Background Sows in breeding herds are often mass vaccinated against porcine reproductive and respiratory syndrome (PRRS) every few months using modified live vaccines (MLV). Field veterinarians repeatedly report that multiple vaccinated sows test negative in ELISA. Obviously, this creates uncertainty when assessing the compliance of vaccination and the status of sows.
Methods In the present study, four commercial ELISAs were used to assess the serological PRRS status in gilts and sows of three farms that were PRRS MLV vaccinated every four months. Animals were tested before vaccination (BV) and postvaccination (PV). Total and neutralising antibodies and cell-mediated responses were also measured in animals that yielded negative results in all ELISAs.
Results The proportion of seronegative animals BV varied depending on the farm and the ELISA used. When samples were analysed using only one ELISA, a substantial number of negative results obtained BV remained as negative afterwards. Five animals were negative BV and PV with all the examined ELISAs. Those animals also yielded negative results in all the other immunological assays.
Conclusion Our findings suggest that the use of ELISA for monitoring multiple PRRS MLV vaccinated sows is very limited due to the variability of the humoral responses and the moderate agreement between tests.
- Porcine reproductive and respiratory syndrome (PRRS)
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Funding The study was partially funded by CONPRRS (platform created with the aim of developing PRRS control programs in Spain composed by researchers from UAB, UdL, UCM and IRTA, and supported by Hipra, Merial, MSD and SYVA Laboratories).
Competing interests None declared.
Ethics approval The present study has been approved by ethics committee for animal experimentation from the Universitat Autònoma de Barcelona (Id. 5796) and the Animal experimental commission from the local government (Departament de Medi Ambient i Habitatge from the Generalitat de Catalunya).
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement All data relevant to the study are included in the article.
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