Detection and characterisation of porcine circoviruses in wild boars in northeastern Serbia

The objective was to expand and update the knowledge on the presence and genotype diversity of porcine circoviruses 2 and 3 (PCV2 and PCV3) in the wild boar populations from the hunting grounds in northeastern Serbia. The presence of PCV3 was not determined, and PCV2 was confirmed in 40.32% of the organ samples from 124 wild boars hunted from 2018 to 2019, indicating their significance in virus circulation since traditional pig farms with irregular PCV2 vaccination strategies are widespread in this region. The most prevalent genotype was PCV2d, followed by PCV2b and PCV2a in 55.6%, 38.9%, and 5.5% of the examined samples, respectively. Nucleotide sequences of the detected strains were homogenous within the genotype and clustered within the subgroups PCV2d-2, PCV2b-1A/B, and PCV2a-2D with high identity to European, Chinese, and Serbian domestic pig sequences suggesting their origin. Wild boars presented with no clinical or pathological signs of infection, implying that these animals might be less susceptible to disease, particularly since the cofactors present in pig farming systems that support the disease development are absent in the wild. The high PCV2 detection frequency demonstrates the importance of wildlife monitoring to track virus population dynamics, especially in regions with free-range pig farming in order to plan adequate disease control strategies.

Current Understanding of the Pathogenesis of Porcine Circovirus 3

Circoviruses are closed, circular, single-stranded DNA viruses belonging to the family Circoviridae and the genus Circovirus. To date, at least four porcine circoviruses (PCVs) have been recognized, including PCV1 to PCV4, respectively. Similar to PCV2 pathogenesis, PCV3 has been reported worldwide with myriad clinical and pathological presentations such as reproductive disorders, respiratory diseases, diarrhea etc. Current understanding of PCV3 pathogenesis is very limited since the majority of studies were mostly field observations. Interpretation of the results from such studies is not always simple. Various confounding factors affect the clinical appearance and pathological changes of the infected pigs. Recently, several experimental PCV3 infection studies have been reported, providing a better understanding of its pathogenesis. In this review, we focused on novel findings regarding PCV3 pathogenesis from both field observation and experimental infection studies. Possible factors involved in the conflicting results among the experimental infection studies are also discussed. This review article provides important insight into the current knowledge on PCV3 pathogenesis which would aid in prioritizing research in order to fill the knowledge gaps.

Comprehensive Analysis of Codon Usage Patterns in Chinese Porcine Circoviruses Based on Their Major Protein-Coding Sequences

Porcine circoviruses (PCVs) are distributed in swine herds worldwide and represent a threat to the health of domestic pigs and the profits of the swine industry. Currently, four PCV species, including PCV-1, PCV-2, PCV-3 and PCV-4, have been identified in China. Considering the ubiquitous characteristic of PCVs, the new emerged PCV-4 and the large scale of swine breeding in China, an overall analysis on codon usage bias for Chinese PCV sequences was performed by using the major proteins coding sequences (ORF1 and ORF2) to better understand the relationship of these viruses with their host. The data from genome nucleotide frequency composition and relative synonymous codon usage (RSCU) analysis revealed an overrepresentation of AT pair and the existence of a certain codon usage bias in all PCVs. However, the values of an effective number of codons (ENC) revealed that the bias was of low magnitude. Principal component analysis, ENC-plot, parity rule two analysis and correlation analysis suggested that natural selection and mutation pressure were both involved in the shaping of the codon usage patterns of PCVs. However, a neutrality plot revealed a stronger effect of natural selection than mutation pressure on codon usage patterns. Good host adaptation was also shown by the codon adaptation index analysis for all these viruses. Interestingly, obtained data suggest that PCV-4 might be more adapted to its host compared to other PCVs. The present study obtained insights into the codon usage pattern of PCVs based on ORF1 and ORF2, which further helps the understanding the molecular evolution of these swine viruses.

Detection of respiratory viruses in cases of porcine respiratory disease in nurseries.

Respiratory disease in weaned pigs is a common problem in the field, with a complex aetiology of both viruses and bacteria. In the present study, we investigated the presence of eleven viruses in nasal swabs collected from nurseries (fifty-five clinical outbreaks) under the suspicion of swine influenza A virus (swIAV) by cough and fever. The other ten viruses included influenza B (IBV) and influenza D viruses (IDV), Porcine reproductive and respiratory syndrome virus (PRRSV), Porcine respiratory coronavirus (PRCV), Porcine cytomegalovirus (PCMV), porcine circoviruses 2 (PCV2), 3 (PCV3) and 4 (PCV), Porcine parainfluenza 1 virus (PPIV1) and Swine orthopneumovirus (SOV). Twenty-nine swIAV-positive cases and twenty-six cases of swIAV-negative respiratory disease were primarily established. IBV, IBD, PCV4 and PPIV1 were not found in any case, while PRCV, SOV, and PCMV were more likely to be found in swIAV-positive nurseries with respiratory disease ( p<0.05) although, globally, PCV3, PRRSV, and PCMV were the most frequently detected agents on herd level. At an individual level, the prevalence of different viruses was: swIAV 48.6%; PRCV 48.0%; PRRSV 31.6%; SOV 33.8%; PCMV 48.3%, PCV2 36.0%; and PCV3 33.0%. Beyond that, it was common to find animals with low Ct values (< 30) for all agents except for PCV2 and PCV3. When analysed the association between different pathogens, PRCV was the one with the most associations. It positively interacted ( p < 0.05) with swIAV and SOV but was negatively associated ( p < 0.05) with PRRSV and PCVM. Besides these, swIAV and PRRSV were negatively related (p < 0.05). Further analysis of suckling pigs showed that circulation of PRCV, PCMV, SOV, and PCV3 started in the maternities, suggesting a role of the sows in the transmission. Overall, our data may contribute to a better understanding of the complex aetiology and the epidemiology of respiratory disease in weaners. This is the first report of SOV in Spain.

