Diagnosis of post-weaning multisystemic wasting syndrome in pigs in Brazil caused by porcine circovirus type 2

Implementation of point-of-care platforms for rapid detection of porcine circovirus type 2

BACKGROUND

Porcine circovirus type 2 (PCV2) infection is ubiquitous around the world. Diagnosis of the porcine circovirus-associated disease requires clinic-pathological elements together with the quantification of viral loads. Furthermore, given pig farms in regions lacking access to sufficient laboratory equipment, developing diagnostic devices with high accuracy, accessibility, and affordability is a necessity.

OBJECTIVES

This study aims to investigate two newly developed diagnostic tools that may satisfy these criteria.

METHODS

We collected 250 specimens, including 170 PCV2-positive and 80 PCV2-negative samples. The standard diagnosis and cycle threshold (Ct) values were determined by quantitative polymerase chain reaction (qPCR). Then, two point-of-care (POC) diagnostic platforms, convective polymerase chain reaction (cPCR, qualitative assay: positive or negative results are shown) and EZtargex (quantitative assay: Ct values are shown), were examined and analyzed.

RESULTS

The sensitivity and specificity of cPCR were 88.23% and 100%, respectively; the sensitivity and specificity of EZtargex were 87.65% and 100%, respectively. These assays also showed excellent concordance compared with the qPCR assay (κ = 0.828 for cPCR and κ = 0.820 for EZtargex). The statistical analysis showed a great diagnostic power of the EZtargex assay to discriminate between samples with different levels of positivity.

CONCLUSIONS

The two point-of-care diagnostic platforms are accurate, rapid, convenient and require little training for PCV2 diagnosis. These POC platforms can discriminate viral loads to predict the clinical status of the animals. The current study provided evidence that these diagnostics were applicable with high sensitivity and specificity in the diagnosis of PCV2 infection in the field.

Development and validation of a real-time PCR for the detection and quantification of porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is a spherical and non-enveloped virus belonging to the genus Circovirus of the Circoviridae family with a single stranded circular DNA genome. This virus, already detected worldwide, has been associated to several diseases and was implicated as the etiological agent of a disease named postweaning multisystemic wasting syndrome. Several methods have been described for the detection of PCV2, being real-time PCR the most simple and reliable. As far as we know, all the real-time PCR systems described until now are based on ORF2 gene, that exhibit the highest variability. This paper reports the development and validation of a real-time PCR targeted to ORF1 and based on a TaqMan probe for the detection of porcine circovirus type 2 DNA in swine samples. Due to the lack of PCV1 samples, the ability of the test to discriminate between PCV1 and PCV2 positive samples was evaluated in silico. Estimations of 100% specificity and 100% sensitivity were obtained based on the qPCR results with panel of 81 swine samples (known PCV2-positive (n = 50); known PCV2-negative (n = 17); samples positive to other common swine viral pathogens (n = 13) and one sample from a BFDV-positive parrot (n = 1)). Intra- and inter-assay coefficients of variation obtained with three positive samples of different viral charges in five replicates or in five independent assays were below the acceptance threshold. The limit of detection determined with a recombinant plasmid containing the amplicon, led to conclude that this assay can detect at least three plasmid copies.

A porcine circovirus-2 mutant isolated in Brazil contains low-frequency substitutions in regions of immunoprotective epitopes in the capsid protein

Porcine circovirus-2 (PCV2) is the etiologic agent of several diseases in pigs, including multi-systemic wasting syndrome (PMWS). In this work, a new mutant PCV2b was isolated from PMWS-affected pigs on a Brazilian farm. Its genome showed high sequence similarity (>99% identity) to those from a group of emerging mutants isolated from cases of PMWS outbreaks in vaccinated pigs in China, the USA and South Korea. Here, we show that these isolates share a combination of low-frequency substitutions (single amino acid polymorphisms with a frequency of ≤25%) in the viral capsid protein, mainly in regions of immunoprotective epitopes, and an additional lysine residue at position 234. These isolates were phylogenetically grouped in the PCV2b clade, reinforcing the idea of the emergence of a new group of mutants PCV2b associated with outbreaks worldwide. The identification of these polymorphisms in the viral capsid highlights the importance of considering these isolates for the development of more-effective vaccines.

Identification of an Emergent Porcine Circovirus-2 in Vaccinated Pigs from a Brazilian Farm during a Postweaning Multisystemic Wasting Syndrome Outbreak

Three porcine circovirus-2 strains were isolated from pigs on a Brazilian farm during an outbreak, indicating a vaccine failure. They present identical genomic sequences, with high identities to other isolates that were also related to vaccination failures, supporting the recent theory about an antigen drift being associated with vaccine failures throughout the world.

