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PEDv IFA

Porcine Epidemic Diarrhea virus (PEDv) Antibody Test now available at ISU VDL

Beginning on Wednesday, August 28th, the VDL will start offering an Indirect Immunofluorescence Assay (IFA) to detect the presence of PEDv antibodies in swine serum. The test has been made available through the development of efforts of ISU VDL Virologists (Dr. K.J. Yoon and Dr. JQ Zhang), their graduate students, and the financial support of the Iowa Pork Producers Association. Upon establishing methods to successfully isolate and readily propagate PEDv in cell culture, the development of the IFA quickly followed.

The test will be offered as a screen with either a positive or negative result rendered at a 1:40 dilution. The cost of the screen will be $5.50 per sample. The VDL will also offer a 4 dilution IFA that will report titers from <40 to > 320 with the cost being $15.00 per sample.

Many of the serology questions received regarding PEDv involve the desire to increase confidence in the PEDv status of replacement females and/or better understanding the prevalence of PEDv within a region. Field reports from ISU VDL clientele suggest that the clinical presentation of PEDv infection in growing pigs can be variable in its severity and not readily distinguishable from the myriad of other causes of diarrhea in growing pigs. Our suggestion would be to approach antemortem PEDv surveillance with the same rationale more commonly used in PRRSv surveillance that incorporates the use of both antigen and antibody based diagnostic tools. We recommend using the PEDv PCR on either fecal or oral fluids samples coupled with IFA antibody assessment of serum samples. The PEDv PCR will detect early infection and viral shedding during the lag time between infection and seroconversion; while the antibody-based IFA will detect historical evidence of exposure in animals that may no longer be shedding the virus in their feces. Pigs experimentally infected with PEDv developed a detectable IFA antibody titer by 3 to 4 weeks post-infection. There have also been questions about the magnitude of the antibody titer and a possible relationship to protective immunity and/or cessation of fecal shedding. At this point we cannot say if such a correlation exists. A serum virus neutralization assay is also being developed by Dr. Yoon’s research group that may better address the protective immunity question in the future.

As you consider requesting the PEDV IFA, remember that IFAs are subjectively read and by the very nature of the test are more labor-intensive than ELISAs. IFA assays also don’t lend themselves to high volume sample throughput like ELISAs. This is due to the need for technicians to examine each sample well under a fluorescent microscope to evaluate sample results, as opposed to an automated 96 well plate reader used to evaluate ELISA results. The R&D group is now exploring potential ELISA applications that could be adapted for PEDv in order to enhance sample throughput in the future.