Evaluation of serological cross-reactivity and cross-neutralization between the United States porcine epidemic diarrhea virus prototype and S-INDEL-variant strains

Abstract

Background: At least two genetically different porcine epidemic diarrhea virus (PEDV) strains have been identified in the United States (U.S. PEDV prototype and S-INDEL-variant strains). The current serological assays offered at veterinary diagnostic laboratories for detection of PEDV-specific antibody are based on the U.S. PEDV prototype strain. The objectives of this study were: 1) isolate the U.S. PEDV S-INDEL-variant strain in cell culture; 2) generate antisera against the U.S. PEDV prototype and S-INDEL-variant strains by experimentally infecting weaned pigs; 3) determine if the various PEDV serological assays could detect antibodies against the U.S. PEDV S-INDEL-variant strain and vice versa.

Results: A U.S. PEDV S-INDEL-variant strain was isolated in cell culture in this study. Three groups of PEDV-negative, 3-week-old pigs (five pigs per group) were inoculated orally with a U.S. PEDV prototype isolate (previously isolated in our lab), an S-INDEL-variant isolate or virus-negative culture medium. Serum samples collected at 0, 7, 14, 21 and 28 days post inoculation were evaluated by the following PEDV serological assays: 1) indirect fluorescent antibody (IFA) assays using the prototype and S-INDEL-variant strains as indicator viruses; 2) virus neutralization (VN) tests against the prototype and S-INDEL-variant viruses; 3) PEDV prototype strain whole virus based ELISA; 4) PEDV prototype strain S1-based ELISA; and 5) PEDV S-INDEL-variant strain S1-based ELISA. The positive antisera against the prototype strain reacted to and neutralized both prototype and S-INDEL-variant viruses, and the positive antisera against the S-INDEL-variant strain also reacted to and neutralized both prototype and S-INDEL-variant viruses, as examined by IFA antibody assays and VN tests. Antibodies against the two PEDV strains could be detected by all three ELISAs although detection rates varied to some degree.

Conclusions: These data indicate that the antibodies against U.S. PEDV prototype and S-INDEL-variant strains cross-reacted and cross-neutralized both strains in vitro. The current serological assays based on U.S. PEDV prototype strain can detect antibodies against both U.S. PEDV strains.

Keywords: ELISA; IFA; PEDV; Porcine epidemic diarrhea virus; Prototype; S-INDEL; Variant; Virus neutralization.

Fig. 1

IFA antibody testing of antisera against the U.S. PEDV prototype and S-INDEL-variant strains. The average IFA antibody titers are shown at the top and the number of IFA antibody positive samples is shown at the bottom. Pro antisera: antisera collected from the U.S. PEDV prototype strain-inoculated pigs; Var antisera: antisera collected from the U.S. PEDV S-INDEL-variant strain-inoculated pigs; Neg antisera: antisera collected from negative control pigs; Pro IFA: the U.S. PEDV prototype strain-based IFA; Var IFA: the U.S. PEDV S-INDEL-variant strain-based IFA

Fig. 2

Testing of antisera against the U.S. PEDV prototype and S-INDEL-variant strains by ProWV ELISA (a), ProS1 ELISA (b) and VarS1 ELISA (c). For each assay, the solid black line indicates the S/P ratio above which the sample was positive; the dot black line indicates the S/P ratio below which the sample was negative; samples with S/P ratios between the solid and dot black line were suspect. ProWV ELISA: the U.S. PEDV prototype strain whole virus-based ELISA; ProS1 ELISA: the U.S. PEDV prototype strain S1-based ELISA; VarS1 ELISA: the U.S. PEDV S-INDEL-variant strain S1-based ELISA

Fig. 3

Virus neutralization antibody testing of antisera against the U.S. PEDV prototype and S-INDEL-variant strains. The average VN antibody titers are shown at the top and the number of VN antibody positive samples is shown at the bottom. Pro VN: the U.S. PEDV prototype strain-based VN; Var VN: the U.S. PEDV S-INDEL-variant strain-based VN