Seroprevalence, Genetic Characteristics, and Pathogenicity of Korean Porcine Sapeloviruses

Abstract

Although porcine sapelovirus (PSV) is generally subclinical, it can cause a wide range of clinical signs in some individuals, including respiratory distress, acute diarrhea, pneumonia, skin lesions, reproductive failure, and neurological diseases. In this study, we investigated the prevalence and genotype of PSV isolated from domestic pigs and wild boars in Korea. We also analyzed potential recombination events, and assessed the pathogenicity of the virus through animal experiments. In wild boars, the prevalence of PSV antibodies decreased slightly (by 1.8%) over 5 years (from 2019 to 2024); however, prevalence increased significantly (by 17.8%) in breeding sows. In samples from animals with diarrhea and respiratory clinical signs, the prevalence of PSV alone was 21.1%, whereas the prevalence of PSV mixed with other pathogens was also 21.1%. The whole genome of the PSV/Goryeong/KR-2019 strain isolated from a piglet with diarrhea was closely related to the Jpsv447 strain isolated in Japan in 2009, and recombination analysis predicted that the PSV/Goryeong/KR-2019 strain was generated by genetic recombination between the KS05151 strain and the Jpsv447 strain. However, when the PSV/Goryeong/KR-2019 strain was orally administered to 5-day-old suckling pigs, diarrhea clinical signs were mild, and no significant changes were observed in villus height and ridge depth in the duodenum, jejunum, or ileum. In addition, no neurological clinical signs were observed when the isolated virus was administered to 130-day-old pigs, and no specific lesions were found upon histopathological examination of brain tissue. In conclusion, PSV/Goryeong/KR-2019 appears to be a weakly pathogenic virus that does not cause severe diarrhea in suckling pigs, and does not cause neurological clinical signs in fattening pigs. Therefore, it is presumed that most PSVs detected in Korean pig farms are weakly pathogenic strains.

Keywords: PSV; clinical signs; phylogenetic tree; pig; seroprevalence.

Figure 1

Changes in seroprevalence and antibody levels against PSV in wild boars and sows. (A) Seroprevalence and (B) distribution of neutralizing antibodies in sows and wild boars between 2019 and 2024.

Figure 2

Isolation and identification of PSV. (A) Cytopathic effects (CPEs) and immunofluorescence assay (IFA) results of ST cells inoculated with PSV-positive samples. (B) RT-PCR of viral RNA in cell culture supernatants obtained from serially passaged PSV-positive samples. (C) Growth kinetics of PSV in ST cells.

Figure 3

Phylogenetic trees of PSV ORF and VP1. (A) ML tree based on (6969–7266 nucleotide) 75 complete open reading frame (ORF) sequences including those of the PSV/Goryeong/KR-2019 strain and 74 reference strains, and (B) Phylogenetic analysis based on (858–894 nucleotide) 72 VP1 gene sequences including those of the PSV/Goryeong/KR-2019 strain and 71 reference strains. The trees were constructed using the maximum-likelihood method (with the Tamura–Nei model) and 1000 bootstrap replications.

Figure 4

Recombination analysis of the PSV/Goryeong/KR-2019 strain. (A) Similarity plot generated using SimPlot (version 3.5.1) software (window size: 200 bp; step size: 20 bp; Kimura 2-parameter model). The similarity between the Jpsv447 (Japan, minor parent) strain (red line) and the KS05151 (Korea, major parent) strain (blue line) was compared based on the PSV/Goryeong/KR-2019 strain. (B) Schematic representation of the PSV genome, showing the coding regions for structural (VP4–VP1) and nonstructural (2A–3D) proteins. (C) BootScan analysis performed using the RDP4 program. The yellow line represents the recombinant strain PSV/Goryeong/KR-2019, the teal line indicates the minor parent strain KS05151 (South Korea), and the purple line indicates the minor parent strain Jpsv447 (Japan).

Figure 5

Clinical signs and necropsy results for suckling piglets. (A) Body weight changes. (B) Diarrhea scores. (C) PSV RNA copy number in feces. (D) Villus height/crypt depth ratio. (E) Histopathological images. The PSV and control groups are marked as blue and black, respectively. Tissues were stained with hematoxylin and eosin (H&E). Scale bar = 100 μm.

Figure 6

Histopathological images of lung, ileum, and brain tissues from PSV-infected and control fattening pigs. Tissues were stained with hematoxylin and eosin (H&E). Scale bar = 100 μm.