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PubMed2002

Improvement of serological discrimination between herpesvirus-infected animals and animals vaccinated with marker vaccines.

Control/eradication plans of bovine herpesvirus 1 (BHV1) and suid herpesvirus 1 (SHV1) infections involve vaccination with inactivated or attenuated gE-deleted marker vaccines and associated companion serological tests to discriminate naturally infected from vaccinated animals. Blocking or competitive enzyme-linked immunosorbent assays (ELISAs) have been designed for the detection of specific antibodies against BHV1 or SHV1 gE glycoprotein. The antigen source usually consists of a crude viral preparation in which gE is associated with other envelope glycoproteins. Such assays suffer from a lack of specificity which is not due to serological cross-reactions with other pathogens. Interestingly, false-positive results occur with sera collected from multivaccinated cattle or pigs. After multivaccination with a marker vaccine, the binding of the conjugated monoclonal antibody used as a tracer, could be hampered by antibodies directed against the other viral glycoproteins. In order to validate the steric hindrance hypothesis, a simple preadsorption of such samples was carried out with a preparation of antigen devoid of gE, prior to the blocking ELISA itself. The decrease in antibody concentrations against the major glycoproteins, clearly leads to a better discrimination between positive and negative samples; that is between infected and multivaccinated animals, without significant loss of sensitivity. This experiment confirms the steric hindrance hypothesis, therefore serum preadsorption could be an easy way to improve the specificity of currently available diagnostic tests.

Animals↗
PubMed2006

Marker vaccine strategies and candidate CSFV marker vaccines.

Classical swine fever (CSF) is an economically important highly contagious disease of swine worldwide. Classical swine fever virus (CSFV) is its etiological agent, and the only natural hosts are domestic pigs and wild boars. Although field CSFV strains vary in the virulence, they all result in serious losses in pig industry. Highly virulent field strains generally cause acute disease and high mortality; moderately virulent field strains raise subacute or chronic infections; postnatal infection by low virulent field strains produces subclinical infection and mortality in the new-born piglets. CSFV can cross the placental barrier, and this transplacental transmission usually results in mortality of fetuses and birth of congenitally infected pigs with a late-onset disease and death. Two main strategies to control CSF epidemic are systematic prophylactic vaccination with live attenuated vaccines (such as C-strain) and non-vaccination stamping-out policy. But neither of them is satisfying enough. Marker vaccine and companion serological diagnostic test is thought to be a promising strategy for future control and eradication of CSF. During the past 15 years, various candidate marker vaccines were constructed and evaluated in the animal experiments, including recombinant chimeric vaccines, recombinant deletion vaccines, DNA vaccines, subunit vaccines and peptide vaccines. Among them, two subunit vaccines entered the large scale marker vaccine trial of EU in 1999. Although they failed to fulfil all the demands of the Scientific Veterinary Committee, they successfully induced solid immunity against CSFV in the vaccinated pigs. It can be expected that new potent marker vaccines might be commercially available and used in systematic prophylactic vaccination campaign or emergency vaccination in the next 15 years. Here, we summarized current strategies and candidate CSFV marker vaccines. These strategies and methods are also helpful for the development of new-generation vaccines against other diseases.

Animals↗
PubMed1996

An attenuated bovine herpesvirus 1 marker vaccine induces a better protection than two inactivated marker vaccines.

A comparative study on the efficacy of 3 bovine herpesvirus 1 (BHV1) marker vaccines was carried out. An attenuated gE-negative vaccine, an inactivated gE-negative vaccine and an experimental gD-subunit vaccine were tested twice in a vaccination-challenge experiment in cattle. The attenuated vaccine induced the best clinical protection as evidenced by the total absence of clinical signs and fever in cattle. In addition, the attenuated vaccine reduced the shedding of challenge virus significantly more than the inactivated vaccines. Of the inactivated vaccines, the gE-negative vaccine induced a better clinical protection than the gD-subunit vaccine.

