Development of a reverse transcription-nested polymerase chain reaction assay for differential diagnosis of transmissible gastroenteritis virus and porcine respiratory coronavirus from feces and nasal swabs of infected pigs

Transmissible gastroenteritis virus (TGEV), a coronavirus, replicates in in testinal enterocytes and causes diarrhea in young pigs. Porcine respiratory coronavirus (PRCV), a spike (S) gene natural deletion mutant of TGEV, has a respiratory tissue tropism and causes mild or subclinical respiratory inf ections. Conventional antigen-based diagnostic tests fail to differentiate TGEV and PRCV, and a blocking ELISA test to serologically differentiate TGE V/PRCV-infected pigs is conducted on convalescent serum retrospectively aft er disease outbreaks. A reverse transcription (RT)-nested polymerase chain reaction (PCR) with primers targeted to the S gene deletion region to diffe rentiate TGEV/PRCV was developed. The specificity of the RT-nested PCR was confirmed with reference and recent field strains of TGEV/PRCV, and its sen sitivity was analyzed by testing nasal and fecal samples collected from pig s at various days postinoculation (DPI) with TGEV or PRCV. Specific PCR pro ducts for TGEV/PRCV were detected only with the homologous reference or fie ld coronaviruses and for 10-14 DPI of pigs with TGEV (feces) or PRCV (nasal samples). The RT-nested PCR assay was more sensitive than antigen-based as says on the basis of duration of virus detection in experimentally infected pigs and was directly applicable to nasal as well as fecal specimens from the field.