Evaluation of FTA cards as a sample collection method for detection of BVDV in persistently infected beef cattle

Abstract

The accuracy of test outcome is directly related to the quality of samples arriving at the diagnostic laboratory. However, in certain field situations sample storage conditions may be less than optimal. Flinders Technology Associates (FTA) cards are a sample collection and storage tool suitable for field conditions. For the evaluation of FTA cards, nasal swabs and EDTA blood samples were collected by traditional methods from a group of known bovine viral diarrhea virus (BVDV) persistently infected (PI) animals, as well as from animals in a herd never diagnosed with BVDV infection. Diagnostic performance parameters of the reverse transcription real-time PCR assay (RT-r PCR) were compared between whole-blood and nasal-swab samples collected onto FTA cards from the same animals taken at the same time. Sensitivity and specificity based on the dichotomous classification of BVDV-positive or negative were 100% for the samples collected using traditional methods, and for those collected onto FTA cards. Real-time PCR cycle threshold values demonstrated a lower analytic sensitivity for samples collected onto FTA cards, although samples from FTA cards correctly identified all PI animals tested. One animal from the PI group tested BVDV-positive only in the nasal specimen, suggesting the positive resulted from contact exposure rather than from systemic viral production. To further evaluate the potential of the FTA cards, a subset of BVDV-positive samples (n=29) were sub-typed by direct sequencing of the BVDV qRT PCR products obtained from the case material. BVDV-1 was detected in 75.9% (22/29) of cases, BVDV-2 in 13.8% (4/29) of cases, and both serotypes were simultaneously detected in the remaining 10.3% (3/29) cases. Time savings associated with use of FTA cards for sample collection was calculated to be 23.5 seconds per blood sample. The FTA cards provide a method for diagnostic sample handling that helps overcome sample quality issues associated with improper storage conditions and shipping concerns.