Currently, the laboratory diagnosis of
toxocariasis, caused by Toxocara canis or T. cati, mainly relies on serological tests. Unfortunately, however, the specificities of most of the commercial tests that are available for the serodiagnosis of this disease are not very high and this may cause problems, especially in tropical countries where
co-infections with other helminths are common. In an effort to develop a serological assay with improved specificity for the detection of Toxocara
infection, an IgG(4)-ELISA based on a recombinant version (rTES-30USM) of the 30-kDa
Toxocara excretory-secretory antigen (TES-30) has recently been developed. To produce the
antigen, the TES-30 gene was cloned via assembly PCR, subcloned into a His-tagged prokaryotic expression vector, and purified by affinity chromatography using Ni(2+)-
nitrilotriacetic-acid (Ni-NTA) resin. The performance of the ELISA based on the recombinant
antigen was then compared with that of commercial kit, based on an
IgG-ELISA, for the serodiagnosis of
toxocariasis (Toxocara
IgG-ELISA; Cypress Diagnostics, Langdorp, Belgium). Both assays were used to test 338 serum samples, including 26 samples from probable cases of
toxocariasis. Assuming that all the probable cases were true cases, the assay based on rTES-30USM demonstrated a sensitivity of 92.3% (24/26) and a specificity of 89.6% (103/115) whereas the commercial kit exhibited a sensitivity of 100% (26/26) but a specificity of only 55.7% (64/115). The high sensitivity and specificity exhibited by the new IgG(4)-ELISA should make the assay a good choice for use in tropical countries and any other area where potentially cross-reactive helminthic
infections are common.