Post-Weaning Multisystemic Wasting Syndrome and Other PCV2-Related Problems in Pigs: a 12-Year Experience

Porcine circovirus type 2 and Glaesserella parasuis serotype 4 co-infection activates Snail1 to disrupt the intercellular junctions and facilitate bacteria translocation across the tracheal epithelium

Clinically, Porcine circovirus type 2 (PCV2) often causes disease through coinfection with other bacterial pathogens, including Glaesserella parasuis (G. parasuis), which causes high morbidity and mortality. However, the mechanism of PCV2 and G. parasuis serotype 4 (GPS4) co-infection is still not fully understood. In this study, swine tracheal epithelial cells (STEC) were used as a barrier model, and our results showed that PCV2 infection increased the adhesion of GPS4 to STEC, while decreasing the levels of ZO-1, Occludin and increasing tracheal epithelial permeability, and ultimately facilitated GPS4 translocation. Snail1 is a transcriptional repressor, and has been known to induce epithelial-to-mesenchymal transition (EMT) during development or in cancer metastasis. Importantly, we found that Snail1, as a transcriptional repressor, was crucial in destroying the tracheal epithelial barrier induced by PCV2, GPS4, PCV2 and GPS4 coinfection. For the first time, we found that PCV2, GPS4, PCV2 and GPS4 coinfection cross-activates TGF-β and p38/MAPK signaling pathways to upregulate the expression of Snail1, down-regulate the levels of ZO-1 and Occludin, and thus disrupt the integrity of tracheal epithelial barrier then promoting GPS4 translocation. Finally, PCV2 and GPS4 co-infection also can activate TGF-β and p38/MAPK signaling pathways in vivo and upregulate Snail1, ultimately down-regulating the expression of ZO-1 and Occludin. Our study elucidates how PCV2 infection promotes GPS4 to breach the tracheal epithelial barrier and aggravate clinical manifestations.

Revisiting Porcine Circovirus Infection: Recent Insights and Its Significance in the Piggery Sector

Porcine circovirus (PCV), a member of the Circoviridae family within the genus Circovirus, poses a significant economic risk to the global swine industry. PCV2, which has nine identified genotypes (a-i), has emerged as the predominant genotype worldwide, particularly PCV2d. PCV2 has been commonly found in both domestic pigs and wild boars, and sporadically in non-porcine animals. The virus spreads among swine populations through horizontal and vertical transmission routes. Despite the availability of commercial vaccines for controlling porcine circovirus infections and associated diseases, the continuous genotypic shifts from a to b, and subsequently from b to d, have maintained PCV2 as a significant pathogen with substantial economic implications. This review aims to provide an updated understanding of the biology, genetic variation, distribution, and preventive strategies concerning porcine circoviruses and their associated diseases in swine.

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.

Welfare of pigs on farm

This scientific opinion focuses on the welfare of pigs on farm, and is based on literature and expert opinion. All pig categories were assessed: gilts and dry sows, farrowing and lactating sows, suckling piglets, weaners, rearing pigs and boars. The most relevant husbandry systems used in Europe are described. For each system, highly relevant welfare consequences were identified, as well as related animal-based measures (ABMs), and hazards leading to the welfare consequences. Moreover, measures to prevent or correct the hazards and/or mitigate the welfare consequences are recommended. Recommendations are also provided on quantitative or qualitative criteria to answer specific questions on the welfare of pigs related to tail biting and related to the European Citizen's Initiative 'End the Cage Age'. For example, the AHAW Panel recommends how to mitigate group stress when dry sows and gilts are grouped immediately after weaning or in early pregnancy. Results of a comparative qualitative assessment suggested that long-stemmed or long-cut straw, hay or haylage is the most suitable material for nest-building. A period of time will be needed for staff and animals to adapt to housing lactating sows and their piglets in farrowing pens (as opposed to crates) before achieving stable welfare outcomes. The panel recommends a minimum available space to the lactating sow to ensure piglet welfare (measured by live-born piglet mortality). Among the main risk factors for tail biting are space allowance, types of flooring, air quality, health status and diet composition, while weaning age was not associated directly with tail biting in later life. The relationship between the availability of space and growth rate, lying behaviour and tail biting in rearing pigs is quantified and presented. Finally, the panel suggests a set of ABMs to use at slaughter for monitoring on-farm welfare of cull sows and rearing pigs.

Genotype Shift of Malaysian Porcine Circovirus 2 (PCV2) from PCV2b to PCV2d within a Decade

Simple Summary

This study aims to provide an updated Malaysian porcine circovirus 2 (PCV2) situation after a knowledge gap of one decade. Molecular detection rates of 83.78% and 83.54% at farm and sample population level were reported, close to previous publication. However, an obvious genotype shift from genotype PCV2b to PCV2d was revealed. Substitution rate for PCV2 cap gene sequences in this study was estimated at 1.102 × 10⁻³ substitutions/site/year, in agreement with the high substitution rate expected from PCV2 strains. Phylogenetic clustering pattern according to the year of sample origin was observed, suggesting possible nucleotide mutation occurring over time. Concurrent circulation of different PCV2 strains within one farm and within a single individual were also observed. This study also reports detection of PCV2 antigen across all production age groups from fetuses to sows; in abattoir lung samples from clinically healthy finishers; and in the wild boar population roaming Peninsular Malaysia. These observations of high molecular detection rates in farms, clinically healthy abattoir samples and in the wild boar population; and most importantly, a new wave of genotype shift from PCV2b to PCV2d—warrant further attention on the Malaysian PCV2 situation pertinent to the control and management strategy applicable to local swine farming.

Abstract

This paper aims to update the molecular status of porcine circovirus 2 (PCV2) in Malaysia. Firstly, the molecular detection rate of PCV2 in farm and sampled pig population were reported to be 83.78% (31/37 farms) and 83.54% (66/79 pigs) positive for PCV2, respectively. PCV2 was detected across all age groups, from fetuses, porkers to sows. Co-detection of PCV2 and PCV3 antigens was also reported at a rate of 28.77% (21/73). Secondly, PCV2 antigen was also detected in Malaysian abattoir lung samples: 18 out of 19 (94.74%) samples originating from clinically healthy finishers were tested positive. Further, this is the first study to confirm the circulation of PCV2 in the wild boar population roaming Peninsular Malaysia, where 28 out of 28 (100%) wild boar lung samples were found positive. One decade earlier, only genotype PCV2b was reported in Malaysia. This most recent update revealed that genotypes PCV2a, PCV2b and PCV2d were present, with PCV2d being the predominant circulating genotype. PCV2 cap gene nucleotide sequences in this study were found to be under negative selection pressure, with an estimated substitution rate of 1.102 × 10⁻³ substitutions/site/year (ssy).

Prevalence and Evolution Analysis of Porcine Circovirus 3 in China from 2018 to 2022

Simple Summary

An increasing number of studies have shown that the PCV3 virus causes signs and symptoms similar to PDNS in pigs, and since first being identified in the United States, it has caused reproductive failure in pigs. Studies have shown that it has spread worldwide, especially in China. However, to date, there are only a few reports of PCV3 detection and sequence variation, and limited information is known about its distribution in China’s major swine-producing regions. This study examined the prevalence of PCV3 in China and its evolutionary relationship. A high level of PCV3 infection has been found in serum samples, and it has been found that PCV3 infection has a widespread distribution among Chinese pig herds. The ORF2 genes of the strains were analyzed and compared with other PCV3 strains, which were downloaded from the NCBI. Our phylogenetic analysis indicated a close relationship with the strains previously described in pigs, and additional analysis revealed that all isolates obtained in this study could be divided into two sub-clades: 3a and 3b. Overall, this study showed that PCV3 prevalence in China is high and there is a lot of genetic divergence among the strains, which may pose a threat to the porcine industry.

