Porcine circovirus type 2a or 2b based experimental vaccines provide protection against PCV2d/porcine parvovirus 2 co-challenge

Comparison of immune effects of porcine circovirus type 2d (PCV2d) capsid protein expressed by Escherichia coli and baculovirus-insect cells

Porcine circovirus type 2 (PCV2) is an important pathogen harmful to global pig production, which causes immunosuppression and serious economic losses. PCV2 capsid (Cap) protein expressed by E. coli or baculovirus-insect cells are often used in preparation of PCV2 subunit vaccines, but the latter is expensive to produce. It is therefore crucial to comparison of the immune effects of Cap protein expressed by the above two expression systems for reducing the production cost and guaranteeing PCV2 vaccine quality. In this study, the PCV2d-Cap protein lacking nuclear localization signal (NLS), designated as E. coli-Cap and Bac-Cap, was expressed by E. coli and baculovirus-Spodoptera frugiperda Sf9 (Bac-Sf9) cells, respectively. The expressed Cap proteins could self-assemble into virus-like particles (VLPs), but the Bac-Cap-assembled VLPs were more regular. The two system-expressed Cap proteins induced similar specific IgG responses in mice, but the neutralizing antibody levels of Bac-Cap-immunized mice was higher than those of E. coli-Cap. After PCV2 challenge, IL-10 in Bac-Cap immunized mice decreased significantly than that in E. coli-Cap. The lesions and PCV2 antigen positive cells in tissues of mice immunized with E. coli-Cap and Bac-Cap were significantly reduced, and Bac-Cap appeared mild lesions and fewer PCV2 antigen-positive cells compared with E. coli-Cap immunized mice. The study indicated that Cap proteins expressed by E. coli and Bac-Sf9 cells could induce specific protective immunity, but the latter induced more effective immunity, which provides valuable information for the research and development of PCV2 vaccine.

Porcine circovirus type 2 infection promotes the SUMOylation of nucleophosmin-1 to facilitate the viral circular single-stranded DNA replication

The mechanism of genome DNA replication in circular single-stranded DNA viruses is currently a mystery, except for the fact that it undergoes rolling-circle replication. Herein, we identified SUMOylated porcine nucleophosmin-1 (pNPM1), which is previously reported to be an interacting protein of the viral capsid protein, as a key regulator that promotes the genome DNA replication of porcine single-stranded DNA circovirus. Upon porcine circovirus type 2 (PCV2) infection, SUMO2/3 were recruited and conjugated with the K263 site of pNPM1's C-terminal domain to SUMOylate pNPM1, subsequently, the SUMOylated pNPM1 were translocated in nucleoli to promote the replication of PCV2 genome DNA. The mutation of the K263 site reduced the SUMOylation levels of pNPM1 and the nucleolar localization of pNPM1, resulting in a decrease in the level of PCV2 DNA replication. Meanwhile, the mutation of the K263 site prevented the interaction of pNPM1 with PCV2 DNA, but not the interaction of pNPM1 with PCV2 Cap. Mechanistically, PCV2 infection increased the expression levels of Ubc9, the only E2 enzyme involved in SUMOylation, through the Cap-mediated activation of ERK signaling. The upregulation of Ubc9 promoted the interaction between pNPM1 and TRIM24, a potential E3 ligase for SUMOylation, thereby facilitating the SUMOylation of pNPM1. The inhibition of ERK activation could significantly reduce the SUMOylation levels and the nucleolar localization of pNPM1, as well as the PCV2 DNA replication levels. These results provide new insights into the mechanism of circular single-stranded DNA virus replication and highlight NPM1 as a potential target for inhibiting PCV2 replication.

