Description:
The Toxocara ELISA test is a semi-quantitative enzyme immunoassay for the detection of antibodies to Toxocara, in samples of human serum or plasma.
This test is intended to be performed by trained medical technologists only.
Toxocariasis is the infection caused by roundworm of the genus Toxocara (usually T. canis, rarely T. cati) and is acquired by ingesting soil contaminated with embryonated eggs from an animal’s feces. These eggs become embryonated after 2 to 5 weeks after being passed by the animal. Thus, human infection does not occur by contact with fresh feces. In addition, infected humans cannot pass the infection to other humans.6
The disease manifests itself as visceral larval migrans (VLM) and ocular larval migrans (OLM). Signs and symptoms of VLM may vary from an asymptomatic state with mild eosinophilia to a severe and potentially fatal disorder.Patients with OLM also vary widely in presentation, from acute lesions in the eye to asymptomatic infections. Toxocara larva migrans is believed to be the second most common helminth infection in developed countries.1,2
There is no definitive method to diagnose Toxocara infections, thus true sensitivity and specificity of serologic tests cannot be accurately determined. The diagnosis is further complicated by the fact that the antibody response varies depending on worm burden and location. However, numerous studies have shown that immunoassays using a purified excretory antigen from the larval stage, as in this ELISA, have shown dramatically improved sensitivities and specificities when compared to assays using crude antigens.1-6
The microwells are coated with Toxocara Excretory antigen. During the first incubation with the diluted patient’ sera, any antibodies which are reactive with the antigen will bind to the coated wells. After washing to remove the rest of the sample, the Enzyme Conjugate is added. If antibodies have been bound to the wells, the Enzyme Conjugate will then bind to these antibodies. After another series of washes, a chromogen (tetramethylbenzidine or TMB) is added. If the Enzyme Conjugate is present, the peroxidase will catalyze a reaction that consumes the peroxide and turns the chromogen from clear to blue. Addition of the Stop Solution ends the reaction and turns the blue color to a bright yellow color. The reaction may then be read visually or with an ELISA reader.