Pig herds having a single reactor to serum antibody tests to Aujeszky's disease virus.

The introduction of Aujeszky's disease virus into a herd of pigs usually results in a rapid spread of the virus and a high percentage of pigs become seropositive. However, herd monitoring for the virus occasionally reveals a single seropositive breeding pig, referred to as a single reactor. The seropositive status of single reactors may be due to previous vaccination against Aujeszky's disease, or to exposure to a field strain of the virus, or to a false positive reaction in the serological assay. During a monitoring programme in Minnesota, 30 pig herds with single serological reactors were detected. Twenty-seven of these single reactors from 19 herds were segregated from their herds immunosuppressed with dexamethasone. Aujeszky's disease virus was isolated from four of the 27 pigs. Three of the four herds subsequently had outbreaks of Aujeszky's disease, suggesting that some single reactors were infected with Aujeszky's disease virus and had the potential to spread the virus within and between herds.     

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)     

Immune response in pigs to Aujeszky's disease viruses defective in glycoprotein g1 or gX.

Two Aujeszky's disease virus glycoprotein genes, gX and g1, have been used to produce deletion mutants which have then been developed into vaccines. These deletions then allow differentiation between pigs infected with wild type virus and those given the vaccine. It is not clear whether the glycoproteins encoded for by these genes are needed to induce a full protective immune response, in which case deletion mutants would suffer from lack of potency. To test this, commercially available Aujeszky's virus vaccines which lacked either gX or g1 were compared and isogenic constructs were made which differed only in the absence or presence of gX and, or, g1. These constructs and vaccines were used to vaccinate the natural host of Aujeszky's disease, the pig, and potency was measured using challenge with wild type virus. In all cases vaccines which lacked g1 performed significantly less well than those in which g1 was present, whereas deletions of gX had no significant effect on vaccine performance.     

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.     

Infection of pigs by aerosols of Aujeszky's disease virus and their shedding of the virus

On three consecutive days, six pigs were exposed for 15 minutes to aerosols of Aujeszky's disease virus. The total estimated dose was 4·5 log₁₀ 50. Within each isolation room, a sentinel pig was placed on a deck two feet away from the infected pig. The breath of the pigs that had inhaled the aerosols was collected on days 3, 7 and 13. The respiratory and other clinical signs of the infected pigs resembled those in field cases of Aujeszky's disease. All the pigs infected with Aujeszky's disease virus seroconverted within seven to 10 days after infection. Among the sentinel pigs, clinical signs were minimal and only three seroconverted.     

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.     

Subclinical Aujeszky's disease virus infection in a pig herd and the characterisation of the strain of virus isolated

The spread of antibody to Aujeszky's disease virus through a susceptible pig herd was monitored after the probable introduction of infection by a recently purchased boar. The infection spread slowly through the herd but no clinical signs of Aujeszky's disease were seen. The strain of virus isolated was designated NIA-6. It has been characterised by a series of experimental infections and extends the known range of virulence of isolates of Aujeszky's disease virus made in Northern Ireland. The strain caused no disease in four-week-old piglets and is therefore less virulent than other isolates from Northern Ireland pigs. However, it killed rabbits and a proportion of experimentally infected two-week-old piglets, which differentiates it from the avirulent bovine isolate (NIA-4).     

Aujeszky's disease (pseudorabies) virus detection in cerebrospinal fluid in experimentally infected pigs

The presence of Aujeszky's disease virus in cerebrospinal fluid of experimentally infected pigs was studied using the techniques of virus isolation and PCR. Pigs, some of which were previously vaccinated against Aujeszky's disease, were inoculated with different doses of the Aujeszky's disease NIA-3 strain. At the time of death or sacrifice, a sample of cerebrospinal fluid was taken and tested for the presence of virus using the mentioned techniques. Virus was isolated only from one sample, while it was detected by PCR in most of them. The higher sensitivity of the PCR technique and the possible presence of antiviral antibodies in the cerebrospinal fluid are reasons that can be argued to explain this fact. By PCR, the virus was detected more efficiently when digested cerebrospinal fluid cells were used as DNA source than when using whole cerebrospinal fluid, suggesting that the virus could be cell-associated. Aujeszky's disease virus could not be detected by PCR in pigs which survived the acute phase of the infection and were euthanased at 8 weeks post-inoculation, when they were latently infected. This indicated that the cerebrospinal fluid is not an adequate sample for the diagnosis of latency. Since Aujeszky's disease virus was detected from most of the tested samples, we believe that this could be an adequate procedure for the quick diagnosis of Aujeszky's disease.     

