Bovine viral diarrhea virus isolated from fetal calf serum enhances pathogenicity of attenuated transmissible gastroenteritis virus in neonatal pigs

A bovine viral diarrhea virus (BVDV-C) was isolated from swine tissue cultu re cells used to attenuate the transmissible gastroenteritis virus (TGEV) a fter 68 passes. Piglets given a pure culture of BVDV-C developed clinical s igns similar to those of a mild TGEV infection and recovered by 10 days pos texposure. Villous blunting and fusion was observed in the small intestine, and a lymphocyte depletion was observed in Peyer's patches in the ileum. P iglets given a combination of BVDV-C and attenuated TGEV developed clinical signs similar to those of a virulent TGEV infection and were euthanized. T he combined infection induced a generalized lymphocyte depletion throughout the lymphatic system and villous atrophy in the intestinal tract. Piglets exposed to a another type I strain of BVDV (NY-1) either alone or in combin ation with the attenuated TGEV had mild clinical signs similar to those of a TGEV infection. Moderate villous atrophy in the ileum and a lymphocyte de pletion in the mesenteric lymph node were observed in these piglets postmor tem. The data indicate a potential problem for diagnostic laboratories in r elation to a diagnosis of virulent TGEV infections and in the field for you ng piglets exposed to a BVDV-contaminated TGEV vaccine.