Experimental subunit vaccine against classical swine fever development and trial

Classical swine fever (CSF), the highly contagious viral disease, remains the major threat to pork industry in top ten pork producing countries save the United States. Disease outbreaks and following restrictions in international trade are causing major economic losses worldwide. Wild boars are the natural reservoir of the virus. They represent high danger to pork industry in regions with high density of wild boar population. Live attenuated vaccine has been used in Russia for decades for the total swine population vaccination. Today Russia belongs to world leaders in the pork production, but it still has to be recognized as CSF virus (CSFV) free country (or region) to be incorporated in a global market. The first step in this direction would be the implementation of non-replicating marker vaccines, allowing the differentiation between infected and vaccinated animals (DIVA). Here we first report results of recombinant E2 protein-based vaccine formulations trial in Russian Federation, where optimal administration protocol, adjuvant, dosage of specific component were selected. From the formulations tested, safe and effective vaccine formulation was selected, that needs to be tested for antigen stability and immunity duration in vaccinated animals, and then undergo clinical trial on farm. The aim of our study is the development of the vaccine based on CSFV recombinant surface glycoprotein E2 according to requirements for the country/region free of CSFV. We performed the series of animal trials on Sus scrofa landrace-duroc breed (total number of pigs 84, divided into 9 experimental and 2 control groups) to assess the vaccination schedule, antigen dosage, and choice of adjuvant. Highly pathogenic CSFV Shi-Men strain was used for challenge in 5×105 LD50 dose (ARRIAH collection). Double shot introduction of 10 mg or 30 mg of antigen as well as single shot with 30 or 60 mg of E2 had not provided sufficient level of protection. Oil adjuvant was reactogenic at the inoculation spot even when used once, while polymeric adjuvant has not produced local or systemic reactions after the administration single time or twice. Double administration with the vaccine containing 60 µg of the antigen and polymeric adjuvant has completely protected pigs from the death after the challenge, while in non-vaccinated/challenged control group 5 out of 11 animals died within 14 days post-challenge. Vaccinated animals had less pronounced fever that lasted shorter (rise of the rectal temperature was delayed for 2 days, release of fever 2 days before the control challenge group), frequency and longevity of viremia and virus shedding in nasal swabs were significantly (p ≤ 0.05) reduced as compared to inoculated control piglets. Animals in this vaccinated group gained weight every day after the challenge, being slightly behind non-vaccinated/non-challenged controls. The high levels of antibodies against E2 protein were detected in sera of vaccinated animals before the challenge and they all were negative for antibodies to Erns protein. After the challenge antibodies to Erns proteins started to raise in sera of all animals save non-vaccinated/non-challenged controls, thus we developed the product that may be implemented as a marker vaccine against CSFV.