Infection of pigs by Aujeszky's disease virus via the breath of intranasally inoculated pigs

Aujeszky's disease is a worldwide problem in the pig industry. In this experiment, four pigs chosen to act as shedder pigs were intranasally infected with Aujeszky's disease virus. Next, on three consecutive days, eight recipient pigs were exposed to the breath of a pair of shedder pigs via a mask-to-mask module. Except for the virtual absence of CNS signs, shedder pigs expressed clinical signs that were similar to pigs infected naturally or experimentally. Only mild respiratory signs occurred in recipient pigs, but all were infected by aerosols of Aujeszky's disease virus as evidenced by seroconversion. The pig is a much more sensitive indicator of airborne virions than our aerosol collection methods. We conclude that the mild respiratory disease acquired by the aerogenous route in recipient pigs is an easily managed model for studying the transmission of airborne respiratory infections and the immune responses to this type of infection.     

Detection of Aujeszky's disease virus in nasal cells of fattening pigs by immunoassay

Both conventional and specific pathogen free pigs were inoculated intranasally with a strain of Aujeszky's disease virus (ADV). Nasal cells were collected daily by swab, aspiration or wash. The nasal cells were examined for ADV by isolation on cell culture, direct or indirect immunofluorescence and immunoperoxidase staining by monoclonal antibodies. The infected pigs were studied for nasal shedding of infected cells until 30 days after infection. The study was also extended to naturally infected farm pigs. Swabbing, washing and aspiration proved effective methods of collecting between 10(5) and 10(8) pavement or columnar epithelial cells and non-epithelial cells. Macrophages and polymorphonuclear leucocytes were also identified. Infected nasal cells were detected by immunofluorescence and immunoperoxidase from one to 21 days after infection. The viral antigen was detected in both epithelial and non-epithelial cells, the fluorescence was nuclear and, or, 'cytoplasmic', in the latter case only the cell membrane was stained. ADV antigens were detected in nasal cavity cells in pigs infected with a virulent and a hypovirulent strain. Nasal swabs proved effective in confirming infection both by virus isolation and immunological assay, and the latter was shown to be a useful experimental tool for the rapid diagnosis of Aujeszky's disease virus infection in fattening pigs suffering from acute respiratory distress.     

利用ELISA法对猪伪狂犬病检测的结果分析

本试验利用伪狂犬全抗体检测试剂盒和伪狂犬gE抗体检测试剂盒对广东某猪场的猪只按照一定的采血要求,进行了伪狂犬病全抗体和gE抗体的检测。我们初步发现该场伪狂犬病的抗体变化及该场伪狂犬病感染的规律。     

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.     

Survival of Aujeszky's disease virus in slurry at various temperatures.

Survival of Aujeszky's disease virus in pig slurry was investigated during anaerobic storage at 5, 20, 35, 40, 45, 50 and 55 degrees C using 100-ml laboratory models simulating the conditions in slurry tanks during winter and summer seasons and during anaerobic digestion in batch reactors. The inactivation rate was found to increase with increasing temperature. Virus was inactivated at 5 and 20 degrees C in 15 weeks and 2 weeks, respectively. At 35 degrees C (mesophilic conditions) the virus was inactivated in 5 hours and at 55 degrees C (thermophilic conditions) no virus could be detected after 10 minutes.     

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.     

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.     

Safety of an Aujeszky's disease vaccine based on deletion mutant strain 783 which does not express thymidine kinase and glycoprotein I

