Eradication of Aujeszky's disease (pseudorabies) virus from pig herds : alternatives to depopulation

This thesis summarises and discusses the results of studies which were carried out to obtain experience with and knowledge about Aujeszky’s disease (AD) in pig herds as a basis for the National eradication programme in Sweden.This thesis summarises and discusses the results of studies which were carried out to obtain experience with and knowledge about Aujeszky’s disease (AD) in pig herds as a basis for the National eradication programme in Sweden.Breeding animals in 11 weaner pig-producing and 3 farrow-to-finish herds infected with Aujeszky’s disease virus (ADV) were followed serologically in order to quantify the seroconversion rate to ADV and to investigate whether it would be possible to eradicate the virus by gradually replacing seropositive animals with seronegative, either with or without implementing a vaccination programme. In unvaccinated herds blood samples were analysed by an ELISA test used for routine diagnosis. In vaccinated herds, marker vaccines (glycoprotein E negative vaccines) were used and blood samples were analysed by commercially available gE ELISA test kits.In the unvaccinated herds it was demonstrated that it is difficult to avoid contact between infected and uninfected animals under normal conditions, and that contact was frequent in these herds. Even so, transmission from latently infected animals to susceptibles appeared to be limited, as all the unvaccinated study herds experienced long periods without seroconversion and 3 herds became free from ADV during the study. However, once transmission takes place among unvaccinated animals, there is always a risk that this may lead to an outbreak. Three of the largest unvaccinated herds did experience severe outbreaks and vaccination was subsequently applied in these herds.All 7 herds which applied vaccination eradicated ADV. In these herds, no outbreaks occurred and the incidence of seroconversion was very low, except for one herd where gilts were placed in direct contact with unvaccinated fattening pigs.Today, vaccination against AD using marker vaccines is the main method of control. However, it appears that vaccination may promote risk behaviour in herd managers and it is important that basic principles of biosecurity are not neglected during a vaccination programme