Veterinary session

Porcine circovirus type 2 (PCV2) is a common pathogen causing major economic losses worldwide and also in Hungary, infecting both wild boars and domestic pigs. The control of PCV2 is based on general epidemiological measures and vaccination.

A new recombinant cucumber mosaic virus (RCMV) has been developed in cooperation with the Agricultural Research Institute of the Hungarian Academy of Sciences, the Agricultural Biotechnology Research Centre and the Szent István University, Faculty of Veterinary Science, Department of Microbiology and Infectious Diseases. The virus carries a PCV2 epitope (amino acids 224-233) on its capsid surface. The recombinant virus was able to trigger specific immune response against PCV2 during an experiment in mice. RCMV replication in high quantities using plants offers an inexpensive and easy way for antigen production. Furthermore, the antigen might also be used for oral immunization, inducing specific local immunity on mucosal surfaces.

To evaluate the immunogenicity of RCMV we performed an experiment using 13 piglets weaned at two weeks after birth and divided them into three groups. Five piglets in the first group were vaccinated intramuscularly using RCMV mixed with incomplete Freund’s adjuvant. Another five pigs were immunized using commercially available, inactivated PCV2 vaccine (Circovac, Merial) as positive control. The immunizations were repeated after 10 days. The third group was mock immunized as a negative control. The serum antibody titers were measured weekly during the two-months-long experiment, using indirect immunofluorescence assay. The efficacy of the vaccinations was tested by challenge infection using wild type PCV2. The quantity of the virus was measured by polymerase chain reaction (qPCR) from fecal samples, and the organ samples collected after extermination.

According to the results of the immunofluorescence tests, PCV2 specific antibodies appeared in the sera of pigs vaccinated with RCMV after the second immunizaton, in contrast to the positive control group, where they were detected after the first dosing. None of the animals showed clinical signs of PCV2 associated diseases after the challenge infection. Virus replication was less frequent in the piglets immunized with RCMV, than in mock immunized pigs. There was no detectable virus replication in the positive control group.

It was concluded that the immunogenicity of the recombinant antigen was satisfactory, although the selection of the perfect antigen concentration, formulation and adjuvant requires further experiments.