With the intensification of the pig industries world-wide in the 1960's, Aujeszky's Disease (AD) was recognised as one which had a major impact on pig health and production efficiency. With the development of live adjuvanted vaccines shedding of AD virus was virtually eliminated in vaccinated animals. The differentiation of animals infected by field virus from those with vaccinal antibodies was facilitated by the development of Glycoprotein E (gE) negative vaccines. The development of gE negative ADvaccines was accompanied by new ELISA gE antibody tests which made it possible to distinguish AD vaccinated pigs from infected pigs, thus allowing selective culling of infected pigs from a vaccinated herd for eradication purposes (3). This system was subsequently to form the basis of large scale AD eradication programmes (2). The modern National AD eradication programmes are based on the principal of vaccinating the herd with AD vaccine to prevent virus shedding and then monitoring the herd for virus shedding by regular sampling of animals and testing with the gE antibody ELISA test. Over a period of time as AD free replacement breeding stock are introduced to the AD positive herd, provided they are vaccinated, (low level of virus shedding), the numberof animals within the herd which are positive for the AD field virus decreases over a two to three year period until eventually the herd becomes free from AD.
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