Laboratory confirmation in a reproductive failure
Sows usually abort from 3 to 21 days after the infection. Therefore, diagnostic after 21 days gets more complicated.
In some circumstances, serum from sows should not be considered as one of the first choices to diagnose reproductive failure due to PRRS virus:
- It is difficult to detect the virus in blood by RT-PCR, since viraemia in sows is usually short (from 1 to 7 days). In front of a positive result in a recent vaccinated animal, viraemia due to vaccine virus have to be discarded using sequencing.
- Seroconversion by ELISA cannot be demonstrated in a previously positive or vaccinated animal/herd; seroconversion can be used to demonstrate the involvement of PRRS only when animal was previously negative.