Evaluation of species-specific polyclonal antibodies to detect and differentiate between Neospora caninum and Toxoplasma gondii

Neosporosis and toxoplasmosis are major causes of abortion in livestock worldwide, leading to substantial economic losses. Detection tools are fundamental to the diagnosis and management of those diseases. Current immunohistochemistry (IHC) tests, using sera raised against whole parasite lysates, have not been able to distinguish between Toxoplasma gondii and Neospora caninum. We used T. gondii and N. caninum recombinant proteins, expressed in Escherichia coli and purified using insoluble conditions, to produce specific polyclonal rabbit antisera. We aimed to develop species-specific sera that could be used in IHC on formalin-fixed, paraffin-embedded (FFPE) tissue sections to improve the diagnosis of ruminant abortions caused by protozoa. Two polyclonal rabbit sera, raised against recombinant proteins, anti-Neospora-rNcSRS2 and anti-Toxoplasma-rTgSRS2, had specificity for the parasite they were raised against. We tested the specificity for each polyclonal serum using FFPE tissue sections known to be infected with T. gondii and N. caninum. The anti-Neospora-rNcSRS2 serum labeled specifically only N. caninum-infected tissue blocks, and the anti-Toxoplasma-rTgSRS2 serum was specific to only T. gondii-infected tissues. Moreover, tissues from 52 cattle and 19 sheep previously diagnosed by lesion profiles were tested using IHC with our polyclonal sera and PCR. The overall agreement between IHC and PCR was 90.1% for both polyclonal anti-rNcSRS2 and anti-rTgSRS2 sera. The polyclonal antisera were specific and allowed visual confirmation of protozoan parasites by IHC, but they were not as sensitive as PCR testing.