Porcine deltacoronavirus (PDCoV) was detected by RT-PCR in 12 of 97 (12.4%) intestinal samples collected during 2015 from piglets with diarrhoea in Thailand, Vietnam and Lao PDR. Spike, membrane and nucleocapsid genes were characterized, and phylogenetic analyses demonstrated that PDCoV isolates from Thai and Lao PDR form a novel cluster, separated from US and China isolates, but relatively were more closely related to China PDCoV than US isolates. Vietnam PDCoVs, however, were grouped together with US PDCoV. The analyses of amino acid changes suggested that they were from different lineage.

Increased evidence of porcine deltacoronavirus (PDCoV) causing diarrhoea in pigs has been reported in several countries worldwide. The virus has currently evolved into three separated groups including US, China and Southeast Asia (SEA) groups. In Vietnam, PDCoV was first reported in 2015. Based on phylogenetic analyses of spike, membrane and nucleocapsid genes, it is suggested that Vietnam PDCoV is chimeric virus. In the present study, we retrospectively investigated the presence of PDCoV in Vietnam and the full‐length genomes of six PDCoV isolates identified in 2014–2016 were further characterized. The results demonstrated that Vietnam PDCoV was first detected as early as 2014. All six Vietnam PDCoV are in the SEA group and further divided into two separated subgroups including SEA‐1 and SEA‐2. Vietnam PDCoV in SEA‐2 was closely related to Thai and Lao PDCoV. Recombination analysis demonstrated that three isolates in SEA‐1 were a chimeric virus of which P12_14_VN_0814, the first Vietnam isolate, and US PDCoV isolates were major and minor parents, respectively. The recombination was further evaluated by phylogenetic construction based on 3 recombinant fragments. The first and third fragments, closely related to P12_14_VN_0814, were associated with ORF1a/1b and N genes, respectively. The second fragment, associated with S, E, and M genes, was closely related to US PDCoV isolates. High antigenic and hydrophobic variations were detected in S1 protein. Three‐day‐old pigs challenged with the chimeric virus displayed clinical diseases and villus atrophy. In conclusion, Vietnam PDCoV is genetically diverse influenced by an external introduction from neighbouring countries. The chimeric Vietnam PDCoV can induce a disease similar to Thai PDCoV.

Porcine deltacoronavirus (PDCoV) in Thailand was first detected in 2015. We performed a retrospective investigation of the presence of PDCoV in intestinal samples collected from piglets with diarrhea in Thailand from 2008 to 2015 using RT-PCR. PDCoV was found to be present as early as February 2013. Phylogenetic analysis demonstrated that all PDCoV variants from Thailand differ from those from other countries and belong to a novel group of PDCoV that is separate from the US and Chinese PDCoV variants. Evolutionary analysis suggested that the Thai PDCoV isolates probably diverged from a different ancestor from that of the Chinese and US PDCoV isolates and that this separation occurred after 1994.

Porcine epidemic diarrhea (PED) has been endemic causing sporadic outbreaks in Thailand since 2007. In 2014-2015, several herds had experienced severe PED outbreaks and the reason of the re-current outbreaks was unknown. Whether or not the introduction of exotic strains or continual evolution of existing PEDV, genetic analyses would provide a more understanding in its evolutionary pattern. In the study, 117 complete spike gene sequences of Thai PED virus (PEDV) collected from 2008 to 2015 were clustered along with 95 references of PEDV spike sequences, and analyzed with the US sequences dataset (n=99). The phylogenetic analysis demonstrated that Thai PEDV spike sequences were genetically diverse and had been influenced by multiple introduction of exotic strains. Although Thai PEDV have been evolved into 6 subgroups (TH1-6), Subgroup TH1 strains with the unique 9 nucleotides (CAA GGG AAT) insertion between 688th-689th position of spike (changing amino acid from N to TREY) insertion has become the dominant subgroup since 2014. Thai PEDV spike gene have higher evolutionary rate compare to that of the US sequences. One contributing factor would be the intra-recombination between subgroups. Thailand endemic strain should be assigned into new subclade of G2 (Thai pandemic variant).

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