The ability for producers to succeed depends in part, on their ability to rapidly respond to emerging and existing disease challenges. Submission of fresh samples to diagnostic laboratories in a timely manner often represents a challenge. The use of FTA cards, a filter paper especially designed for the transport and storage of samples, is one option to safely store and rapidly transport biological samples from the field to diagnostic laboratories at a low cost. FTA cards consist of a cellulose-based matrix paper containing chemicals that lyse the cells in the sample while preserving the nucleic acids. Therefore the infectious agents become inactive while their genetic material is preserved.
The objective of this study was to validate the FTA cards for PRRS virus diagnostics. Specifically this study evaluated the FTA cards as an alternative method to transport and store biologic samples to conduct PRRSv molecular testing. Diagnostic sensitivity and specificity of samples embedded on FTA cards was compared to that of samples tested directly (conventional method). Samples originated from both experimentally infected pigs and field submissions to the Veterinary Diagnostic Laboratory.
In vitro validation indicated that detection of PRRSv in FTA cards was possible and that sensitivity was good although lower than testing the samples directly. Results from the experimentally infected animals showed 100% agreement between PCRs from samples embedded on cards and samples tested directly. Sensitivity and specificity was 100%. The samples included serum, blood and tissues (lung, lymph nodes and tonsils) collected from acutely infected animals shortly after euthanasia. PCR sensitivity for samples stored in FTA cards at room temperature or at 4ºC, and stored overnight or for 2 weeks was similar. In addition, sensitivity for field serum samples embedded on FTA cards was 86%. In the case of oral fluids, sensitivity was only 36%.
In summary, diagnostic sensitivity of FTA cards from samples collected from experimentally infected animals was good and similar than testing the samples directly. However, sensitivity was slightly lower when field samples were used. The lower sensitivity for field samples may reflect the variability observed in the field and ultimately may result in false negative results. In addition, further evaluation is required to recommend the use of FTA cards to transport oral fluids.
In conclusion, FTA cards are an alternative method for collecting, transporting and storing sera and tissue samples for PRRSV molecular diagnostics. While the probability of detecting PRRSV in FTA cards is lower than in fresh samples, FTA cards offer advantages to producers which include: a) ease of sample collection and submission in the field, b) safety of samples embedded in the cards making possible to ship samples in a single envelope without need for biohazard labeling, and c) lower cost of submitting samples.
