Cross-Reactions between Toxocara canis and Ascaris suum in the diagnosis of visceral larva migrans by western blotting technique

Abstract

Visceral larva migrans (VLM) is a clinical syndrome caused by infection of man by Toxocara spp, the common roundworm of dogs and cats. Tissue migration of larval stages causes illness specially in children. Because larvae are difficult to detect in tissues, diagnosis is mostly based on serology. After the introduction of the enzyme-linked immunosorbent assay (ELISA) using the larval excretory-secretory antigen of T. canis (TES), the diagnosis specificity was greatly improved although cross-reactivity with other helminths are still being reported. In Brazil, diagnosis is routinely made after absorption of serum samples with Ascaris suum antigens, a nematode antigenically related with Ascaris lumbricoides which is a common intestinal nematode of children. In order to identify T. canis antigens that cross react to A. suum antigens we analyzed TES antigen by SDS-PAGE and Western blotting techniques. When we used serum samples from patients suspected of VLM and positive result by ELISA as well as a reference serum sample numerous bands were seen (molecular weight of 210-200 kDa, 116-97 kDa, 55-50 kDa and 35-29 kDa). Among these there is at least one band with molecular weight around 55-66 kDa that seem to be responsible for the cross-reactivity between T. canis and A. suum once it disappears when previous absorption of serum samples with A. suum antigens is performed.

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.…”

Human toxocariasis: a seroepidemiological survey in the Amazonian city of Yurimaguas, Peru

“…We also note that the presence of mixed infections between Toxocara and other helminthes might increase the frequency of seropositivity using conventional serological tests, but with the previous serum absorption with Ascaris suum antigens, we might diminish or avoid the possible cross-reactions, as recommended by other authors 6,23 .…”

Human toxocarosis. Its seroprevalence in the City of La Plata

“…This value exceeds the percentage found in France by Gueglio et al (1994) (22%). In our study the ELISA test was not made after absorption of serun samples with extracts of Ascaris suum, likely is routinely made in Brasil, what might have avoided confusing serodiagnostics, probably reducing the percentage of seropositives (Nunes et al 1997). …”

“…The sera were not absorbed with Ag de Ascaris suum (Nunes et al 1997). Serologic results were grouped according to a simple scale: 0 (negative), 1 (positive), 2 (highly positive), following a similar criterium as Gueglio et al (1994).…”