Research Summary

Introduction

Bovine Virus Diarrhea (BVD) virus was first recognized as a pathogen in1946, and has been implicated as the cause of one of the most widespread and economically important diseases of cattle.

The importance of bovine virus diarrhea-persistently infected (BVD-PI) cattle in the spread and propagation of BVD virus has been well documented. A persistent BVD infection occurs when a fetus is exposed to the BVD virus in the first 120 days of gestation. At this stage, the developing fetal immune system recognizes the virus as part of "self", therefore, no immune response occurs. After birth, these BVD-PI cattle excrete tremendous amounts of virus from every body orifice throughout most of their lives, and thus are considered to be the most important reservoir for BVD virus. It is estimated that approximately 1% of all cattle are persistently infected.

Although many BVD-PI animals exhibit poor growth rate and an unthrifty appearance, a significant number are clinically normal. Hence, control and eradication of BVD virus has been primarily focused on the development of tests to detect the persistently infected animal. New BVD diagnostic tests, including immunohistochemistry, antigen capture enzyme-linked-immunosorbent-assay (ELISA) and polymerase chain reaction (PCR) are available at many veterinary diagnostic laboratories and are capable of detecting the virus.

Since the BVD-PI state only develops during early gestation and there are no vaccines that protect the fetus from infection, identification and elimination of BVD-PI cattle from the herd prior to exposure to early gestating cows is a critical control point for BVD. This requires that calves be tested before the breeding season, and most of these calves will be carrying maternal antibody titers that may interfere with tests designed to identify BVD-PI animals. Consequently, it is vital to BVD control programs that testing methodology be developed that can identify BVD-PI calves while they are carrying maternal antibody titers.

Two methods of detecting BVD virus in neonatal calves have been developed: immunohistochemistry on skin sections (ear notches) by Dr. Broderson at Nebraska and BVD antigen capture ELISA testing of nasal swabs by Drs. Sorden and Yoon at Iowa State.