Abstract

Porcine circovirus 3 (PCV3) is an emerging virus, causing substantial economic losses in pig populations, that was first detected in 2016. Furthermore, the virus has already been reported in Europe, the Americas, and Asia, including China, indicating that the virus has spread worldwide. However, the molecular epidemiology of PCV3 still needs further study. To investigate PCV3 epidemiological characteristics in China, 2707 serum samples of pigs were randomly collected from 17 provinces in China between September 2018 and March 2022 and analyzed via PCR assays. The study showed that PCV3 infection was prevalent in the overall population with 31.07% (841/2707) and 100.0% (17/17) at sample and province levels, respectively, though the positivity rate of PCV3 varied from 7.41 to 70.0% in different provinces, suggesting that PCV3 infection has a widespread distribution in China. We selected 22 serum samples from different regions that had high levels of viral DNA for amplification and sequenced their ORF2 (Cap) gene. According to the phylogenetic analysis, all isolates in the current study could be grouped into two separate subclades, with 15 strains belonging to clade 3a and 7 strains belonging to clade 3b, indicating that PCV3a and PCV3b were the predominant subtypes in the regions of China studied. Meanwhile, additional analysis revealed that the capsid gene sequences identified in this study displayed 97.46~99.8% nucleotide (nt) and 97.06~100% amino acid (aa) sequence similarity with other PCV3 available reference strains, respectively. In general, our studies provide important insights for understanding the prevalence and evolution of PCV3 in China and will guide future efforts to develop measures for preventing and controlling the disease.

The Evidence for a Causal Link Between Disease and Damaging Behavior in Pigs

Damaging behaviors (DB) such as tail and ear biting are prevalent in pig production and reduce welfare and performance. Anecdotal reports suggest that health challenges increase the risk of tail-biting. The prevalence of tail damage and health problems show high correlations across batches within and between farms. There are many common risk factors for tail-biting and health problems, notably respiratory, enteric and locomotory diseases. These include suboptimal thermal climate, hygiene, stocking density and feed quality. The prevalence of tail damage and health problems also show high correlations across batches within and between farms. However, limited evidence supports two likely causal mechanisms for a direct link between DB and health problems. The first is that generalized poor health (e.g., enzootic pneumonia) on farm poses an increased risk of pigs performing DB. Recent studies indicate a possible causal link between an experimental inflammation and an increase in DB, and suggest a link between cytokines and tail-biting. The negative effects of poor health on the ingestion and processing of nutrients means that immune-stimulated pigs may develop specific nutrient deficiencies, increasing DB. The second causal mechanism involves tail-biting causing poor health. Indirectly, pathogens enter the body via the tail lesion and once infected, systemic spread of infection may occur. This occurs mainly via the venous route targeting the lungs, and to a lesser extent via cerebrospinal fluid and the lymphatic system. In carcasses with tail lesions, there is an increase in lung lesions, abscessation, arthritis and osteomyelitis. There is also evidence for the direct spread of pathogens between biters and victims. In summary, the literature supports the association between poor health and DB, particularly tail-biting. However, there is insufficient evidence to confirm causality in either direction. Nevertheless, the limited evidence is compelling enough to suggest that improvements to management and housing to enhance pig health will reduce DB. In the same way, improvements to housing and management designed to address DB, are likely to result in benefits to pig health. While most of the available literature relates to tail-biting, we suggest that similar mechanisms are responsible for links between health and other DB.

The Swine IFN System in Viral Infections: Major Advances and Translational Prospects

Interferons (IFNs) are a family of cytokines that play a pivotal role in orchestrating the innate immune response during viral infections, thus representing the first line of defense in the host. After binding to their respective receptors, they are able to elicit a plethora of biological activities, by initiating signaling cascades which lead to the transcription of genes involved in antiviral, anti-inflammatory, immunomodulatory and antitumoral effector mechanisms. In hindsight, it is not surprising that viruses have evolved multiple IFN escape strategies toward efficient replication in the host. Hence, in order to achieve insight into preventive and treatment strategies, it is essential to explore the mechanisms underlying the IFN response to viral infections and the constraints thereof. Accordingly, this review is focused on three RNA and three DNA viruses of major importance in the swine farming sector, aiming to provide essential data as to how the IFN system modulates the antiviral immune response, and is affected by diverse, virus-driven, immune escape mechanisms.

Investigating pig survival in different production phases using genomic models

Pig survival is an economically important trait with relevant social welfare implications, thus standing out as an important selection criterion for the current pig farming system. We aimed to estimate (co)variance components for survival in different production phases in a crossbred pig population as well as to investigate the benefit of including genomic information through single-step genomic best linear unbiased prediction (ssGBLUP) on the prediction accuracy of survival traits compared with results from traditional BLUP. Individual survival records on, at most, 64,894 crossbred piglets were evaluated under two multi-trait threshold models. The first model included farrowing, lactation, and combined postweaning survival, whereas the second model included nursery and finishing survival. Direct and maternal breeding values were estimated using BLUP and ssGBLUP methods. Furthermore, prediction accuracy, bias, and dispersion were accessed using the linear regression validation method. Direct heritability estimates for survival in all studied phases were low (from 0.02 to 0.08). Survival in preweaning phases (farrowing and lactation) was controlled by the dam and piglet additive genetic effects, although the maternal side was more important. Postweaning phases (nursery, finishing, and the combination of both) showed the same or higher direct heritabilities compared with preweaning phases. The genetic correlations between survival traits within preweaning and postweaning phases were favorable and strong, but correlations between preweaning and postweaning phases were moderate. The prediction accuracy of survival traits was low, although it increased by including genomic information through ssGBLUP compared with the prediction accuracy from BLUP. Direct and maternal breeding values were similarly accurate with BLUP, but direct breeding values benefited more from genomic information. Overall, a slight increase in bias was observed when genomic information was included, whereas dispersion of breeding values was greatly reduced. Combined postweaning survival presented higher direct heritability than in the preweaning phases and the highest prediction accuracy among all evaluated production phases, therefore standing out as a candidate trait for improving survival. Survival is a complex trait with low heritability; however, important genetic gains can still be obtained, especially under a genomic prediction framework.

