‘Piglet Monitoring’ in Northern Belgium: phylogenetic and geographic distribution of PRRSv isolates

In Flanders, the Porcine Reproductive and Respiratory Syndrome virus (PRRSv) and Porcine Circovirus 2 (PCV2) are endemic on most herds and recognised as two major pathogens with a significant economic impact in the domestic pig. In order to monitor the infection status of a herd concerning PRRSv and PCV2 a voluntary program started in February 2015 with financial support of the Belgian Fund for Animal Health (For more details, refer to the companion abstract ‘Piglet Monitoring’ in Northern Belgium: a tool for veterinarians and farmers to control PRRSv and PCV2). Following-up the circulating PRRSv strains can be used by veterinarians as an interesting tool for evaluating and adapting the advices to the farmers regarding PRRSv surveillance, prevention and control strategies.

A phylogeny study based on partial sequences was performed on PRRSv positive samples collected in herds during two sampling campains. Up to now, 114 individual sequences in the ORF5 region were obtained [Stadejek et al., 2008] and aligned with others available in Genbank, including the European and American vaccine strains and Belgian isolates from 1994 to 2013 for phylogenetic study based on the maximum likelihood method.

Among the 114 sequences, 102 were grouped in the European genotype and specifically in subtype 1.1. They shared identities ranging from 76 to 89% with Lelystad, the subtype reference strain. Two additional isolates were identified as European vaccine strains. In the subtype 2 (North-American) the 10 isolates were identical (96-99%) to the American vaccine strain.

Sample collection points were distributed in the four provinces from Flanders: Oost-Vlaanderen (n=13), West-Vaanderen (n=43), Antwerpen (n=50) and Limburg (n=8). No strict clustering could be observed in relation with the geographical distribution by province. However, one phylogenetic cluster seemed largely present in the four provinces when some others were predominantly distributed in one or two provinces. A more local analysis indicated that up to seven different strains may be circulating on the same municipality or 2 to 3 different strains in the same herd.

The screening that has started in Flanders one year ago has already demonstrated the diversity of the circulating PRRSv isolates in pig herds. The field isolates were all grouped in the European group and particularly in subtype 1.1 clustering with Lelystad strain. Up to now there is no evidence of the presence of field isolate from other European subtypes or from genotype 2. The signification of both geographically dispersed and localised clusters should be further investigated.

Disclosure of Interest: None Declared.