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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.

Okda F, Liu X, Singrey A, Clement T, Nelson J, Christopher-Hennings J, Nelson EA, Lawson S - BMC Vet. Res. (2015)

Bottom Line: The ROC analysis for the FMIA showed estimated sensitivity and specificity of 98.2 and 99.2 %, respectively.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.

View Article: PubMed Central - PubMed

Affiliation: Veterinary & Biomedical Sciences Department, South Dakota State University, Brookings, SD, USA. faten.okda@sdstate.edu.

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.

Conclusion: 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.

No MeSH data available.


Related in: MedlinePlus

Assessment of neutralizing antibody titers in different sample matrices following PEDV exposure. FFN titers were detected in various sample matrices including colostrum (n = 25), milk (n = 23) and serum (n = 27) collected at the time of farrowing and weekly for two weeks post-farrowing. Error bars indicate a 95 % confident interval for mean titers indicated by horizontal lines
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Fig7: Assessment of neutralizing antibody titers in different sample matrices following PEDV exposure. FFN titers were detected in various sample matrices including colostrum (n = 25), milk (n = 23) and serum (n = 27) collected at the time of farrowing and weekly for two weeks post-farrowing. Error bars indicate a 95 % confident interval for mean titers indicated by horizontal lines

Mentions: The FFN assay was initially evaluated using sequential serum samples from experimentally inoculated piglets. Additional evaluation was conducted using 250 serum samples from known PEDV naïve herds and 250 samples from herds with documented PEDV exposure, collected at least 3 weeks after initial PCR diagnosis and whole herd feedback. Experimentally inoculated piglets demonstrated detectable seroconversion by 14 DPI (Fig. 6). Essentially all samples from PEDV naïve animals had serum FFN endpoint titers of <1:20 while most samples from the PEDV positive set had endpoint titers ranging from 1:40 to 1:1280 (data not shown). Further evaluation of the FFN included serum, milk and colostrum samples from 27 sows from a herd that had experienced an acute PEDV outbreak 6 to 7 weeks prior to farrowing. All animals were exposed to live virus twice within the first week of the outbreak, followed by one dose of Harrisvaccines Porcine Epidemic Diarrhea Vaccine, RNA (Harrisvaccines, Inc., Ames, IA) at 1 week pre-farrow. Serum and colostrum samples were tested at the time of farrowing, followed by serum and milk samples at 1 week and 2 weeks later. As shown in Fig. 7, mean colostrum titers were approximately 4-fold higher than serum titers at the time of farrowing. At later time-points, serum and milk titers were similar in magnitude, although substantial animal to animal variation was apparent.Fig. 7


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.

Okda F, Liu X, Singrey A, Clement T, Nelson J, Christopher-Hennings J, Nelson EA, Lawson S - BMC Vet. Res. (2015)

Assessment of neutralizing antibody titers in different sample matrices following PEDV exposure. FFN titers were detected in various sample matrices including colostrum (n = 25), milk (n = 23) and serum (n = 27) collected at the time of farrowing and weekly for two weeks post-farrowing. Error bars indicate a 95 % confident interval for mean titers indicated by horizontal lines
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4522128&req=5

Fig7: Assessment of neutralizing antibody titers in different sample matrices following PEDV exposure. FFN titers were detected in various sample matrices including colostrum (n = 25), milk (n = 23) and serum (n = 27) collected at the time of farrowing and weekly for two weeks post-farrowing. Error bars indicate a 95 % confident interval for mean titers indicated by horizontal lines
Mentions: The FFN assay was initially evaluated using sequential serum samples from experimentally inoculated piglets. Additional evaluation was conducted using 250 serum samples from known PEDV naïve herds and 250 samples from herds with documented PEDV exposure, collected at least 3 weeks after initial PCR diagnosis and whole herd feedback. Experimentally inoculated piglets demonstrated detectable seroconversion by 14 DPI (Fig. 6). Essentially all samples from PEDV naïve animals had serum FFN endpoint titers of <1:20 while most samples from the PEDV positive set had endpoint titers ranging from 1:40 to 1:1280 (data not shown). Further evaluation of the FFN included serum, milk and colostrum samples from 27 sows from a herd that had experienced an acute PEDV outbreak 6 to 7 weeks prior to farrowing. All animals were exposed to live virus twice within the first week of the outbreak, followed by one dose of Harrisvaccines Porcine Epidemic Diarrhea Vaccine, RNA (Harrisvaccines, Inc., Ames, IA) at 1 week pre-farrow. Serum and colostrum samples were tested at the time of farrowing, followed by serum and milk samples at 1 week and 2 weeks later. As shown in Fig. 7, mean colostrum titers were approximately 4-fold higher than serum titers at the time of farrowing. At later time-points, serum and milk titers were similar in magnitude, although substantial animal to animal variation was apparent.Fig. 7

Bottom Line: The ROC analysis for the FMIA showed estimated sensitivity and specificity of 98.2 and 99.2 %, respectively.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.

View Article: PubMed Central - PubMed

Affiliation: Veterinary & Biomedical Sciences Department, South Dakota State University, Brookings, SD, USA. faten.okda@sdstate.edu.

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.

Conclusion: 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.

No MeSH data available.


Related in: MedlinePlus