Coinfection with Porcine Circovirus Type 2 (PCV2) and Streptococcus suis Serotype 2 (SS2) Enhances the Survival of SS2 in Swine Tracheal Epithelial Cells by Decreasing Reactive Oxygen Species Production

Porcine circovirus type 2 (PCV2) and Streptococcus suis serotype 2 (SS2) clinical coinfection cases have been frequently detected. The respiratory epithelium plays a crucial role in host defense against a variety of inhaled pathogens. Reactive oxygen species (ROS) are involved in killing of bacteria and host immune response. The aim of this study is to assess whether PCV2 and SS2 coinfection in swine tracheal epithelial cells (STEC) affects ROS production and investigate the roles of ROS in bacterial survival and the inflammatory response. Compared to SS2 infection, PCV2/SS2 coinfection inhibited the activity of NADPH oxidase, resulting in lower ROS levels. Bacterial intracellular survival experiments showed that coinfection with PCV2 and SS2 enhanced SS2 survival in STEC. Pretreatment of STEC with N-acetylcysteine (NAC) also helps SS2 intracellular survival, indicating that PCV2/SS2 coinfection enhances the survival of SS2 in STEC through a decrease in ROS production. In addition, compared to SS2-infected STEC, PCV2/SS2 coinfection and pretreatment of STEC with NAC prior to SS2 infection both downregulated the expression of the inflammatory cytokines interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and IL-1β. Further research found that activation of p38/MAPK promoted the expression of inflammatory cytokines in SS2-infected STEC; however, PCV2/SS2 coinfection or NAC pretreatment of STEC inhibited p38 phosphorylation, suggesting that coinfection of STEC with PCV2 and SS2 weakens the inflammatory response to SS2 infection through reduced ROS production. Collectively, coinfection of STEC with PCV2 and SS2 enhances the intracellular survival of SS2 and weakens the inflammatory response through decreased ROS production, which might exacerbate SS2 infection in the host.

Porcine circovirus type 2 exploits JNK-mediated disruption of tight junctions to facilitate Streptococcus suis translocation across the tracheal epithelium

Porcine circovirus type 2 (PCV2) is considered as the primary pathogen of porcine circovirus-associated disease (PCVAD), which results in significant economic losses worldwide. Clinically, PCV2 often causes disease through coinfection with other bacterial pathogens, including Streptococcus suis (S. suis), and especially the highly prevalent S. suis serotype 2 (SS2). The present study determined that continuous PCV2 infection in piglets down-regulates tight junction proteins (TJ) ZO-1 and occludin in the lungs. Swine tracheal epithelial cells (STEC) were used to explore the mechanisms and consequences of disruption of TJ, and an in vitro tracheal epithelial barrier model was established. Our results show that PCV2 infection in STEC decreases the expression levels of ZO-1 and occludin and increases the permeability of the tracheal epithelial barrier, resulting in easier translocation of SS2. Moreover, Western blot analysis indicates that PCV2 infection activates the JNK/MAPK pathway. The disruption of TJ in SETC and increased permeability of the epithelial barrier induced by PCV2 could be alleviated by inhibition of JNK phosphorylation, which indicates that the JNK/MAPK pathway regulates the expression of ZO-1 and occludin during PCV2 infection. This study allows us to better understand the mechanisms of PCV2 coinfection with bacterial pathogens and provides new insight into controlling the occurrence of PCVAD.

A Shift in Porcine Circovirus 3 (PCV-3) History Paradigm: Phylodynamic Analyses Reveal an Ancient Origin and Prolonged Undetected Circulation in the Worldwide Swine Population

The identification of a new circovirus (Porcine circovirus 3, PCV-3) has raised a remarkable concern because of some analogies with Porcine circovirus 2 (PCV-2). Preliminary results suggest an extremely recent PCV-3 emergence and high mutation rate. Retrospective studies prove its circulation at least since the early 1990s, revealing that PCV-3 could have been infecting pigs for an even longer period. Therefore, a new evaluation, based on an updated collection of PCV-3 sequences spanning more than 20 years, is performed using a phylodynamic approach. The obtained results overrule the previous PCV-3 history concept, indicating an ancient origin. These evidences are associated with an evolutionary rate far lower (10-5-10-6 substitution/site/year) than the PCV-2 one. Accordingly, the action of selective pressures on PCV-3 open reading frames (ORFs) seems to be remarkably lower compared to those acting on PCV-2, suggesting either a reduced PCV-3 plasticity or a less efficient host-induced natural selection. A complex and not-directional viral flow network is evidenced through phylogeographic analysis, indicating a long lasting circulation rather than a recent emergence followed by spreading. Being recent emergence has been ruled out, efforts should be devoted to understand whether its recent discovery is simply due to improved detection capabilities or to the breaking of a previous equilibrium.

Retrospective Detection and Genetic Characterization of Porcine circovirus 3 (PCV3) Strains Identified between 2006 and 2007 in Brazil

Porcine circovirus 3 (PCV3) is an emerging virus that was first identified in the United States in 2016. Since its first detection, PCV3 has already been found in America, Asia, and Europe. Although PCV3 has already been described in Brazil, knowledge of its detection and sequence variation before 2016 is limited, as well as its distribution in the main swine producing regions of Brazil. In this study, 67 porcine clinical samples collected from nine states in Brazil between 2006 and 2007 were analyzed for PCV3 infection by PCR. Results showed that 47.8% of the samples were PCV3 positive, across all nine states. Of the PCV3-positive samples, 37.5% were also positive for PCV2. Interestingly, no clinical signs were associated with samples that were detected singularly with PCV3 infection. Moreover, the positive PCV3 rate in healthy pigs was higher (29.8%) than that found in unhealthy pigs (17.9%), suggesting that most pigs could live with PCV3 infection without any clinical sign in the analyzed samples. Nucleotide sequence analysis showed that PCV3 strains obtained in this study shared 94.44% to 99.83% sequence identity at the open reading frame 2 (ORF2) gene level with available strains from different countries. PCV3 Brazilian sequences collected in 2006 and 2007 shared 97.94% to 99.62% identity with the strains obtained in 2016. The results of neutrality and selective pressure tests indicated that the PCV3 Cap protein seems unable to tolerate high levels of variation on its sequence. Phylogenetic analysis grouped the Brazilian strains in PCV3a and PCV3b genotypes clusters, both including strains collected in America, Asia, and Europe. Taking the results together, multiple events of introduction of PCV3 may have occurred in Brazil, and Brazilian PCV3 strains may show genetic stability over the past 10 years.

Current Knowledge on Porcine circovirus 3 (PCV-3): A Novel Virus With a Yet Unknown Impact on the Swine Industry

Porcine circovirus 3 (PCV-3) is a recently described virus belonging to the family Circoviridae. It represents the third member of genus Circovirus able to infect swine, together with PCV-1, considered non-pathogenic, and PCV-2, one of the most economically relevant viruses for the swine worldwide industry. PCV-3 was originally found by metagenomics analyses in 2015 in tissues of pigs suffering from porcine dermatitis and nephropathy syndrome, reproductive failure, myocarditis and multisystemic inflammation. The lack of other common pathogens as potential infectious agents of these conditions prompted the suspicion that PCV-3 might etiologically be involved in disease occurrence. Subsequently, viral genome was detected in apparently healthy pigs, and retrospective studies indicated that PCV-3 was already present in pigs by early 1990s. In fact, current evidence suggests that PCV-3 is a rather widespread virus worldwide. Recently, the virus DNA has also been found in wild boar, expanding the scope of infection susceptibility among the Suidae family; also, the potential reservoir role of this species for the domestic pig has been proposed. Phylogenetic studies with available PCV-3 partial and complete sequences from around the world have revealed high nucleotide identity (>96%), although two main groups and several subclusters have been described as well. Moreover, it has been proposed the existence of a most common ancestor dated around 50 years ago. Taking into account the economic importance and the well-known effects of PCV-2 on the swine industry, a new member of the same family like PCV-3 should not be neglected. Studies on epidemiology, pathogenesis, immunity and diagnosis are guaranteed in the next few years. Therefore, the present review will update the current knowledge and future trends of research on PCV-3.

