Vaccination with Viral Protein-Mimicking Peptides Postpones Mortality in Domestic Pigs Infected by African Swine Fever Virus

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Vadim Ivanov1, Evgeniy E. Efremov2, Boris V. Novikov3, Vladimir M. Balyshev3, Sodnom Zh. Tsibanov3, Tatiana Kalinovsky1, Denis V. Kolbasov3, Aleksandra Niedzwiecki1, Matthias Rath1.
1, Dr Rath Research Institute BV, 1260 Memorex Drive, Santa Clara, CA, USA
2, Cardiology Research Center, 121552 Moscow, Russia.
3, National Research Institute for Veterinary Virology and Microbiology, 601120, Pokrov, Russia
Molecular Medicine Reports 2011, 4:395-401

Periodic outbreaks of African Swine Fever Virus (ASFV) infection around the world threaten local populations of domestic pigs with lethal disease and provide grounds for pandemic spread. Effective vaccination might bring this threat under control. We investigated the effectiveness of select peptides mimicking viral protein in raising a protective immune response. Forty six synthetic peptides were based on the analysis of the complete nucleotide sequence of ASFV and tested for immunogenicity in mice. The seventeen best immune response-inducing peptide candidates were selected for further investigation.

Twenty-four domestic pigs, three-four month old at 20 to 25 kg body weight, were divided into six groups (n=4) and immunized by subcutaneous injections using a standard three-round injection protocol with one of four-peptide combinations prepared from the seventeen peptides (Groups 1-4) or with carrier only (Group 5). Group 6, the control, was not vaccinated. Animal body temperature and behavior were monitored during and post immunization for health assessment. Two weeks after the last round of immunizations, pigs were infected with live ASFV (Espania 70) at 6.0 Ig GAE50/cm3. Survival rate was monitored. Blood samples were collected for analysis the day before infection and on days 3, 7, and 10 post-infection, or from deceased animals. Serum titer of specific immunoglobulins against synthetic peptides and whole inactivated ASFV were determined by enzyme immunoassay before and after infection. Presence of viral DNA in blood serum samples was determined by polymerase chain reaction. Viral infection activity in blood sera was determined by heme absorption in cultured PBM (porcine bone marrow) and PL (porcine leukocyte) cells. Repeating injections of synthetic peptides both in mice and pigs produced an immune response specific to individual peptides, which differed widely on the intensity scale. Specific anti-whole virus immunoglobulin binding activity in swine serum samples was below detection limit in all animals. Viral DNA was positively identified in all animal samples infected with viral preparation. Viral infection activity was present in all infected animals and it steadily increased with time. On day 3 after infection, the viral titer in group 1 and 3 animals vaccinated with peptides was significantly lower than in unvaccinated controls.  In deceased animals, the viral titer in groups 1 and 3 was significantly lower than in controls. All infected animals died within 17 days after infection. Average survival rate in groups 1 and 3 was significantly higher (12.0 days and 14.3 days, respectively) than in controls (9.8 days). Vaccination with specific synthetic peptides significantly delayed mortality in domestic pigs infected with ASFV. These results justify further investigation toward development of effective vaccine against ASFV infection.

Key Words
ASF infection; protein-mimicking peptides; vaccination; domestic pigs; mortality

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