The Potential of MIC17A both as an Entero-epithelial and Chronic Stage Marker for Detection of Feline Toxoplasmosis

Toxoplasma gondii is a zoonotic protozoan with significant clinical relevance. As the definitive host, felids are the key drivers of the parasite to intermediate hosts, including humans. Thus, early detection of infection in cats is critical to control toxoplasmosis. The micronemal protein MIC17A is a known marker of feline toxoplasmosis; however, its diagnostic performance in PCR-tested cases has not been evaluated. This study assessed 422 feline sera (56 RT-PCR positive, 366 RT-PCR negative) by indirect-ELISA (rMIC17A-based ELISA). The parasite seroprevalence was 41.9% by rMIC17A compared to tachyzoite lysate antigen (TLA)-based ELISA (37.2%). Based on both markers, the overall detection of feline toxoplasmosis increased to 54.7%. Of the 56 RT-PCR-positive samples, 50% and 42.8% were seropositive by the rMIC17A and TLA-based ELISAs, respectively, with an overall detection rate of 64.2%. Among the RT-PCR-negative 366 samples, 40.7% and 36.34% were seropositive according to the rMIC17A and TLA-based ELISAs, respectively. The detection rate increased to 53.27% once the outcome from both markers were considered. The higher seropositivity rate of the rMIC17A-based ELISA in PCR-positive cats suggests that naturally expressed MIC17A can induce IgG response earlier than tachyzoite antigens, which is consistent with its expression in the merozoite-primed presexual stage. Moreover, the diagnostic performance of rMIC17A is also detected higher in PCR-negative samples suggesting that it is also a late-stage infection marker consistent with its high transcript levels in bradyzoites. In conclusion, rMIC17A may represent both entero-epithelial (EES) and chronic-stage detection marker for feline toxoplasmosis and improve diagnostic accuracy when combined with conventional markers.