The importance of on-farm biosecurity: Sero-prevalence and risk factors of bacterial and viral pathogens in smallholder pig systems in Uganda

BACKGROUND

The productivity of pigs in smallholder systems is affected by high disease burden, most of which might not be obvious, with their epidemiology and impact being poorly understood. This study estimated the seroprevalence and identified the risk factors of a range of bacterial and viral pathogens of potential economic and public health importance in domestic pigs in Uganda. A total of 522 clinically healthy pigs were randomly selected from 276 pig farms in Masaka (142) and Lira (134) districts of Uganda in 2015.

RESULTS

Overall the highest animal prevalence was found for Streptococcus suis 73.0% (CI95: 67.0-78.3) in Lira and 68.2% (CI95: 62.7-73.4) in Masaka; followed by Porcine circovirus type 2 with 50.8% (CI95: 44.5-57.2) in Lira and 40.7% (CI95: 35.2-46.5) in Masaka and Actinobacillus pleuro-pneumoniae, 25.6% (CI95: 20.4-31.6) in Lira and 20.5% (CI95: 16.2-25.6) in Masaka. Mycoplasma hyopneumonia prevalence was 20.9% (CI95: 16.2-26.6) in Lira and 10.1% (CI95: 7.1-14.1) in Masaka, while Porcine parvovirus was 6.2% (CI95: 4.0-9.7) in Masaka and 3.4% (CI95: 1.7-6.6) in Lira. Less common pathogens were Influenza A, 8.5% (CI95: 5.6-12.8) in Lira and 2.0% (CI95: 0.9-4.5) in Masaka and Porcine Reproductive and Respiratory Syndrome Virus, 1.7% (CI95: 0.7-4.3) in Lira and 1.3% (CI95: 0.5-3.5) in Masaka. Even less common was Rotavirus A with 0.8% (CI95: 0.2-3.0) in Lira and 0.7% (CI95: 0.2-2.5) in Masaka; the same was for Aujeszky virus with 0.4% (CI95: 0.7-2.4) in Lira and 0.0% (CI95: 0.0-0.1) in Masaka. Co-infection with two pathogens was common and there was a significant association of M. hyo and PCV2 co-occurrence (p = 0.016). Multivariate analysis showed that for S. suis the use of disinfectant reduced odds of sero-positivitey (OR = 0.15; p = 0.017) and pigs less than 6 months were more likely to be infected than older pigs (OR = 3.35; p = 0.047). For M. hyo, crossbred pigs had higher odd of infection compared to local breeds (OR = 1.59; p < 0.001).

CONCLUSIONS

The studied pathogens have high prevalences in smallholder pig production systems and might be silent killers, thus affecting productivity and there is a possibility that some pathogens could spread to humans. Given the limited knowledge of veterinary workers and the poor diagnostic capacities and capabilities in these systems, the diseases are potentially usually under-diagnosed. These findings constitute baseline data to measure the impact of future interventions aiming to reduce disease burden in the pig production systems in Uganda.

The emergence of porcine circovirus 2 infections in the Northeastern part of India: A retrospective study from 2011 to 2017

Porcine circovirus (PCV) infection has emerged as an alarming threat to the pig population of India, especially in the Northeastern region (NER) over the last 10 years. The present study is a comprehensive report of the seroepidemiology of PCV2 and its incidences in the pig population from organized and unorganized farms of the entire NER of India from 2011 to 2017. A total of 5697 serum samples were screened by ELISA and the mean positivity of PCV2 antibodies in suspected sera was 31.27%. A total of 22 confirmed cases of PCV2 infection were recorded during the years 2014-2017. Seroprevalence of PCV2 infection in sows causing reproductive disorders in NER suggested its higher incidence in organized farms (65.7%) as compared to unorganized farms (17.6%). A detailed pathological and histopathological examination of the tissue samples collected from the affected animals indicated the presence of PCV2. Molecular characterization and phylogenetic analysis of four PCV2 isolates depicted the circulation of PCV2d genotype in the states of Meghalaya and Assam.

A Slaughterhouse Survey for Porcine Circovirus Type 2 in Commercial Pigs in Ibadan, Southwest Nigeria

Porcine circovirus type 2 (PCV2) is recognized as one of the most important agents of reproductive disorders in gilts and sows worldwide. It is associated with considerable economic losses in the swine industry due to the unthriftiness, and variable morbidity and mortality it causes in pigs. In spite of the devastation caused by this virus to the global pig industry, there is little or no report of its occurrence in Nigeria. Hence, a slaughterhouse based survey was conducted to determine the prevalence of PCV2 infections in pigs in Ibadan, southwest Nigeria. Using a commercial ELISA kit, 364 pig sera collected from a major abattoir were screened for IgG antibodies against PCV2. The overall prevalence of anti-PCV2 antibodies in the pigs was 1.4 % (5/364), with more female pigs (4/237, 1.7 %) being seropositive than males (1/127, 0.8 %). Since there is no routine vaccination against this swine disease in Nigeria, thus the antibodies detected in the pig sera indicated a natural exposure to the virus. The absence of clinical disease in the pigs also suggests the possibility of a carrier status for these animals and shows that they could serve as hosts for the perpetuation of the disease. These findings underscore the need for continuous surveillance for PCV2 among pigs in Nigeria in order to determine its contribution to production losses incurred in the Nigerian swine industry and aid the development of prevention and control strategies against the disease.

Porcine Circoviruses and Xenotransplantation

Allotransplantation and xenotransplantation may be associated with the transmission of pathogens from the donor to the recipient. Whereas in the case of allotransplantation the transmitted microorganisms and their pathogenic effect are well characterized, the possible influence of porcine microorganisms on humans is mostly unknown. Porcine circoviruses (PCVs) are common in pig breeds and they belong to porcine microorganisms that still have not been fully addressed in terms of evaluating the potential risk of xenotransplantation using pig cells, tissues, and organs. Two types of PCVs are known: porcine circovirus (PCV) 1 and PCV2. Whereas PCV1 is apathogenic in pigs, PCV2 may induce severe pig diseases. Although most pigs are subclinically infected, we do not know whether this infection impairs pig transplant functionality, particularly because PCV2 is immunosuppressive. In addition, vaccination against PCV2 is able to prevent diseases, but in most cases not transmission of the virus. Therefore, PCV2 has to be eliminated to obtain xenotransplants from uninfected healthy animals. Although there is evidence that PCV2 does not infect—at least immunocompetent—humans, animals should be screened using sensitive methods to ensure virus elimination by selection, Cesarean delivery, vaccination, or embryo transfer.

Passive immunisation, an old idea revisited: Basic principles and application to modern animal production systems

Immunisation by administration of antibodies (immunoglobulins) has been known for more than one hundred years as a very efficient means of obtaining immediate, short-lived protection against infection and/or against the disease-causing effects of toxins from microbial pathogens and from other sources. Thus, due to its rapid action, passive immunisation is often used to treat disease caused by infection and/or toxin exposure. However immunoglobulins may also be administered prior to exposure to infection and/or toxin, although they will not provide long-lasting protection as is seen with active immunisation (vaccination) in which an immunological memory is established by controlled exposure of the host to the pathogen in question. With multi-factorial infectious diseases in production animals, especially those that have proven hard to control by vaccination, the potential of passive immunisation remains big. This review highlights a number of examples on the use of passive immunisation for the control of infectious disease in the modern production of a range of animals, including pigs, cattle, sheep, goat, poultry and fish. Special emphasis is given on the enablement of passive immunisation strategies in these production systems through low cost and ease of use as well as on the sources, composition and purity of immunoglobulin preparations used and their benefits as compared to current measures, including vaccination (also comprising maternal vaccination), antibiotics and feed additives such as spray-dried plasma. It is concluded that provided highly efficient, relatively low-price immunoglobulin products are available, passive immunisation has a clear role in the modern animal production sector as a means of controlling infectious diseases, importantly with a very low risk of causing development of bacterial resistance, thus constituting a real and widely applicable alternative to antibiotics.

