Molecular characterization and phylogenetic analysis of PRRSV strains in Greek swine farms

Porcine reproductive and respiratory syndrome virus (PRRSV) is widespread among swine population, causing reproductive disorders in sows and respiratory disease in pigs of all ages. In Greece, PRRSV was first detected in 1993. Today, PRRSV appears in an enzootic form, with elevations and declines of reproductive problems in breeding stock and increases of respiratory problems in growing-finishing pigs, causing economic losses. The aim of this study is to detect and molecularly characterize PRRSV strains which circulate in Greek swine farms.

During 2012-15, over 1460 blood serum samples were obtained from pigs residing in 50 commercial pig farms of Greece with previous history of PRRS. The specimens underwent RNA isolation, and extracts were tested with two genotype-specific real-time RT-PCR protocols (North American / European). DNA sequencing was performed in RT-PCR-positive samples from 13 farms, aiming to molecularly characterize ORF 4. Moreover, post-mortem examination was performed in dead piglets derived from the aforementioned farms. Tissues from various organs were obtained for histopatholgoical testing, as well as PRRSV antigen detection via immunohistochemistry.

The results of the molecular testing indicated that only the European genotype was circulating, in 70% of the tested farms. Additionally, analysis of nine ORF 4 sequences which were obtained revealed the presence of 6 distinct phylogenetic clades, with large phylogenetic distances. The variability of the neutralizing epitopes of Gp4 protein was high in the obtained sequences. Gross pathology and histopathological findings were compatible to those of PRRS. Immunochistochemical testing showed presence of viral antigens in lymphoid tissues and lungs.

The present study comprises the first report on PRRSV molecular characterization in Greece. Although only European genotype strains were detected in all tested farms, the high variability of the strains raises questions regarding their introduction in the farms, as well as for the protection offered by commercial vaccines.

Disclosure of Interest: S. Chaintoutis Conflict with: Zoetis Inc., V. Papatsiros Conflict with: Zoetis Inc., G. Brellou Conflict with: Zoetis Inc., E. Tzika Conflict with: Zoetis Inc., I. Tsakmakidis Conflict with: Zoetis Inc., I. Vlemmas Conflict with: Zoetis Inc., V. Psychas Conflict with: Zoetis Inc., C. Dovas Conflict with: Zoetis Inc.