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Test Catalog

Test ID: TOXOC    
Toxocara Antibody, IgG, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Aiding in the diagnosis of Toxocara infection

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Toxocariasis is a zoonotic parasitic disease caused by the nematode, Toxocara, of which there are 2 species: T canis and T cati. Toxocara eggs are shed in the feces of infected animals and once in the environment, become infectious within 2 to 4 weeks. Humans are accidental hosts and become infected through ingestion of dirt or contaminated material containing Toxocara eggs. Although uncommon, individuals can also get toxocariasis by eating undercooked or raw meat from infected animals. Upon ingestion, Toxocara eggs hatch and larvae are released, which can penetrate the intestinal wall travel, through the bloodstream, and migrate to a variety of tissues (eg, liver, heart, lungs, brain, muscles, eyes). Although Toxocara larvae do not undergo any further development at these sites, they can cause severe local inflammatory reactions that are the basis of toxocariasis.

 

While the majority of infected people do not have any symptoms, the 2 primary clinical presentations of toxocariasis are visceral larva migrans (visceral toxocariasis) and ocular larva migrans (ocular toxocariasis). Manifestations of toxocariasis reflect parasitic burden, immune response, and resulting inflammation. Symptoms of larva migrans may be characterized by Loffler's syndrome (eg, fever, coughing, wheezing, abdominal pain), hepatomegaly, eosinophilia, or irreversible eye problems. Rarely, larvae migrate to the central nervous system, causing eosinophilic meningoencephalitis or granuloma formation in the central nervous system (CNS). Larvae can also migrate to and penetrate the eye, resulting in ocular toxocariasis, which may lead to retinal scarring, decreased vision, and leukocoria.

 

A recent Toxocara seroprevalence study in the United States showed that approximately 5% of the US population is infected with Toxocara. Globally, toxocariasis is found in many countries, and rates of prevalence can be as high as 40%, particularly in tropical regions where eggs remain viable in the soil. Children and adolescents under the age of 20, as well as dog owners, are at higher risk of infection.

 

Diagnosis of Toxocara infections involves obtaining relevant clinical and exposure history and relies on antibody detection to Toxocara species. Eosinophilia may also be present, more commonly in visceral toxocariasis. Stool examination for ova and parasites is not useful since eggs are not excreted by humans, only by domestic animals. Currently, antibody testing is the only means of confirming a clinical diagnosis. The recommended serologic test for toxocariasis is an enzyme-linked immunosorbent assay (ELISA) using larval-stage antigens. However, a measureable titer does not distinguish between current and past Toxocara infection. Laboratory findings should be correlated with clinical history.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Negative

 

Reference values apply to all ages.

Interpretation Provides information to assist in interpretation of the test results

Positive:

IgG antibodies to Toxocara species detected, suggesting current or past infection. False-positive results may occur in patients with other helminth infections (eg, Ascaris lumbricoides, Schistosoma species, Strongyloides).

 

Negative:

No antibodies to Toxocara species detected. Repeat testing may be considered in patients presenting soon after possible exposure to Toxocara.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

A single negative result does not rule-out infection. Assay sensitivity may be decreased depending on the site of infection, in cases of low parasitic burden, and timing of sample collection relative to exposure. In ocular toxocariasis, Toxocara antibody levels in serum can be low or absent despite clinical disease. Repeat testing should be considered in patients who are at high risk of exposure or infection.

 

False-negative results may occur in severely immunosuppressed patients.

 

Positive results should be interpreted with patient's clinical status and exposure history.

 

Positive results by this assay do not distinguish acute versus remote infection.

 

False-positive results may occur in patients with other helminth infections.

 

This assay uses synthetic antigens derived from Toxocara canis. Studies evaluating the sensitivity of this assay in patients infected with T cati have not been performed.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Smith HV: Antibody reactivity in human toxocariasis. In Toxocara and toxocariasis: clinical, speidemiological, and molecular persectives. Edited by JW Lewis, RM Maizels. London, UK: Institute of Biology and the British Society for Parasitology; 1993, pp 91-109

2. Liu EW, Chastain HM, Shin SH, et al: Seroprevalence of antibodies to Toxocara species in the United States and associated risk factors, 2011-2014. Clin Infect Dis. 2018;66:206-212

3. Woodhall DM, Fiore AE: Toxocariasis: A review for pediatricians. J Pediatric Infect Dis Soc. 2014;June;3(2):154-159