Porcine circovirus type 2 (PCV2) enteric disease: an independent condition or part of the systemic disease?

Intestinal disorders in growing and finishing pigs have been associated with several infectious agents, including Porcine circovirus type 2 (PCV2). This virus has been mainly related with PCV2-systemic disease (PCV2-SD); nevertheless, some authors have suggested a possible restricted intestinal infection of this virus associated with enteric clinical signs. This condition has been referred as PCV2-enteric disease (PCV2-ED). The present study analysed retrospectively, from a pathological point of view, the relation between intestinal disorders and PCV2 infection in nursery and growing-finishing pigs. Among the 96 selected pigs suffering from enteric disease and submitted for necropsy between 1998 and 2011, the most prevalent enteric lesions were catarrhal enteritis/colitis (77.1%), followed by fibrinous lesions (11.5%), granulomatous inflammation (4.2%) and other lesions such as haemorrhages or ulceration (4.2%). Seventy-two pigs (75%) were positive for PCV2 by in situ hybridization (ISH). Among positive pigs for PCV2 ISH, 39 animals suffered from PCV2-SD and 33 had no lymphoid lesions but low amount of viral nucleic acid in several lymphoid tissues, therefore, these animals did not qualify for PCVD-ED. In conclusion, all animals with enteric disorders that were positive to PCV2 by ISH had evidence of viral systemic infection. These results suggest that PCV2-ED is probably a negligible condition and PCV2 mainly contributes to enteric clinical disorders in relation to PCV2-SD occurrence.

Variation in time and magnitude of immune response and viremia in experimental challenges with Porcine circovirus 2b

Background

Porcine circovirus 2 is the primary agent responsible for inducing a group of associated diseases known as Porcine Circovirus Associated Diseases (PCVAD), which can have detrimental effects on production efficiency as well as causing significant mortality. The objective of this study was to evaluate variation in viral replication, immune response and growth across pigs (n = 974) from different crossbred lines. The approach used in this study was experimental infection with a PCV2b strain of pigs at an average of 43 days of age.

Results

The sequence of the PCV2b isolate used in the challenge was similar with a cluster of PCV2b isolates known to induce PCVAD and increased mortality rates. The swine leukocyte antigen class II (SLAII) profile of the population was diverse, with nine DQB1 haplotypes being present. Individual viremia and antibody profiles during challenge demonstrate variation in magnitude and time of viral surge and immune response. The correlations between PCV2 specific antibodies and average daily gain (ADG) were relatively low and varied between - 0.14 to 0.08 for IgM and −0.02 and 0.11 for IgG. In contrast, PCV2 viremia was an important driver of ADG decline following infection; a moderate negative correlation was observed between viral load and overall ADG (r = − 0.35, P < 0.001). The pigs with the lowest 10% level of viral load maintained a steady increase in weekly ADG (P < 0.0001) compared to the pigs that had the 10% greatest viral load (P < 0.55). In addition, the highly viremic group expressed higher IgM and IgG starting with d 14 and d 21 respectively, and higher tumor necrosis factor – alpha (TNF-α) at d 21 (P < 0.005), compared to low viremic group.

Conclusions

Molecular sources of the observed differences in viremia and immune response could provide a better understanding of the host factors that influence the development of PCVAD and lead to improved knowledge of swine immunity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-014-0286-4) contains supplementary material, which is available to authorized users.

Influence of porcine circovirus type 2 vaccination on the probability and severity of pneumonia detected postmortem

To evaluate the influence of porcine circovirus type 2 vaccination (PCV-2) on the probability and severity of pneumonia, postmortem findings of 247,505 pigs slaughtered between 2008 and 2011 were analysed by applying a cumulative link mixed model. Three major effects could be observed: (1) PCV-2 vaccination significantly (P<0.01) reduced the odds (coefficient: −0.05) of postmortem findings of mild, moderate and severe pneumonia for vaccinated pigs. (2) Pigs from fattening farms were less likely (coefficient: −0.44; P<0.05) to exhibit signs of pneumonia at slaughter than pigs from farrow-to-finish farms. (3) When vaccinated, the odds of detecting postmortem signs showed an even more pronounced reduction (coefficient: −0.19; P<0.001) for pigs from fattening farms. Combining PCV-2 vaccination, farm type and interaction effects between these two factors, a pig vaccinated against PCV-2 from a fattening farm had only half the chance (OR 0.51) of pneumonia being detected at postmortem than a non-vaccinated pig from a farrow-to-finish farm. The study demonstrates the benefit of a vaccination programme against PCV-2 as an important tool to reduce the risk of postmortem pneumonia findings and the severity of pneumonia in pigs at slaughter.

The effects of sow viremia and maternal antibodies in porcine circovirus 2 on viral infection and weight of piglets

The aim of this study was to characterize the porcine circovirus 2 (PCV2) infections in farrowing sows and to evaluate an association with piglet viremia and weight. Twenty sows and 100 newborn piglets were studied. Colostrum and serum of the sows were obtained on the day of parturition. Milk samples were collected on day 20 postpartum. Blood samples were taken and the piglets were weighed on days 1, 20, 42, 63 and 84 postpartum. Colostrum, milk and serum were evaluated for PCV2 DNA load. Serum was evaluated for neutralizing antibodies. PCV2 DNA was found in 17/20 serum samples, 14/20 colostrum samples and 11/20 milk samples. On day 1 postpartum 29% of piglets were viremic. PCV2 viral load ranged from 3.02 to 6.75 log10 copies/mL considering all sampled days. There was no correlation between sow viremia, antibody levels or PCV2 load in colostrum and piglet viremia on day 1 postpartum. The PCV2 load in colostrum and milk was associated with viremia in piglets from weaning to 84 days postpartum. Piglets' PCV2 viremia and viral load could not be associated with weight throughout this study.

PCV2 on the spot-A new method for the detection of single porcine circovirus type 2 secreting cells

A porcine circovirus type 2 SPOT (PCV2-SPOT) assay was established to enumerate virus-secreting lymphocytes obtained from naturally infected pigs. The assay is based on the same principle as general ELISPOT assays but instead of detecting cytokine or immunoglobulin secretion, PCV2 particles are immobilized and detected as filter spots. The method was used to evaluate the influence of various cell activators on the PCV2 secretion in vitro and was also applied to study the PCV2 secretion by lymphocytes obtained from pigs in healthy herds and in a herd afflicted by postweaning multisystemic wasting disease (PMWS). Peripheral blood mononuclear cells (PBMCs) obtained from a pig with severe PMWS produced PCV2-SPOTs spontaneously whereas PBMCs obtained from pigs infected subclinically only generated PCV2-SPOTs upon in vitro stimulation. The PCV2 secretion potential was related to the PCV2 DNA content in the PBMCs as determined by two PCV2 real-time PCR assays, developed to differentiate between Swedish PCV2 genogroups 1 (PCV2a) and 3 (PCV2b). Besides the current application these qPCRs could simplify future epidemiological studies and allow genogroup detection/quantitation in dual infection experiments and similar studies. The developed PCV2-SPOT assay offers a semi-quantitative approach to evaluate the potential of PCV2-infected porcine cells to release PCV2 viral particles as well as a system to evaluate the ability of different cell types or compounds to affect PCV2 replication and secretion.

