Porcine circovirus type 3 (PCV3) is a newly identified circovirus from swine in the USA, China and Poland. This novel circovirus has been associated with porcine dermatitis and nephropathy syndrome (PDNS), reproductive failure and multisystemic inflammation; moreover, PCV3 poses a potential threat to the swine industry. In this retrospective study, a phylogenetic analysis was conducted to address the epidemiology and evolutionary dynamics of this novel circovirus. The total positive sample rate of PCV3 was 26.7% (76/285) and has increased gradually over the past 3 years. Of these PCV3-positive samples, 22.3% (17/76) were coinfected with PCV2. PCV3 can be detected in multiple sample types with different positive rates, and the positive rate is highest among stillborn. We also divide PCV3 into three clades (PCV3a, PCV3b and PCV3c) based on two amino acid mutations (A24V and R27K) on the cap protein in this study. In addition, the origin of PCV3 was approximately 1966 and may have originated from a bat-associated circovirus. Our results suggested that PCV3 is widely distributed in southern China and has been circulating in swine herds for nearly half a century. PCV3 has evolved into different clades caused by mutations in cap proteins; thus, further research on PCV3 epidemiology should be conducted.

In 2011, a new virus was isolated from pigs with influenza-like symptoms and subsequently also from cattle, which are the main reservoir of the virus. It is similar to Influenza C virus (ICV), a (predominantly) human pathogen, causing respiratory disease in children. Since the virus is unable to reassort with ICV (and based on several other criteria as discussed in the text) it is now officially named as Influenzavirus D (IDV), a new genus of the Orthomyxoviridae. We summarize the epidemiology, pathology and evolution of IDV and its biological characteristics with emphasis on the only glycoprotein HEF. Based on the limited data available we finally consider whether IDV represent a public health threat.

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Coronaviruses have a wide host range and can cause a variety of diseases with varying severity in different animals. Several enteric coronaviruses have been identified that are associated with diarrhea in swine and that have caused substantial economic losses. In this study, a newly emerged porcine enteric alphacoronavirus (PEAV), PEAV-GD-CH/2017, was identified from suckling piglets with diarrhea in southern China, and a full-length genome sequence of PEAV was obtained for systematic analysis. The novel PEAV sequence was most identical to that of bat-HKU2, and the differences between them were comprehensively compared, especially the uniform features of the S protein, which was shown to have a close relationship with betacoronaviruses and to perhaps represent unrecognized betacoronaviruses. In addition, Bayesian analysis was conducted to address the origin of PEAV, and the divergence time between PEAV and bat-HKU2 was estimated at 1926, which indicates that PEAV is not newly emerged and may have circulated in swine herds for several decades since the interspecies transmission of this coronavirus from bat to swine. The evolutionary rate of coronaviruses was estimated to be 1.93 × 10 substitutions per site per year for the RdRp gene in our analysis. For the origin of PEAV, we suspect that it is the result of the interspecies transmission of bat-HKU2 from bat to swine. Our results provide valuable information about the uniform features, origin and evolution of the novel PEAV, which will facilitate further investigations of this newly emerged pathogen.