An indirect ELISA for Neosporosis: Associating recombinant Neospora caninum proteins NcSRS2 and NcSAG1.

Neosporosis is caused by infection with the protozoa Neospora caninum. It manifests as various neurological symptoms and is considered as one of the main causes of abortion in cattle, and induces uncommon congenital infection in sheep. The standard diagnosis is based on indirect immunofluorescence (IFI); however, cross-reactivity with other protozoa proteins is common. Aiming a more specific diagnosis, recombinant antigens have been tested in several immunoassays; of these, NcSAG1 (surface antigen-1) and NcSRS2 (SAG1-related sequence 2) were the most promising. In this context, we developed an indirect ELISA with recombinant NcSRS2 (ELISA-rNcSRS2) and NcSAG1 (ELISA-rNcSAG1) proteins alone and in association (ELISA-rNcSRS2/rNcSAG1) for the diagnosis of cattle and ovine neosporosis. A total of 216 samples from cattle and 154 samples from sheep were used to evaluate the ELISAs. The sensitivity and specificity results of the ELISA-rNcSRS2 were 91.5 % and 96.4 % for cattle, and 89.6 % and 96.3 % for sheep, respectively. For the ELISA-rNcSAG1, the sensitivity and specificity were 84.9 % and 97.3 % for cattle, and 89.6 % and 92.6 % for sheep, respectively. The sensitivity and specificity of the ELISA-rNcSRS2/rNcSAG1 was 98.1 % and 99.1 % for cattle, 100 % and 97.2 % for sheep, respectively. These results indicated that indirect ELISA using the rNcSRS2 and rNcSAG1 proteins are a highly sensitive and specific method, especially when used in association, for detecting antibodies in cattle and ovine populations infected with N. caninum.