Porcine Circovirus: a small virus that causes a great problem
Circovirus porcino: un virus pequeño que genera un gran problema
Porcine circoviruses type 1 and type 2 (PCV-1 and PCV-2) are very small (17 nm), nonenveloped, icosahedral viruses (Tisher y col., 1982), with circular, single stranded DNA genomes of approximately 1,700 nucleotides length, encoding 2 major ambisense open reading frames (Mankertz y col., 1998; Hamel y col., 1998). Together with a number of avian viruses with similar molecular characteristics, the porcine circoviruses are classified in the genus Circovirus within the family Circoviridae. Although PCV-1 persists in the pig population, the presence of PCV-1 has not been associated with any recognised clinical signs or pathology. In contrast, PCV-2 has been implicated as the mayor causative agent of Postweaning Multisystemic Wasting Syndrome (PMWS). It is characterized mainly by loose of weight, general wasting, and severe immunosuppressive effects with premature death of piglets. PCV-2 effects are generated by inhibition of plasmacytoid dendritic cells (pdc) so called natural interferon-Î± producing cells (NIPCs) unlinking the innate and acquired immune systems, and renderinga host susceptible to secondary or concomitant microbial infections. Therefore, PCV-2 additionally is associated with other porcine diseases and syndromes, such as reproductive failure, respiratory disease complex, congenital tremor, porcine dermatitis and nephropathy syndrome, nectrotizing tracheitis and exudative epidermitis, together with other viral and bacterial agents, including Parvovirus, PRRSV (Porcine Reproductive and Respiratory Syndrome virus), Influenza, Aujeszky and Mycoplasma pneumoniae, Actinobacillus pleuropneumoniae, Streptococcus suis and Pastereulla multocida. Nowadays, these diseases are known as PCVAD or PCV-2-associated diseases, in order to group all the diseases attributed to porcine circovirus type 2. The PCV-2-associated diseases, mainly PMWS, at present are considered to be the greatest economic problem associated with the pig industry world-wide.