Influence of vaccination on Aujeszky's disease virus and disease transmission

Parenteral vaccination of fattening pigs with either modified live or inactivated Aujeszky's disease virus did not prevent infection with field strain virus or the development of clinical disease. The duration and severity of the clinical syndrome was, however, reduced and vaccinated pigs did not suffer the severe weight loss and high mortality experienced by non-vaccinated pigs in the acute phase of disease. The range of tissues in which challenge virus replication took place was more restricted in vaccinated animals and the concentration of virus in infected tissues was reduced. Vaccination shortened the duration of field virus excretion and carriage in the tonsil. Replication of modified live vaccine virus was restricted to the site of inoculation in the neck and associated lymph nodes for two days after vaccination and it was not excreted by vaccinated pigs. Attempts to infect pigs by feeding them tissues taken from non-vaccinated or vaccinated pigs soon after challenge infection were unsuccessful.     

Electron microscopy of Aujeszky's disease virus in explants of Gasser's ganglion from pigs with a latent infection

Different developmental stages of the Aujeszky's disease virus were demonstrated by electron microscopy in the ultra-thin slices by the cultivated fragments of the Gasserian ganglion (G. g.) of two pigs latently infected with the Aujeszky's disease virus (ADV). In a pig vaccinated with the inactivated vaccine against the disease, the virus was detected in the G. g. cells 186 days after virus challenge, the reactivation of latency being obtained after immunosuppression with dexamethasone. In the non-vaccinated pig the virus was detected in G. g. cells after three months from experimental infection. In the ultra-thin slices the largest amount of virus was located in the nuclei and cytoplasm of satellite and Schwann's cells, in the connective-tissue cells and in the extracellular space. In the ganglion cells the virus was present in the cytoplasm and sporadically in the myelinized axons.     

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.     

Serological response of pigs infected with Aujeszky's disease virus

The temporal development of antibody in four groups of pigs infected with different Aujeszky's disease virus isolates was examined. The enzyme-linked immunosorbent assay detected antibody by five to six days after infection and the antibody-dependent cell-mediated cytotoxicity assay detected antibody seven to nine days after infection. Neutralising antibody was first detected nine to 10 days after infection, whereas assays measuring complement mediated antibody lysis did not detect antibody until 10 days after infection. These results are discussed in terms of their importance to the diagnosis of and recovery from Aujeszky's disease.     

Survival of Aujeszky's disease virus in frozen pig meat

The survival of Aujeszky's disease virus was studied in muscle, lymph node and bone marrow frozen at -18 degrees C, following infusion of a large dose of the virus into the hindquarter of a freshly killed pig. Previous attempts to induce an adequate viraemia for such studies, using intranasal and intravenous routes of inoculation of large doses of virus in live pigs, were unsuccessful. In frozen meat and marrow, the virus showed a biphasic inactivation curve with time, similar to that seen with cell-cultured virus. Most virus was rapidly inactivated initially but a small population of more stable virus persisted for a considerable period of time. In contrast, virus in lymph node showed a uniform inactivaton rate, like that of the more stable componet only. Virus was not detectable in any of the tissues after 35 days of storage at -18 degrees C.     

Survival of Aujeszky's disease virus in infected pig slurry

It has been demonstrated that after experimental infection of pig slurry from the space under the slatted floor (infection dose of 10(6)PFU per ml), the Aujeszky's disease virus (ADV) survived for 72 hours at the temperature of 15 degrees C and at pH 6.5, but was inactivated after 96 hours. When technologically treated pig slurry from the storage tanks was saturated with water and infected with ADV at the dose of 10(5)PFU per ml, the virus survived for 23 days when kept at 15 degrees C and 4 degrees C and at pH 6.8, but was inactivated under the same conditions after 30 days. When the infective ADV dose in the technologically treated pig slurry in the storage tanks was reduced to 10(4)PFU per ml, the virus survived 16 days at +4 degrees C and pH 7.0 and 8.0 but was inactivated within 23 days after infection.     

