Comparative pathology of HPCD pigs infected with wild-type and ara-T-resistant strains of Aujeszky's disease virus

Fourteen 1- to 4-week-old hysterectomy-produced and colostrum-deprived (HPCD) pigs were inoculated intranasally with wild-type and ara-T-resistant strains of Aujeszky's disease virus (ADV), and the pathological lesion induced by the two strains was compared. The wild-type strain (YS-81) led to high mortality, and the pigs developed multifocal necrosis throughout the body and encephalitis. In comparison, the ara-T-resistant strain (YS-81TR) of the virus killed only 1-week-old HPCD pigs inoculated with 10(6.0) PFU per ml of the virus and did not kill pigs more than 2-weeks of age. The latter revealed consistently severe pneumonitis on post-inoculation day (PID) 14. Results of the present study indicated that the ara-T-resistant strain of ADV was less virulent for HPCD pigs than the parental wild-type strain of ADV and that it was able to grow better in the lung than in any other tissue.     

Invasion and spread of equine herpesvirus 9 in the olfactory pathway of pigs after intranasal inoculation.

The neuropathogenesis of equine herpesvirus 9 (EHV-9) in pigs was investigated by intranasal inoculation of the virus together with intramuscular administration of dexamethasone (DM). All infected pigs developed characteristic meningo-encephalitis, accompanied by basophilic intranuclear inclusion bodies in the neuronal cells. One non-DM-treated and two DM-treated pigs had prominent malacic lesions in the rhinencephalon. Associated with the encephalitic lesions, there was invariably an increase in the number of nucleated cells in the cerebrospinal fluid (CSF). EHV-9 antigen was first detected in the nasal and olfactory epithelial cells in the nasal cavity, and in the neuroglial cells in the olfactory bulb. Subsequently it was demonstrated in the amygdaloid and caudate nuclei, and putamen. The virus was not isolated from the CSF. These results suggest that, after intranasal inoculation, EHV-9 replicates in the olfactory epithelial cells, spreading to the central nervous system via the olfactory pathway.     

Immunological experimental arthritis in pigs. III. Inflammatory reactions in the brain of pigs immunized with the attenuated virus of Aujeszky's disease.

Histopathological brains and spinal cords of pigs were examined at different times of immunization with the virus of Aujeszky's disease (AD). Temporary inflammatory reaction was found to have the features of non-suppurative disseminated inflammation in the second week after the second virus dose had been given. Perivascular and subependymal lymphocytic infiltrations were observed and the focal multiplication of microglia.     

Polymerase chain reaction amplification of latent Aujeszky's disease virus in dexamethasone treated pigs

Summary A polymerase chain reaction (PCR) amplification assay was developed for the detection of Aujeszky's disease virus (ADV) DNA in cell cultures and clinical samples. Pigs vaccinated with commercial ADV vaccines and challenged with a field isolate of ADV were immunosuppressed by dexamethasone treatment. Nasal swabs collected from the pigs at various times post-immunosuppression showed that ADV was excreted for at least four to six days starting from day 8 or day 10 following dexamethasone treatment, by virus isolation and/or PCR. However, PCR only detected latent ADV in the trigeminal ganglia, mandibular lymph node, spleen and tonsils, but not in the brain stem, pons and olfactory lobe of two pigs following dexamethasone treatment, whereas tissue explanation and cocultivation failed to demonstrate the presence of the virus.     

Immunological experimental arthritis in pigs. II. The level of complement in the pigs immunized with the Erysipelothrix rhusiopathiae and virus of Aujeszky's disease.

The level of complement was studied in 3 groups of pigs. One group was immunized with Erysipelothrix rhusiopathiae and two remaining groups with virus of Aujeszky's disease. The lowest titers, irrespective of the starting level were shown to exist in all the studied groups in the third week after the last dose of the virus.     

Occurrence and reactivation of latent Aujeszky's disease virus following challenge in previously vaccinated pigs

Pigs which were vaccinated with an inactivated ADV vaccine developed a latent ADV infection up to 18 months after ADV challenge. Up to 6.5 months p.i. latent virus could be demonstrated by co-cultivation of different organ tissues (lungs, tonsils, olfactory bulb, brain stem, medulla). Afterwards, reactivation of latent virus was only achieved by immunosuppression of the animals. Immunosuppression led to a limited virus replication in nasal mucosa, tonsils, lymph nodes and central nervous system. In addition ADV was detected in the nasal secretions., Humoral and cellular immunity was investigated before and after immunosuppression of the animals. Before immunosuppression most of the animals displayed SCC, ADV-ADCC and ADV-LYST, and all animals had medium to high titres of neutralizing serum antibodies. After immunosuppression the number of pigs reacting in SCC and ADV-LYST, assays was distinctly reduced, but the number of animals reacting in ADV-ADCC assays remained unaltered. A significant reduction of serum antibody titres occurred only in 2 of 12 animals one day after the end of immunosuppression.     

