The use of PCR genome mapping for the characterisation of TGEV strains

Previous studies on different transmissible gastroenteritis virus (TGEV) strains, including porcine respiratory coronavirus (PRCV), have identified regions within the genome that are polymorphic as regards insertions and deletions. For example the 672 base deletion within the S gene and multiple deletions 5', within and 3' of the ORF-3a gene were detected in strains of PRCV. The presence of deletions may be associated with a change in the virulence, attenuation or tissue tropism of the isolate. The Nouzilly (188-SG) TGEV vaccine strain was attenuated by passage of a cell culture adapted virulent isolate D-52 188 times through swine testis cells after treatment with gastric juice. PCR amplification with oligonucleotides, corresponding to known TGEV sequences, were used to analyse D-52 and 188-SG for genetic variation. Results with several pairs of oligonucleotides within the first 1565 nucleotides of the S gene did not identify a deletion within this region of the genome from either strain. However, oligonucleotides directed against the ORF-3a/3b region detected a deletion of about 250 nucleotides within the 188-SG genome but not in the D-52 genome. Since all the attenuated TGEV strains so far sequenced, PRCV, Miller SP and 188-SG, contained deletions within the ORF-3a/3b, it would suggest that this region of the TGEV genome is involved in regulating viral virulence.