Virus-Host Protein Interaction Network of the Hepatitis E Virus ORF2-4 by Mammalian Two-Hybrid Assays

Throughout their life cycle, viruses interact with cellular host factors, thereby influencing propagation, host range, cell tropism and pathogenesis. The hepatitis E virus (HEV) is an underestimated RNA virus in which knowledge of the virus-host interaction network to date is limited. Here, two related high-throughput mammalian two-hybrid approaches (MAPPIT and KISS) were used to screen for HEV-interacting host proteins. Promising hits were examined on protein function, involved pathway(s), and their relation to other viruses. We identified 37 ORF2 hits, 187 for ORF3 and 91 for ORF4. Several hits had functions in the life cycle of distinct viruses. We focused on SHARPIN and RNF5 as candidate hits for ORF3, as they are involved in the RLR-MAVS pathway and interferon (IFN) induction during viral infections. Knocking out (KO) SHARPIN and RNF5 resulted in a different IFN response upon ORF3 transfection, compared to wild-type cells. Moreover, infection was increased in SHARPIN KO cells and decreased in RNF5 KO cells. In conclusion, MAPPIT and KISS are valuable tools to study virus-host interactions, providing insights into the poorly understood HEV life cycle. We further provide evidence for two identified hits as new host factors in the HEV life cycle.

The Novel Porcine Parvoviruses: Current State of Knowledge and Their Possible Implications in Clinical Syndromes in Pigs

Parvoviruses (PVs) affect various animal species causing different diseases. To date, eight different porcine parvoviruses (PPV1 through PPV8) are recognized in the swine population, all of which are distributed among subfamilies and genera of the Parvoviridae family. PPV1 is the oldest and is recognized as the primary agent of SMEDI, while the rest of the PPVs (PPV2 through PPV8) are called novel PPVs (nPPVs). The pathogenesis of nPPVs is still undefined, and whether these viruses are putative disease agents is unknown. Structurally, the PPVs are very similar; the differences occur mainly at the level of their genomes (ssDNA), where there is variation in the number and location of the coding genes. Additionally, it is considered that the genome of PVs has mutation rates similar to those of ssRNA viruses, that is, in the order of 10-5-10-4 nucleotide/substitution/year. These mutations manifest mainly in the VP protein, constituting the viral capsid, affecting virulence, tropism, and viral antigenicity. For nPPVs, mutation rates have already been established that are similar to those already described; however, within this group of viruses, the highest mutation rate has been reported for PPV7. In addition to the mutations, recombinations are also reported, mainly in PPV2, PPV3, and PPV7; these have been found between strains of domestic pigs and wild boars and in a more significant proportion in VP sequences. Regarding affinity for cell types, nPPVs have been detected with variable prevalence in different types of organs and tissues; this has led to the suggestion that they have a broad tropism, although proportionally more have been found in lung and lymphoid tissue such as spleen, tonsils, and lymph nodes. Regarding their epidemiology, nPPVs are present on all continents (except PPV8, only in Asia), and within pig farms, the highest prevalences detecting viral genomes have been seen in the fattener and finishing groups. The relationship between nPPVs and clinical manifestations has been complicated to establish. However, there is already some evidence that establishes associations. One of them is PPV2 with porcine respiratory disease complex (PRDC), where causality tests (PCR, ISH, and histopathology) lead to proposing the PPV2 virus as a possible agent involved in this syndrome. With the other nPPVs, there is still no clear association with any pathology. These have been detected in different systems (respiratory, reproductive, gastrointestinal, urinary, and nervous), and there is still insufficient evidence to classify them as disease-causing agents. In this regard, nPPVs (except PPV8) have been found to cause porcine reproductive failure (PRF), with the most prevalent being PPV4, PPV6, and PPV7. In the case of PRDC, nPPVs have also been detected, with PPV2 having the highest viral loads in the lungs of affected pigs. Regarding coinfections, nPPVs have been detected in concurrence in healthy and sick pigs, with primary PRDC and PRF viruses such as PCV2, PCV3, and PRRSV. The effect of these coinfections is not apparent; it is unknown whether they favor the replication of the primary agents, the severity of the clinical manifestations, or have no effect. The most significant limitation in the study of nPPVs is that their isolation has been impossible; therefore, there are no studies on their pathogenesis both in vitro and in vivo. For all of the above, it is necessary to propose basic and applied research on nPPVs to establish if they are putative disease agents, establish their effect on coinfections, and measure their impact on swine production.

