No Aujeszky's disease or PRRS in FinlandP.M.-L. Veijalainen and H. Tapiovaara
National Veterinary and Food Research Institute (EELA), Virology Unit, P.O. Box 368, 00231 Helsinki, Finland
Abstract - Although no outbreaks or typical, clinical signs indicating Aujeszky's disease (AD) or Porcine reproductive and respiratory syndrome (PRRS) have ever been reported in Finland, annual screenings for AD antibodies were started in 1993. It was estimated that increasing import of live animals and frozen meat is a threat to pig population. By constant evaluation of different swine herds it might be possible to detect and eradicate outbreaks before they become an epidemic and thus maintain the present, excellent disease status. Each year, blood samples have been randomly collected from 7% of breeding sows, from all slaughtered boars and 3 000 fattening pigs in every Finnish pig slaughtering abattoir. In addition, AD and PRRS antibody testing has been included in the Health Scheme of boar stations and elite breeding herds. The primary test methods were virus neutralisation for AD antibodies and enzyme-linked immunoassay (ELISA, IDEXX, France) for PRRS antibodies. Toxic and suspect samples have been retested with a serological AD ELISA (SVANOVA, Sweden) or with a PRRS immunoperoxidase monolayer assay (IPMA). Individuals from all pig categories, elite breeding sows and boars, breeding sows, fattening pigs, and even housed wild boars, tested for AD antibodies were seronegative. Similarly, no antibodies to PRRS virus were detected in random samples collected from slaughterhouses or elite breeding herds. The number of sera tested for AD varied from 12 000 to 15 000 per year and for PRRS from 2 000 to 3 000. Due to random sampling, 50% of Finnish pig herds have been annually included in the survey. Approximately 1% of samples were toxic for cultured cells in virus neutralisation test and have been assayed with ELISA with negative results. Some false positive PRRS antibody reactions (0.2%) have been obtained with the PRRS ELISA. In those cases the herd has been examined for clinical signs and new samples have been collected. The second testing has categorised the reactions as false positives. The majority of field cases with respiratory signs or abortions has been subjected to isolation tests for the AD or PRRS viruses. The isolation attempts in PK-15, Marc cell line or in primary macrophages have been negative. According to the results of annual surveys, Finland has been declared free of Aujeszky's disease. The disease free status has been confirmed by the EU Commission decision 94/961/EC. The results also strongly indicate that Finland is free of PRRS infection. The good disease situation is the result of several factors, which decrease the risk of infection. The pig husbandry in Finland is in the hands of small family farms rearing a medium of 50 breeding sows or rearing on fattening farms 200 pigs at a time. Infection risks increase in industrial pig production housing a large number of animals. Piggeries are located separately, the distance between facilities being more than 1 km. There are no pig dense areas, where herds more likely get infected. The top of the breeding pyramid, elite breeding herds and two boar stations, has a health scheme which includes measures for several infectious diseases. The epidemics can be stopped at an early stage. The annual serological survey has the same effect. The import of breeding animals is controlled by the Farmers Union. The use of testing and quarantine efficiently prevents the transmission of infections from abroad. Furthermore, Finland is separated from the neighbours by the Baltic Sea which is a natural barrier against the invasion of diseases.
Corresponding author: P.M.-L. Veijalainen Tel.: (358) 3931 926; fax: (358) 3931 811;
© INRA, EDP Sciences 2000