly the lungs, liver, eyes, and brain.

Diagnosis requires the identification of larvae in a patient.

PCR, ELISA, and serological testing are commonly used to diagnose infection.

Serological tests are not very specific for diagnosis.

ELISAs have a 78% sensitivity and a 90% specificity.

Ocular larva migrans is often diagnosed after a clinical examination.

Granulomas can be found throughout the body and can be visualized by a multitude of imaging tecniques.

Toxocariasis often resolves spontaneously, because the Toxocara larvae cannot mature within human hosts.

In severe cases of visceral larval migrans and in ocular larval migrans corticosteroids are given.

Albendazole or mebendazole as second line therapy may be prescribed.

Eye granulomas can be surgically removed, or laser photocoagulation can be used to destroy ocular granulomas.

Most cases seen in people under the age of twenty.

Seroprevalence is higher in developing countries.

Seroprevalence in the US is 14%, with 10,000 clinical cases noted annally, with about 10% of cases ocular larval migrans.

Young children are at the greatest risk of infection.

Dog ownership is a risk factor for transmission.

Significant correlation exists between high Toxocara antibody titers and epilepsy in children.

Larval loads as high as 300 in a single gram of liver have been noted in humans, and their outer epicuticle coat incites the host’s immune response.

The development of VLM and OLM is believed to be between 100 and 200 larvae, with the lighter infection in OLM is believed to stimulate a lower immune response and allow for migration of a larva into the eye.

Larvae enter the eye through the optic nerve, central retinal artery, short posterior ciliary arteries, soft tissues, or cerebrospinal fluid forming ocular granulomas that form around a larva typically are peripheral in the retina or optic disc.

Pregnant or lactating dogs and cats and their offspring have the highest, active parasitic load andshould be placed on a deworming program.

Pet feces may contain Toxocara eggs and should be disposed of.

Sandboxes should be covered to prevent cats from using them as litter boxes.

Hand washing before eating and after playing with pets reduces the chances of ingesting Toxocara eggs.

Preventing transmission includes washing fruits and vegetables, keeping pets out of gardens and thoroughly cooking meats.

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