VIROLOGICAL PROTECTION OF SOWS UPON CHALLENGE WITH AUJESZKYS-DISEASE VIRUS AFTER MULTIPLE VACCINATIONS WITH ATTENUATED OR INACTIVATED VACCINES

The frequency with which sows are vaccinated during eradication progra mmes has been determined rather arbitrarily in the past, without the n ecessary scientific support. In the present study the efficacy of repe ated vaccinations against Aujeszky's disease virus (ADV) with two inac tivated vaccines and with one attenuated ADV-strain (Bartha) suspended in either oil-in-water or saline was evaluated in 40 breeding sows or iginating from five farms by the assessment of the clinical and virolo gical protection upon an experimental challenge. Sows with two differe nt histories of number of booster vaccinations after a base immunizati on were selected: young sows which had received 1-3 booster vaccinatio ns and old sows which had received 8-10 booster vaccinations. Two sero negative and two gE-positive sows were included as controls. After cha llenge, clinical signs such as anorexia and fever were observed in the two seronegative sows and only in four out of the 18 sows which had r epeatedly been vaccinated with inactivated vaccines. The mean duration of virus-excretion significantly differed (P < 0.05) between the expe rimental groups. In seronegative sows, virus shedding lasted for 12.5 days. This period was reduced to 6.8-7.9 days in the groups of sows va ccinated with inactivated vaccines having no effect by the number of b ooster vaccinations and type of vaccine. In the groups of sows vaccina ted with Bartha vaccine, challenge virus was detected during 3.7-5.3 d ays when revaccinated 1-3 times. A reduction to 0.7-1.2 days was obtai ned with a higher number of boosters (8-10) but only when the vaccine virus was suspended in o/w. Considering the mean cumulative values of virus excretion (area under the curve) it can be stated that sows freq uently vaccinated with inactivated vaccines excrete significantly (P < 0.05) higher amounts of virus (26.0-31.5) than sows frequently vaccin ated with attenuated ones (1.6-23.7). We may conclude from the present data that the attenuated vaccine virus Bartha, especially when suspen ded in o/w is superior to inactivated vaccines for inducing clinical a nd virological protection of sows in the field during their whole bree ding period.