Mucosal disease induced in cattle persistently infected with bovine viral diarrhea virus by antigenically different cytopathic virus

Summary.  Four cattle persistently infected with non-cytopathic (NCP) bovine viral diarrhea (BVD) virus were challenged with cytopathic (CP) BVD virus that was antigenically different from the persistent virus. Two of the animals were injected with dexamethasone (DM) and then challenged. They developed mucosal disease on days 21 and 33 post-challenge. CP-BVD viruses were isolated from their lymph nodes but not from the sera. The isolates were antigenically different from the persistent virus and the nucleotide sequence of a 787 base region in the E2 gene was markedly different. One of the isolates was indistinguishable from the challenge virus by virus neutralization tests and the nucleotide sequence showed high homology with that of the challenge CP-BVD virus. The other two cattle, challenged with the CP-BVD virus without DM treatment, developed mucosal disease at 30 and 264 days post-inoculation. CP-BVD virus was isolated from the sera as well as the lymph nodes of the cattle and was antigenically and genetically similar to the persistent virus and different from the challenge CP-BVD virus. The present results indicate that cattle persistently infected with NCP-BVD virus can develop mucosal disease induced by antigenically different CP-BVD viruses when their cellular immunity is suppressed, although they are not immunotolerant to the virus. Accepted November 1, 2000 Received July 25, 2000