Characterization and cross-protection of experimental infections with
SeCoV and two PEDV variants.
Abstract
Global emergence and re-emergence of Porcine epidemic diarrhea
virus (PEDV), an Alphacoronavirus which causes a highly contagious
enteric disease, have led to several studies addressing its variability.
The aim of this study was to characterize the infection of weaned pigs
with Swine enteric coronavirus (SeCoV) -a chimeric virus most
likely originated from a recombination event between PEDV and
Transmissible gastroenteritis virus, or its mutant Porcine
respiratory coronavirus-, and two PEDV G1b variants, including a
recently described recombinant PEDV-SeCoV (rPEDV-SeCoV), as well as to
determine the degree of cross-protection achieved against the
rPEDV-SeCoV. For this purpose, forty-eight 4-week-old weaned pigs were
randomly allocated into four groups of 12 animals; piglets in groups B,
C and D were orally inoculated with a PEDV variant (B and D) or SeCoV
(C), while piglets in group A were mock inoculated and maintained as
controls. At day 20 post-infection all groups were exposed to
rPEDV-SeCoV; thus, group D was subjected to a homologous re-challenge,
groups B and C to a heterologous re-challenge (PEDV/rPEDV-SeCoV and
SeCoV/rPEDV-SeCoV, respectively) and group A was primary challenged
(-/rPEDV-SeCoV). Clinical signs, viral shedding, microscopic lesions and
specific humoral and cellular immune responses (IgG, IgA, neutralizing
antibodies and IgA and IFN-γ-secreting cells) were monitored. After
primo-infection all three viral strains induced an undistinguishable
mild-to-moderate clinical disease with diarrhea as the main sign and
villus shortening lesions in the small intestine. In homologous
re-challenged pigs, no clinical signs or lesions were observed, and
viral shedding was only detected in a single animal. This fact may be
explained by the significant high level of rPEDV-SeCoV-specific
neutralizing antibodies found in these pigs before the challenge. In
contrast, prior exposition to a different PEDV G1b variant or SeCoV only
provided partial cross-protection, allowing rPEDV-SeCoV replication and
shedding in feces.