Pathological and Ultrastructural Changes of Intestinal Tract from Newborn Piglets (Sus scrofa domesticus) Infected with Porcine deltacoronavirus
HOU Yu-Chen1, CAO Ya-Nan2, DU Xiao-Mei2, JIN Li-Ya2, CHEN Zhen-Hai1, WU Zheng-Chang2, BAO Wen-Bin2,3,*, ZHANG Shuai2,*
1 College of Veterinary Medicine, Yangzhou University, Yangzhou 225009, China; 2 Key Laboratory for Animal Genetic, Breeding, Reproduction and Molecular Design of Jiangsu Province/College of Animal Science and Technology, Yangzhou University, Yangzhou 225009, China; 3 Joint International Research Laboratory of Agriculture & Agri-Product Safety, Yangzhou University, Yangzhou 225009, China
Abstract：Porcine deltacoronavirus (PDCoV) is a emerging porcine intestinal coronavirus in recent years, causing huge economic losses to the pig industry. To investigate the pathogenicity and the ultrastructural changes of the intestinal tract from PDCoV-infected newborn piglets (Sus scrofa domesticus), the clinical manifestations, autopsy and histopathological changes, tissue tropism and intestinal ultrastructural changes in 1-day-old neonatal piglets infected with PDCoV CHN-GD16-05 strain were observed and analysed. Severe vomiting, diarrhea, listless, and lethargy were observed in PDCoV-challenged piglets at day 3 post-infection. An autopsy revealed that PDCoV-challenged newborn piglets displayed intestinal bloating and dilation, exhibited thin and transparent intestinal walls with an accumulation of yellow liquid in the intestinal lumen. Additionally, PDCoV mainly infected duodenum, jejunum and ileum of newborn piglets determined by qPCR and Western blot, with extremely significantly higher levels of PDCoV-Nucleocapsid (PDCoV-N) gene and protein in the jejunum than in the duodenum and ileum (P<0.01). Further hematoxylin eosin staining of jejunal tissue sections showed that PDCoV infection disrupted the structure of the intestinal villi, and increased crypt cells proliferation and crypt depth, causing diffuse intestinal villi atrophy and even fusion. Electron microscope also showed that the intestinal villi of PDCoV-infected piglets were atrophied, the microvilli of intestinal epithelial cells were broken and shed, the tight junctions between cells were disrupted, the cytoplasmic vacuolated cells were increased, and the mitochondria were enlarged in size and reduced in number. Moreover, PDCoV infection stimulated the expression of antiviral genes in the host, such as interferon α (IFN-α), IFN-β, IFN-λ, and their downstream interferon-stimulated genes, such as myxovirus resistance 1 (MX-1), interferon-stimulating gene 15 (ISG-15), interferon induced protein with tetratricopeptide repeats 1 (IFIT1), 2'-5'-oligoadenylate synthetase 1 (OAS1), 2'-5'-oligoadenylate synthetase like (OASL), inflammatory factors such as tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), IL-6, and C-C motif chemokine ligand 20 (CCL20). Taken together, the results indicated that PDCoV infection could rapidly invade the small intestine of newborn piglets, and effectively replicate in the jejunal epithelial cells, resulting in degeneration and necrosis of infected epithelial cells, which in turn caused intestinal villi atrophy, and ultimately result in osmotic diarrhoea. This study provides a theoretical basis for elucidating the pathogenic mechanism of PDCoV-infected piglets.
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