Standardization of dot-ELISA for the serological diagnosis of toxocariasis and comparision of the assay with ELISA

Abstract

The dot-enzyme-linked immunosorbent assay (dot-ELISA) was standardized using somatic (S) and excretory-secretory (ES) antigens of Toxocara-canis for the detection of specific antibodies in 22 serum samples from children aged 1 to 15 years, with clinical signs of toxocariasis. Fourteen serum samples from apparently normal individuals and 28 sera from patients with other pathologies were used as controls. All samples were used before and after absorption with Ascaris suum extract. When the results were evaluated in comparison with ELISA, the two tests were found to have similar sensitivity, but dot-ELISA was found to be more specific in the presence of the two antigens studied. Dot-ELISA proved to be effective for the diagnosis of human toxocariasis, presenting advantages in terms of yield, stability, time and ease of execution and low cost.

Frequency of human toxocariasis in a rural population from Cajamarca, Peru determined by DOT-ELISA test

“…It is known that there are antigenic similarities among Ascaris species, but it is very interesting to note that the A. suum antigens may help us to decrease the cross-reactions in cases of patients with H. nana, taking in consideration that this parasite belongs to other Phylum. Although statistically no significant (t = 2.23; p = 0.068), this serum absorption procedure could eliminate totally or partially the crossreactions in some cases, these findings demonstrates that the previous serum absorption with A. suum antigens would improve the dot-ELISA performance, as mentioned by others 4,26,31 . On the other hand, we could not exclude the possibility of mixed infections between Toxocara sp.…”

“…Many authors refer that the main cause of crossreactions in serological tests for immunodiagnostics of toxocariasis are the presence of other helminth infections, while protozoa and coccidia are less related 4,15,23,26 . In our study, we observed false positive reactions in sera from parasitized subjects.…”

“…In order to improve the specificity of dot-ELISA, all serum samples were performed with and without previous absorption with Ascaris suum antigens 4,31 . Briefly, NC strips of 1 x 6 cm were dotted on marked round areas with 2 µl of TES antigens (0.01 µg/mL) diluted in bicarbonate buffer, pH 9.6, containing 1% of ovalbumin.…”

“…The method of choice for serodiagnosis has been the ELISA test using Toxocara larvae excretion-secretion (TES) antigens 19 , which shows 78.3% to 100% of sensitivity and 90% to 92.3% of specificity 4,19,31 .…”

Human toxocariasis: contribution by Brazilian researchers

“…The author considered that after the absorption of the serum with Ascaris suum antigens, titers above 1:64 were related to possible cases of toxocariasis in humans. CAMARGO et al 18 standardized the DOT-ELISA technique for the diagnosis of toxocariasis in Brazil and when they compared this technique with the ELISA test, they concluded that the DOT-ELISA presented advantages in relation to stability, the short duration of execution and lower cost. In 2006, ELEFANT et al 42 standardized the ELISA IgG, IgA and IgE tests after using TES in the serological follow-up of patients with toxocariasis after chemotherapy in São Paulo.…”