Intranasal vaccination of pigs against Aujeszky's disease

Abstract

A pilot experiment in 10‐week‐old sero‐negative pigs showed that intranasal (i.n.) vaccination with 10⁴ to 10⁸ plaque forming units of Bartha's K strain of Aujeszky's disease (A D) virus induced a good antibody response and resulted in nearly complete protection against disease following severe i.n. challenge two months post‐vaccination (p.v.). In addition, excretion of challenge virus was much reduced as compared to that in unvaccinated controls. The main experiment was performed with 12‐week‐old pigs from dams revaccinated shortly before parturition. One group was vaccinated intranasally with 10⁶ TCID₅₀ of the Bartha strain, two groups parenterally with a commercially available modified live virus vaccine based on the same strain and one group was left unvaccinated. Intramuscular (i.m.) vaccination had a slow but distinct serologic effect; a second i.m. vaccination after 24 days resulted in a booster response. I.n. vaccination gave a faster serologic effect than i.m. vaccination and titres continued to increase over a long period. Six pigs of each group were challenged after 6 weeks and four pigs after 4 months, together with four or five unvaccinated litter‐mates. At 6 weeks p.v., one of the control pigs died after the challenge and the other controls showed a mean growth arrest period of 12 days, reflecting severe clinical disease. No vaccinated pigs died. The animals vaccinated once intramuscularly were less severely affected than the controls, the mean growth arrest period being 6.5 days. The pigs vaccinated intranasally or twice intramuscularly were very well protected and on an average did not loose weight. At 4 months p.v., all pigs survived the challenge, but clinical disease of varying severity developed in all groups. The intranasally vaccinated pigs were markedly better protected than the pigs vaccinated once or twice intramuscularly. The mean growth arrest periods of the different groups were more than 19 days for the controls, 13.5 and 12 days for the pigs vaccinated intramuscularly once or twice and 7 days for the intranasally vaccinated pigs. Particularly after the challenge at 6 weeks p.v., the intranasally vaccinated pigs excreted much less virus than the parenterally vaccinated pigs. In this respect there was little difference between pigs vaccinated intramuscularly once or twice, but both categories excreted less virus than the controls. It is concluded that i.n. vaccination of pigs against A D is promising enough to warrant further study, particularly as a means to overcome interference of maternal antibodies with active immunization.