Detection and molecular characterization of porcine circovirus type 2 (PCV2) from piglets with exudative epidermitis in Uruguay

Porcine circovirus type 2 (PCV2) is an economically important emerging pathogen associated with distinct syndromes and diseases in swine, collectively known as porcine circovirus associated diseases (PCVAD). The main purpose of this study was to investigate the presence of PCV2 in piglets affected with exudative epidermitis (EE) in Uruguay. In addition we aimed to analyze the phylogenetic relationships of the isolated strains. In June 2011 an outbreak of EE detected in a small herd was reported. Piglets presented skin lesions compatible with EE and symptoms associated with postweaning multisystemic wasting syndrome (PMWS) were also observed. Sera from affected and healthy animals were tested for the presence of viral DNA. Exclusively, diseased piglets were infected with PCV2. Phylogenetic analysis showed that PCV2 isolates belonged to PCV2b genotype. We report the detection and molecular characterization of PCV2 strains for the first time in Uruguay.

Transmission of porcine circovirus 2 (PCV2) by semen and viral distribution in different piglet tissues

Porcine circovirus infections are caused by the porcine circovirus 2 (PCV2). Among six different clinical manifestations involving respiratory, enteric, nervous and reproductive signs, the postweaning multisystemic wasting syndrome (PMWS) is the most important and studied disease. However, reproductive failures associated with PCV2 have been increasingly reported. Some studies have shown the possible contamination of sows by semen of PCV2 positive boars. In order to investigate the transmission of PCV2 by contaminated semen and its ability to infect the sow and piglets, 20 PCV2 negative sows were inseminated, 10 with negative boar semen and 10 with previously nested-PCR tested positive boar semen. The sows were weekly monitored and blood samples were collected. Based on the results, 4 out 20 sows were selected (1 sow was PCR negative and inseminated with a negative semen, 2 sows were PCR negative and inseminated with a positive semen and 1 sow was PCR negative and inseminated with a positive semen, but became PCR positive around the 30 days of pregnancy). After weaning, 12 male piglets, 3 of each sow, were selected and maintained under isolation. In order to investigate which organs harbored the virus, the young pigs were necropsied around 9 months of age. Samples of serum collected monthly were tested by immunocitochemistry (ICC), and all 12 pigs serum converted. Samples of lymphoid, systemic and reproductive organs were analyzed by nested-PCR and immunohistochemistry (IHC). Evaluation of the samples by nested-PCR, revealed that several tissues were positive in 10 of 12 pigs, mainly the lymph nodes, bone marrow and spleen. Various samples were positive by IHC in 8 of 12 piglets, being the lymph nodes, tonsils and bulbourethral glands the most frequently positive. Thus, the results of testing different samples, in the 3 tests (ICC, nested-PCR and IHC) were complementary. These results show that PCV2 transmission through semen to the sows and piglets may occur and may also represent a potential risk for the herd.

Surto de Circovirose (Síndrome Definhante Multissistêmica de Suínos Desmamados) no estado do Rio de Janeiro

Descreve-se o primeiro surto de Síndrome Definhante Multissistêmica de Suínos Desmamados (SDMSD) na Região Sudeste do Brasil, no estado do Rio de Janeiro. A enfermidade que afetou principalmente suínos desmamados com idade em torno de 4 meses, levou a morte pelo menos 14 animais. A granja onde o surto ocorreu, tinha péssimas condições sanitárias e de manejo. Clinicamente, a doença caracterizou-se por má condição corporal, pouco desenvolvimento, tosse, taquipnéia, dispnéia, diarréia, ataxia, tremores após estímulo, decúbito e convulsões, com evolução aguda a subaguda. À necropsia, os achados mais importantes foram um aumento de volume de linfonodos e pulmões não-colapsados, com áreas consolidadas, principalmente nos lobos craniais e porção anterior dos lobos médios. O exame histológico revelou, com maior freqüência, infiltração linfo-histiocítica com células sinciciais em linfonodos, baço, placas de Peyer, rim, pulmão e fígado, depleção ou hiperplasia linfóide, bem como pneumonia bronco-intersticial linfo-histiocitária e áreas de broncopneumonia secundária. O diagnóstico firmou-se pela observação dos sintomas e das lesões histológicas típicas e foi confirmado por exame imunohistoquímico e PCR. O estudo teve por objetivo caracterizar os aspectos epidemiológico e clínico-patológico desse surto, já que a mesma tem causado grandes perdas econômicas, diretas ou indiretas, à suinocultura mundial.