Interaction between host cell proteins and open reading frames of porcine circovirus type 2

Postweaning multisystemic wasting syndrome (PMWS) is caused by a systemic inflammation after porcine circovirus type 2 (PCV2) infection. It was one of the most economically important pathogens affecting pig production worldwide before PCV2 vaccine was first introduced in 2006. After the development of a vaccine against PCV2a type, pig farms gradually restored enormous economic losses from PMWS. However, vaccine against PCV2a type could not be fully effective against several different PCV2 genotypes (PCV2b - PCV2h). In addition, PCV2a vaccine itself could generate antigenic drift of PCV2 capsid. Therefore, PCV2 infection still threats pig industry worldwide. PCV2 infection was initially found in local tissues including reproductive, respiratory, and digestive tracks. However, PCV2 infection often leads to a systemic inflammation which can cause severe immunosuppression by depleting peripheral lymphocytes in secondary lymphoid tissues. Subsequently, a secondary infection with other microorganisms can cause PMWS. Eleven putative open reading frames (ORFs) have been predicted to encode PCV2 genome. Among them, gene products of six ORFs from ORF1 to ORF6 have been identified and characterized to estimate its functional role during PCV2 infection. Acquiring knowledge about the specific interaction between each PCV2 ORF protein and host protein might be a key to develop preventive or therapeutic tools to control PCV2 infection. In this article, we reviewed current understanding of how each ORF of PCV2 manipulates host cell signaling related to immune suppression caused by PCV2.

Phylogenetic and Structural Analysis of Porcine Circovirus Type 2 from 2016 to 2021 in Jilin Province, China

Porcine circovirus disease (PCVD) caused by porcine circovirus type 2 (PCV2) is widely distributed in pig farms. Up until now, nine genotypes of PCV2, PCV2a to 2i, have been identified in diseased pigs worldwide. This study analyzed 302 samples collected in the Jilin Province of China from 2016 to 2021, followed by genetic analysis of the PCV2 isolates. Meanwhile, the antigen epitopes, amino acid mutations, 3D structure of the PCV2 isolates and commercially available vaccine strains were evaluated and compared. The results showed that the predominant genotypes of PCV2 were PCV2b, followed by PCV2e and PCV2d in Jilin Province during 2016-2021. Although mutations were detected in the isolates, no recombination occurred in the PCV2 isolates, indicating a stable genotype of PCV2 in Jilin Province during these years. Moreover, the B cell epitopes in the Cap and Rep proteins of eighteen PCV2 isolates and T cell epitopes in the Cap of the isolates were changed compared to three currently used vaccine strains. The mutations in the Cap and Rep proteins did not affect their spatial conformation. Therefore, bivalent or multivalent vaccines with different genotypes of PCV2 might improve the protective effect of vaccines.

Comparative Efficacy of Chimeric Porcine Circovirus (PCV) Vaccines against Experimental Heterologous PCV2d Challenges

