Abstract: Porcine circovirus type 3 (PCV3) is a new genotype of porcine circovirus firstly reported cause reproductive in sows in the United States in 2016, pathogenesis is not fully known. In order to study the pathogenicity of PCV3 in weaned piglets, a PCV3 strain was isolated using PK-15 cells from clinical tissue samples in this study and was named as PCV3/CH/HB/XY/2018, which belonged to PCV3a-IM genotype indicated by whole genome sequencing (WGS). Groups of five 28-day old weaned piglets were infected by both nasal inoculation and intramuscular injection with PCV3 positive tissue homogenate and the 8^th generation virus culture, respectively, meanwhile, a blank control group was set up. The results of infection test in piglets were evaluated in terms of clinical manifestation, body temperature, weight gain, viremia, tissue distribution and pathological changes. The results showed that after infection with PCV3 positive tissue homogenate or virus culture, the piglets in both groups showed high body temperature, emaciation, dermatitis and slow growth, and viremia lasted 14 days but disappear before 21 days post infection. Meanwhile, PCV3 was mainly found in tonsils and lymph nodes, and the highest viral load of PCV3 was found in spleen, lung and tonsils, the pathological changes in the lungs were characterized by interstitial pneumonia, lymphoid nodular hyperplasia and eosinophilia. This study proved that PCV3/CH/HB/XY/2018 was pathogenic to weaned piglets, and the isolation of this virus laid a foundation for the PCV3's pathogenesis mechanism research of PCV3-associate disease.

Key words: porcine circovirus type 3, isolation, pathogenicity, viral load