Efficacy of Suvaxyn CSF Marker (CP7_E2alf) in the presence of pre-existing antibodies against Bovine viral diarrhea virus type 1

Classical swine fever (CSF) is still one of the most important viral diseases of pigs worldwide and outbreaks are notifiable to the OIE. The different control options also include (emergency) vaccination, preferably with a vaccine that allows differentiation of infected from vaccinated animals (DIVA principle). Recently, the chimeric pestivirus CP7_E2alf' (Suvaxyn (R) CSF Marker, Zoetis) was licensed as live attenuated marker vaccine by the European Medicines Agency (EMA). In the context of risk assessments for an emergency vaccination scenario, the question has been raised whether pre-existing anti-pestivirus antibodies, especially against the vaccine backbone Bovine viral diarrhea virus type 1 (BVDV-1), would interfere with CP7_E2alf vaccination and the accompanying DIVA diagnostics. To answer this question, a vaccination-challenge-trial was conducted with Suvaxyn CSF Marker and the gold-standard of live-modified CSF vaccines C-strain (RIEMSER (R) Schweinepestvakzine) as comparator. Pre-existing antibodies against BVDV-1 were provoked in a subset of animals through intramuscular inoculation of a recent field isolate from Germany (two injections with an interval of 2 weeks). Twenty-seven days after the first injection, intramuscular vaccination of pre-exposed and naive animals with either CP7_E2alf or C-strain Riems was performed. Seven days later, all vaccinated animals and two additional controls were oro-nasally challenged with highly virulent CSF virus (CSFV) strain Koslov. It was demonstrated that pre-existing BVDV-1 antibodies do not impact on the efficacy of live attenuated vaccines against CSF. Both C-strain Riems and marker vaccine CP7_E2alf' were able to confer full protection against highly virulent challenge seven days after vaccination. However, slight interference was seen with serological DIVA diagnostics accompanying the vaccination with CP7_E2alf. Amended sample preparation and combination of test systems was able to resolve most cases of false positive reactions. However, in such a co-infection scenario, optimization and embedding in a well-defined surveillance strategy is clearly needed. (C) 2016 Elsevier Ltd. All rights reserved.