Porcine Circovirus Type 3 in Pig Farms Experiencing Diarrhea in Jiangxi, China: Prevalence, Genome Sequence and Pathogenicity

SIMPLE SUMMARY: Porcine circovirus 3 (PCV3) is a new species of PCV that was associated with porcine dermatitis and nephropathy syndrome (PDNS), respiratory disease, cardiac and multisystem inflammation in nursery and finishing pigs, and reproductive failure problems, including abortion, mummified fetuses, and stillbirth in sows. To date, the reports on the PCV3 present in diarrhea pigs are limited and the genetic characteristics of PCV3 from diarrheal pigs and pathogenicity on pigs were inconsistent. This study aimed to investigate the prevalence of PCV3 in pigs with/without diarrhea, to analyze the genome sequence of PCV3 from diarrheal pigs, and to inquire into the associated pathogenicity of PCV3 to piglets experimentally infected with PCV3-positive intestinal contents. The results demonstrated that PCV3 was widely circulating in diarrheal suckling and weaned piglets. Clinical signs, gross lesions, and histological changes were observed in suckling piglets inoculated with PCV3. The complete genome of a PCV3a strain was determined and two mutations (V24A and K27R) were present when compared with PCV3b strains. The findings of this study increase the knowledge of the epidemiology, viral genetics, pathogenicity, and pathogenesis of PCV3. ABSTRACT: Porcine circovirus 3 (PCV3) infections have been reported in different clinical presentations. However, the prevalence and pathogenicity of PCV3 associated with diarrhea in piglets have been limited. Herein, we present an investigation and genome analyses of PCV3 in piglets experiencing diarrhea, and observed clinical signs, gross lesions, and histological changes in pigs negative for all known pathogens associated with diarrhea but positive for PCV3 alone. Among the feces (n = 141) tested, 16.31% (23/141) were positive for PCV3. Of which, 27.28% (15/55) and 14.29% (5/35) were present in diarrheal samples from suckling and weaned piglets, respectively. Moderate to severe atrophic villi was confined in duodenum, jejunum, and ileum, and significantly decreased average heights of villi, and the depths of crypt were observed in PCV3-infected piglets. The complete genome of a representative strain of PCV3, designated as JX/CH/2018, was determined. Multialignment analysis indicated that JX/CH/2018 had 97.7–99.7% nucleotide identity at the complete genome level, and 97.2–100% at the amino acid level of the capsid protein when compared with reference PCV3 strains. Phylogenetic analysis showed that the PCV3 strain identified in this study belonged to PCV3a lineage. The present study demonstrated that PCV3 is a common virus in diarrheal suckling and weaned piglets.