Pathological changes in HPCD pigs with prednisolone induced recrudescence of pseudorabies virus

In HPCD pigs inoculated with PRV, latent PRV could be reactivated in-vivo by the administration of large doses of prednisolone 3 months after the primary infection. In two pigs, virus shedding was without clinical signs of disease, whereas depression of circulating lymphocytes was prominent. Reactivation of PRV was also demonstrated by cultivation of the brain cortex on the 7th day and the mandibular lymph node on the 9th day after the prednisolone began treatment. Coincident with the virus isolation, characteristic lesions were observed in 2 pigs in the central nervous tissues and mandibular lymph nodes and these were composed of cell necrosis and eosinophilic intranuclear inclusion bodies. Cells containing the intranuclear inclusion bodies had immature and mature PRV particles. Results of the present study with HPCD pigs indicated that the lesions in the brain and lymph node accompanied by eosinophilic intranuclear inclusion bodies were pathogonomonic lesions induced by reactivation of PRV.     

Immunopathology in Aujeszky's disease virus-infected pigs exposed to fluctuating temperatures.

Pigs exposed to fluctuating temperatures (high, 30 +/- 2 degrees C; low, 4 +/- 1 degrees C) were intranasally inoculated with Aujeszky's disease virus (ADV). ADV-infected pigs, exposed to the fluctuating temperatures, showed severe clinical signs and ADV in the nasal secretions persisted longer than in the ADV-infected control pigs kept at the normal temperature (20 +/- 2 degrees C). High concentrations of ADV were isolated from nasal secretions on the 1st day after inoculation of the virus. Pathologically, all ADV-infected pigs had non-suppurative encephalitis and trigeminal ganglionitis. The lesions were more widely distributed in pigs exposed to fluctuating temperatures than in infected control pigs. Two infected pigs given the stress had severe malacic foci in the frontal lobe and four of them had prominent interstitial pneumonia. In the pigs exposed to fluctuating temperatures, a significant number of immunoglobulin-containing cells, especially IgM-containing cells, did not respond to ADV infection. A significant (P < 0.01) difference in the number of IgG- and IgM-containing cells was observed between the ADV-infected pigs exposed to the fluctuating temperature and ADV-infected control pigs, respectively. These results demonstrated that the stress of fluctuating temperatures enhanced the susceptibility to ADV infection.     

Immunological experimental arthritis in pigs. IV. Reaction of the synovial membrane of the non-immunized and immunized pigs after intraarticular administration of the virus of Aujeszky's disease.

7 days after intramuscular administration of the attenuated virus of Aujeszky's disease, strain TK 300 L, it was found: in non-immunized animals--immunological arthritis with fibrinoid necrosis and abundant infiltrations from lymphoid cells; in animals of low antibodies titer--only few infiltrations from lymphoid and plasmic cells round the sub-synovial vessels; in animals of high antibodies titer--vast areas of fibrinoid necrosis, abundant infiltrations from lymphoid cells and presence of gigantic cells.     

Immunological characteristics of Aujeszky's disease virus glycoprotein

A panel of monoclonal antibodies (MAbs) specific to glycoprotein D (gD) of Aujeszky's disease virus (ADV, Suid herpesvirus 1) was produced and characterized. MAbs were used to identify 9 topologically different epitopes and epitopic groups on gD. The majority of the identified epitopes were conformational. Most gD-specific MAbs possessed virus-neutralizing activity in the presence and absence of the complement. MAbs neutralized the virus at the stage of its penetration into the cell and inhibited the cell-to-cell spread of viruses. Two immunodominant epitopes and one immunodominant domain that induce the most prominent humoral immune response were identified when the animals were infected and immunized. A method was developed for affinity purification of ADV glycoprotein D. Immunization of mice with affinity-purified gD induced a strong humoral immune response and protected mice against lethal ADV challenge. In passive immunization, the majority of gD-specific MAbs protected mice against infection. The findings confirm the important role of ADV glycoprotein D in inducing protective anti-ADV immunity.     

Pathogenesis of Aujeszky's disease virus infection in swine tracheal organ culture.

Two different strains of Aujeszky's disease virus (ADV) were inoculated into swine tracheal organ culture. Both viruses replicated in and destroyed the tracheal epithelium and epithelial cells. ADV antigen was first localized in ciliated epithelial cells by fluorescent antibody and immunoperoxidase examinations. Corresponding to the distribution of ADV antigen, many ADV particles were observed in ciliated epithelial cells. Results demonstrated that the tracheal epithelium infected with ADV is reduced in its ciliary activity.     

Immunological experimental arthritis in pigs. V. Reaction of the synovial membrane in the pigs non-immunized and immunized with the virus of Aujeszky's disease after the intraarticular administration of the immunological complexes.

Immunized animals were given intraarticular complexes formed in vitro from the autologous serum and virus AD. 7 days after complex administration with excess of the virus, weak inflammatory reactions of the immunological type were noted. After neutral complex administration virulent immunological inflammation of the synovial membrane took place. The histological picture resembled rheumatoid arthritis in the man and the changes obtained after the virus administration to the joints with a high level of antibodies. Administration of complexes and homological serum alone to the joints of the nonimmunized animals caused the occurrence of superficial focuses of fibrinoid necrosis, but there was a lack of cellular reactions.     

