Aiding in the diagnosis of Toxocara infection
Enzyme-Linked Immunosorbent Assay (ELISA)
Preferred: Serum gel
Acceptable: Red top
Specimen Volume: 0.5 mL
|Specimen Type||Temperature||Time||Special Container|
|Serum||Frozen (preferred)||30 days|
Aiding in the diagnosis of Toxocara infection
Toxocariasis is a zoonotic parasitic disease caused by the nematode, Toxocara, of which there are 2 species: Toxocara canis and Toxocaracati. 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 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. 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 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 apply to all ages.
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).
No antibodies to Toxocara species detected. Repeat testing may be considered in patients presenting soon after possible exposure to Toxocara.
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.
1. Smith HV: Antibody reactivity in human toxocariasis. In: Lewis JW, Maizels RM, eds. Toxocara and Toxocariasis: Clinical, Speidemiological, and Molecular Persectives. Institute of Biology and the British Society for Parasitology; 1993:91-109
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 Jan 6;66(2):206-212
3. Woodhall DM, Fiore AE: Toxocariasis: A Review for Pediatricians. J Pediatric Infect Dis Soc. 2014 Jun;3(2):154-159
Microtiter strip wells are precoated with synthetic Toxocara canis antigens to bind corresponding antibodies of the specimen. After washing the wells to remove all unbound sample material horseradish peroxidase-labeled protein A conjugate is added. This conjugate binds to the captured Toxocara canis-specific antibodies. The immune complex formed by the bound conjugate is visualized by adding tetramethylbenzidine substrate, which gives a blue reaction product. The intensity of this product is proportional to the amount of Toxocara canis-specific antibodies in the specimen. Sulfuric acid is added to stop the reaction. This produces a yellow endpoint color. Absorbance at 450 nm is read using an enzyme-linked immunosorbent assay (ELISA) microwell plate reader.(Package insert: Gold Standard Diagnostics Toxocara canis ELISA IgG Test Kit. Gold Standard Diagnostics; 11/02/2021)
This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.
|Test Id||Test Order Name||Order LOINC Value|
|TOXOC||Toxocara Ab, IgG, S||40674-4|
|Result Id||Test Result Name||
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|65873||Toxocara Ab, IgG, S||40674-4|