Dynamics of antibody response and viraemia following natural infection of porcine circovirus 2 (PCV-2) in a conventional pig herd

Porcine circovirus 2 (PCV-2) is a primary agent of post-weaning multi-systemic wasting syndrome (PMWS), ubiquitous in pig herds. The course of viraemia and seroconversion in naturally infected pigs were investigated in piglets from the 2nd week of their life. Piglets were divided into seropositive (Ab(+)) and seronegative (Ab(-)) groups. Subsequently, after vaccination against PCV-2 (Ingelvac(®) CIRCOFLEX™, Böehringer Ingelheim), they were further divided into non-vaccinated seronegative (NVAC/Ab(-)) and seropositive (NVAC/Ab(+)), and vaccinated seronegative (VAC/Ab(-)) and seropositive (VAC/Ab(+)). PCV-2 colostral antibodies failed to prevent development of natural PCV-2 infection in conventional piglets; however, this occurred at a higher age in comparison with seronegative pigs. Neither colostral nor post-infection antibodies prevented development of viraemia, which persisted up to the end of the study (the 19th week), but without clinical signs of PMWS. Vaccination failed to prevent development of natural PCV-2 infection, but viraemia was limited to between the 8th and 10th week. The presence of colostral anti-PCV-2 antibodies did not show any untoward effect to vaccination; on the contrary, VAC/Ab(+) animals showed the lowest titre of viraemia.

The blurred border between porcine circovirus type 2-systemic disease and porcine respiratory disease complex

Porcine respiratory disease complex (PRDC) is the name used to describe a clinical presentation characterized by respiratory signs and poor growth in growing-finishing pigs. Porcine circovirus type 2 (PCV2) is one of the pathogens potentially involved in the presentation of this complex, although, it has been mainly linked to PCV2-systemic disease (PCV2-SD). However, some reports have suggested that PCV2 can cause respiratory lesions in the absence of systemic lymphoid damage; this apparently different condition has been referred as PCV2-lung disease (PCV2-LD). The present study analysed retrospectively the relation between PRDC and PCV2 infection from a pathological point of view. Of the 317 selected pigs suffering from PRDC and submitted for necropsy between 1998 and 2011, the most prevalent lesions were subacute interstitial pneumonia (27.7%) and the combination of subacute interstitial pneumonia plus catarrhal-purulent bronchopneumonia (28.4%). Two hundred and twenty-six pigs were positive for PCV2 by in situ hybridization (ISH); using immunohistochemical techniques, 77 were positive for porcine reproductive and respiratory syndrome virus and 3 for swine influenza virus. Among positive pigs for PCV2 ISH, 184 animals suffered from PCV2-SD. The rest of 42 PCV2 ISH positive pigs had no lymphoid lesions and low amount of viral nucleic acid in these tissues and, therefore, did not qualify for PCVD-SD; only 9 had concomitant PCV2 ISH positivity in the lung, also to a low amount. In conclusion, all PRDC-PCV2 ISH positive cases had evidence of viral systemic infection. These results suggest that PCV2-LD is probably a negligible condition and PCV2 mainly contributes to PRDC in relation to PCV2-SD occurrence.

Infectious risk factors for individual postweaning multisystemic wasting syndrome (PMWS) development in pigs from affected farms in Spain and Denmark

Two prospective longitudinal studies in 13 postweaning multisystemic wasting syndrome (PMWS)-affected farms from Spain (n=3) and Denmark (n=10) were performed. Blood samples from pigs were longitudinally collected from 1st week until the occurrence of the PMWS outbreak. Wasted and healthy age-matched pigs were euthanized, necropsied and histopathologically characterised. PMWS diagnosis was confirmed by means of lymphoid lesions and detection of porcine circovirus type 2 (PCV2) in these tissues by in situ hybridization or immunohistochemistry. Serological analyses were performed in longitudinally collected serum samples to detect antibodies against, PCV2, porcine reproductive and respiratory syndrome virus (PRRSV), porcine parvovirus (PPV), swine influenza virus (SIV) and Lawsonia intracellularis (law), Mycoplasma hyopneumoniae, Aujeszky's disease virus (ADV) and Salmonella spp. A Cox proportional hazards model was used to investigate the simultaneous effects of seroconversion and maternal immunity against the studied pathogens. Results showed that high levels of maternal immunity against PCV2 had a protecting effect in farms from both countries. Moreover, for the Danish dataset, seroconversion against law had an overall protecting effect, but for animals with very low levels of maternal antibody levels against this pathogen, the effect appeared neutral or aggravating. Otherwise, for the Spanish dataset, maternal immunity against PPV and PRRSV gave protective and aggravating effects, respectively. In conclusion, the present study reflects the complex interaction among different pathogens and their effects in order to trigger PMWS in PCV2 infected pigs.

Porcine circovirus type 2 infection before and during an outbreak of postweaning multisystemic wasting syndrome on a pig farm in the UK

The presence of porcine circovirus type 2 (PCV-2) and other pathogens before and during an outbreak of postweaning multisystemic wasting syndrome (PWMS) in pigs is evaluated in this study. At the time of the outbreak on a large commercial pig farm in the UK, serum samples and data were collected in two independent on-going research projects, one in weaned pigs and the other in sows. Serum samples of growing pigs and sows were PCV-2-antibody and PCR positive before and during the PMWS outbreak. Upon sequencing, PCV-2 isolates collected before the outbreak were identified as PCV-2a, and isolates collected during the outbreak were identified as PCV-2b, suggesting a shift of PCV-2 genotypes present on the farm. Pigs in the weaner study were from sows originating from different breeders and an association of sow origin and PCV-2 serostatus in offspring was found. Further, pigs had higher odds to be PCV-2 antigen positive if the sow was PCV-2 antibody positive around farrowing, the sow was of higher parity, and were less likely to test antigen positive if the sow was sourced from a particular breeder. The findings of this study highlight the potential role of the immune status of the sow on the occurrence of PMWS.

Naked PCV-2 cloned genomic DNA is infectious by mucosal (intratracheal or oro-nasal) inoculation

Porcine circovirus type 2 (PCV-2) is involved in several diseases named porcine circovirus-associated diseases and is transmitted by oro-faecal route. In this study we inoculated porcine-circovirus free piglets by mucosal routes (intratracheal or oro-nasal routes) with a plasmid carrying two copies of PCV-2 genomic DNA and compared the results to the intramuscular route. We observed that this PCV-2 naked DNA serves as template for viral replication and infectious PCV-2 particles are detected in the whole body after parenteral (intramuscular) or mucosal (intratracheal or oro-nasal) delivery. These results suggest that PCV-2 genome could play a role in in vivo transmission.