The objective of this study was to evaluate the efficacy of two multivalent commercial porcine circovirus (PCV) vaccines against heterologous PCV2d challenges. A total of 24 crossbred male pigs aged 26 days selected from a specific pathogen-free herd were randomly divided into four groups (six pigs per group) and assigned as follows: negative control (unvaccinated/sham-challenge), vaccinated with chimeric PCV1-2a vaccine (PCV1-2a/PCV2d-challenge), vaccinated with chimeric PCV1-2a-2b vaccine (PCV1-2a-2b/PCV2d-challenge) and positive control (unvaccinated/PCV2d-challenge). At 21 days after vaccination, the pigs were intranasally and intramuscularly inoculated with either sham or field isolates of PCV2d (PCV2d/149/TH/2020). After being challenged, blood samples were obtained weekly and analyzed for levels of PCV2d viremia, neutralizing antibodies, and IgG against PCV2. At 30 days post-challenge (DPC), the pigs were euthanized and then subjected to pathological evaluations and molecular analysis. The results indicated that pigs in the PCV1-2a-2b/PCV2d-challenge and the PCV1-2a/PCV2d-challenge groups possessed significantly greater levels of PCV2d-neutralizing antibody titer when compared with the positive control group. Moreover, pigs in the PCV1-2a-2b/PCV2d-challenge group exhibited a lower degree of severity in terms of gross lesion scores and lower levels of PCV2 viremia when compared with the positive control group. This study demonstrated that vaccinating pigs with either the PCV1-2a or PCV1-2a-2b chimeric vaccines elicits a potent immune response against PCV2d infection and reduces viremia after PCV2d inoculation in pigs.

The gC1qR Binding Site Mutant PCV2 Is a Potential Vaccine Strain That Does Not Impair Memory CD4+ T-Cell Generation by Vaccines

PCV2 has been reported to reduce the protective effects of various vaccines on immunized pigs. Our previous studies showed that the interaction of Cap and host protein gC1qR mediated the PCV2 infection-induced suppression of immune response. Thus, we wondered whether the gC1qR binding site mutant PCV2RmA could be a vaccine strain and whether this mutant PCV2RmA impairs other vaccines. Herein, we showed that PCV2 infection reduced the classic swine fever virus (CSFV) vaccine-induced generation of memory CD4⁺ T cells through the interaction of Cap with gC1qR. PCV2RmA can effectively induce the production of PCV2-specific antibodies, neutralizing antibodies, and peripheral blood lymphocyte proliferation in piglets at the same levels as the commercial inactivated PCV2 vaccine. The PCV2RmA-induced anti-PCV2 immune responses could eliminate the serum virus and would not lead to pathological lesions like wild-type PCV2. Moreover, compared to the commercial inactivated PCV2 vaccine, PCV2RmA is capable of inducing more durable protective immunity against PCV2 that induced production of PCV2-specific antibodies and neutralizing antibodies for a longer time via stronger induction of memory CD4⁺ T cells. Importantly, PCV2RmA infection did not impair the CSFV vaccine-induced generation of memory CD4⁺ T cells. Collectively, our findings showed that PCV2 infection impairs memory CD4⁺ T-cell generation to affect vaccination and provide evidence for the use of PCV2RmA as an efficient vaccine to prevent PCV2 infection. IMPORTANCE PCV2 is one of the costliest pathogens in pigs worldwide. Usage of PCV2 vaccines can prevent the PCV2 infection-induced clinical syndromes but not the viral spread. Our previous work found that PCV2 infection suppresses the host type I interferon innate immune response and CD4⁺ T-cell-mediated Th1 immune response through the interaction of Cap with host gC1qR. Here, we showed that the gC1qR binding site mutant PCV2RmA could effectively induce anti-PCV2 immunity and provide more durable protective immunity against wild-type PCV2 infection in pigs. PCV2RmA would not impair the generation of memory CD4⁺ T cells induced by classic swine fever virus (CSFV) vaccines as wild-type PCV2 did. Therefore, PCV2RmA can serve as a potential vaccine strain to better protect pigs against PCV2 infection.

Pathological Evaluation of Porcine Circovirus 2d (PCV2d) Strain and Comparative Evaluation of PCV2d and PCV2b Inactivated Vaccines against PCV2d Infection in a Specific Pathogen-Free (SPF) Yucatan Miniature Pig Model

