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".     

Vaccination against classical swine fever virus: limitations and new strategies

The most widely used vaccines for the control of classical swine fever (CSF) in countries where it is endemic are live attenuated virus strains, which are highly efficacious, inducing virtually complete protection against challenge with pathogenic virus. In the European Union (EU), the combination of prophylactic mass vaccination and culling of infected pigs in endemic regions has made it possible to almost eradicate the disease. However, it is not possible to discriminate between infected and vaccinated animals, thus hampering disease control measures that rely on serology. Therefore, vaccination was banned at the end of 1990 before the internal common market was established in the EU. Vaccination is allowed only in severe emergencies. In addition, there are strict restrictions on the international trade in pig products from countries using vaccination. To circumvent these problems, marker vaccines which allow differentiation of infected from vaccinated animals (DIVA) have been developed. There are several approaches, ranging from protective peptides, single expressed proteins, naked DNA and chimeric viruses. To date, two subunit vaccines based on the E2 glycoprotein are commercially available and have been tested extensively for their efficacy. The accompanying discriminatory tests are based on an ELISA detecting another viral glycoprotein, the E(rns). The subunit vaccines were found to be less efficacious than live attenuated vaccines. In addition, the currently available discriminatory tests do not provide high enough specificity and sensitivity. Although there is an urgent need for more advanced marker vaccines and better discriminatory tests, the development of new DIVA vaccines against CSF is hampered by the small market potential for these products.     

The influence of maternal immunity on the efficacy of a classical swine fever vaccine against classical swine fever virus,genogroup 2.2, infection

In Thailand, where vaccination is routinely employed, there has been an increased incidence of chronic classical swine fever (CSF) outbreaks during the past decade. The major causative virus has been identified to be the moderate virulence, classical swine fever virus (CSFV) of the genogroup 2.2. An investigation was made into the efficacy of a CSF vaccine against this genogroup 2.2 challenge. Five-week-old pigs, grouped by their level of passive antibody titer were immunized with lapinized Chinese-strain CSF vaccine and challenged with CSFV genogroup 2.2, 13 days after vaccination. The group containing passive titers of lower than 64 at the time of immunization, had significantly higher number of CSFV-specific IFN-gamma secreting cells and was completely protected against the challenge. Interestingly, both cellular and antibody responses were inhibited in the pigs with the higher passive titer. Furthermore, following challenge, CSFV could be isolated from 50% of the pigs in this group. It was demonstrated that the CSF vaccine could induce complete protection in pigs, provided that the maternal derived titer at the time of vaccination was lower than 64. The result implied that an increase in CSFV outbreaks might be due to the inappropriate timing of vaccination as well as the nature of the CSFV genogroup 2.2.     

Efficacy of E2-sub-unit marker and C-strain vaccines in reducing horizontal transmission of classical swine fever virus in weaner pigs

At present, two types of vaccines against classical swine fever (CSF) virus are commercially available: E2 sub-unit marker vaccines and the conventional attenuated live C-strain vaccines. To evaluate the reduction of the horizontal virus transmission, three comparable experiments were carried out in which groups of weaner pigs (vaccinated with a marker vaccine or a C-strain vaccine) were challenged with CSF virus at 0, 7, and 14 days post-vaccination (dpv). Virus transmission was prevented totally when the challenge occurred at 14 dpv with an E2-marker vaccine (0/12 contact pigs positive in virus isolation (VI); R = 0 (0; 1.5)). At 7 dpv, transmission was reduced slightly (5/12 contact pigs positive in VI; R = 1.0 (0.3; 3.0)), whereas at 0 dpv, vaccination had no effect on transmission (10/12 contact pigs positive in VI; R = 2.9 (1.5; 10.8)). In the C-strain-vaccinated pigs, no virus transmission was detected even when the challenge was performed at the same day as the vaccination (0/12 contact pigs positive in VI; R = 0 (0; 1.5)).     

腺病毒/甲病毒复制子嵌合载体猪瘟疫苗rAdV-SFV-E2最早提供完全攻毒保护时间的研究

本实验室前期构建了腺病毒/甲病毒复制子嵌合载体猪瘟疫苗rAdV-SFV-E2,其免疫效力与商品化猪瘟C株疫苗相同,并具有鉴别检测特性.为进一步确定该嵌合载体猪瘟疫苗最早提供完全攻毒保护的时间,本研究将rAdV-SFV-E2免疫健康仔猪(n=5),免疫后于不同时间点采用猪瘟病毒(CSFV)强毒石门株进行攻毒,并检测其抗体应答、临床症状、病毒血症、病理学及组织病理学变化等.结果显示,rAdV-SFV-E2免疫后1周和2周,分别能对致死性CSFV强毒的攻击提供部分保护(3/5存活)和不完全保护(全部存活,但出现了短暂的发热和低水平的病毒血症);免疫后3周和4周,能够完全抵抗致死性CSFV强毒的攻击,表现为无病毒血症,无临床症状,无病理变化和组织病理学变化.该研究进一步证实rAdV-SFV-E2能够作为一种新型猪瘟标记疫苗,在猪瘟的紧急防控中能够起到一定的作用.     

