The role of vaccinations using deleted vaccines in decreasing the spread of Aujeszky's disease virus in pig farms covered within the "vaccination-eradication programme"

Vaccinations play an important role in the control of Aujezky's disease (AD ) because they interrupt the chain of piglet morbidity and mortality as wel l as decreasing the spread of Herpesvirus suis type 1 (SHV-1). Conventional vaccines, however, preclude serological differentiation between vaccinated and SHV-1 infected pigs. Such differentiation has only become possible aft er the creation of deleted (marker) vaccines, which, together with the appr opriate serological tests (ELISA), have enabled the realisation of a "vacci nation - eradication programme" and presented a new perspective on AD eradi cation in those countries where pigs are vaccinated. The purpose of this st udy was to evaluate the influence of an intensive vaccination programme usi ng deleted vaccine in decreasing the spread of SHV-1 in two highly infected pig farms covered in the "vaccination - eradication programme". All pigs w ere vaccinated with deleted, gE- and TK-negative, live attenuated Nobi - Po rvac Aujesky Live Begonia (at present Porcilis Begonia) vaccine - Intervet Int. Holland according to its accepted programme: reproductive pigs 4 month s apart and fattening pigs twice at 10-12 and 14-16 week of age. Control se rological examinations with gE-ELISA using CHEKIT-PRV-gI-EIA, dr Bommeli AG , Switzerland were performed. In groups of sows a gradual, slow decrease of SHV-1 infection rates from 100% before vaccination to 60% in farm R and 41 .7% in farm B after the 4(th) re-vaccination were observed. A more rapid de crease of SHV-1 infection rates among fattening pigs - from 90% to 10% afte r 13 months and 0% after the 19 month of herd vaccinations in farm R, and f rom 80% to 0% as early as after 7 months of herd vaccination in farm B were observed. Serological examinations of all sows and boars after 2.5 years of herd vacc ination revealed a decrease of SHV-1 infection rates from 100% to 34.9% far m R and 28.2% in farm B respectively. This demonstrated that appropriately prepared and consequently realised vaccination programmes of all pigs, usin g a good quality deleted vaccine, radically decreases the spread of virulen t SHV-1 virus in infected herds. The possibilities of serological different iation between immunised and infected pigs combines with a natural rotation of infected reproductive pigs and, next, with an appropriate and properly conducted, economically viable elimination of seropositives creates a reali stic chance of eliminating virulent SHV-1 even from highly infected swine h erds.