Animals↗
PubMed1997

Inactivated bovine herpesvirus 1 marker vaccines are more efficacious in reducing virus excretion after reactivation than a live marker vaccine.

A comparative study was carried out to evaluate the efficacy of three bovine herpesvirus 1 (BHV1) marker vaccines to reduce the reexcretion of virus after reactivation of latent BHV1. A live gE-negative vaccine, an inactivated gE-negative vaccine and an experimental gD-subunit vaccine were tested in three identical experiments in which cattle, latently infected with BHV1, were vaccinated twice before they were treated with high doses of dexamethasone. Virus excretion after dexamethasone treatment was compared with that in BHV1-infected, unvaccinated cattle which served as controls. All cattle, controls and vaccinees, excreted virus. However, the inactivated vaccines reduced virus excretion more efficiently than did the live vaccine.

Animals↗
PubMed2001

[Comparison of performance of dairy herds that were or were not vaccinated with a bovine herpes virus 1 marker vaccine in 1998].

This study analysed the effects of the use of bovine herpesvirus 1 (BHV1) marker vaccine on the performance of dairy cattle. In Spring of 1999, vaccination of 12 herds with the BHV1 marker vaccine resulted in severe animal health problems and mortality. The vaccines used on these farms were all from a batch that appeared to be contaminated with bovine virus diarrhoea virus type 2. This led to a general call to farmers and veterinary practitioners to report side-effects of this vaccine. As a result, more than 7000 farmers reported symptoms. The information was obtained by means of a questionnaire; there was no control group. To determine the effects of the use of the marker vaccine, it was necessary to perform a study based on objectively acquired information. The information collected by the Royal Dutch Cattle Syndicate and the office of Identification and Registration was complied into herd indices on production, udder health, reproduction, and culling. Two groups of dairy farms that had used the BHV1 marker vaccine (attenuated and inactivated vaccine) were compared with farms that were certified BHV1-free. The analyses were performed based on intra-herd comparisons, meaning that per herd each index calculated over a certain period of time after the use of the marker vaccine was compared to a similar period of time prior to the use of the marker vaccine. A total of 144 comparisons were made. Seven comparisons were statistically significant. In two comparisons, the results were in favour of the BHV1-free farms and in five comparisons, the result were in favour of the vaccinated farms. Thus use of the BHV1 marker vaccine could not be proven to affect herd performance. The sensitivity of the tests was very high, so with a high level of probability even very small differences in indices between groups would have been detected.

Animals↗
PubMed2001

Spatial and stochastic simulation to compare two emergency-vaccination strategies with a marker vaccine in the 1997/1998 Dutch Classical Swine Fever epidemic.

Two alternative emergency-vaccination strategies with a marker vaccine that could have been applied in the 1997/1998 Dutch Classical Swine Fever (CSF) epidemic were evaluated in a modified spatial, temporal and stochastic simulation model: InterCSF. In strategy 1, vaccination would be applied only to overcome a shortage in destruction capacities. Destruction of all pigs on vaccinated farms distinguishes this strategy from strategy 2, which assumes intra-Community trade of vaccinated pig meat. InterCSF simulates the spread of CSF between farms through local spread and three contact types. Disease spread is affected by control measures implemented through different mechanisms. Economic results were generated by a separate model that calculated the direct costs (including the vaccination costs) and consequential losses for farmers and related industries subjected to control measures. The comparison (using epidemiological and economic results) between the different emergency-vaccination strategies with an earlier simulated preventive-slaughter scenario led to some general conclusions on the Dutch CSF epidemic. Both emergency-vaccination strategies were hardly more efficient than the non-vaccination scenario. The intra-Community trade strategy (vaccination-strategy 2) was the least costly of all three scenarios.

Animals↗
PubMed2006

Detection of classical swine fever vaccine virus in blood and tissue samples of pigs vaccinated either with a conventional C-strain vaccine or a modified live marker vaccine.