Porcine circovirus type 2 (PCV2) is an economically important swine pathogen that causes porcine circovirus-associated diseases (PCVADs). The objective of this study was to evaluate the use of specific pathogen-free Yucatan miniature pigs (YMPs) as an experimental model for PCV2d challenge and vaccine assessment because PCV2-negative pigs are extremely rare in conventional swine herds in Korea. In the first experiment, every three pigs were subjected to PCV2d field isolate or mock challenge. During three weeks of experiments, the PCV2d infection group exhibited clinical outcomes of PCVAD with high viral loads, lymphoid depletion, and detection of PCV2d antigens in lymphoid organs by immunohistochemistry. In the second experiment, three groups of pigs were challenged with PCV2d after immunization for three weeks: a nonvaccinated group (three pigs), a PCV2b-Vac group vaccinated with a commercial PCV2b-based inactivated vaccine SuiShot^® Circo-ONE (five pigs), and a PCV2d-Vac group vaccinated with an experimental PCV2d-based inactivated vaccine (five pigs). During the three weeks of the challenge period, nonvaccinated pigs showed similar clinical outcomes to those observed in the PCV2d infection group from the first experiment. In contrast, both the PCV2b and PCV2d vaccinations produced good levels of protection against PCV2d challenge, as evidenced by reduced viral loads, improved growth performance, high virus-neutralizing antibody titers, and less development of PCV2-associated pathological lesions. Taken together, these data suggest that YMPs could be an alternative model for PCV2 challenge experiments, and these animals displayed typical clinical and pathological features and characteristics of protective immunity induced by the vaccines that were consistent with those resulting from PCV2 infections in conventional pigs.

Flavonoids as Potential Antiviral Agents for Porcine Viruses

Flavonoids are types of natural substances with phenolic structures isolated from a variety of plants. Flavonoids have antioxidant, anti-inflammatory, anticancer, and antiviral activities. Although most of the research or applications of flavonoids are focused on human diseases, flavonoids also show potential applicability against porcine virus infection. This review focuses on the recent progress in antiviral mechanisms of potential flavonoids against the most common porcine viruses. The mechanism discussed in this paper may provide a theoretical basis for drug screening and application of natural flavonoid compounds and flavonoid-containing herbs to control porcine virus infection and guide the research and development of pig feed additives.

Prevalence of porcine parvovirus 1 through 7 (PPV1-PPV7) and co-factor association with PCV2 and PRRSV in Korea

Background

Classical porcine parvovirus (PPV1) and novel porcine parvoviruses designated porcine parvovirus 2 through 7 (PPV2-PPV7) are widespread in pig populations. The objective of this study was to investigate the prevalence rates of PPV1-PPV7 in Korea by detecting PPVs in serum, lung and fecal samples and to elucidate the association of PPVs with porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory virus (PRRSV), major pathogens involved in porcine respiratory disease complex (PRDC). A total of 286 serum, 481 lung, and 281 fecal samples collected from 2018 to 2020 were analyzed.

Results

The results showed that PPVs are widespread in Korea; the highest detection rates were found in lung samples and ranged from 7.9% (PPV1) to 32.6% (PPV2). Regarding age groups, fattening pigs had the highest detection rates of PPVs, ranging from 6.4% (PPV1) to 36.5% (PPV6); this finding suggests the chronic nature of PPV infections and the continual circulation of these viruses. When compared with PCV2- and PRRSV-negative lung samples, PCV2-positive samples with or without PRRSV positivity had significantly higher detection levels of PPV1 and PPV6. In contrast, the prevalence of PPV2 and PPV7 was significantly higher in PRRSV-infected lung samples regardless of PCV2 detection. PPV5 was detected significantly more frequently in samples  with both PCV2 and PRRSV positivity.

Conclusions

This study could offer a better understanding of the role of PPVs in PCV2 and/or PRRSV infection though further studies are needed to experimentally assess the impact of PPVs in coinfections.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03236-1.

