Porcine epidemic diarrhea virus (PEDV): An update on etiology, transmission, pathogenesis, and prevention and control

Abstract

Porcine epidemic diarrhea virus (PEDV), a member of the genus Alphacoronavirus in the family Coronaviridae, causes acute diarrhea and/or vomiting, dehydration and high mortality in neonatal piglets. Two different genogroups of PEDV, S INDEL [PEDV variant containing multiple deletions and insertions in the S1 subunit of the spike (S) protein, G1b] and non-S INDEL (G2b) strains were detected during the diarrheal disease outbreak in US swine in 2013-2014. Similar viruses are also circulating globally. Continuous improvement and update of biosecurity and vaccine strains and protocols are still needed to control and prevent PEDV infections worldwide. Although the non-S INDEL PEDV was highly virulent and the S INDEL PEDV caused milder disease, the latter has the capacity to cause illness in a high number of piglets on farms with low biosecurity and herd immunity. The main PEDV transmission route is fecal-oral, but airborne transmission via the fecal-nasal route may play a role in pig-to-pig and farm-to-farm spread. PEDV infection of neonatal pigs causes fecal virus shedding (alongside frequent detection of PEDV RNA in the nasal cavity), acute viremia, severe atrophic enteritis (mainly jejunum and ileum), and increased pro-inflammatory and innate immune responses. PEDV-specific IgA effector and memory B cells in orally primed sows play a critical role in sow lactogenic immunity and passive protection of piglets. This review focuses on the etiology, transmission, pathogenesis, and prevention and control of PEDV infection.

Keywords: Coronavirus; PEDV; Pathogenesis; Pigs; Porcine epidemic diarrhea virus; Prevention.

Fig. 1

Immunohistochemical detection and distribution of PEDV antigen-positive cells in the proximal jejunum, mid-jejunum, or distal jejunum of a gnotobiotic 9-day-old pig inoculated with the original US non-S INDEL PEDV strain PC21A. The pig exhibited vomiting (but no diarrhea) at post-inoculation hour (PIH) 16 and was euthanized. (A) Proximal jejunum distant by 15 cm from the pylorus, showing low numbers of PEDV antigen-positive cells (red color) in the villus-crypt interface (arrows). (B) Proximal jejunum distant by 30 cm from the pylorus, showing high numbers of PEDV antigen-positive cells (red color) in most of the villous epithelium. (C) Mid-jejunum [mid-location of the small intestine (duodenum to ileum)], showing extremely high numbers of PEDV antigen-positive cells (dark red color) in most of the epithelium of mildly atrophied villi. (D) Distal jejunum, showing moderate numbers of PEDV antigen-positive cells (red color) in the villus-crypt interface. Original magnification, all ×40. Fast Red, Gill’s hematoxylin counterstain.

Fig. 2

Histologic (A and B) and immunohistochemical (C) localization of mammary IgA-secreting cells, and expression of mucosal addressin cellular adhesion molecule 1 (MAdCAM-1) (D) and chemokine ligand 25 (CCL25) (E) by immunofluorescent (IF) staining in the mammary gland tissue of PEDV naïve gilts. (A) Hematoxylin and eosin–stained mammary gland tissue of a gilt at 4 days post-farrowing, showing fully expanded alveoli, with mostly empty lumens. (B) Higher magnification of Panel A (inset), showing clusters of plasma cells characterized by the typical peripheral nuclei in the abundant cytoplasm in the interlobular stroma. Original magnification, ×200 (A) and ×400 (B). (C) Immunohistochemistry (IHC)-stained mammary gland tissue of a gilt at 5 days post-farrowing, showing a moderate number of IgA-positive cells (dark brown) in the intralobular or interlobular stroma (arrows). Original magnification, ×200. IHC was done using a polyclonal goat antibody to pig IgA conjugated with peroxidase (Bio-RAD) and DAB substrate. (D) IF-stained mammary gland tissue of a gilt at 4 days pre-farrowing, showing moderate expression of MAdCAM-1 (green) on the endothelial cells lining the intralobular and interlobular vessels (arrows). Original magnification, ×200. (E) IF-stained mammary gland tissue of a gilt at 4 days post-farrowing, showing moderate expression of CCL25 (green) on the endothelial cells lining the intralobular and interlobular vessels (arrows). Original magnification, ×200. IF staining was done using monoclonal antibodies against human MAdCAM-1 and CCL25 (Novus Biologicals).