Studies on the fluorescent antibody test in the diagnosis of Toxoplasma gondii - induced ovine abortion

Abstract

The work was carried out to look at a discrepancy between results from the immunofluorescent test and other diagnostic techniques in the diagnosis of Toxoplasma-induced abortion in lambs. Several Veterinary Investigation Centres, including the one at Edinburgh, had used the immunofluorsecent test for some years, but had become increasingly cautious in the interpretation of the results.

An analysis of data accumulated by the Edinburgh Veterinary Investigation Centre was carried out to examine correlations between the immunofluorescent test, the indirect haemagglutination test and mouse inoculation.

Toxoplasma was observed in sections of mouse tissues, using the immunofluorescent technique. This was followed by titration of test reagents using toxoplasmas as antigen, and, at the beginning of the lambing season, by titration using lamb spleen smear cells. The numbers and types of fluorescing spleen cells were examined both before and after counterstaining with Evan's blue.

Finally, fluorescent spleen smear cells were examined after restaining with Giemsa and an attempt made to identify the cell types.

Analysis of data revealed no correlation between results from the immunofluorescent test and those from serological and mouse inoculation techniques.

The titration of reagents using Toxoplasma and spleen smear cells revealed that the fluorescence observed in the spleen cells could not be related to specific fluorescence caused by Toxoplasma. Further, spleen cells fluoresced under ultra-violet light without the addition of fluorescein-labelled conjugate.

Although the fluorescing spleen smear cells appeared to be granular, attempts to identify them after restaining with Giemsa were unsuccessful.

The conclusion is made that the immunofluorescent test described is not specific for Toxoplasma-induced ovine abortion.