Epidemiological Analysis From 2018 to 2020 in China and Prevention Strategy of Porcine Circovirus Type 2

Porcine circovirus type 2 (PCV2) is one of the smallest known animal viruses and is the main pathogen of PCV-associated diseases (PCVAD). Epidemiological surveillance results have shown that the PCV2 infection rate is on the rise in China, thus, PCV2 disease prevention and control has become a huge challenge for the Chinese swine industry. We collected clinical samples from multiple different provinces in China from 2018 to 2020 and found that the positive rate of PCV2 was 53% (3619/6872), identity between the cloned 62 ORF2 genes was 84.4-100% and identity between the cloned 62 ORF2 sequences and reference sequence was 72.9-99.8%. Genetic evolution analysis found that PCV2d accounted for 79% (49/62 samples), PCV2a for 12.9% (8/62 samples), PCV2b for 8% (5/62 samples), and PCV2c and PCV2e genotypes were not found. However, most commercial PCV2 subunit vaccines are based on the PCV2a genotype, and there are very few vaccines based on PCV2b or PCV2d. Therefore, the homologous and heterologous protection ability of PCV2b and PCV2d Cap proteins based on the baculovirus against the PCV2b and PCV2d infections was evaluated, which is expected to design and develop excellent PCV2 protein vaccine candidates. This study found that both PCV2b and PCV2d Cap proteins can increase the level of humoral immunity and cellular immune response in mice. Importantly, both PCV2b and PCV2d cap proteins can provide homologous and heterologous protection against the PCV2b and PCV2d viruses. Overall, this study provides a reference for the prevention and control of PCVAD in mainland China and the development of PCV2 vaccines.

Cellular and humoral immunity following vaccination with two different PCV2 vaccines (containing PCV2a or PCV2a/PCV2b) and challenge with virulent PCV2d

Porcine Circovirus type 2 (PCV2) associated disease is one of the most economically important swine diseases worldwide. Vaccines reduce PCV2 disease by inducing humoral immunity (neutralizing antibodies) and cell-mediated immunity (CMI) but may be improved by optimizing the immune response they induce. This study evaluated immune responses to a trivalent inactivated Porcine Circovirus (PCV) Type 1-Type 2a chimera (cPCV2a), cPCV2b and Mycoplasma hyopneumoniae (MH) (an experimental serial of Fostera® Gold PCV MH, also marketed as Circomax® Myco) vaccine or a bivalent recombinant PCV2a baculovirus expressed ORF2 capsid plus MH vaccine (Circumvent® PCV-M G2). Treatment Groups (T) received two doses of placebo (T01), one full or two split doses of the trivalent vaccine (T02, T03) or two split doses of the bivalent vaccine (T04) where two doses were given, there was a three-week period between administrations. All pigs were challenged with a virulent field isolate of PCV2d. CMI was measured as PCV2-specific IFN-γ secreting cells in blood and lymph node. Humoral immunity was measured as PCV2 antibodies. Vaccine efficacy was determined as viremia and fecal shedding of virus. There was a robust antibody response in T02 and T04 post the second vaccination and all vaccinated groups post challenge. There was a robust PCV2-specific IFN-γ response following the 1^st dose in T02 and T03 and after the second dose in T02. T04 induced a low but detectable PCV2-specific IFN-γ response only after the 2^nd dose. Among lymph node cells (study day 52), there was a significantly higher PCV2-specific, IFN-γ response to replicase and PCV2d capsid peptides in T01, consistent with active viral replication in non-vaccinated pigs. The trivalent chimeric vaccine induced robust CMI and protective efficacy, following a one dose regimen or splitting the dose into two vaccine administrations.

Genotyping of Porcine Circovirus 2 (PCV-2) in Vaccinated Pigs Suffering from PCV-2-Systemic Disease between 2009 and 2020 in Spain

