Development of a Highly Specific RecombinantToxocara canisSecond-Stage Larva Excretory-Secretory Antigen for Immunodiagnosis of Human Toxocariasis

Abstract

The specificity of the recombinant Toxocara canisantigen developed for the immunodiagnosis of human toxocariasis was compared with that of the excretory-secretory antigen from T. canis second-stage larvae (TES) by enzyme-linked immunosorbent assay. A total of 153 human serum samples from patients infected with 20 different helminths, including 11 cases of toxocariasis, were examined. No false-negative reactions were observed for the toxocariasis cases. When the TES was used at concentrations of 0.5 and 0.125 μg/ml, cross-reactions were observed in 79 (55.6%) and 61 (43.0%) of 142 cases, respectively. In contrast, when the recombinant antigen was tested at a concentration of 0.5 μg/ml, cross-reactions were observed in 19 (13.4%) of 142 cases. At a concentration of 0.125 μg/ml, however, the cross-reaction rate decreased sharply to only 2.1%, corresponding to 3 of 142 cases. The cross-reactions occurred with one case each of gnathostomiasis, paragonimiasis withParagonimus miyazakii, and spirometriasis, in which high antibody titers were detected. In addition, the recombinant antigen showed negative reactions with serum samples from patients infected with Ascaris and hookworms, which are the most common parasites in the world. These findings are also supported by experiments with animals infected with Ascaris and hookworm. From these results, the recombinant antigen is highly specific for toxocariasis and may provide more reliable diagnostic results than other methods.

Prevalence of Toxocara and Toxascaris infection among human and animals in Iran with meta-analysis approach

“…As previously mentioned, TES-based ELISA tests are mostly used for human seroprevalence studies. Despite having proper immunogenicity, native TES antigens may cross-react with antibodies elicited against other helminths specifically Ascaris lumbricoides which decreases test specificity [39]. Therefore, the results may be regarded as suspicious, particularly when no immunoblotting confirmation is done, specifically in endemic regions where there exists the possibility of helminth co-infections.…”

National Seroprevalence and Risk Factors for Zoonotic Toxocara spp. Infection

“…Furthermore, when this assay is used in conjunction with a presumptive diagnosis to confirm Toxocara infection, the predictive values are raised. 26 Although this assay does not distinguish between acute and chronic Toxocara infections and progress has been made on the development of highly specific recombinant antigen tools, [38][39][40] this test is still the most widely used serologic tool in nontropical settings. Because NHANES III was not designed spe-cifically to evaluate risk factors associated with Toxocara infection, further studies should be conducted to confirm results obtained in this study.…”

Toxoplasma gondii and Toxocara spp. Co-infection

“…For populations from tropical areas, recombinant antigens have been used to increase specificity. 23,24 The risks for T. gondii, Toxocara spp., and coinfection seropositivity were lowest in the western United States ( Table 1). The lower risk for seropositivity in the west may be caused by the more arid climate; both T. gondii and Toxocara spp.…”