Attenuated live classical swine fever (CSF) viruses are the most efficacious vaccines against the disease. However, little is known about the distribution and detection of CSF vaccine viruses in the host. We therefore compared the new recombinant attenuated marker vaccine virus CP7_E2alf with the conventional C-strain vaccine concerning virus isolation, antigen-, and genome-detection in different samples within the first 42 days post-vaccination (p.v.). Leukocytes and several organs such as tonsils, lymph nodes, spleen, thymus, parotis and kidney were also tested using highly sensitive real-time reverse transcription-polymerase chain reaction (RT-PCR) techniques. It was demonstrated that vaccine virus could be detected by live animal sampling only in a few leukocytes samples at very low titres and genome copy numbers within the first 14 days after immunisation. Vaccine virus could also be isolated from individual tonsil samples within the first 6 days after vaccine application. In contrast, vaccine virus genomes were consistently detected in the tonsils up to day 42 by real-time RT-PCR. Distribution, amount of virus and viral genome levels were similar for both tested vaccines. In conclusion, blood samples could be the sample material of choice for detecting CSF wild type virus infection even in vaccinated animals after more than 14 days p.v., while tonsil sampling provided appropriate material for long-term detection of both tested CSF vaccine viruses using real-time RT-PCR methods.

Animals↗
PubMed2001

[Did vaccination with an infectious bovine rhinotracheitis (IBR) marker vaccine on thirteen cattle farms give rise to chronic wasting among dairy cattle?].

At the end of May 1999 the author was asked by the Dutch Animal Health Service (GD) to evaluate problems with 'chronic wasting' cows on 13 farms. The cows were thought to have become ill after vaccination with an IBR marker vaccine. On nine farms a number of cows aborted shortly after vaccination. On eight farms lameness was a problem, as was mastitis. Diarrhoea occurred on four farms. A number of farms had problems with stillbirth, subfertility, abomasal displacement, and decreasing body condition. It was concluded that the abortions, stillbirth, and weak calves at birth in the first weeks after vaccination might be associated with the vaccination. However, the author found no indication that the other problems were associated with the vaccination. This was because the symptoms on the 13 farms were not uniform, and many of the herds already had problems before the herd was vaccinated. The 'chronic wasting' problem cannot be attributed to vaccination with the IBR marker vaccine. 'Chronic wasting' concerns a multifactorial complex of diseases, and has always been present, but has increased in incidence in the last years as a result of 'Holsteinization', a very high milk production, longer periods of housing indoors (and in many cases insufficient quality of the stable and cubicles), a too high work load, and insufficient management.

Abortion, Veterinary↗
PubMed1996

The use of marker vaccines in eradication of herpesviruses.

Marker vaccines are vaccines that allow serological differentiation between infected and vaccinated individuals. This differentiation is based on the absence of one or more microbial proteins in the vaccine that are present in the wild-type micro-organism. Consequently, after infection, but not after vaccination, an antibody response against that specific protein(s) can be detected. With a protein-specific antibody test infected individuals can thus be distinguished from vaccinated individuals. Marker vaccines against pseudorabies virus (PRV) and against bovine herpesvirus 1 (BHV1) infections have been developed, along conventional routes and by recombinant DNA technology. These vaccines have been shown to be efficacious in reducing (a) clinical signs after infection, (b) wild-type virus replication after infection, and (c) transmission of wild-type virus in the laboratory and in the field. At present, PRV vaccines that lack the gene for the glycoprotein gE are used worldwide in novel eradication programmes. The first phase of such a programme consists of systematic vaccination of pigs on a farm, in a region or an entire country. Experiences in the Netherlands show that it is feasible to eradicate PRV by the intensive use of marker vaccines. Whether, this also holds true for BHV1 is now under investigation.

Animals↗
PubMed2001

Classical swine fever (CSF) marker vaccine. Trial III. Evaluation of discriminatory ELISAs.