High Co-infection Status of Novel Porcine Parvovirus 7 With Porcine Circovirus 3 in Sows That Experienced Reproductive Failure

Porcine parvoviruses (PPVs) and porcine circoviruses (PCVs) infect pigs worldwide, with PPV1–7 and PCV2 infections common in pigs. Although PPV7 was only identified in 2016, co-infection of PPV7 and PCV2 is already common, and PPV7 may stimulate PCV2 replication. PCV3, a novel type of circovirus, is prevalent in pig populations worldwide and considered to cause reproductive disorders and dermatitis nephrotic syndrome. In recent studies, pigs were commonly infected with both PCV3 and PPV7. Our objective was to investigate the co-infections between PPV7 and PCV3 in samples from swine on farms in Hunan, China, and assess the potential impacts of PPV7 on PCV3 viremia. A total of 209 samples, known to be positive (105) or negative (104) for PCV3, were randomly selected from serum samples that were collected from commercial swine herds in seven regions from 2016 to 2018 in our previous studies; these samples were subjected to real-time PCR to detect PPV7. Of these samples, 23% (48/209) were positive for PPV7. Furthermore, the PPV7 positive rate was significantly higher in PCV3 positive serum (31.4%, 33/105) than in PCV3 negative serum (14.4%, 15/104). Another 62 PCV3 positive sow serum samples and 20 PCV3 positive aborted fetuses were selected from 2015 to 2016 in our other previous study. These samples were designated as being from farms with or without long-standing histories of reproductive failure (RF or non-RF), respectively, and they were also subjected to real-time PCR to detect PPV7 and to determine whether PPV7 affected PCV3 viremia. Among the 62 serum samples (39 PCV3 positive RF-serum and 23 PCV3 positive non-RF-serum), 45.1% (28/62) were positive for PPV7 and PCV3, and the PPV7 positive rate was significantly higher in PCV3 positive RF-serum (51.2%, 20/39) than in PCV3 positive non-RF-serum (34.8%, 8/23). In addition, there was a higher positive rate of PPV7 (55%, 11/20) in PCV3 positive aborted fetus samples. In addition, the copy number of PCV3 in PPV7 positive samples was significantly higher than that in PPV7 negative serum samples. Based on these findings, we concluded that PPV7 may stimulate PCV3 replication.

Porcine circoviruses

Porcine circoviruses have become an integral part of the pig production landscape. They are an evolving pathogen whose impact spans non-pathogenic to association with some of the most serious and far-reaching pathological conditions of pigs.

Complete Genome Sequences of Two Type 3 Porcine Circoviruses, WB17KW and WB20GG, Isolated from Korean Wild Boar

ABSTRACT Porcine circovirus type 3 (PCV3) in domestic pigs was first reported in South Korea in 2017. Here, we report the first complete genome sequences of two PCV3 strains isolated from Korean wild boar, which enhance our understanding about the genetic relatedness of PCV3 in domestic pigs and wild boar.

The main DNA viruses significantly affecting pig livestock

Swine DNA viruses have developed unique mechanisms for evasion of the host immune system, infection and DNA replication, and finally, construction and release of new viral particles. This article reviews four classes of DNA viruses affecting swine: porcine circoviruses, African swine fever virus, porcine parvoviruses, and pseudorabies virus. Porcine circoviruses belonging to the Circoviridae family are small single-stranded DNA viruses causing different diseases in swine including poly-weaning multisystemic wasting syndrome, porcine dermatitis and nephropathy syndrome, and porcine respiratory disease complex. African swine fever virus, the only member of the Asfivirus genus in the Asfarviridae family, is a large double-stranded DNA virus and for its propensity to cause high mortality, it is currently considered the most dangerous virus in the pig industry. Porcine parvoviruses are small single-stranded DNA viruses belonging to the Parvoviridae family that cause reproductive failure in pregnant gilts. Pseudorabies virus, or suid herpesvirus 1, is a large double-stranded DNA virus belonging to the Herpesviridae family and Alphaherpesvirinae subfamily. Recent findings including general as well as genetic classification, virus structure, clinical syndromes and the host immune system responses and vaccine protection are described for all four swine DNA virus classes.