Porcine epidemic diarrhea (PED) was first observed in the 1970s in Europe[1, 2], from where it spread to other parts of the globe and, currently, causes huge economic losses in the pig industry. Before 2010, there was no large-scale outbreak of PED in China, and it was mostly sporadic or in the form of local epidemics[3, 4]. However, since the end of 2010, diarrhea outbreaks among neonatal piglets characterized by severe vomiting, watery diarrhea, and high mortality were found to be mainly caused by porcine epidemic diarrhea virus (PEDV) mutant strains in pig farms in China; the outbreaks successively spread from the South to the North and from the East to the West[5, 6]. In particular, variant strains of this virus in China are characterized by sudden onset, rapid spread, a wide epidemic range, and a long epidemic time. Transmission occurs via the fecal-oral route and nasal inhalation. Once inside piglets, the virus attacks the intestinal cells, which lose the ability for digestion and absorption of nutrients from breast milk and food. Acute diarrhea, vomiting, dehydration, and death tend to occur in piglets, most of which are infected within 7 days after birth, and the fatality rate in young piglets is as high as 100%[9, 10]. Antibiotics have limited efficacy in the control of this disease, and the morbidity and mortality are currently very high .Additionally, the genetic variations in PEDV strains in recent years have led to changes in the antigen epitopes of the virus, and the currently available inactivated and attenuated vaccines against PEDV do not offer adequate immunoprotection . It is important to understand the genetic and epidemiological basis of this infection in order to develop strategies to curb and prevent its spread.
PEDV is a non-segmented single-stranded plus-stranded cystic RNA virus that belongs to Nidovirales, Coronaviridae, α-coronavirus. As observed in other known coronaviruses, the genome is approximately 28 kb in size and has a cap structure at the 5′ end and a poly A tail at the 3′ end. The full-length genome of PEDV contains a 5′ uncoded region, a 3′ uncoded region, and seven open reading frames. The seven open reading frames encode three non-structural proteins (PP1A, PP1B, and ORF3) and four structural proteins (S, E, M, and N)[15, 16]. Among viral proteins, glycoprotein S is considered to be the most antigenic protein; it contains 1383 amino acids and has a molecular weight of about 150 kDa[14, 17, 18]. Previous studies have shown that glycoprotein S plays an important role in promoting the fusion of the virus and cell membranes, virulence, induction of neutralizing antibodies, and adhesion of virus particles to receptors on host cells[19, 20]. This protein is commonly used to identify the genetic relationships between different PEDV strains and the epidemiological status of pig farms [21, 22]. With regard to PEDV strains in China, researchers such as Su, Wen et al. have carried out a series of studies on the pathogen. The results showed that the PEDV strains currently prevalent in China are new genotypes and, due to genetic variation, the prevention and control from some existing vaccines are not ideal. It is necessary to select vaccines with high antigen content that match with the circulating strains [23, 24]. Therefore, it is necessary to obtain comprehensive and accurate data on the prevalence and molecular characteristics of the currently circulating PEDV strains.
The present study aimed to investigate the molecular epidemiological and phylogenetic features of recent PEDV strains in China. To this end, seven strains of PEDV were isolated from 793 fecal and intestinal samples of piglets with diarrhea were collected from 72 pig farms in five regions of Jiangsu Province, China, from 2020 to 2021. The nucleotide sequences of the S1 gene of the seven isolated strains were analyzed and compared with PEDV reference strains from China, Japan, the United Kingdom, South Korea, Switzerland, and Spain. This study provides the latest information on the prevalence of PEDV in Jiangsu Province from 2020 to 2021. This information will help in the development of new strategies for PEDV prevention and control in China.