BackgroundPorcine circovirus type 3 (PCV3), as an emerging circovirus species, was reported to be widely circulating in the United States, China, South Korea and Poland. Previous studies revealed that PCV3 was mainly concentrated in sick animals with respiratory disease, skin disease, reproductive disorders and so on. However, the circulating status of PCV3 in pigs with other clinical presentations (especilly asymptomatic or diarrhea) was not well established.FindingsIn this study, to conduct a comparative epidemiological survey of PCV3, 80 weaned pig serum samples with severe respiratory disease (SRD), 175 weaned pig serum samples with mild respiratory disease (MRD), 216 asymptomatic weaned pig serum samples, 35 diarrheal weaned pig samples and 35 non-diarrheal weaned pig samples were collected from eight provinces of China. Via qPCR testing, PCV3 was circulating in all sampling provinces, with total positive rates varying from 1.04% to 100%. Interestingly, the PCV3-positive rate was significantly higher in weaned pigs with SRD (63.75%, 51/80) than in those weaned pigs with MRD (13.14%, 23/175) and asymptomatic pigs (1.85%, 4/216) (P < 0.01). Similarly, the PCV3-positive rate was significantly higher in diarrheal weaned pigs (17.14%, 6/35) than in non-diarrheal weaned pigs (2.86%, 1/35) (P < 0.05). Moreover, the lower Ct values of qPCR were frequently found in those weaned pigs or fattening pigs with respiratory disease and diarrhea rather than that in asymptomatic pigs. Sequence analysis showed that low genetic diversity existed among those PCV3 sequences collected from pigs with different clinical presentations.ConclusionsThe present study further extends evidence that newly described PCV3 widely circulates in six additional provinces of Southern and Northern China and has high similarity to previously reported isolates. As an emerging virus of swine, although the present case-control study reveals that PCV3 has a potential association with swine respiratory disease and diarrhea, further investigations into the pathogenesis are needed to ascertain the role of PCV3 in swine health.Electronic supplementary materialThe online version of this article (10.1186/s12985-017-0892-4) contains supplementary material, which is available to authorized users.

Molecular tests revealed influenza D viruses of D/OK lineage widely circulating in farmed animal species in Guangdong Province, southern China. In particular, we found high levels of influenza D virus infection in goats and pigs. We also detected viral RNA in serum specimens and feces of animals with certain severe diseases.

Currently, porcine circovirus type 2 (PCV2) is considered the major pathogen of porcine circovirus associated-diseases (PCVAD) that causes large economic losses for the swine industry in the world annually, including China. Since the first report of PCV2 in 1998, it has been drawing tremendous attention for the government, farming enterprises, farmers, and veterinary practitioners. Chinese researchers have conducted a number of molecular epidemiological work on PCV2 by molecular approaches in the past several years, which has resulted in the identification of novel PCV2 genotypes and PCV2-like agents as well as the description of new prevalence patterns. Since late 2009, commercial PCV2 vaccines, including the subunit vaccines and inactivated vaccines, have already been used in Chinese swine farms. The aim of this review is to update the insights into the prevalence and control of PCV2 in China, which would contribute to understanding the epidemiology, control measures and design of novel vaccines for PCV2.

Porcine circovirus (PCV) is one of the smallest known DNA viruses in mammals. At present, PCVs are divided into three species, PCV1, PCV2, and PCV3. PCV1 and PCV2 were found in the 1970s and the 1990s, respectively, whereas PCV3 was discovered recently in 2016. PCV1 does not cause diseases in pigs. However, PCV3, similar to PCV2, is reported to be associated with several swine diseases, including porcine dermatitis and nephropathy syndrome (PDNS) and reproductive failure. PCVs are very common in domestic pigs as well as wild boars. However, PCVs have been occasionally isolated from non-porcine animals, including ruminants (such as cattle, goats, wild chamois, and roe deers), rodents (such as NMRI mice, BALB/c mice, Black C57 mice, ICR mice, Mus musculus, and Rattus rattus), canines (such as dogs, minks, foxes, and raccoon dogs), insects (such as flies, mosquitoes, and ticks), and shellfish. Moreover, PCVs are frequently reported in biological products, including human vaccines, animal vaccines, porcine-derived commercial pepsin products, and many cell lines. PCVs are also abundant in the environment, including water samples and air samples. Interestingly, PCV1 and/or PCV2 antibody or antigen has also been detected in sera, stool samples and respiratory swab samples of human, revealing zoonotic potential of PCVs. Thus, PCVs inhabit many types of reservoirs. In this review, we summarize the reservoirs of PCVs, and this information would be helpful in understanding the natural circulating status and possible cross-species transmission of PCVs.