Immunological experimental arthritis in pigs. I. Propagation dynamics of the attenuated strain of Aujeszky's disease virus in the pig organism and the humoral immunity formation.

Studies on the propagation dynamics of Aujeszky's disease virus and the formation of general and local joint immunity were to provide information explaining the mechanism of experimental rheumatoid arthritis in animals. It was shown that: Aujeszky's disease virus administered intramuscularly caused viremy on 3-4th day after its application and disappeared from the blood circulation on 5-6th day, introduced into the pig ankle joint, the virus was eliminated from the articular fluid two hours after injection, but it appeared again 3-7 days later probably due to the propagation in the cells of the synovial membrane, and that first parenteral administration of the virus induced the formation of neutralizing antibodies in low titer (5-10 units); application of the virus for the second time brought about a considerable increase of antibodies titer within 40-80 units.     

Multiplication and distribution of Aujeszky's disease (pseudorabies) virus in vaccinated and non-vaccinated pigs after intranasal infection

Summary The primary sites of Aujeszky's disease virus (ADV) multiplication in intranasally (i.n.) infected pigs were found to be in the nasopharyngeal, tracheal and pulmonary regions. From the second day post infection (DPI) onward ADV invaded the central nervous system and other organs. The virus was isolated from the nasopharyngeal region for at least 2 weeks. In serum ADV was present with low levels from DPI 1 to DPI 7.In pigs vaccinated with an inactivated vaccine and then challenged the distribution of ADV was rather similar to that in non-vaccinated animals, in spite of the presence of neutralizing antibodies. The virus titres in the organs generally were lower than in non-vaccinated animals up to DPI 7. Thereafter, titre differences were no longer significant. Virus was isolated from the tonsils and the lungs for at least 2 weeks. Interferon production in vaccinated infected pigs was significantly lower than in non-vaccinated infected pigs. Though multiplication and dissemination of ADV occurred, vaccinated pigs did not show clinical symptoms of Aujeszky's disease.Traces of ADV were detected in a small percentage of white blood cells (WBC) of non-vaccinated infected pigs. ADV was isolated from the lymphocyte-enriched and polymorphnuclear leukocyte-enriched fractions, but not from the monocyte-enriched fractions, apparently on account of the small cell number. Multiplication of ADV was demonstrated in cultured WBC from some of the vaccinated and non-vaccinated infected animals.The results are discussed with regard to neural spread of ADV and the role of haematogenic or lymphatic dissemination of the virus by WBC and to humoral and cell-mediated immunity in vaccinated pigs.Abbrevations ADV Aujeszky's disease virus - CNS central nervous system - DPI day(s) post infection - FCS fetal calf serum - i.n. intranasal(ly) - Ly lymphocyte(s) - MEM Eagle's minimal essential medium - Mono monocyte(s) - PMNL polymorphonuclear leukocyte(s) - WBC white blood cells (buffy coat) With 1 Figure     

Cell-binding properties of glycoprotein B of Aujeszky's disease virus

The glycoprotein B (gB) of Aujeszky's disease virus (ADV) has a role in virus entry and cell-to-cell spread. In this report we examined the cell-binding properties of native ADV gB purified from the virus envelope by affinity chromatography. The binding of gB to the surface of susceptible cells BHK-21 and MDBK was specific, dose-dependent, and nearly saturable, which is characteristic of conventional receptor-ligand interactions. The purified gB was shown to specifically bind to immobilised heparin. The addition of soluble exogenous heparin and heparinase treatment of cells inhibited the binding of gB to the cells. Cell-associated gB could also be dissociated from the cells by soluble heparin. The results indicated that ADV gB binds specifically to cellular heparan sulphate. The binding of gB to cells inhibited the attachment of virus to cells and thus the formation of viral plaques. The results suggest that ADV gB may have a function in the initial attachment of ADV to the surface of susceptible cells.     

Intranasal delivery of siRNA to the olfactory bulbs of mice via the olfactory nerve pathway

Loss of vestibular function has been associated with cognitive impairment, including attentional problems. The aim of this study was to investigate the effects of the D₂ dopamine receptor antagonist, eticlopride (0.02, 0.04 and 0.06 mg/kg; s.c.), on attention and impulsivity in rats at 2 months following bilateral vestibular deafferentation (BVD), using a 5 choice serial reaction time task (5CSRTT). The levels of the D₂ receptor protein in the frontal cortex were measured at 1 and 6 months post-BVD using western blotting. Eticlopride caused a dose-dependent decrease in response in the 5CSRTT, which was greater for sham than for BVD rats in terms of the percentage of correct responses and the number of perseverative responses. There were no changes in the amount of the D₂ receptor in the frontal cortex at 1 or 6 months post-BVD; however, D₂ receptor levels were significantly higher on the right side than the left in both sham and BVD animals. These results suggest that BVD causes an increase in perseverative behaviour that D₂ receptor blockade does not eliminate, but that D₂ receptors in the frontal cortex are unchanged.