Porcine epidemic diarrhea virus (PEDV) detection and antibody response in commercial growing pigs

Abstract

Background: Longitudinal samples from two production sites were used to (1) describe the pattern of PEDV shedding (rRT-PCR) in individual rectal swabs, pen fecal samples, and pen oral fluids (OF); (2) describe the kinetics of PEDV antibody by ELISA (IgA, IgG) testing of pig serum and pen oral fluid samples; and (3) establish cutoffs and performance estimates for PEDV WV ELISAs (IgA, IgG). Site One was PEDV positive; Site Two was PEDV negative. On Site One, pen samples (feces and oral fluids) and pig samples (rectal swabs and sera) were collected both before and after the population was exposed to PEDV.

Results: On Site Two, pen oral fluid samples and individual pig serum samples were negative for both PEDV antibody and nucleic acid. On Site One, PEDV was detected by rRT-PCR at 6 days post exposure (DPE) in all sample types. The last rRT-PCR positives were detected in rectal swabs and oral fluids on 69 DPE. IgG and IgA were detected in oral fluids and serum samples by 13 DPE. Analysis of the PEDV serum IgG WV ELISA data showed that a sample-to-positive (S/P) cutoff of ≥ 0.80 provided a diagnostic sensitivity of 0.87 (95% CI: 0.82, 0.91) and specificity of 0.99 (95% CI: 0.98, 1.00). Serum IgG results declined slowly over the monitoring period, with 60% of serum samples positive (S/P ≥ 0.80) at the final sampling on 111 DPE. Analysis of the PEDV oral fluid IgA WV ELISA found that a cutoff of S/P ≥ 0.80 provided a diagnostic sensitivity of 1.00 (95% CI: 0.92, 1.00) and a diagnostic specificity of 1.00 (95% CI: 0.99, 1.00). The oral fluid IgA response increased through 96 DPE and began to decline at the last sampling on 111 DPE.

Conclusions: This study showed that oral fluid-based testing could provide an easy and "animal-friendly" approach to sample collection for nucleic acid and/or antibody-based surveillance of PEDV in swine populations.

Keywords: Antibody kinetics; IgA; IgG; Oral fluids; PEDV; Surveillance; Virus shedding.

Fig. 1

Detection of porcine epidemic diarrhea virus (PEDV) in pig rectal swabs, pen-based oral fluids, and pen-based fecal specimens from Site One by rRT-PCR. At 13 weeks of age, the producer exposed the pigs to PEDV-positive fecal material mixed with water using a hand-held sprayer. a (above): Mean adjusted quantification cycle (Cq) (35 – sample Cq) of positive samples. b (below): Proportion of positive samples

Fig. 2

PEDV Whole Virus ELISA IgG and IgA responses in oral fluid samples following exposure to PEDV at 13 weeks of age. a (above): Oral fluid IgG and IgA responses over time. b (below): Proportion of positive oral fluid IgA samples at three different S/P cutoffs

Fig. 3

PEDV Whole Virus ELISA IgG and IgA response in serum samples following exposure to PEDV at 13 weeks of age. a (above): Serum IgG and IgA responses over time. b (below): Proportion of positive serum IgG samples at three different S/P cutoffs