Pooled OF sampling is representative at litter level if collection is successful (> 2 ml of fluids collected). In order to improve the success rate of collection, pre-exposing the piglets with a rope one day prior to sampling is effective

In Europe, modified live vaccines (MLV) are commonly used to control porcine reproductive and respiratory syndrome virus (PRRSV) infection. However, they have been associated with safety issues such as reversion to virulence induced by mutation and/or recombination. On a French pig farm, we identified a field recombinant strain derived from two PRRSV-1 MLV. Estimation of transmission parameters revealed fastest transmission and longest duration of infectiousness for pigs exposed to the recombinant strain.

We showed that MDNAs impair vaccine efficacy against PRRSV both in inoculated and contact piglets, probably by reducing vaccine replication.

IFNa may also interfere with PRRSV vaccination. These new data could help improving vaccination protocols.

The rate of detection of PRRSV-1 was about the same in OF and blood samples. Virus sequencing, if

required, should be performed on individual serum samples but we failed to sequence virus from OF (higher Ct).