Comparison of antibody values in sera of pigs vaccinated with a subunit or an attenuated vaccine against classical swine fever

Ten pigs, aged 85 days, were vaccinated with a subunit vaccine containing 32 g of classical swine fever virus glycoprotein E2 (gp E2) (group 1), and a further 10 pigs were vaccinated with a C strain vaccine (10^4±0.15 TCID₅₀/ml), produced by amplification in minipig kidney (MPK) cell culture (group 2). Nine non-vaccinated pigs served as a control group (group 3). Serum samples were collected before (day 0) and at 4, 10, 21 and 28 days after vaccination and were analysed by two commercially available enzyme immunoassays and by a neutralizing peroxidase-linked assay (NPLA). At the same times, peripheral blood was taken for determining the total leukocyte count and the body temperature was taken daily. Antibodies were not detected in serum samples collected before vaccination (day 0), and no side-effects that could be connected with vaccination were observed during the trial. Ten days after vaccination 6/10 pigs vaccinated with the subunit vaccine were seropositive. On days 21 and 28, the ratios of serologically positive to vaccinated pigs were 9/10 and 10/10, respectively. Four of the ten pigs that were vaccinated with the C strain vaccine were positive on day 21 and 9/10 on day 28. However, the results of the NPLA showed that only 4/10 pigs had an antibody titre >1:32 at the end of the trial in both the vaccinated groups, even though the subunit vaccine initiated an earlier and higher level of neutralizing antibodies than the vaccine produced from the C strain. Challenge was performed 28 days after vaccination on four randomly selected pigs from both vaccinated groups. The pigs survived the challenge without showing any clinical signs of classical swine fever (CSF), while two nonvaccinated control pigs died on the 10th and 12th days after infection.     

Prevention of transplacental transmission of moderate-virulent classical swine fever virus after single or double vaccination with an E2 subunit vaccine

The use of a vaccine against classical swine fever virus (CSFV) during an outbreak of CSF should lead to a reduction in the horizontal or vertical transmission of CSFV. The reduction of vertical, i.e. transplacental, transmission of a moderate-virulent strain of CSFV from the sow to its offspring was studied in sows vaccinated once or twice with a CSFV E2 subunit vaccine. Two groups of nine sows were vaccinated with one PD95 dose of the E2 subunit vaccine, approximately four weeks before insemination. A third group of nine inseminated sows served as controls. One group of nine sows were vaccinated again at two weeks after insemination. At ten weeks after the primary vaccination, approximately six weeks after insemination, all 27 sows were challenged intranasally with 10(5) TCID50 of a moderate-virulent strain of CSFV, the Van Zoelen strain. The sows were euthanized at five weeks after challenge, and samples from the sows and fetuses were collected for detection of CSFV. All 27 sows were in gestation at the time of slaughter, CSFV was detected in the fetuses of all unvaccinated sows but it was not detected in any of the samples collected from fetuses of the double-vaccinated sows. Virus was however recovered from the fetuses of one out of nine sows vaccinated once. All the sows, except four double-vaccinated sows, developed CSFV Erns antibodies. Transplacental transmission of CSFV was reduced significantly (p <0.001) in all vaccinated sows. When the results from the experiment were extrapolated to a herd level, it could be concluded that, with 95% certainty, approximately 11% (single vaccination) or 0% (double vaccination), confidence intervals of 0.01-0.44 and 0.0-0.30 respectively, of the pregnant sows would still not be protected against vertical transmission of moderate-virulent CSFV. We conclude that vaccination with the CSFV E2 subunit vaccine can reduce the transmission of moderate-virulent strain of CSFV from the sow to its offspring significantly.     

