Comparative studies on the virulence of strains of Aujeszky's disease virus]

Comparative Studies on Virulence of Aujeszky's Disease Virus Strains Clinical, virological, pathomorphological and immunofluorescence examinations were performed in 24 piglets, 4 of them being experimentally infected with a virulent (B) and 6 of them with a low virulent virus strain of Aujeszky's disease (K). 14 animals were kept in enzootically infected practice stock for contact exposure. Results revealed differences in clinical and morphological signs of the disease in several experimental groups due to different virulence and tissue tropism of the used virus strains. Piglets infected with strain B showed clinical changes characteristic for the disease. In animals infected with strain K no clinical signs could be observed in the same observation period. In contact animals only respiratory disorders occurred. Histological changes of the central nervous system were established in animals of all experimental groups. In animals infected with strain K and in the contact animals in addition there were ascertained morphological changes of the interstice of the lungs in form of interstitial pneumonia of the lymphohistiocytic types. Low virulent strains are proved to show a distinct pneumotropism.     

Aujeszky's disease in a cow

A non-suppurative encephalitis accompanied by intraneuronal intranuclear inclusions were observed in the brain from a cow that died within 10 hours of developing nervous signs. Immunogold-silver staining located Aujeszky's disease virus antigen in neuronal cytoplasm and the virus was isolated from large volumes of suspensions of nervous tissues and tonsils. Fattening pigs in adjacent buildings had high antibody titres to Aujeszky's disease virus. The methods by which the cow could have acquired infection are considered, and the significance of transient low titres of antibodies to Aujeszky's disease virus in in-contact cows is discussed.     

Aujeszky's disease in a horse

A horse with neurological signs and severe meningoencephalitis caused by Aujeszky's disease is described. The diagnosis was established by immunohistochemistry, DNA-in situ hybridization and serological tests. Aujeszky's disease virus antigen and Aujeszky's disease viral DNA were detected in neurons of the cerebrum. In the serum of the horse antibodies against Aujeszky's disease virus were detected in a virus neutralization test, in a blocking ELISA which specifically detects antibodies against the glycoprotein I (Ig) of the virus, in an indirect double sandwich ELISA and with colloidal gold immunoelectron microscopy which detects antibodies directed against the envelope and nucleocapsid of the virus. Intranasal infection of two points with a high dose of Aujeszky's disease virus caused very wild and transient signs. Although the experimental infection induced virus neutralizing antibodies, it failed to induce gI specific antibodies.     

Aujeszky's disease in captive bears

Five of eight bears died during an outbreak of Aujeszky's disease in a travelling circus in the north of Spain. The bears had been fed on a diet which included raw pigs' heads. One of three Himalayan bears and a Kodiak bear died acutely with signs of the disease. One of four polar bears died acutely without signs, another died with signs of Aujeszky's disease while it was being treated, and a third died with enteritis and disseminated intestinal coagulation some time later without showing signs of the disease. A fourth polar bear recovered from the same gastrointestinal problem without showing signs of the disease. Although one of the two surviving Himalayan bears showed some signs referrable to Aujeszky's disease, the results of tests for neutralising antibodies were negative. Two of the polar bears, the Himalayan bear and the Kodiak bear were examined postmortem and three of them were examined histologically. No lesions referable to Aujeszky's disease were found. The tissues from one female polar bear were examined and shown to be positive for Aujeszky's disease virus by virus isolation, polymerase chain reaction, electron microscopy and fluorescent antibody tests. The DNA of the isolate was shown to be similar to that of the strains of the virus circulating in pigs in northern Spain some years earlier.     

Pathology of Aujeszky's disease in mink

Lesions in 21 mink which died of Aujeszky's disease included hemorrhages in lungs, heart, mediastinum, thymus, diaphragm, gastric wall, pancreas, and enteric wall. Microscopically, hyalin and fibrinoid degeneration and necrosis of vessel walls were present in cardiac muscle, brain, gastrointestinal wall and occasionally elsewhere in the body. Hemorrhages, exudation of plasma proteins and necrosis were associated with the angiopathy. Inflammation was minimal or absent. Other findings were congestion and extravasation of blood (lungs, liver), necrosis of lymphoid cells, and hemoglobinuric nephrosis. Aujeszky's disease virus was isolated from all but three animals. After experimental infection of three mink, similar though less pronounced lesions were found to those observed in the field cases.     

Eradication of Aujeszky's disease in Germany

Aujeszky's disease (AD) manifested itself in both German states in 1960. Owing to the historical development, in the subsequent two decades, the development of the disease and of its control in the Western and Eastern parts of Germany went different ways. This article describes differences and particularities in the development of AD in Germany leading to the establishment of a national AD eradication programme after re-unification of the two German states at the beginning of the last decade. The basic principles of the German AD eradication programme are described, and the results of 10 years of efforts to control the disease are presented and discussed. Without any doubt, as in other European countries, implementation of the national eradication programme resulted in a considerable progress in the eradication of AD. Since the eradication programme has been established in 1989, particularly in West Germany, the number of AD outbreaks has decreased steadily from about 2000 cases in 1987 to 0 cases recorded in 2001. Recently, Germany has been declared as officially AD-free by the European Commission.