The objective of the marker vaccine trial was to test the two available CSF marker vaccines in scenarios which are likely to occur in the field and to evaluate the reliability of the discriminatory tests. The evaluation of the discriminatory tests was of special importance because there is no requirement for formal data concerning their performance by the European Medicinal Products Evaluation Agency (EMEA) in London. EMEA is responsible for the licensing procedure of the marker vaccines within the EU. Sixteen National Swine Fever Laboratories (NSFL) participated in testing the discriminatory ELISAs. They were tested for sensitivity, specificity, reproducibility and practicability. Reference sera (CSFV and BVDV antibody positive) and field sera were used as well as sera from the weaner and sow experiments produced during the marker vaccine trial. Both discriminatory ELISAs were less sensitive than conventional CSF antibody ELISAs, although there was considerable variation between them. One discriminatory ELISA was less specific than the other, but more sensitive, and vice versa. Neither discriminatory ELISA consistently detected the marker-vaccinated, CSF-challenged weaner pigs correctly as 'CSF positive', although CSF-challenged pregnant sows were identified correctly. The limitations of the discriminatory ELISAs used in the trial was the major factor that would prevent the use of these two marker vaccines under emergency field conditions.

Animals↗
PubMed2005

Regulatory considerations for marker vaccines and diagnostic tests in the U.S.

Marker vaccines and diagnostic tests can prove to be invaluable in disease eradication and control programs, as was found in the pseudorabies (Aujeszky's Disease) virus eradication program in the U.S. During that campaign, numerous gene-deleted vaccines and companion diagnostic test kits were used to differentiate infected animals from vaccinated animals, in a strategy that ultimately led to eradication of the disease in commercial swine herds. The United States Department of Agriculture played a key role in delivery of that success by developing biologics policy, evaluating each product, and ensuring that the conditions of licensure were met. What was most critical in the overall eradication effort, however, was the detailed and dedicated interaction among key players: the biologics regulators, manufacturers, Federal, State, and local regulatory partners, veterinary researchers, industry associations, and animal owners. A good disease control program has to include all of these. The regulatory requirements for licensure of marker vaccines and diagnostic test kits are not different from that for other products. There are several mechanisms for vaccine approval, some more rapid than others, but only a few that could apply to these products. Generally, the platforms that might support marker vaccines and companion diagnostic kits are those based on genetic engineering or protein manipulation. If the product is derived from the application of biotechnology, then additional regulatory considerations are applicable. Most important of these are the considerations found in the National Environmental Policy Act (NEPA), wherein deliberate release of any organism containing recombinant DNA into the environment is subject to review and approval by appropriate federal agencies. Environmental release and NEPA compliance are discussed.

Animal Diseases↗
PubMed2001

Classical swine fever (CSF) marker vaccine. Trial II. Challenge study in pregnant sows.

The efficacy of two marker vaccines against classical swine fever (CSF) was tested in a large scale laboratory trial in several National Swine Fever Laboratories (NSFL) of the EU member states. The vaccines were: BAYOVAC CSF Marker (Vaccine A) from Bayer, Leverkusen, Germany and PORCILIS PESTI (Vaccine B) from Intervet, Boxmeer, The Netherlands. At the NSFL of Belgium, The Netherlands and Germany experiments were carried out to examine the ability of the vaccines to prevent transplacental transmission of CSF virus. In Belgium and The Netherlands pregnant sows were vaccinated once and challenged with virulent CSF virus 14 days later, which was around day 60 of gestation. At the NSFL in Germany sows were vaccinated twice, on days 25 and 46 of pregnancy and were challenged fourteen days after booster vaccination (day 60 of gestation). Apart from minor inflammatory reactions in some sows, no reactions post vaccination were noticed in either vaccine group. Sows vaccinated with Vaccine A were better protected against clinical CSF than sows vaccinated with Vaccine B. The antibody response after vaccination with Vaccine A was more pronounced than after vaccination with Vaccine B. After single vaccination six out of eight sows vaccinated with Vaccine A and all eight sows vaccinated with Vaccine B had viraemic piglets. After double vaccination one out of four litters from sows vaccinated with Vaccine A and four out of five litters from sows vaccinated with Vaccine B were found to be viraemic. However, both vaccines reduced the transmission probability significantly (Vaccine A: P=0.004, Vaccine B: P=0.024) after booster vaccination. However, Vaccine A appeared in this regard more potent as the estimated probability of fetal infections was lower. Nevertheless the risk of virus spreading after vaccination via transplacental transmission is still present and has to be addressed from an epidemiological point of view.