Tripping over emerging pathogens around the world: a phylogeographical approach for determining the epidemiology of Porcine circovirus-2 (PCV-2), considering global trading

Porcine circovirus-2 (PCV-2) is an emerging virus associated with a number of different syndromes in pigs known as Porcine Circovirus Associated Diseases (PCVAD). Since its identification and characterization in the early 1990s, PCV-2 has achieved a worldwide distribution, becoming endemic in most pig-producing countries, and is currently considered as the main cause of losses on pig farms. In this study, we analyzed the main routes of the spread of PCV-2 between pig-producing countries using phylogenetic and phylogeographical approaches. A search for PCV-2 genome sequences in GenBank was performed, and the 420 PCV-2 sequences obtained were grouped into haplotypes (group of sequences that showed 100% identity), based on the infinite sites model of genome evolution. A phylogenetic hypothesis was inferred by Bayesian Inference for the classification of viral strains and a haplotype network was constructed by Median Joining to predict the geographical distribution of and genealogical relationships between haplotypes. In order to establish an epidemiological and economic context in these analyses, we considered all information about PCV-2 sequences available in GenBank, including papers published on viral isolation, and live pig trading statistics available on the UN Comtrade database (http://comtrade.un.org/). In these analyses, we identified a strong correlation between the means of PCV-2 dispersal predicted by the haplotype network and the statistics on the international trading of live pigs. This correlation provides a new perspective on the epidemiology of PCV-2, highlighting the importance of the movement of animals around the world in the emergence of new pathogens, and showing the need for effective sanitary barriers when trading live animals.

Porcine circovirus type 2 and its associated diseases in Korea

This review describes the characterization of porcine circovirus type 2 (PCV2), the field situation of porcine circovirus-associated disease (PCVAD) and the PCV2 vaccine in Korea. PCVAD has been considered the most devastating disease in Korean livestock history since its first outbreak in 1999. Postweaning multisystemic wasting syndrome (PMWS) and porcine respiratory disease complex (PRDC) are the most common clinical forms of PCVAD. Interestingly, only PCV2b strains have been isolated from pigs with PMWS since 2005, but only PCV2a strains were isolated from pigs with PMWS in 2000 to 2001. Clinically, PMWS is divided into two stages: early and late. Early PMWS primarily occurs in pigs between 4 and 8 weeks of age. This form is a typical presentation of PMWS and is characterized clinically by wasting, decreased weight gain, enlarged lymph nodes, and dyspnea. Late PMWS primarily occurs in pigs between 8 and 12 weeks of age. The main clinical manifestation is diarrhea, which is often accompanied by salmonellosis coinfection. In recent years, the PCVAD disease pattern has slightly changed. The occurrence of PMWS has decreased while PRDC cases are increasing in frequency.

Coreplication of the major genotype group members of porcine circovirus type 2 as a prerequisite to coevolution may explain the variable disease manifestations

A member of the family Circoviridae, porcine circovirus type 2 (PCV2), is associated with postweaning multisystemic wasting syndrome (PMWS), a recent emerging disease worldwide. PCV2 is also found in clinically asymptomatic animals. This paradoxical finding makes the syndrome etiology challenging. We developed new assays to study PCV2 with links to syndrome etiology. For analysis, we used PCV2-infected tissues from subclinically infected and diseased piglets. We compared antigen- and PCV2 DNA-derived signals for tissue localization and intensity. Oligonucleotides were designed to the signature motif of the PCV2 capsid open reading frame to discriminate experimentally between PCV2 genotype groups by PCR, in situ hybridization (ISH), and fluorescence in situ hybridization (FISH). Unexpectedly, all PCV2-infected animals carried both PCV2a and PCV2b genotype group members. Using confocal microscopy, genotype single-cell infections and cell superinfections were visible. Additionally, we discriminated replicative DNA from total PCV2 DNA isoforms with FISH. This aided in our inquiry into cellular genotype-specific replication. Importantly, single-genotype-group replication was not observed. In infected cells with replicating virus, both genotype groups were equally present. These findings suggest PCV2 genotype group members relaxed replication regulation requirements and may even point to PCV2 replication cooperativity in vivo. These observations explain the readily seen PCV2 DNA recombinations and the high overall PCV2 genome plasticity. Hence, we suggest a novel mechanism of syndrome etiology that consists of a continuously changing PCV2 genome pool in hosts and pig herds, posing a constant challenge to the individual maturing immune system.

Intestinal gene expression in pigs experimentally co-infected with PCV2 and PPV

The objective of the present study was to characterize the local immune reaction in the intestine of pigs experimentally infected with PCV2 and PPV. Archived intestinal material from an experimental study in which pigs were co-infected with a Swedish isolate of PCV2 (S-PCV2) and PPV, or a reference isolate of PCV2 (PCV2-1010) and PPV, were used. The intestinal samples were analysed by qPCR for expression of a number of selected cytokines and the overall gene expression in the intestine was screened by cDNA microarray. Analyses by qPCR showed that pigs infected with PCV2-1010/PPV displayed a significantly increased mRNA expression for IL-6 (p<0.05), IL-10 (p<0.05) and IFN-γ (p<0.05). The microarray screening revealed a strong up-regulation of IFITM3 along with several other interferon-stimulated genes (ISGs) in pigs infected with PCV2/PPV. The analyses also indicated differences between the two isolates. Fewer pigs infected with S-PCV2/PPV expressed the cytokines detected by qPCR, compared to pigs infected with PCV2-1010/PPV, and pigs infected with S-PCV2/PPV displayed a higher proportion of down-regulated genes than PCV2-1010/PPV-infected pigs.

Spread of porcine circovirus associated disease (PCVAD) in Ontario (Canada) swine herds: Part I. Exploratory spatial analysis

Background

The systemic form of porcine circovirus associated disease (PCVAD), also known as postweaning multisystemic wasting syndrome (PMWS) was initially detected in the early 1990s. Starting in 2004, the Canadian swine industry experienced considerable losses due to PCVAD, concurrent with a shift in genotype of porcine circovirus type 2 (PCV2). Objectives of the current study were to explore spatial characteristics of self-reported PCVAD distribution in Ontario between 2004 and 2008, and to investigate the existence and nature of local spread.

Results

The study included 278 swine herds from a large disease-monitoring project that included porcine reproductive and respiratory syndrome (PRRS) virus-positive herds identified by the diagnostic laboratory, and PRRS virus-negative herds directly from the target population. Herds were included if they had growing pigs present on-site and available geographical coordinates for the sampling site. Furthermore, herds were defined as PCVAD-positive if a producer reported an outbreak of circovirus associated disease, or as PCVAD-negative if no outbreak was noted. Spatial trend was investigated using generalized additive models and time to PCVAD outbreak in a herd using Cox's proportional hazard model; spatial and spatio-temporal clustering was explored using K-functions; and location of most likely spatial and spatio-temporal clusters was investigated using scan statistics. Over the study period, the risk of reporting a PCVAD-positive herd tended to be higher in the eastern part of the province after adjustment for herd PRRS status (P = 0.05). This was partly confirmed for spread (Partial P < 0.01). Local spread also appeared to exist, as suggested by the tentative (P = 0.06) existence of spatio-temporal clustering of PCVAD and detection of a spatio-temporal cluster (P = 0.04).

Conclusions

In Ontario, PCVAD has shown a general trend, spreading from east-to-west. We interpret the existence of spatio-temporal clustering as evidence of spatio-temporal aggregation of PCVAD-positive cases above expectations and, together with the existence of spatio-temporal and spatial clusters, as suggestive of apparent local spread of PCVAD. Clustering was detected at small spatial and temporal scales. Other patterns of spread could not be detected; however, survival rates in discrete Ontario zones, as well as a lack of a clear spatial pattern in the most likely spatio-temporal clusters, suggest other between-herd transmission mechanisms.