An experimental infection (II) to investigate the importance of indirect classical swine fever virus transmission by excretions and secretions of infected weaner pigs

An experiment was set up to investigate the role of excretions and secretions in the indirect transmission of classical swine fever virus (CSFV). In five small pens, 10 weaner pigs (two pigs per pen) were housed and inoculated with CSFV. Experimental infection was successful in all pigs. The infected pigs were kept in the pens for a period of 15 days after which the pens were depopulated and pigs were killed. At the moment of depopulation, all inoculated pigs were visibly clinically diseased and had high fever. Ten hours later the same pens were repopulated with five pairs of susceptible pigs. From inoculation onwards and especially between depopulation and restocking, the pens were neither cleaned nor disinfected. Four days post-repopulation, three of the susceptible pigs were detected positive on virus isolation. A fourth pig was detected positive 2 days later. Later on, the remaining pigs also became infected, most probably due to contact and between pen infections. It can be concluded that transmission of the virus via excretions and secretions succeeded in four of 10 pigs. This result indicates that transmission of CSFV via excretions and secretions can be of importance in a late, clinical stage of disease.     

Efficacy and stability of a subunit vaccine based on glycoprotein E2 of classical swine fever virus

The purpose of this study was to determine the efficacy and stability of an E2 subunit vaccine against classical swine fever virus (CSFV). The vaccine, which contains E2 produced in insect cells by a baculovirus expression vector is a potential marker vaccine, as it allows discrimination between infected and vaccinated pigs. Several vaccination-challenge experiments were performed to determine the dose that protects 95% of the vaccinated pigs (PD95), and to determine the stability and efficacy of the vaccine several months after production. A single vaccination with a vaccine dose of 32 microg E2 - the estimated PD95 - in a water-oil-water adjuvant prevented clinical signs and mortality due to a CSFV challenge-inoculation three weeks after vaccination. Moreover, virus transmission to susceptible sentinel pigs was prevented in nearly all groups of pigs vaccinated with this dose. The vaccine was stable for at least 18 months, and retained its full potency. These findings indicate that the E2 marker vaccine merits further evaluation for suitability for use in a control program during an outbreak of CSF.     

Efficacy of a live attenuated vaccine in classical swine fever virus postnatally persistently infected pigs

Classical swine fever (CSF) causes major losses in pig farming, with various degrees of disease severity. Efficient live attenuated vaccines against classical swine fever virus (CSFV) are used routinely in endemic countries. However, despite intensive vaccination programs in these areas for more than 20 years, CSF has not been eradicated. Molecular epidemiology studies in these regions suggests that the virus circulating in the field has evolved under the positive selection pressure exerted by the immune response to the vaccine, leading to new attenuated viral variants. Recent work by our group demonstrated that a high proportion of persistently infected piglets can be generated by early postnatal infection with low and moderately virulent CSFV strains. Here, we studied the immune response to a hog cholera lapinised virus vaccine (HCLV), C-strain, in six-week-old persistently infected pigs following post-natal infection. CSFV-negative pigs were vaccinated as controls. The humoral and interferon gamma responses as well as the CSFV RNA loads were monitored for 21 days post-vaccination. No vaccine viral RNA was detected in the serum samples and tonsils from CSFV postnatally persistently infected pigs for 21 days post-vaccination. Furthermore, no E2-specific antibody response or neutralising antibody titres were shown in CSFV persistently infected vaccinated animals. Likewise, no of IFN-gamma producing cell response against CSFV or PHA was observed. To our knowledge, this is the first report demonstrating the absence of a response to vaccination in CSFV persistently infected pigs.     

不同剂量氟苯尼考对猪血液生化指标及猪瘟抗体的影响

40头70日龄健康猪随机分为高、中、低剂量组和对照组,每组10头,各试验组注射猪瘟弱毒疫苗(2头份/猪),同时高、中、低剂量组分别按每千克体质量于饲料中加入120、60、30 mg氟苯尼考,连续给药7 d,停药后1、8、15、22、29 d,对相关的血液生化指标以及猪瘟抗体水平进行检测分析.结果表明,停药后1、8 d,所有氟苯尼考添加组的猪瘟抗体滴度下降,仅120 mg/kg组差异显著(P<0.05),停药15 d后抗体水平恢复至正常水平;60和120mg/kg给药组TP含量在停药后1、8 d均显著下降(P<0.05);所有给药组的ALT活性在所有检测时间内均显著上升(P<0.05或P<0.01);所有给药组的γGT活性在停药后1 d均显著上升(P<0.05),而60和120 mg/kg组γGT在第8天仍显著上升(P<0.05);所有给药组的BUN含量在停药后1 d均显著升高(P<0.05或P<0.01);AST、LDH、CHE活性和ALB、CRE含量与对照组相比无显著差异(P>0.05);表明每千克体质量60 mg以上氟苯尼考在饲料中饲喂7 d后,对部分生化指标有一定的影响,应引起重视.     

