The results of serological monitoring for Aujeszky's disease in pigs performed during the period of 1991-1997

Abstract - The data concerning etiology, pathogenesis and eradication of Aujeszky's disease (AD) have been extensively presented in many publications, however information of its occurrence and of the losses caused by the disease in Poland is limited. Over the last decade, the possibility of AD eradication has favourably changed due to the general use of marker vaccines. As a result, many European countries (Germany, the Netherlands, France) and the USA have adopted actions aimed at the eradication of this disease. In some other countries (Denmark, Sweden, Great Britain, Czech Republic) Aujeszky's disease has already been eradicated. According to the latest EU directives, Aujeszky's disease was not included amongst the group of diseases for which eradication is compulsory in the EU. It can, however, be found on the list of diseases that can be eradicated in particular regions or countries. The implementation of certain rules for the eradication of AD is possible. These rules would only allow the introduction of animals having no specific AD virus (ADV) antibodies and originating from AD-free countries or regions into those areas considered to be AD-free. In 1997 in Poland, Aujeszky's disease was included on the list of notifiable diseases. A nation-wide eradication programme is therefore expected to be launched in the near future. The estimation of ADV infection spreading is undoubtedly a very important element of the eradication procedures that will be developed. The aim of this study was to estimate the frequency of ADV infections in Poland as well as to evaluate the rate at which they spread. A total number of 50 023 blood samples submitted during the period of 1991-1997 from 48 out of 49 provinces were used. The samples were collected from mid- and large-scale farms. The serological evaluation for the presence of specific antibodies directed against Aujeszky's disease virus was performed with an ELISA kit produced by IDEXX Laboratories, Inc. (USA), under the name Pseudorabies Virus gpl Antibody Test Kit. The results of the serological evaluation for specific ADV antibodies indicate that during the seven years of studies the number of provinces in which seropositive animals were detected tended to decrease. In the period described, no AD virus seropositive animals were found in 21 provinces. The best situation with regards to AD was noted in the south-eastern part of the country. Over the last seven years, not a single, AD positive animal was found in as many as 13 provinces of this region. When analysing ADV infection spreading it can be assumed that for many years, the infections with this pathogen were mainly observed in the north-western part of the country. The greatest number of seropositive animals was registered in the following provinces: Wroclaw, an average 8.21%; Gorzów Wlkp, 6.53%; Pila, 5.55%; Olsztyn, 6.53%. Moreover, antibodies to ADV were found in pigs from the provinces of Bydgoszcz, Elblag, Koszalin, Leszno, Poznan, Slupsk and Zielona Góra. The analysis of the percentages of ADV seropositive animals in the whole country revealed that during the last seven years, these percentages were maintained at a similar level ranging between 1.0% and 4.61%. To sum up, it can be stated that although no radical actions aimed at ADV eradication were undertaken in our country, the epizootic situation in this regard did not deteriorate over the last 7 years. This surprisingly favourable situation originates from the virus biology and the small size of pig farms that dominates in a significant part of the country, as well as relatively low concentrations and densities of pig populations in the AD-free provinces. Evidence for this favourable epizootic situation can also be seen by the small number of new, clinical outbreaks of AD, registered during the last 7 years. On the basis of the results presented here, it can be stated that large regions of the country are still AD-free, which gives a good forecast for the actions aimed at eradication of this dangerous disease in Poland.