We are planning to start piglet vaccination with PRRS MLV in a PRRS negative sow farm because of PRRS problems on the fattening farms. Is there any risk of spreading the vaccine strain on the farm? Will it be better to do the sow vaccination before starting piglet vaccination? What should we do to minimize the risk of vaccine strain circulation?
When MLV is administered, we know that the virus can spread for a few days between animals, and this will be more obvious if the farm is PRRS negative. Differences in virus circulation will depend on the ease with which MLV multiplies in host cells.
Obviously, if only piglets are vaccinated on a negative farm, MLV will infect some sows and they will spread it to the rest.
The viruses contained in commercial vaccines have been attenuated by different techniques and therefore should not cause great problems, but situations have been described where some clinical signs can be temporarily observed.
These temporary clinical signs could be prolonged in cases of uncontrolled circulations which could be the case when only piglets are vaccinated.
For this reason, I would advise you to vaccinate the sows first in order to have them immune at the time of vaccinating the piglets, thus avoiding uncontrolled circulations of the vaccine PRRS virus.
Moura et al. Assessment of immediate production impact following attenuated PRRS type 2 virus vaccination in swine breeding herds. Porcine Health Management (2019).
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