title: Development of an indirect ELISA, blocking ELISA, fluorescent microsphere immunoassay and fluorescent focus neutralization assay for serologic evaluation of exposure to North American strains of Porcine Epidemic Diarrhea Virus.
abstract: BACKGROUND
  Recent, severe outbreaks of porcine epidemic diarrhea virus (PEDV) in Asia and North America highlight the need for well-validated diagnostic tests for the identification of PEDV infected animals and evaluation of their immune status to this virus. PEDV was first detected in the U.S. in May 2013 and spread rapidly across the country. Some serological assays for PEDV have been previously described, but few were readily available in the U.S. Several U.S. laboratories quickly developed indirect fluorescent antibody (IFA) assays for the detection of antibodies to PEDV in swine serum, indicating prior exposure. However, the IFA has several disadvantages, including low throughput and relatively subjective interpretation. Different serologic test formats have advantages and disadvantages, depending on the questions being asked, so a full repertoire of tests is useful. Therefore, the objective of this study was to develop and validate multiple improved serological assays for PEDV, including an indirect ELISA (iELISA); a highly specific monoclonal antibody-based blocking ELISA (bELISA); fluorescent microsphere immunoassays (FMIA) that can be multiplexed to monitor exposure to multiple antigens and pathogens simultaneously; and a fluorescent focus neutralization assay (FFN) to measure functional virus neutralizing antibodies.
  
  
  RESULTS
  A recombinant North American nucleoprotein (NP) based iELISA was developed and validated along with a bELISA using newly developed PEDV-NP specific biotinylated monoclonal antibodies (mAbs) and an FMIA using magnetic beads coupled with expressed NA PEDV-NP. Receiver operating characteristic (ROC) analysis was performed using swine serum samples (iELISA n = 1486, bELISA n = 1186, FMIA n = 1420). The ROC analysis for the FMIA showed estimated sensitivity and specificity of 98.2 and 99.2 %, respectively. The iELISA and bELISA showed a sensitivity and specificity of 97.9 and 97.6 %; and 98.2 and 98.9 %, respectively. Inter-rater (kappa) agreement was calculated to be 0.941 between iELISA and IFA, 0.945 between bELISA and IFA and 0.932 between FMIA and IFA. Similar comparative kappa values were observed between the iELISA, bELISA and FMIA, which demonstrated a significant level of testing agreement among the three assays. No cross-reactivity with the closely related coronaviruses, transmissible gastroenteritis virus (TGEV) or porcine respiratory coronavirus (PRCV) was noted with these assays. All three assays detected seroconversion of naïve animals within 6-9 days post exposure. The FFN assay allows relative quantitation of functional neutralizing antibodies in serum, milk or colostrum samples.
  
  
  CONCLUSIONS
  Well-validated iELISA, bELISA and FMIA assays for the detection of PEDV antibodies were developed and showed good correlation with IFA and each other. Each assay format has advantages that dictate how they will be used in the field. Newly developed mAbs to the PEDV-NP were used in the bELISA and for expediting FFN testing in the detection and quantitation of neutralizing antibodies. In addition, these PEDV mAbs are useful for immunohistochemistry, fluorescent antibody staining and other antigen-based tests. Measurement of neutralizing antibody responses using the FFN assay may provide a valuable tool for assessment of vaccine candidates or protective immunity.
authors.affiliation: Veterinary & Biomedical Sciences Department, South Dakota State University, Brookings, SD, USA. faten.okda@sdstate.edu.|National Research Center, Giza, Egypt. faten.okda@sdstate.edu.
authors.forename: Faten
authors.initials: F
authors.lastname: Okda
authors.affiliation: Veterinary & Biomedical Sciences Department, South Dakota State University, Brookings, SD, USA. xiaodong.liu@sdstate.edu.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Liu
authors.affiliation: Veterinary & Biomedical Sciences Department, South Dakota State University, Brookings, SD, USA. aaron.singrey@sdstate.edu.
authors.forename: Aaron
authors.initials: A
authors.lastname: Singrey
authors.affiliation: Veterinary & Biomedical Sciences Department, South Dakota State University, Brookings, SD, USA. travis.clement@sdstate.edu.
authors.forename: Travis
authors.initials: T
authors.lastname: Clement
authors.affiliation: Veterinary & Biomedical Sciences Department, South Dakota State University, Brookings, SD, USA. julie.nelson@sdstate.edu.
authors.forename: Julie
authors.initials: J
authors.lastname: Nelson
authors.affiliation: Veterinary & Biomedical Sciences Department, South Dakota State University, Brookings, SD, USA. jane.hennings@sdstate.edu.
authors.forename: Jane
authors.initials: J
authors.lastname: Christopher-Hennings
authors.affiliation: Veterinary & Biomedical Sciences Department, South Dakota State University, Brookings, SD, USA. eric.nelson@sdstate.edu.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Nelson
authors.affiliation: Veterinary & Biomedical Sciences Department, South Dakota State University, Brookings, SD, USA. steven.lawson@sdstate.edu.
authors.forename: Steven
authors.initials: S
authors.lastname: Lawson
mesh_terms: D000818:Animals; D000914:Antibodies, Viral; D000956:Antigens, Viral; D002522:Chlorocebus aethiops; D018352:Coronavirus Infections / Q000097:blood / Q000175:diagnosis / Q000662:veterinary* / Q000821:virology; D007118:Immunoassay / Q000379:methods / Q000662:veterinary*; D008863:Microspheres; D009656:North America; D053485:Porcine epidemic diarrhea virus / Q000302:isolation & purification*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012698:Serologic Tests / Q000379:methods / Q000662:veterinary*; D013552:Swine; D013553:Swine Diseases / Q000097:blood / Q000175:diagnosis* / Q000821:virology; D014709:Vero Cells
chemical_list: D000914:Antibodies, Viral; D000956:Antigens, Viral