Spread of porcine circovirus associated disease (PCVAD) in Ontario (Canada) swine herds: Part II. Matched case-control study

Background

The emergence of porcine circovirus associated disease (PCVAD) was associated with high mortality in swine populations worldwide. Studies performed in different regions identified spatial, temporal, and spatio-temporal trends as factors contributing to patterns of the disease spread. Patterns consistent with spatial trend and spatio-temporal clustering were already identified in this dataset. On the basis of these results, we have further investigated the nature of local spread in this report. The primary objective of this study was to evaluate risk factors for incidence cases of reported PCVAD.

Results

A time-matched case-control study was used as a study design approach, and conditional logistic regression as the analytical method. The main exposure of interest was local spread, which was defined as an unidentified mechanism of PCVAD spread between premises located within 3 kilometers of the Euclidean distance. Various modifications of variables indicative of local spread were also evaluated. The dataset contained 278 swine herds from Ontario originally sampled either from diagnostic laboratory submissions or directly from the target population. A PCVAD case was defined on the basis of the producer's recall. Existence of apparent local spread over the entire study period was confirmed (OR = 2.26, 95% CI: 1.06, 4.83), and was further identified to be time-varying in nature - herds experiencing outbreaks in the later part of the epidemic were more likely than control herds to be exposed to neighboring herds experiencing recent PCVAD outbreaks. More importantly, the pattern of local spread was driven by concurrent occurrence of PCVAD on premises under the same ownership (OR_{EXACTwithin ownership} = 25.6, 95% CI: 3.4, +inf; OR_{EXACToutside ownership} = 1.3, 95% CI: 0.45, 3.3). Other significant factors included PRRSv status of a herd (OR_EXACT = 1.9, 95% CI: 1.0, 3.9), after adjusting for geographical location by including the binary effect of the easting coordinate (Easting > 600 km = 1; OR_EXACT = 1.8, 95% CI: 0.5, 5.6).

Conclusions

These results preclude any conclusion regarding the existence of a mechanism of local spread through airborne transmission or indirectly through contaminated fomites or vectors, as simultaneous emergence of PCVAD could also be a result of concurrent change in contributing factors due to other mechanisms within ownerships.

Epidemiology and horizontal transmission of porcine circovirus type 2 (PCV2)

Porcine circovirus type 2 (PCV2) is a small, non-enveloped, circular, single-stranded DNA virus of economic importance in the swine industry worldwide. Based on the sequence analyses of PCV2 strains, isolates can be divided into five subtypes (PCV2a–e). PCV2 is an ubiquitous virus based on serological and viremia data from countries worldwide. In addition, PCV2 DNA was discovered in archived samples prior to the first recognition of clinical disease. Recently, a worldwide shift in PCV2 subtype from PCV2a to PCV2b occurred. PCV2 DNA can be detected in fecal, nasal, oral and tonsillar swabs as well as in urine and feces from both naturally and experimentally infected pigs. PCV2 DNA can be detected early in the infectious process and persists for extended periods of time. The effectiveness of disinfectants for reducing PCV2in vitrois variable and PCV2 is very stable in the pig environment. Limited data exist on the horizontal transmission of PCV2. Direct transmission of PCV2 between experimentally or naturally infected animals and naïve animals has been documented and the incorporation of clinical or subclinically infected animals into a population represents a risk to the herd. Indirect transmission through the oral, aerosol or vaccine routes is likely a lesser risk for the transmission of PCV2 in most swine populations but may be worth evaluating in high heath herds. The objective of this review was to discuss data on the epidemiology and horizontal transmission of PCV2.

Cytokine induction by immunostimulatory DNA in porcine PBMC is impaired by a hairpin forming sequence motif from the genome of Porcine Circovirus type 2 (PCV2)

Porcine Circovirus type 2 (PCV2) can cause postweaning multisystemic wasting syndrome (PMWS) in young pigs with severe immunosuppression as a major characteristic of the disease complex. Despite the dramatic involvement of the immune system, the interaction between PCV2 and the host is until date not well understood. The DNA genome of PCV2 contains sequences that in synthetic form (oligodeoxyribonucleotides; ODNs) can act immunomodulatory on porcine peripheral blood mononuclear cells (poPBMCs) in vitro. One such sequence (ODN PCV2/1) acts inhibitory on interferon (IFN)-α production induced by immunostimulatory DNA but not that induced by RNA, and the inhibitory activity is dependent on secondary structure formation. In the present study, the characteristic of ODN PCV2/1 was examined further by altering the nucleotide sequence to disrupt hairpin structure formation but still enable multimer structures through G-tetrads. This modification resulted in loss of IFN-α-inhibitory activity of the ODN and thus indicated the importance of hairpin structures. In addition, ODN PCV2/1 was compared to another inhibitory ODN (IRS 869) previously used in human and murine cells. In contrast to ODN PCV2/1, ODN IRS 869 did not inhibit IFN-α production induced by class A ODN 2216 but was a more efficient inhibitor of IFN-α production induced by plasmid DNA than ODN PCV2/1. In cultures induced by the RNA stimulator Poly I:C, however, a strong synergistic IFN-α stimulatory effect was seen in combination with ODN IRS 869. These results indicate that ODN PCV2/1 and ODN IRS 869 function through separate mechanisms to affect cytokine production by immune cells. The effect of ODN PCV2/1 was studied further by monitoring the expression of mRNA for IFN-α, IL-12p40, IL-10, IL-6, IFN-γ, IL-1β, TGF-β, and TNF-α in cultures of poPBMC stimulated with ODN 2216 or Poly I:C. Results from qPCR analyses showed that ODN PCV2/1 clearly inhibited the expression of IFN-α, IL-12p40, IL-10 and IL-6 when induced by ODN 2216, but did not seem to affect any of the cytokines examined when induced by Poly I:C. Initial studies using confocal microscopy and fluorochrome labelled ODNs indicate that ODN 2216 and ODN PCV2/1 co-localize in subpopulations of poPBMC.

Bronchiolitis obliterans organizing pneumonia in Swine associated with porcine circovirus type 2 infection

Bronchiolitis obliterans organizing pneumonia (BOOP) is a chronic respiratory disease. Although the pathogenesis of BOOP is still incompletely understood, BOOP is responsive to steroids and has a good prognosis. In our five pigs with chronic postweaning multisystemic wasting syndrome (PMWS), typical BOOP lesions were revealed. All five porcine lungs showed typical intraluminal plugs, and porcine circovirus type 2 (PCV2) was identified. They also exhibited similar pathologic findings such as proliferation of type II pneumocytes and myofibroblasts (MFBs), extracellular collagen matrix (ECM) deposition, and fragmentation of elastic fibers. MFBs migration correlative molecules, for instance, gelatinase A, B and osteopontin, appeared strongly in the progressing marginal area of polypoid intraluminal plugs of fibrotic lesion. These molecules colocalized with the active MFBs. Both gelatinase activity and intercellular level of active MFBs were significantly increased (P < .05). Porcine chronic bronchopneumonia leads to BOOP and it is associated with PCV2 persistent infection. Swine BOOP demonstrates similar cellular constituents with human BOOP. Perhaps their molecular mechanisms of pathogenesis operate in a similar way. Thus we infer that the swine BOOP can be considered as a potential animal model for human BOOP associated with natural viral infection. Moreover, it is more convenient to obtain samples.