Aujeszky's disease virus infection patterns in European wild boar

Evidence of exposure (i.e. seroprevalence) to Aujeszky's disease virus (ADV) is high among wild boars from south-central Spain. This research aims to determine the presence of ADV by molecular detection, and to describe the patterns of ADV infection in wild boars. Tonsils (TN) and trigeminal ganglia (TG) for ADV molecular detection, and sera were collected from wild boars (n = 192) in 39 hunting estates from south-central Spain (2004/2005). A nested polymerase chain reaction (PCR) for a fragment of the ADV surface glycoprotein B was performed on collected tissues. Individual status of presence of viral DNA was tested against explanatory variables by means of a Generalized Linear Mixed Model (GLIMMIX) analysis. Viral detection prevalence was 30.6 ± 6.7%. Although there was an increasing pattern with age and females presented higher prevalences, no statistically significant influence of sex and age was found for viral presence. Molecular testing in TN and TG allowed classifying infection status into (i) ADV negative (in both TN and TG), (ii) only positive in TN, (iii) only positive in TG and (iv) positive in both TN and TG. ADV DNA was statistically more frequently evidenced in TN in females than in males. With the exception of one individual, all wild boars with presence of ADV DNA in TN and TG or only in TG reacted positive in the ELISA. In contrast, animals with only ADV DNA in TN serorreacted positively and negatively. Interestingly, 45% of the PCR positive wild boars (n = 59) were seronegative in the serological test, all of them with viral DNA only in TN. Our results provide evidence for latency of ADV in wild boars and stress the fact that antibody detection based tests may fail to detect a proportion of recently infected animals. This is of great concern since current management schemes in our study promote animal translocation for hunting purposes, with the associated risk of under-detecting ADV infected individuals when using serology to screen for ADV infection.     

Enzyme-linked immunosorbent assay for detecting antibodies to Aujeszky's disease virus in pigs

An indirect micro enzyme-linked immunosorbent assay (ELISA) for detecting antibodies to Aujeszky's disease virus in pigs is described. A control antigen prepared from infected cells was included for each serum tested. Of 243 sera from serologically positive farms, 175 (72 per cent) and 147 (60 per cent) were positive by the ELISA test and microtitre serum neutralisation test, respectively. Failure to include a control antigen for each serum would have resulted in 14 sera (6 per cent) being differently recorded. Results for sera from experimental and field infections indicated that seroconversion was more quickly detected by the ELISA test than the microtitre serum neutralisation test. In addition to greater sensitivity the ELISA test has other advantages over the serum neutralisation test. ELISA is a rapid, cheap test which is not dependent on a continuous supply of cell cultures and which can be readily automated.     

Effects of swab materials and transport media on Aujeszky's disease virus.

The effect of swab materials on the recovery of Aujeszky's disease virus from various transport media held at 4 degrees C was investigated over a five day period. No significant loss in infectivity was found in control preparations, approximately 50 per cent of infectivity was recovered from fluids containing applicator wire and approximately 10 per cent from fluids containing polyester fibre or cotton wool. Virus recovery from fluids containing wooden applicator sticks ranged from no virus recovery in protein free media to from 1 to 10 per cent in protein containing media. Freezing followed by thawing was the most effective of the physical methods used for eluting virus from swab materials.     

In vitro comparison between four variants of Aujeszky's disease virus

Four Aujeszky's disease (pseudorabies) virus variants were characterized in vitro by investigation of their resistance to heat at 48 degrees C, sensitivity to trypsin and ability to replicate in pig alveolar macrophages, two of these variants (Ls-1 and Ls-2) were cloned previously from a single isolate of virus and showed differing pathogenicity for pigs; the virulent Stanley strain; and the non-virulent NIA-4 strain were included for comparison. Heat treatment produced slight decreases in infectivity but no significant differences were observed in the rates of inactivation. Both Ls-1 and Ls-2 were significantly more sensitive to trypsin treatment than the other two. The comparison of progeny virus titres after replication in alveolar macrophages allowed further differentiation among variants. Ls-1 and Ls-2 had similar titres in cultures infected with high virus input but in cultures infected with low virus input (0.1 TCID50/cell) Ls-1 produced higher titre. The difference in titres at 48 h post-infection was statistically significant (P less than 0.05). The cytopathogenicity for macrophages of the strains was correlated with their virulence for pigs, Stanley strain being the most cytopathogenic and NIA-4 the least.     

Molecular biology of pseudorabies (Aujeszky's disease) virus.

In this review, some of the aspects concerning the molecular biology of pseudorabies virus (PrV), the causative agent of Aujeszky's disease, will be discussed. It will mainly focus on new findings concerning viral glycoproteins, factors determining PrV virulence, the problem of PrV latency and the development regarding genetically engineered vaccines.     

The effect of vaccination on the intrauterine transmission of Aujeszky's disease virus in sows

Eight of ten sows of the Large White breed were vaccinated in different stages of pregnancy, with an inactivated vaccine against Aujeszky's disease. The other two sows remained untreated. Two virulent strains of the Aujeszky's disease virus were used for the infection of all sows, either orally or intravenously. Neither of the two ways of infection led to the transmission of the virus to the foetus in any of the eight vaccinated sows. On the other hand, in the two unvaccinated sows, the virus was transmitted to the foetus only after intravenous infection, whereas oral infection did not lead to the transmission of the virus to the foetus.