Comparison of virus isolation and reverse transcription polymerase chain reaction assay for detection of bovine viral diarrhea virus in bulk milk tank samples

Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14850, USA.

The use of a reverse transcriptase polymerase chain reaction (RT-PCR) assay to screen bulk milk tank samples for bovine viral diarrhea virus (BVDV) has proven to be a sensitive and economical means to evaluate the lactating animals in a herd. The assay is capable of detecting the presence of a single persistently infected animal within a group of several hundred cows. Over a 3-year period, 144 samples from 97 farms were tested for BVDV using an RT-PCR assay in conjunction with a classical virus isolation (VI) procedure to measure the relative effectiveness of the techniques. Virus could be detected with both methods when the milk from a single persistently infected animal was diluted 1:600 with the milk from a herd of BVDV-negative animals. Based on individual farms, there was an overall prevalence of 12.4% BVDV infection, and the correlation between the 2 assays was 95.9%. In terms of sensitivity, specificity, and turnaround time, RT-PCR was superior to VI. However, of the 17 samples that were VI positive, 4 were RT-PCR negative. RT-PCR may not detect all naturally occurring BVDV isolates because they may contain minor sequence variations in the primer regions. VI and RT-PCR are both suitable for detection of BVDV in bulk milk samples when used independently, but to increase the probability of successful detection and to provide cross-checks against assay contamination, it is desirable to utilize both methods in parallel.

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