Evaluation of crude and purified Toxocara canis antigens in serodiagnosis of human toxocariasis.

Three serological tests: Immunodiffusion (ID), Counterimmunoelectrophoresis (CIEP) and Enzyme-linked immunosorbent assay (ELISA) were used to study the role of crude adult worm antigen (CAWA) of Toxocara canis and each of its purified fractions in the serodiagnosis of human toxocariasis. Sensitivities of the three tests were lower in the ocular than in the visceral group, using different antigens. Purified fraction 1 showed more sensitive and specific reactions in the three tests, compared to CAWA or purified fraction 2 (P-F2) antigen. The other purified fractions (P-F3, P-F4 and P-F5) gave no positive reactions in any of the three tests. Using P-F1 antigen, ELISA was the most sensitive technique for diagnosis of both visceral and ocular toxocariasis followed by CIEP and then ID and the difference was statistically significant. However, CIEP was the most specific test followed by ELISA and lastly ID test. The ELISA test using Excretory-Secretory (E-S) larval antigen of Toxocara canis was less sensitive than the ELISA test using P-F1, although it was 100% specific. Thus, ELISA test using P-F1 is the test of choice for diagnosis of human toxocariasis, but when the specificity of a reaction is in doubt, CIEP test using the same antigen can be of value.