Animals↗
PubMed2000

Efficacy of the classical swine fever (CSF) marker vaccine Porcilis Pesti in pregnant sows.

The efficacy of the classical swine fever (CSF) subunit marker vaccine Porcilis Pesti based on baculovirus expressed envelope glycoprotein E2 of CSF virus (CSFV) was evaluated in pregnant sows. Ten gilts were vaccinated with one dose of marker vaccine, followed by a second dose 4 weeks later. Four gilts remained unvaccinated and received a placebo at the same times. Thirty-three days after the second vaccination all animals were artificially inseminated. Neither local or systemic reactions nor an increase of body temperature were observed after vaccinations. All gilts showed a normal course of pregnancy. Thirty-five days after first vaccination all animals developed E2 specific neutralising antibodies with titres in the range of 5.0 and 7.5 log(2). No antibodies to CSFV-E(rns) were found in ELISA. On day 65 of gestation (126 days after the first immunisation) all sows were infected intranasally using 2ml (10(6.6) TCID(50)/ml) of the low virulent CSFV strain "Glentorf". After challenge in two of the unvaccinated control sows a slight transient increase of body temperature was observed, whereas leukopenia was demonstrated in all control animals. In addition all controls became viraemic. Vaccinations with the CSFV subunit vaccine protected the animals from clinical symptoms of CSF. In two sows a moderate decrease of leukocyte counts was detected on day 5 post infection. In contrast to the unvaccinated control sows in none of the vaccinated animals virus was isolated from the nasal swabs or the blood. Approximately 40 days after challenge all sows were killed and necropsy was done. The sows and their offspring were examined for the presence of CSFV in blood, bone marrow and different organs. No virus was found in any of the sows. In contrast, in all litters of the control sows CSFV was found in the blood as well as in the organ samples. Nine out of 10 litters of the vaccinated sows were protected from CSFV infection. Blood samples, lymphatic organs and bone marrow of these animals were all virologically negative. When sera were tested for CSFV-antibodies all sows had developed E(rns)-specific antibodies but no CSFV-specific antibodies were found in any of the progeny. It was concluded that vaccination with CSF subunit marker vaccine Porcilis((R)) Pesti protected 90% of the litters from viral infection when sows were challenged mid-gestation using the CSFV-strain "Glentorf".

Animals↗
PubMed2001

[Outbreak of bovine virus diarrhea on Dutch dairy farms induced by a bovine herpesvirus 1 marker vaccine contaminated with bovine virus diarrhea virus type 2].

On 23 February 1999, the Dutch Animal Health Service advised all Dutch veterinary practices to postpone vaccination against bovine herpesvirus 1 (BHV1) immediately. The day before severe disease problems were diagnosed on four dairy farms after vaccination with the same batch of BHV1 marker vaccine. Using monoclonal antibodies, bovine virus diarrhoea virus (BVDV) type 2 was found in the vaccine batch. This paper describes an outbreak of BVDV type 2 infection caused by the use of a batch of modified live BHV1 marker vaccine contaminated with BDVD. Sources of information used were reports of farm visits, minutes of meetings, laboratory results, and oral communications from the people involved. The first symptoms of disease were observed on average six days after vaccination. Morbidity was high on 11 of the 12 farms. On five farms more than 70% of the animals became ill, while on one farm no symptoms could be detected. During the first week after vaccination, feed intake and milk production decreased. During the second week, some animals became clinically diseased having nasal discharge, fever, and diarrhoea. At the end of the second week and at the start of the third week, the number of diseased animals increased rapidly, the symptoms became more severe, and some animals died. Mortality varied among herds. Necropsy most often revealed erosions and ulcers of the mucosa of the digestive tract. In addition, degeneration of the liver, hyperaemia of the abomasum, and swollen mesenterial lymph nodes and swollen spleen were found. On 11 of the 12 farms all animals were culled between 32 and 68 days after vaccination after an agreement was reached with the manufacturer of the vaccine. This was the third outbreak of BVD in cattle after administration of a contaminated vaccine in the Netherlands. The possibilities to prevent contamination of a vaccine as a consequence of infection of fetal calf serum with BVDV are discussed. Improvement of controls to prevent contamination before and during vaccine production, and improvement of the monitoring of side-effects is necessary.