Feed contaminated with classical swine fever vaccine virus (LOM strain) can induce antibodies to the virus in pigs

In November 2004, antibodies to classical swine fever virus (csfv) were detected in finishing pigs during the annual serological surveillance in Jeju Province, Korea. In addition, csf vaccine viruses (lom strain) had recently been isolated from pigs raised on farms known to have csfv antibody-positive pigs. In contrast with mainland Korea, Jeju Province had been csf free and its pigs had not been vaccinated against csf for more than five years. An epidemiological investigation team from the National Veterinary Research and Quarantine Service investigated the current status of csf prevention on the Korean mainland and in Jeju Province to determine possible routes of introduction of the virus into the province. It was concluded that improperly processed blood meals, manufactured on mainland Korea, had been contaminated with the csf vaccine lom strain, and that the lom strain had been transmitted to pigs fed feed or feedstuffs containing the contaminated meal.     

Prevalence of African swine fever virus and classical swine fever virus antibodies in pigs in Benue State,Nigeria

Tropical Animal Health and Production - This study investigated the prevalence of African swine fever virus (ASFV) and classical swine fever virus (CSFV) antibodies in pigs in Benue State, Nigeria....     

Development of a classical swine fever subunit marker vaccine and companion diagnostic test

The development of a classical swine fever (CSF) subunit marker vaccine, based on viral envelope glycoprotein E2, and a companion diagnostic test, based on a second viral envelope glycoprotein E(RNS), will be described. Important properties of the vaccine, such as onset and duration of immunity, and prevention of horizontal and vertical transmission of virus were evaluated. A single dose of the vaccine protected pigs against clinical signs of CSF, following intranasal challenge with 100LD(50) of virulent classical swine fever virus (CSFV) at 2 weeks after vaccination. However, challenge virus transmission to unvaccinated sentinels was not always completely inhibited at this time point. From 3 weeks up to 6 months after vaccination, pigs were protected against clinical signs of CSF, and no longer transmitted challenge virus to unvaccinated sentinels. In contrast, unvaccinated control pigs died within 2 weeks after challenge. We also evaluated transmission of challenge virus in a setup enabling determination of the reproduction ratio (R value) of the virus. In such an experiment, transmission of challenge virus is determined in a fully vaccinated population at different time points after vaccination. Pigs challenged at 1 week after immunization died of CSF, whereas the vaccinated sentinels became infected, seroconverted for E(RNS) antibodies, but survived. At 2 weeks after vaccination, the challenged pigs seroconverted for E(RNS) antibodies, but none of the vaccinated sentinels did. Thus, at 1 week after vaccination, R1, and at 2 weeks, R=0, implying no control or control of an outbreak, respectively. Vertical transmission of CSFV to the immune-incompetent fetus may lead to the birth of highly viraemic, persistently infected piglets which are one of the major sources of virus spread. Protection against transplacental transmission of CSFV in vaccinated sows was, therefore, tested in once and twice vaccinated sows. Only one out of nine once-vaccinated sows transmitted challenge virus to the fetus, whereas none of the nine twice-vaccinated sows did. Finally, our data show that the E(RNS) test detects CSFV-specific antibodies in vaccinated or unvaccinated pigs as early as 14 days after infection with a virulent CSF strain. This indicates that the E2 vaccine and companion test fully comply with the marker vaccine concept. This concept implies the possibility of detecting infected animals within a vaccinated population.     

Experimental infection of slaughter pigs with classical swine fever virus: transmission of the virus, course of the disease and antibody response.

The spread of classical swine fever virus was investigated in an isolation unit containing four pens, each containing six slaughter pigs. One pig in the middle pen of three adjacent pens was inoculated intramuscularly and intranasally with the virus. The fourth pen was located in a separate compartment. The pens were visited in a strict order to study, first, the effect of indirect contact via contaminated clothing and footwear on the spread of the virus to adjacent pens and, secondly, the airborne transmission of the virus between compartments. The pigs were examined and blood samples were taken every other day for 62 days for virological and serological analyses. The virus was highly contagious for the five pigs that were in direct contact with the inoculated pig, but spread to the other pens only after all the pigs in the originally infected pen had become viraemic. The spread of the virus was promoted by contaminated clothing and footwear, but airborne transmission contributed considerably to the spread of the virus within the pighouse. The first clinical signs observed after the virus was introduced into a pen were decreased feed intake, increased mean rectal temperature and apathy. Neither the clinical course of the infection, nor the pattern of seroconversion observed over time, was affected by the differences in the intensity of contact with the virus between the pigs in the different pens.     

