A PCR assay with high sensitivity and specificity for the detection of swine toxoplasmosis based on the GRA14 gene.

Toxoplasma gondii, an intracellular apicomplexan protozoan parasite, can infect all warm-blooded animals. Infected swine are considered one of the most important sources of T. gondii infection in humans. Rapidly and effectively diagnosing T. gondii infection in swine is essential. PCR-based diagnostic tests have been fully developed, and very sensitive and specific PCR is crucial for the diagnosis of swine toxoplasmosis. In this study, we used the T. gondii dense granule protein 14 (GRA14) gene as a target to design specific primers and established a high-specificity and high-sensitivity PCR detection method for swine toxoplasmosis. Notably, this PCR method could detect T. gondii tachyzoite DNA in the acute infection phase. The GRA14 gene PCR assay detected a minimum of 2.35 tachyzoites of T. gondii and can be used for T. gondii detection in blood, tissue, semen, urine and waste feed specimens. A total of 5462 blood specimens collected from pigs in 5 provinces and autonomous regions in southern China during 2016-2017 were assessed by the newly established GRA14 gene PCR method. The overall T. gondii infection rate was 18.9 % (1033/5462). According to the statistical analysis of different regions in China, the positive rates of swine toxoplasmosis from 2016 to 2017 were highest in the Shaanxi, Fujian and Guangdong areas, at 31.7 % (44/139), 21.9 % (86/391) and 18.8 % (874/4645), respectively. Specimens collected in 2017 had a higher positive rate (19.1 %) than those collected in 2016 (16.1 %). In addition, specimens collected in autumn (39.4 %), spring (22.8 %) and winter (18.2 %) had higher positive rates than those collected in summer (3.8 %). These results indicate that the new PCR method based on the T. gondii GRA14 gene has utility for the diagnosis of swine toxoplasmosis and can facilitate the diagnosis of toxoplasmosis in clinical laboratories.