Animals↗
PubMed2001

Duration of the protection of an E2 subunit marker vaccine against classical swine fever after a single vaccination.

The period during which pigs are protected after vaccination is important for the successful usage of a marker vaccine against classical swine fever virus (CSFV) in an eradication programme. In four animal experiments with different vaccination-challenge intervals we determined the duration of protection of an E2 subunit marker vaccine in pigs after a single vaccination. Unvaccinated pigs were included in each group to detect transmission of the challenge virus. Three groups of six pigs were vaccinated once and subsequently inoculated with the virulent CSFV strain Brescia after a vaccination-challenge interval of 3, 51/2, 6 or 13 months. All vaccinated pigs, 16 out of 18, with neutralising antibodies against CSFV at the moment of challenge, 3, 51/2, 6 or 13 months later, survived, whereas unvaccinated control pigs died from acute CSF or were killed being moribund. A proportion of the vaccinated pigs did however develop fever or cytopenia after challenge and two vaccinated pigs were viremic after challenge. Virus transmission of vaccinated and challenged pigs to unvaccinated sentinel pigs did not occur in groups of pigs which were challenged 3 or 6 months after a single vaccination. Two out of eight vaccinated pigs that were found negative for CSFV neutralising antibody at 13 months after vaccination died after subsequent challenge. The findings in this study demonstrate that pigs can be protected against a lethal challenge of CSFV for up to 13 months after a single vaccination with an E2 subunit marker vaccine.

Animals↗
PubMed2005

Evaluation of the epidemiological importance of classical swine fever infected, E2 sub-unit marker vaccinated animals with RT-nPCR positive blood samples.

It has been demonstrated that pigs that have been double vaccinated with an E2 sub-unit marker vaccine and that are infected with classical swine fever virus (CSFV) through a natural contact infection may react positive in a CSFV detecting RT-nPCR test, whereas no virus could be isolated by using the conventional virus isolation (VI) technique. To evaluate whether these vaccinated and infected pigs may spread the virus, three experiments were set up. In the first, susceptible pigs were inoculated with serum originating from vaccinated RT-nPCR positive pigs. In the second, vaccinated RT-nPCR positive pigs were brought into contact with sentinel animals. In the third, vertical transmission was evaluated in RT-nPCR positive vaccinated pregnant gilts. In the first two experiments, no proof of virus transmission was found, whereas in the third vertical transmission was observed. The conclusion is that in vaccinated pigs that are positive in RT-nPCR but negative in VI, the level of circulating virus is probably not high enough for horizontal transmission, whereas vertical transmission of the virus is possible.

Animals↗
PubMed2001

Classical swine fever (CSF) marker vaccine. Trial I. Challenge studies in weaner pigs.