Vaccination against porcine circovirus 2 (PCV-2) is a common practice all over the world. Vaccines can prevent PCV-2-systemic disease (PCV-2-SD) outbreaks but not PCV-2 infection, which can be detectable in a percentage of vaccinated animals. Occasionally, PCV-2-SD is diagnosed in vaccinated farms. The objective of this study was to genotype the PCV-2 strains detected in vaccinated animals diagnosed with PCV-2-SD. Additionally, the evolution of the frequency of PCV-2 genotype detection at Spanish, European, and world levels was assessed. Fifty cases diagnosed as PCV-2-SD between 2009 and 2020 were included in this study. PCV-2 genotype was determined by sequencing the Cap gene region. Among them, only PCV-2b (23/50, 46%) and PCV-2d (27/50, 54%) genotypes were detected. Although the frequency of detection of these two genotypes was similar, their temporal distribution was different. Whereas most PCV-2b sequences (17/23, 74%) were detected between 2009 and 2012, PCV-2d sequences were obtained from 2013 to 2020. Indeed, a predominance of the PCV-2d genotype was observed from 2013 onwards, a trend also noticed at European and world levels. The results suggest that detection of particular genotypes in vaccinated animals probably reflects the general prevalence of the genotypes over time rather than genotype-specific vaccine-immunity escaping.

First report of canine parvovirus molecular detection in Bangladesh

Background and Aim:

Canine parvovirus (CPV) is the most important cause of mortality in dogs in many parts of the world. Clinical cases exhibit characteristic signs, including foul-smelling bloody diarrhea, vomiting, fever, and dehydration. This study assessed field and vaccine variants of parvovirus in the Chattogram metropolitan area, Bangladesh. The investigation also aimed to identify risk factors for this disease. This research is the first to identify the presence of CPV in Bangladesh through molecular examination.

Materials and Methods:

From October to December 2019, a total of 100 dogs were included in the study. Rectal swabs were taken from all dogs. Twenty dogs showed clinical signs of parvovirus. All clinically affected animals along with 20 randomly selected healthy dogs were tested using amplification refractory mutation system (ARMS)-polymerase chain reaction (PCR) to identify variants from the samples. Logistic regression model analysis was performed to determine the possible risk factors for CPV.

Results:

ARMS-PCR showed the presence of all three variants, CPV2a, CPV2b, and CPV2c, in clinically ill dogs, and vaccines available in the study area showed either CPV2a or CPV2b strain. The CPV2c variants showed a higher incidence than the other variants. All apparently healthy animals tested were molecularly negative. Multivariable logistic regression model (generalized linear mixed model) indicated that exotic breeds were 3.83 times more likely to be infected by CPV than local breeds. Furthermore, dogs reared in semi-intensive and extensive management systems were 3.64 and 3.79 times more likely to be infected, respectively, than those reared in an intensive management system.

Conclusion:

These findings provide practitioners and pet owners information on the occurrence of different variants and help design effective prevention strategies for CPV infection.

Porcine Circovirus 2 Genotypes, Immunity and Vaccines: Multiple Genotypes but One Single Serotype

Identified for the first time in the 1990s, Porcine circovirus 2 (PCV-2) should not be considered an emerging virus anymore. Nevertheless, many aspects of its biology and epidemiology are still controversial. Particularly, its high evolutionary rate has caused the emergence of several variants and genotypes, alternating on the worldwide proscenium. The biological and practical implications of such heterogenicity are unfortunately largely unknown. The effectiveness of currently available vaccines against new genotypes that have emerged over time has been the topic of an intense debate and often inconclusive or contradictory results between experimental, field, and epidemiological studies have been gathered. The challenge in establishing an effective PCV-2 disease model, the peculiarities in experimental design and settings and the strains involved could justify the observed differences. The present work aims to summarize and critically review the available knowledge on PCV-2 genetic heterogeneity, immunity, and vaccine efficacy, organizing and harmonizing the available data from different sources, shedding light on this complex field and highlighting current knowledge gaps and future perspectives. So far, all vaccines in the market have shown great efficacy in reducing clinical signs associated to diseases caused by PCV-2, independently of the genotype present in the farm. Moreover, experimental data demonstrated the cross-protection of PCV-2a vaccines against the most widespread genotypes (PCV-2a, PCV-2b, and PCV-2d). Therefore, despite the significant number of genotypes described/proposed (PCV-2a to PCV-2i), it seems one single PCV-2 serotype would exist so far.