Demonstration of a herpesvirus from piglets with lesions of Aujeszky's disease in New Zealand

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Sir, — Four suckling piglets have been examined at this laboratory from a Taranaki herd in which sudden death, chorea and convulsions were the clinical features.     

Aujeszky's disease outbreak

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Madam: — In June 1986, I was called to a piggery in the West Auckland area. The piggery consists of a breeding and fattening unit. Piglets from two hundred sows are taken through to pork and bacon weight. All pigs are meal fed. The dry sows and farrowing unit are separated within the same building. The weaners and fatteners are in two separate buildings in close proximity. Boars and gilts are brought in from more than one source.     

Development of an ELISA to differentiate between animals either vaccinated with or infected by Aujeszky's disease virus

The use of two monoclonal antibodies specific for glycoproteins GI and GIII of the pseudorabies virus led to the development of a competitive ELISA which made it possible to differentiate animals infected with pseudorabies virus from animals vaccinated with the strains of the virus Bartha, NAI4 or Norden. A postvaccinal serological response could be detected from three to four weeks after vaccination. After the virulent challenge of these vaccinated pigs an infectious serological response became apparent two weeks after the challenge.     

Evaluation of two ELISA kits for the detection of Aujeszky's disease antibodies in pigs.

This work describes the evaluation of two commercial ELISA kits for the detection of gI antibodies against Aujeszky's disease. A collection of experimental sera from infected pigs, field sample sera, and sera from pigs vaccinated with seven different modified gI-negative commercial vaccines were used to evaluate each test. Both ELISA kits showed good reproducibility, and specificity, but differences could be appreciated in sensitivity when sera obtained at early stages of infection was analysed. These results also indicated that both kits could be used in conjunction with the seven vaccines evaluated in this study.     

The genomic diversity and stability of field strains of suid herpesvirus 1 (Aujeszky's disease virus).

The genomic diversity among isolates of suid herpesvirus 1 (SHV-1) collected in the same herd and among clones from the same isolate was studied by restriction fragment pattern (RFP) analysis using BamHI. Tentatively defining a field strain as a transmissible entity, it was concluded that strains of SHV-1 commonly comprise distinguishable genomic variants. Contrary to the hypothesis of genomic lability, it is suggested that the pool of variants is sufficiently stable to specifically characterize a strain. The impact of the results on epizootiological methods based on identification of field isolates is discussed in connection with Aujeszky's disease in Denmark.     

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.     

Use of immunoenzyme (ELISA) diagnosis of Aujeszky's disease in pigs during the recovery period

Samples of blood and blood serums of pigs were examined for the presence of antibodies to the Aujeszky's disease virus. The virus-neutralizing (VN) test and the enzymoimmunologic (ELISA) method were used for this examination. As indicated by comparison of the average titres of antiviral antibodies determined by both methods, the ELISA method is 60 to 600 times more sensitive than the VN test. The high sensitivity of the ELISA method enabled to detect antiviral antibodies even in samples considered as negative after VN-testing. The method has been used with success for the sanitation of three swine stocks where the Aujeszky's disease was eradicated without interruption of operation.     

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.