Variation of Aujeszky's disease viruses in wild swine in USA

In the United States of America, Aujeszky's disease (pseudorabies) has been eradicated from all domestic swine. Some re-emergence of infection occurred as vaccine use diminished. Sporadic outbreaks have also occurred because of the reservoir of infection in feral swine that have spread across the southern two-thirds of the country and Hawaii. In order to be able to understand the origins of re-emerging virus, sequence analysis of variable genes in pseudorabies virus (PRV) has been used to differentiate strains. Most PRV from feral swine can be distinguished from virus circulating in domestic pigs during the national epizootic. However, several feral swine isolates of PRV from south central states are closely related or identical in sequence to strains from domestic pigs. Extensive study by PCR for the presence of virus in the oral cavity of feral pigs disclosed that the viral DNA is distributed widely in tonsils salivary glands, taste buds and even mucosa in the vicinity of tusks. Clearly the virus in feral swine has multiple mechanisms of transmission to insure persistent infection and the threat of re-emergence in domestic swine continues.     

Evaluation of a diagnostic antigen for the detection of Aujeszky's disease virus-infected subunit-vaccinated pigs

An early virus protein complex that is found in the maintenance medium of Aujeszky's disease (AD) virus-infected cells was evaluated as a subunit diagnostic antigen (SUDA) in the enzyme-linked immunosorbent assay (ELISA). This antigen was found in purer form and in larger quantities for up to 12 h post-infection in the maintenance medium of AD virus-infected MDBK cell cultures than in the maintenance medium of virus-infected porcine Fallopian tube (PFT) and PK1a cell cultures. The SUDA was shown to be compatible with a lectin-derived subunit vaccine by the absence of positive ELISA reactions for antibody to this antigen in 25 AD virus-free subunit-vaccinated pigs. Following virus challenge, all fo 24 surviving vaccinated pigs seroconverted to SUDA within 10 days. Compatibility with the vaccine was further demonstrated by the absence of positive ELISA reactions for antibody to SUDA in 12 pigs that received five or six consecutive vaccine doses at 3-wk intervals. The sensitivity of the ELISA with SUDA was demonstrated by the detection of antibody in virus-infected vaccinated and non-vaccinated pigs for at least 15 and 22 weeks, respectively, following exposure to virus. The SUDA was also economical: it was calculated that 8000-14 000 tests could be run with the antigen present in the maintenance medium of one 850 cm2 plastic tissue culture roller bottle of virus-infected MDBK cells.     

Skin test as herd diagnosis for Aujeszky's disease (Pseudorabies) in swine

Summary The value of a skin test for the diagnosis of Aujeszky's disease (pseudorabies) in swine was examined. Semipurified and concentrated antigens, obtained by ether/tween 80 inactivation of Aujeszky's disease virus, were inoculated intradermally into seronegative, experimentally infected and vaccinated swine and into pigs with maternal antibodies. A specific skin reaction, characterized by a visible indurated swelling, was observed within 24 hours in animals with active immunity, No reaction was seen in pigs with maternal immunity or in seronegative uninfected and unvaccinated animals. In the infected and vaccinated groups, 89% and 58% respectively of the animals with seroneutralizing antibodies were positive by the skin test response. Positive reactions were observed as early as 8 days after the infection. All but one seronegative animals remained free of antibodies after 2 consecutive skin tests and the course of decline of maternal antibodies was not changed. An earlier skin test did not lead to sensitization for a later application. The present results, together with field experience on 8 farms, revealed that the skin test could be considered a reliable method for diagnosis of Aujeszky's disease in swine on a herd basis.     

Antigens involved in vaccination of swine against Aujeszky's disease (pseudorabies) virus.

The polypeptide and glycopolypeptide composition of a local virulent Aujeszky's disease virus (suid herpesvirus 1, SHV-1) strain (E-974) was determined in order to characterize the individual SHV-1 antigens inducing the serological responses in immunized and non-immunized animals. A commercially available inactivated vaccine of known efficacy and three experimental immunogen preparations (whole inactivated SHV-1 particles, lectin-purified glycoproteins from SHV-1 culture, and a combination of both) were used for immunization. Sera of two-month old immunized and non-immunized animals were analyzed by ELISA, seroneutralization and Western immunoblotting prior to and following challenge with E-974. Sera of 7- to 30-day-old piglets littered by immunized and non-immunized sows were likewise analyzed by immunoblotting. The following variables were determined: the total level of anti-SHV-1 antibodies, the level of neutralizing antibodies, the IgG responses to individual SHV-1 antigens, and the clinical parameters and degree of protection of the animals. The whole-particle experimental immunogen conferred greatest protection, but correlation between antibody levels and the degree of protection was imperfect. Serological responses seemed to be directed against certain structural polypeptides and viral envelope glycoproteins. The glycoprotein immunogen caused a selective response to bands which closely resemble the glycopolypeptides gII and gIII. A 71 kDa component of uncertain location within the viral structure appeared to be one of the main antigens involved in porcine serological response to SHV-1 and colostral protection of piglets.     

Aujeszky's disease: sanitation of swine herds in enzootically infected areas using labelled vaccines

Both in the Federal Republic of Germany and in some neighbouring countries the epizootic situation of Aujeszky's disease has been unsatisfactory for a long time, especially in areas with a high pig density. New findings on vaccines with certain protein deletions have recently indicated the possibility that the disease might be eradicated even in vaccinated herds. By using labelled vaccines it seems possible to distinguish the carriers of vaccine virus antibodies from the carriers of field virus antibodies and to eliminate the animals infected with field virus, while leaving the other animals in the herd and protecting them from infection by vaccination. This procedure would also be practicable in epizootically infected areas and would be less expensive than eradicating the disease on the basis of serological tests without using vaccines. A skeleton of an eradication programme, which was discussed and agreed with scientific experts and with the Federal Laender, as well as rough estimates of costs are being presented.     

Immunogenicity in Aujeszky's disease virus structural glycoprotein gVI (gp50) in swine.

Aujeszky's disease virus (ADV) envelope glycoprotein gVI (gp50) was purified from virus-infected Vero cells by ion-exchange and immunoaffinity chromatography and its usefulness as a subunit vaccine was evaluated in active and passive immunization studies. Four-week-old piglets were immunized intramuscularly (IM) with purified gVI twice two weeks apart and challenged intranasally (IN) 10 days after the second immunization with 30 LD50 (10(8)PFU) of a virulent strain of ADV. Pigs, vaccinated with 100 micrograms of purified gVI, produced virus neutralizing antibodies and did not develop clinical signs after challenge exposure. The challenge virus was not isolated from nasal swabs and tonsils of gVI-vaccinated pigs, whereas non-vaccinated control pigs developed illness after challenge exposure with the same virulent ADV strain which was later recovered from their nasal swabs and tonsils. Pregnant sows vaccinated twice with purified gVI (IM) at a three week interval produced virus neutralizing antibodies in colostrum. Four-day-old sucking piglets born of vaccinated sows were passively protected by colostral antibodies against intranasal challenge with a lethal dose of virulent ADV. Sera from gVI-vaccinated pigs were distinguished from experimentally infected swine sera by their differential reactivity in enzyme-linked immunosorbent assay (ELISA) using four major viral glycoproteins (excluding gVI) as antigen purified by the use of lentil-lectin.