Two commercial marker vaccines against classical swine fever virus (CSFV) and companion diagnostic tests were examined in 160 conventional pigs. To test the vaccines in a "worst case scenario", group of 10 weaners were vaccinated using a single dose of an E2 (gp55) based vaccine at days -21, -14, -10 or -7, and subsequently challenged at day 0. The challenge virus was CSFV 277, originating from a recent outbreak of classical swine fever (CSF) in Germany. In all groups, only 5 out of 10 pigs were challenged; the remaining 5 pigs served as vaccinated contact controls. Also, three control groups, each consisting of 10 non-vaccinated pigs, were challenged in parallel to the vaccinated animals. CSFV could be isolated from all non-vaccinated pigs. Among these pigs 40% displayed a chronic course of the infection (virus positive for more than 10 days). Pigs vaccinated 21 or 14 days before challenge displayed no clinical signs of CSFV after challenge. However, they were still able to replicate CSFV when challenged, as measured by reisolation of CSFV from leukocytes of the directly challenged pigs. CSFV could be isolated from the leucocytes of 25% of the pigs vaccinated 21 days before challenge and 50% of the pigs vaccinated 14 days before challenge. Chronic infection was not observed, but transmission to one vaccinated contact pig occurred. From all pigs vaccinated 10 or 7 days before challenge, CSFV could be reisolated. We observed a chronic course of infection in 5% of pigs vaccinated 10 days before challenge and in 30% of pigs vaccinated 7 days before challenge. The mortality rate was 20% in the pigs vaccinated 10 days before challenge, and varied between 20 and 80% in pigs vaccinated 7 days prior to challenge. The contact animals had lower mortality (0-20%) than directly challenged pigs, probably mirroring the delayed time point of infection. There was thus some protection against clinical illness by both marker vaccines, but not a solid protection against infection and virus shedding. The efficacy of the vaccine was best if used 3 weeks before challenge and a clear correlation between time interval from vaccination to challenge and the level of virus shedding was observed. Each vaccine had its own accompanying discriminatory ELISA, but 18% of the virus positive pigs never seroconverted in these tests.

Animals↗
PubMed2000

Laboratory diagnosis, epizootiology, and efficacy of marker vaccines in classical swine fever: a review.

Detection of classical swine fever virus (CSFV) can be achieved by a range of assays of which the most commonly used are: immunohistochemical and virus culture techniques. New developments have enabled the detection of viral proteins by enzyme-linked immunosorbent assays (ELISAs) and the detection of the viral genome by RT- PCR. So far, laboratory findings show that the latter assays may supplement or replace the conventional techniques in the near future. The detection of serum antibody against structural and non-structural proteins of CSFV has been improved by developments in recombinant DNA techniques and has lead to a range of ELISAs. Although the characteristics of these ELISAs are excellent, positive results still need to be confirmed in the virus neutralization test. The available amount of sequence data enables diagnosticians to type strains of CSFV as different by comparing several parts of the genome. In some cases, this can provide conclusive evidence if a primary or secondary outbreak has been detected. Increased efforts focused on the retrieval of relevant data on the introduction of CSFV in a pig holding and the spread of CSFV in- and between pig holding(s) has generated more insight into the epizootiology of the disease. A successful control and eradication programme for classical swine fever (CSF) can consist of zoosanitary measures and/or vaccination. The latter can compromise the export of live pigs and pig products considerably unless marker vaccines have been used. Several studies were performed to determine the efficacy of an E2 subunit vaccine and live recombinant vaccine candidates. Firstly, we determined the 95% protective dose of an E2 subunit vaccine at 32 microg E2 per dosage after a single application. Further studies with a single administration of the subunit vaccine showed that: the vaccine was stable for a prolonged period after production, was able to reduce horizontal and vertical transmission of CSFV among vaccinated pigs, and provided protection for at least 6 months. An E(rns) antibody discriminatory assay was developed for use in combination with the subunit vaccine. Evaluation of the E(rns) ELISA showed that the sensitivity of the assay was lower than but that the specificity was equal to that of existing antibody assays. Two live recombinant marker vaccines were evaluated for the induction of clinical protection and reduction of transmission of CSFV shortly after vaccination. Results showed that these vaccines provided good clinical protection 1 week after a single vaccination. Research has shown that marker vaccines can be used in the future to support the control and eradication of CSFV.

Animals↗