Immunoperoxidase study of Aujeszky's disease in pigs

Viral antigen was detected by an immunoperoxidase technique in histological sections from pigs with Aujeszky's disease. The antigen was found mainly in association with focal necrosis in the cerebellum, tonsils, oral and nasal mucosa, salivary glands, lungs, liver, kidneys, pancreas, spleen and adrenal glands. Cells at the margin of the necrotic foci especially were strongly positive. Viral antigen was also demonstrated in the cerebral cortex and in the brain stem. Two types of intranuclear inclusion bodies were found to contain viral antigen and one type also contained viral nucleic acids. Inflammatory cells usually contained no viral antigen. The possible significance of some of these infected tissues in the excretion of the virus is discussed.     

Spread and control of Aujeszky's disease (AD).

The review deals with practical aspects of control and eradication of Aujeszky's disease (AD) and the various factors concerned with it. These are resistance of virus to environmental conditions, amounts of virus necessary for infection, virus excretion, virus latency, mode of virus transmission, and vaccination. Notification of AD is a precondition of control. Several measures are necessary on the infected farm to prevent virus spread. Eradication can be done by slaughter of all the seropositive animals. However, until recently this is impossible in severely infected vaccinated areas on economic reasons. The development of glycoprotein-deleted vaccines now allows the differentiation between vaccinated and infected animals by ELISA. Thus, a combination of vaccination and removal of infected pigs is possible, resulting in a more economic way of expanded eradication.     

Experimental Aujeszky's disease in pigs: excretion, survival and transmission of the virus

Airborne Aujeszky's disease virus was recovered from looseboxes containing groups of pigs infected with virus strains from England, Northern Ireland and Denmark from days 1 to 7 after infection. Pigs sampled individually excreted most airborne virus on days 2 and 3 after infection. On a 24 hour basis the maximum amount of airborne virus excreted per pig was log10 5.3 TCID50. Subclinical infection was transmitted from a clinically affected group of pigs to a seronegative group held in separate looseboxes when air was drawn through ducting connecting one box with the other. Tissues taken from pigs killed at varying times after infection showed that the main sites of virus replication were in the head and neck region. Aujeszky's disease virus was detected for up to 40 days in a range of tissues taken from pigs at the acute stage of disease and stored at -20 degrees C.     

Exploratory spatial analysis of Aujeszky's disease during four phases of the eradication programme in Catalonia, Spain (2003-2007)

An exploratory spatial analysis of Aujeszkys disease virus infection from 2003 to 2007 was conducted in Catalonia (north eastern Spain), the largest pig-producing region in the country. The analysis was divided into four periods in relation to the different eradication phases of the programme established in the region. Different purely spatial analyses, based on the Bernoulli model, were run with SaTScan v6.1 in each period. Clusters of positive sow farms (farrow to weaning and farrow to finish) and/or fattening farms were identified in the four study periods in the western part of the region, in the three first periods in the central part and in the last three periods in the north eastern part of the region. The prevalence ratio values of these clusters increased throughout the study period due to the fact that the risk of disease decreased faster outside the clusters than inside the clusters. In order to study the evolution of the disease, we explored for areas where more negative sow farms became infected and areas where more sow farms eliminated the infection. These analyses demonstrated areas with significantly higher proportions of sow farms that became negative, which indicates that the eradication of the disease had a spatial component. Clusters of negative sow farms that were infected again (reinfections) were also detected in the four study periods. The relative risk values of these clusters were much higher compared to the other cluster analyses. There was a geographical association between the clusters of positive sow farms, positive fattening farms and re-infected sow farms. This association could be attributable to the local spread of Aujeszkys disease virus. Pig farm density could be a factor influencing the local spread of infection and was therefore evaluated for clusters of re-infected sow farms and clusters of sow farms that eliminated the infection. The mean density of pig farms was 0.40 farms/km(2) (median of 0.28 and standard deviation of 0.33) in clusters of sow farms that became negative and 1.51 (median of 0.70 and standard deviation of 1.61) in clusters where more sow farms became positive (p-value<0.05).     

