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New Diagnostic Method Detects Five Pig Viruses in One Run

Researchers of CReSA and the Centro Nacional de Sanidad Agropecuria (CENSA) have developed a real-time PCR system for the detection and differentiation of porcine circovirus 2 (PCV-2), pseudorabies virus (PRV1), porcine parvovirus (PPV) and swine torque teno viruses 1 (TTSuV1) and 2 (TTSuV2).

In current intensive swine production, it is possible for pigs to be simultaneously infected with two or more viral pathogens. Hence, an aetiological diagnosis based on clinical signs is difficult, especially for respiratory and reproductive syndromes. Thus, the development of rapid and reliable methods for detection of these viruses is essential for epidemiological surveillance and disease management.

Real-time PCR techniques have improved the diagnosis of important viral livestock diseases and have become established scientific tools in veterinary virology and disease control. Particularly, the SYBR Green I-based real-time assay has proven to be one of the most effective tools in the rapid and differential detection of a variety of viral pathogens. The SYBR Green I assay is considered a flexible and cost-effective approach that, coupled with melting curve analysis, ensures reaction specificity along with multiplex detection of distinct targets.

The present study by CReSA and CENSA was undertaken to develop and evaluate a multiple SYBR Green I-based real-time PCR system for the detection and differentiation of PCV-2, PRV, PPV, TTSuV1 and TTSuV2 in a single run. The analytical and diagnostic performances obtained from the assessment of field samples, as well as the repeatability of the tests in the system; indicate the usefulness of this tool for laboratory diagnosis and epidemiological investigations.

This paper was published in Journal of Virological Methods by Pérez L.J., Perera C.L., Frías M.T., Núñez J.I., Ganges L., de Arce H.D. A multiple SYBR Green I-based real-time PCR system for the simultaneous detection of porcine circovirus type 2, porcine parvovirus, pseudorabies virus and Torque teno sus virus 1 and 2 in pigs. J Virol Methods. 2012 Jan;179(1):233-41.

Viruses studied

Porcine circovirus 2 (PCV-2) is recognised as the essential infectious agent of postweaning multisystemic wasting syndrome (SDPD), a multifactorial disease that causes significant financial losses in pig production worldwide. Several studies have shown that co-infections of pigs with PCV-2 and other viral pathogens, such as porcine parvovirus (PPV), pseudorabies virus (PRV) and swine torque teno sus viruses (TTSuVs), may enhance CVP2-associated lesions and increase the incidence of SDPD under both experimental and field conditions.

PCV-2 is a small non-enveloped virus with a single-stranded circular DNA genome of 1767-1768 nucleotides. The virus belongs to the genus Circovirus, family Circoviridae. This viral agent exhibits a high rate of evolution and can be divided into three viral genotypes. Moreover, PCV-2 is currently considered one of the most important emerging pig pathogens, and it is associated with a number of conditions collectively grouped as porcine circovirus diseases (PCVD).

PRV, also known as suid herpesvirus 1, is a member of the family Herpesviridae, subfamily Alphaherpesvirinae, genus Varicellovirus. The virus has a double-stranded linear DNA genome of approximately 150 kilobases (kb) in length. PRV is the causative agent of the pseudorabies (PR) or Aujeszky's disease, an infection that leads to severe economic losses in the swine industry worldwide.

PPV is an autonomous parvovirus classified into the genus Parvovirus, the subfamily Parvovirinae and the family Parvoviridae. PPV has a single-stranded DNA (minus-strand) genome that is approximately 5kb in size. This viral pathogen is a major causative agent in a reproductive failure syndrome in pregnant sows. More recently, PPV has attracted the attention of the veterinarian community because of the genetic variability found among field viral strains and the emergence of a new antigenic variant of PPV that displays a low cross-neutralisation activity against the vaccine viruses.

Swine torque teno viruses (TTVs) are small, non-enveloped circular single-stranded DNA viruses with genomes approximately 2.8 kb in length in the family Anelloviridae. At present, swine TTVs are classified tentatively into two species.

Whether swine TTVs play a significant role in the pathogenesis of specific pig diseases is still a matter of debate. However, both torque teno sus virus species 1 (TTSuV1) and 2 (TTSuV2) have been associated with the development of SDPD, and TTSuV1 has been linked to the induction of clinical porcine dermatitis and nephropathy syndrome (PDNS), suggesting that swine TTVs may serve as co-factors in intensifying diseases in pigs.

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