Enzymatic and acidic sensitivity profiles of selected virulent and attenuated transmissible gastroenteritis viruses of swine.

This study identifies the in vitro differences (markers) between virulent and attenuated transmissible gastroenteritis (TGE) viruses. Exposure of virulent Miller strain and attenuated Purdue strain TGE viruses to a spectrum of acidities indicated that the Miller strain was more stable at pH 2. Acidities at or above pH 3 did not reduce viral infectivity of either strain. When virulent and attenuated viruses were exposed to gastric fluids of either fed or fasted swine, there was a similar degree of sensitivity. Carboxypeptidase B, alpha-amylase, and alkaline phosphatase present in porcine small intestinal fluids did not cause a significant difference in sensitivity between virulent and attenuated virus isolates. The digestive enzymes: trypsin, alpha-chymotrypsin, pancreatin, peptidase, and carboxypeptidase A did not (or only slightly) inactivate virulent Miller strain TGE virus, but greatly reduced infectivity of attenuated viruses (Purdue strain and TGE vaccine virus isolates). The attenuated strains were significantly more sensitive to small intestinal fluids from both fasted and fed adult swine. Differential sensitivities between virulent and attenuated TGE viruses to digestive fluids from stomach and small intestine further substantiate the notion of differential susceptibility to small intestinal proteases as a correlate of viral virulence.