The eradication of Aujeszky's disease from pig production in Sweden

The first recorded outbreak of Aujeszky's disease (AD) in Sweden occurred in 1965. Up to 1980, 41 and up to 1990, an additional 165 new outbreaks were recorded. During the latest period the significant increase in the annual incidence also included an increase in the severity of the outbreaks. A total of 231 outbreaks, defined as clinical signs of AD in verified AD-virus infected animals, were reported before AD was finally eradicated. A stamping out policy was applied in the first three outbreaks. All nucleus herds were compulsorily controlled from 1973 on and parts of the multiplier herds voluntarily, from 1987 on. A national eradication programme was launched in 1991. In preparation for that programme, the national prevalence of AD-virus infected weaner pig producing herds was studied in 1988/89 and found to be on average 5% and up to 28% in individual counties. Different methods for eradication of the AD-virus from infected herds - which did not rely on total depopulation - were evaluated. The use of vaccination in combination with ELISA-tests which discriminated between vaccinated and infected pigs was also studied. The programme was privately operated by the Swedish Animal Health Service based on official regulations and financed mainly by a governmental grant. The programme was based on two serological testings, with a 3 to 6 month- interval, of all sows, gilts and boars older than 6 months and selected testing of fattening pigs in all piglet producing herds. Each animal was tested for antibodies to glycoprotein II (GII) by the ELISA-test (Svanova Biotech). All positive reactions in the primary GII-ELISA were confirmed by repeated testing and by a GI-ELISA. Seronegative herds which obtained AD-free status were followed by annual monitoring of all the boars and 10% of the sows. All confirmed seropositive animals were considered AD-virus infected and were slaughtered. In order to prevent introduction of the AD-virus, all seronegative herds had to implement hygienic routines including isolation and testing of incoming animals. In parallel to the testings of the piglet producing herds, all boars sent to slaughter and 5 000 fattening pigs were tested annually at slaughter during the period 1994-96. Additional tests of fattening pigs in selected herds and boar stations were performed. At the end of the programme, one extra sampling in all the previously AD-infected herds was also performed. The programme was initially voluntary and large efforts were made to motivate and encourage the producers (8 800 herds with 240 000 sows) to join it. In July 1994, the programme was declared compulsory by the Swedish Boad of Agriculture for all herds with sows. The latest outbreak occurred in November 1994. In September 1995, all herds were tested twice or more and declared officially AD-free. Altogether 362 out of 8 880 tested herds (4.1%) and 3 097 animals were found to be AD-virus infected. The vaccination-eradication programme was applied in 20 larger herds, and 3 herds with high prevalence of seropositive animals were totally depopulated. By the serological methods used, unspecific so called singel reactors were detected but found to be of no clinical or epidemiological importance to the programme. In December 1996 Sweden was declared AD free by the European Commission and the annual testing of all sow herds was replaced in 1997 by a monitoring programme in which approximately 5 000 sows and 1 600 boars are tested annually. So far no AD-infected animals have been detected since 1994