A novel concept for the control of Aujeszky's disease: experiences in two vaccinated pig herds

A study was conducted to examine the usefulness of a glycoprotein I (gI)-ELISA to monitor Aujeszky's disease virus infection in two vaccinated pig herds; the gI-ELISA can differentiate between pigs infected with Aujeszky's disease virus and pigs vaccinated against Aujeszky's disease with gI-negative vaccines. The two herds had been vaccinated with gI-negative vaccines for several years. The first survey, in September 1986, revealed that approximately 10 per cent of the breeding pigs in a large multiplier herd were seropositive for antibodies to gI of Aujeszky's disease virus, and it was decided to try to eliminate the virus from the herd by gI-ELISA testing and culling of gI-seropositive pigs. A one month quarantine period for incoming stock was established, and only gI-seronegative pigs were admitted to the herd. After two rounds of testing and culling the herd appeared to be free of wild-type Aujeszky's disease virus, and neither Aujeszky's disease virus nor antibodies could be detected either in 21 sentinel pigs placed on the farm or in 347 stillborn piglets or piglets that died shortly after birth. The herd probably remained free of Aujeszky's disease virus until the end of the 27-month period of monitoring except for two of 639 breeding pigs that were unexpectedly found to be positive in the gI-ELISA in November 1987. These sows were culled. A second breeding herd was monitored for antibodies to gI of Aujeszky's disease virus for two years. The gI-seropositive sows constituted approximately 30 per cent of the herd's breeding pigs, but they were not culled.(ABSTRACT TRUNCATED AT 250 WORDS)     

A natural outbreak of Aujeszky's disease in farm animals

An outbreak of Aujeszky's disease (AD) occurred in a herd of domestic animals that led to the death of seven cattle, three goats, three sheep, two cats and one dog, all of them with CNS signs. The animals were not in direct contact with swine. The ADV was detected in the tissue of affected animals by celi culture methods and PCR. Genome strains of ADV were characterized by restriction endonuclease analysis using BamH I. The results indicated that the strains of virus were identical and belonged to the type genome I of AD. Compared with vaccine and isolated strains obtained from the pig in the same region, considerable differences in DNA patterns were detected. Interestingly, the strains isolated from the dead animals were similar to Buk T-900 reference strains.     

Vaccination and eradication programme against Aujeszky's disease in Sweden, based on a gI ELISA test

A killed gI-negative vaccine combined with a gI enzyme-linked immunosorbent assay (ELISA) test was used for the first time in Sweden in an attempt to eradicate Aujeszky's disease from a weaner pig producing herd. The herd had experienced three severe outbreaks of the disease during a 10 year period and at the start of the programme 96 per cent of the herd's 104 breeding animals were seropositive to the Aujeszky's virus. In addition, there was serological evidence of active virus circulation among younger animals. During the programme, all breeding animals were vaccinated every sixth month and replacement animals were tested free of disease and vaccinated before entry into the herd. When the originally seropositive animals had been rotated out of the herd, all breeding animals and a sample of weaner pigs were tested twice at six weeks' interval. No seroconversions to gI had taken place and the herd was declared Aujeszky's disease-free, 22 months after the start of the programme.     

Marker vaccines, virus protein-specific antibody assays and the control of Aujeszky's disease

Vaccination of pigs is widely practised to control Aujeszky's disease (AD). Molecular biological research revealed that several conventionally attenuated virus vaccines harbour deletions in their genomes. The deleted genes are nonessential for virus replication and can be involved in the expression of virulence. These findings have prompted several groups to construct well-characterized deletion mutants of AD virus that do not express either glycoprotein gI, gX or gIII. These mutants have also been rendered thymidine kinase negative. Although data on vaccine efficacy and safety have been published, widely varying test conditions have made it impossible to identify the most efficacious deletion mutant vaccine(s). Vaccination enhances the amount of virus required for infection and reduces, but does not prevent, the shedding of virulent virus and the establishment of latency in pigs infected with virulent AD virus. Therefore, while a vaccination programme will reduce the circulation of virus in the field, it will not eliminate AD virus from pig populations. To eradicate AD, the ability to differentiate infected from vaccinated pigs is crucial. The use of marker vaccines enables us to identify infected pigs in vaccinated populations by detecting antibodies against the protein whose gene is deleted from vaccine strains. The antibody response to gI appears to persist for more than 2 years, and all of about 300 field strains tested so far express gI. The use of vaccines lacking gI in combination with an enzyme linked immunosorbent assay to detect antibodies to gI and culling of gI-seropositive pigs, may help to eradicate AD in countries where vaccination is widely practised.     

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.     

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