Use of Nonradioactive cDNA Probes to Differentiate Porcine Respiratory Coronavirus and Transmissible Gastroenteritis Virus Isolates

Porcine respiratory coronavirus (PRCV), a member of the family Coronaviridae, is antigenically related to transmissible gastroenteritis virus (TGEV) of swine. PRCV, now thought to be a mutant of TGEV, was first isolated in 1984 from pigs in Belgium that were seropositive for TGEV but did not have a history of clinical transmissible gastroenteritis (TGE). Since the initial isolation of PRCV, it has been found that infections of swine in Europe with PRCV are widespread. PRCV has also been isolated in swine in the United States, 7,11,20,24 but its prevalence in herds within the United States is not known. There are several similarities between PRCV and TGEV. Both viruses have 3 major structural proteins: the surface spike (S) glycoprotein, the integral membrane glycoprotein, and an internal nucleoprotein. Nucleotide sequences of PRCV isolates thus far studied show that they are closely related to TGEV but that there are some striking differences. PRCV isolates have a characteristic deletion in the 5' end of the S gene when compared to TGEV, and PRCV has a different tissue tropism than TGEV. TGEV replicates in both the respiratory and intestinal tissues and causes gastroenteritis, 14 whereas PRCV replicates to high titers in lung tissue of swine and with little or no replication in the intestinal tissues and no evidence of gastroenteritis and villous atrophy. PRCV is antigenically related to TGEV in that polyclonal sera which neutralize TGEV also neutralize PRCV. Thus, conventional serologic methods are not useful in determining if a swine herd with anti-TGEV antibodies has been infected with PRCV or TGEV. Anti-TGEV neutralizing monoclonal antibodies (MAbs) directed against the S glycoprotein readily neutralize PRCV; however, there are some nonneutralizing anti-TGEV MAbs directed against the S glycoprotein that can be used to distinguish between PRCV and TGEV isolates in a competitive binding assay. Of the European PRCV isolates that have had their nucleotide sequences published, all have a 672-nucleotide deletion in the 5' end of the S gene. The US PRCV isolates Ind/89 and ISU-1 have a 681-nucleotide deletion present in the 5' end of the S gene. Recently the PRCV isolates AR310 and LEPP have been shown to have a smaller S gene deletion of 621 nucleotides present. Additionally, the PRCV isolate IA1894 has recently been shown to have a 678-nucleotide deletion in the 5' end of its S gene. Hence, a cDNA probe that encompasses the region of the TGEV S gene that is characteristically deleted from PRCV isolates can be used