An experimental infection to investigate the indirect transmission of classical swine fever virus by excretions of infected pigs

In this experiment transmission of classical swine fever (CSF) virus via excretions of infected pigs was investigated under experimental conditions. Five pairs of pigs were experimentally infected with CSF virus. Eight days after experimental infection, when all pigs were viraemic for at least 3 days, the pens were depopulated and 20 h later, restocked with five pairs of susceptible pigs which stayed in these pens for 35 days. During the first 3 weeks of the experiment, the pens were neither cleaned nor disinfected. During the observation period, none of the susceptible pigs became infected. This result indicates that CSF virus spread via excretions is of minor importance in the early stages of infection. For extrapolation of these findings to the field situation and to increase the validity of the conclusions further research is needed to evaluate the effect of factors like virus strain, interval, ..., that may influence the outcome of the experiment.     

Leukocyte subsets and specific antibodies in pigs vaccinated with a classical swine fever subunit (E2) vaccine and the attenuated ORF virus strain D1701

Total white blood cell (WBC) counts and percentages of CD4a+, CD8a+, CD5a+, CD45RA+, CD45RC+, wCD21+ and SWC3a+ cells in the peripheral blood of pigs were analysed in this study. Blood samples were collected before and on days 4, 10, 21 and 28 after vaccination. Group 1 pigs were vaccinated with a subunit E2 vaccine (gp E2 32 microg/dose), and Group 2 received a subunit vaccine combined with an attenuated ORF virus strain D1701 10(6.45) TCID50/dose. Control pigs received a placebo. The total WBC count and percentage of particular cell types were within the normal range in vaccinated and control pigs. Although the mechanism of attenuated ORF virus activity is not clear, changes were observed in CD4a+, CD5a+, CD8a+, CD45RA+ and CD45RC+ cells in pigs that received the combination of a subunit vaccine and ORF virus. However, the percentage of wCD21+ and SWC3a+ did not differ significantly from that recorded in pigs given only the subunit vaccine. At days 4 and 10 the number of pigs positive to E2 antibodies was higher in the group that received the subunit vaccine and ORF virus than in pigs vaccinated with the subunit vaccine only. A higher percentage of memory cells (CD45RC+) as well as Th and Tc lymphocytes in pigs that received the ORF virus and the subunit vaccine could be ascribed to a nonspecific influence of the ORF virus on the development (through cognate interactions between T and B cells) and the duration (presumed according to the finding of the clonal expression of memory cells) of humoral immunity (assessed by a higher number of seropositive pigs in this group). This seems likely since the proportion of these cells was found to be lower in the pigs that received E2 vaccine only.     

不同剂量的猪瘟活疫苗单次免疫效果评价及疫苗存留试验

用1 200 RID、6 000 RID和24 000 RID 3种不同剂量的猪瘟活疫苗单次免疫9头30日龄的断奶仔猪,检测试验猪的抗体消长和疫苗毒核酸在猪体内的存留时间,并用6头猪进行攻毒保护试验.结果表明:不同免疫剂量的试验猪其抗体水平的动态变化没有显著差异,免疫后21 d试验猪的猪瘟抗体均成阳性,63 d后至578 d猪瘟抗体阻断率仍然高于85％,应用荧光定量RT-PCR技术检测,猪瘟疫苗毒核酸在猪血液和扁桃体中的检出时间分别达28 d和42 d;免疫后370 d进行猪瘟强毒攻击后,免疫猪没有出现明显的临床症状,存活且不带毒.本研究证实,没有其他疫病和母源抗体的仔猪单次接种合理剂量的猪瘟活疫苗就能产生坚强的保护力,提出加强种猪场各种病原监测,淘汰病原阳性种猪,净化种猪群对提高猪瘟疫苗免疫效果,最终控制猪瘟具有重要意义.     

Evidence of indirect transmission of classical swine fever virus through contacts with people

A strict system for visiting experimentally inoculated and susceptible weaner pigs was used to examine the potential indirect transmission of classical swine fever (CSF) virus by people wearing contaminated boots, gloves and coveralls. The inoculated and susceptible pigs were housed in separate compartments, between which the airborne transmission of the virus was impossible. A worst-case scenario with an intensive visiting protocol and no form of disinfection or hygiene was established. Fifteen days after the pigs were inoculated, infection was detected in one contact pig, and it was concluded that under the conditions of the experiment CSF virus could be transmitted by contact with people.