The safety of an Aujeszky's disease virus vaccine based on strain 783, a deletion mutant which does not express glycoprotein I and thymidine kinase, was assessed in pigs, calves and sheep. Four-day-old piglets which were inoculated intranasally and intramuscularly with 10(7) plaque forming units (PFU) developed only slight depression and fever. The virus was transmitted to a sentinel piglet. Six weeks after inoculation, the pigs were injected with high doses of corticosteroids in an attempt to reactivate the vaccine virus. The pigs did not shed Aujeszky's disease virus, did not develop a rise in virus neutralising antibody titres and sentinel pigs remained seronegative to Aujeszky's disease virus. Strain 783 was passaged in two series of three- to five-day old piglets, but after the third and fourth passages virus could no longer be recovered. Pregnant sows were inoculated with 10(7) PFU of virus strain 783 around day 35 or on day 85 of pregnancy, and their fetuses and piglets were assayed for Aujeszky's disease virus and antibodies against Aujeszky's disease virus. No evidence was found for transplacental transmission of the virus. Calves and sheep were given 10(7) PFU of virus strain 783 intranasally or intramuscularly; they survived and did not develop clinical signs of Aujeszky's disease. All the sheep and the calves inoculated intramuscularly developed neutralising antibodies to Aujeszky's disease virus.     

Detection of wild-type Aujeszky's disease virus by polymerase chain reaction in sheep vaccinated with a modified live vaccine strain

An outbreak of Aujeszky's disease occurred in a flock of sheep which had been housed together with pigs. After the death of five sheep with clinical signs of Aujeszky's disease, the remaining sheep were vaccinated with the Bartha vaccine strain, and the pigs were vaccinated with the 783 vaccine strain of Aujeszky's disease virus. Despite vaccination, however, more sheep died. Brain tissues from four sheep were collected for virus isolation and for immunobistological examinations. Only vaccine virus (gE-negative) was detected in the tissue. After DNA restriction enzyme analysis of the isolated virus, DNA of one or both of the vaccine strains was detected in all sheep. In one sheep field virus DNA was also detected. However, when the polymerase chain reaction was performed on samples prepared from paraffin-embedded tissues, DNA of field virus (gE-positive) was detected in all four sheep. It was probable that the sheep had not yet mounted a sufficient immune response to the vaccine virus, or were already infected with field virus at the time of vaccination. We concluded that the sheep died from field virus infection and not from vaccine virus infection and that only the polymerase chain reaction made it possible to specifically detect even very small amounts of field virus DNA among vaccine virus DNA in all investigated sheep.     

Comparison of the biological properties of various strains of Aujeszky's disease viruses

We compared three strains of Aujeszky's disease virus that had been isolated from slaughter pigs from the dormant foci of Aujeszky's disease, with the known virulent strain CVOS and TOP. No significant differences were found out in the following characters: titer value on tissue cultures from chick embryonal cells (KEB) and cellular line MDBK at the temperatures of 37 degrees C and 40 degrees C, cytopathogenic effect (CPE) in the HeLa cells, plaque formation in the KEB tissue culture, pruritus rise and the time of rabbit death after infection. Assessing the results of the comparison, the three new-isolated strains of Aujeszky's disease virus can be evaluated as strongly virulent.     

A comparison of the efficacy of two commercial Aujeszky's disease vaccines with glycoprotein-I deletion in pigs

Two commercial Aujeszky's disease vaccines, a modified killed vaccine and a sub-unit vaccine, both carrying a deletion of glycoprotein-I, were evaluated in pigs. Each vaccine was administered to two groups of four pigs, twice at 4-week intervals, with two pigs held as unvaccinated controls. All pigs were challenged with a New Zealand field isolate of Aujeszky's disease virus 3 weeks after the second vaccination. The results indicate that the sub-unit vaccine was able to protect pigs against clinical Aujeszky's disease much better than the pigs vaccinated with the modified killed vaccine when challenged with a virulent virus. However, the amount and the duration of virulent virus excretion following challenge was greater with the sub-unit vaccine than the modified killed vaccine. Pigs vaccinated with the sub-unit vaccine were shown to be latently infected following challenge. Latent infection was demonstrated by excretion of Aujeszky's disease virus from the nasal cavity after dexamethasone treatment and seroconversion of a sentinel in contact pigs to Aujeszky's disease virus.     

Cell biological and molecular characteristics of pseudorabies virus infections in cell cultures and in pigs with emphasis on the respiratory tract

In the present review, several cell biological and molecular aspects of virus-cell and virus-host (pig) interactions are reviewed for pseudorabies (Aujeszky's disease) virus. Concerning the virus-cell interactions, the complex cascade of events in the virus replication cycle is given together with the different mechanisms of cell-to-cell spread. The pathogenesis of pseudorabies virus infections in pigs is concentrated on the sequence of events in the respiratory tract. Finally, a short overview is given on the control of the disease and eradication of the virus by the combination of marker vaccines and discriminating ELISA.