Case report

Comparison of pooled polymerase chain reaction testing to non-pooled antigen capture enzyme-linked immunosorbent assay to detect bovine viral diarrhea virus persistently infected stocker calves.

Abstract

There are several different methods of testing cattle for persistent infection with bovine viral diarrhea virus (PI-BVDV), including immunohistochemistry (IHC), polymerase chain reaction (PCR), virus isolation, and antigen capture enzyme-linked immunosorbent assay (ACE). The purpose of this report is to describe a case in which a pooled PCR test (28 specimens/pool) was compared for sensitivity against an ACE test (tested as single specimens). Ear notch specimens (fresh) were collected from beef calves purchased by a stocker operation. From January through March 2010, this stocker operation received 2,424 calves and took two ear-notch specimens from each calf for PI-BVDV testing. One specimen from each calf was sent to a commercial PI-BVDV testing laboratory that utilizes real-time PCR technology in specimen pools of 28 (Laboratory A), and a second specimen was sent to a commercial PI-BVDV testing laboratory that utilizes ACE (NS23) technology using non-pooled specimens (Laboratory B). Laboratory A detected four positive specimens out of the 2,424 specimens submitted (0.165% PI prevalence), while Laboratory B detected 12 positive specimens out of the 2,424 specimens submitted (0.495% PI prevalence). The 12 specimens detected by Laboratory B included the same four detected by Laboratory A, as well as eight additional positive specimens. Upon receiving these discordant results, the attending veterinarian requested that the 12 positive specimens detected by Laboratory B be re-tested using the original specimens. These original 12 ACE-positive specimens were then re-tested as single specimens at Laboratory B using a commercially available ACE test (Erns) and real-time PCR technology. The 12 original ACE-positive specimens were again positive by these different tests. Follow-up testing on the 12 calves was conducted more than 30 days after initial testing with a second set of samples from the eight surviving calves (four of the 12 calves died between the original and the second collection). The second set of samples from the eight surviving calves initially ACE-positive by Laboratory B were tested using serum, formalin-fixed ear notches, and fresh ear notches in phosphate buffered saline. All specimens were positive by gel-based reverse transcriptase PCR on serum and ear notches (non-pooled), and all eight formalin-fixed notches were also positive by IHC.