Evaluation of long-term antibody responses to two inactivated bovine viral diarrhoea virus (BVDV) vaccines

The aim of the present study was to determine the serological response of heifers after vaccination with two inactivated bovine viral diarrhoea virus (BVDV) vaccines by means of various ELISA tests. Three dairy farms were selected from the Galicia region of Spain. In each herd, a batch of heifers to be vaccinated for the first time was selected and followed for 15 months. Heifers from farm 1 (n = 25) were vaccinated with Vaccine A, whereas heifers from farm 2 (n = 16) were vaccinated with Vaccine B. Heifers from farm 3 (n = 17), where no BVDV vaccines were used, acted as controls. Blood samples were analyzed periodically for BVDV antibodies, using five commercial ELISAs, based on BVDV p80 antigen or whole virus.At the end of the study, none of the animals vaccinated with Vaccine A seroconverted according to p80 antibody status, whereas up to 80% tested positive by ELISA against whole virus antigen. For the animals vaccinated with Vaccine B, 2/16 animals seroconverted according to p80 antibody ELISAs, whereas all had seroconverted according to the ELISA against whole virus antigen. In most cases, based on the use of ELISAs to detect specific antibodies against the p80 protein, at 15 months post-vaccination with inactivated BVDV vaccines the responses did not seem to interfere with detection of antibody to BVDV infection. However, the finding of a small proportion of vaccinated animals seropositive against BVDV p80 antigen suggests that antibodies that interfere with diagnosis of BVDV infection within the herd could exist, even when using p80 ELISAs.     

Antibody responses against non-structural protein 3 of bovine viral diarrhoea virus in milk and serum samples from animals immunised with an inactivated vaccine

Antibodies against non-structural protein 3 (NS3, p80) of bovine viral diarrhoea virus (BVDV) were determined in milk from cows vaccinated with an inactivated BVDV vaccine and compared to serum antibody levels. Animals in one herd were vaccinated with an inactivated BVDV vaccine according to the standard protocol and animals from a second herd with an intensive schedule. Serum and milk samples were tested for BVDV NS3 antibodies using five commercial ELISAs. With a few exceptions, vaccination according to the standard schedule did not induce BVDV NS3-specific antibodies in serum or milk. However, after vaccination according to the intensive schedule, anti-NS3 antibodies were detected for a short time in serum and, to a lesser extent, in milk. Bulk milk was a suitable substrate for BVDV monitoring of herds vaccinated with the inactivated BVD vaccine.     

基于新城疫病毒V蛋白鉴别鸡群感染与免疫的间接ELISA方法的建立

本研究以新城疫病毒(NDV)V蛋白羧基端结构域(Vc)的重组蛋白为包被抗原,建立了用于检测NDV V蛋白抗体的间接ELISA方法,并采用该方法检测了鸡群免疫或接毒后血清中的V蛋白抗体水平。结果显示:两组不同NDV灭活疫苗组在免疫后的3周内检测结果均为阴性;两组灭活疫苗免疫3周后再人工感染NDV强毒的鸡群,攻毒后第7、14和21 d,NDV阳性率分别为60%、80%、70%和50%、80%、70%;两组不同的NDV弱毒疫苗免疫组鸡群,仅在免疫后第21 d阳性率分别为20%和10%。以上结果表明,NDV疫苗免疫组与强毒感染组的V蛋白抗体阳性率存在明显差异,本方法可在群体水平上区分新城疫疫苗免疫与强毒感染鸡群,为NDV血清学诊断和流行病学调查提供了一种新的检测手段。     

Two newly developed Erns-based ELISAs allow the differentiation of Classical Swine Fever virus-infected from marker-vaccinated animals and the discrimination of pestivirus antibodies

New generations of Classical Swine Fever virus (CSFV) marker vaccines have recently been developed in order to make emergency vaccination in case of a CSF outbreak more feasible. However, the application of a marker vaccine is dependent on the availability of an accompanying discriminatory test allowing differentiation of infected from vaccinated animals (DIVA). CP7_E2alf, the most promising live marker vaccine candidate currently available, is a genetically modified Bovine Viral Diarrhea virus expressing the E2 glycoprotein of CSFV strain Alfort/187. The DIVA principle going along with CP7_E2alf is based on the detection of CSFV E^rns-specific antibodies that are raised in the host upon CSFV infection but not after vaccination with the marker vaccine. The aim of this study was to develop novel DIVA tests to be used in combination with CP7_E2alf. Two indirect ELISAs (one for screening, the other one for confirmation purposes) using bacterially expressed recombinant E^rns proteins were designed and evaluated. Both ELISAs detected CSFV-specific antibodies against a broad range of strains and genotypes, and as early as 10 days after infection. They were able to distinguish CSFV-infected pigs from pigs vaccinated with CP7_E2alf and allowed discrimination of antibodies against ruminant pestiviruses in both, sera from domestic pigs and wild boar. Sensitivity and specificity of the screening ELISA was ≥95%. Thus, the ELISAs represent promising DIVA diagnostic tools, as well as an alternative to traditional pestivirus antibody differentiation by serum neutralization test.     

Protective efficacy of a Classical swine fever virus C-strain deletion mutant and ability to differentiate infected from vaccinated animals

Classical swine fever (CSF) continues to be the most economically damaging pig disease in the world. The disease can be effectively controlled by vaccination with the live C-strain vaccine. This vaccine, however, does not enable the serological differentiation between infected and vaccinated animals (DIVA) and its use can therefore impose severe trade restrictions. CSF-specific diagnostic ELISAs detect antibodies directed against the conserved and immunodominant A domain of the E2 structural glycoprotein. We previously reported the production of a C-strain virus in which the immunodominant TAVSPTTLR epitope of the A domain is stably mutated with the aim to render the virus suitable as a DIVA vaccine. We here report that a single vaccination with this vaccine virus protected pigs from a lethal challenge dose of the highly virulent Brescia strain. Analysis of the sera, however, demonstrated that a commercially available E2 ELISA was unsuitable as an accompanying DIVA test.     

Antibody responses of naive cattle to two inactivated bovine viral diarrhoea virus vaccines,measured by indirect and blocking ELISAS and virus neutralisation

Two groups of naive heifers were given primary courses of two inactivated bovine viral diarrhoea (BVD) virus vaccines licensed for use in the UK. Their humoral responses in serum and milk were assayed by means of an indirect ELISA detecting antibodies to structural viral glycoproteins, a blocking ELISA specific for antibodies to the non-structural protein NS2-3 and the virus neutralisation test (VNT). For each assay, the numbers of serum or milk samples testing positive at each sample point and the mean values were determined. In both vaccine groups, serum antibody responses were detected by the indirect ELISA and the VNT, with both the numbers of seropositive animals and mean values peaking five weeks after the second vaccination. In the 23 heifers vaccinated with Bovilis BVD, the mean NS2-3-specific ELISA values remained low throughout the trial, with no serum or milk samples testing positive. In the 24 heifers vaccinated with Bovidec, the mean NS2-3 responses peaked below the level of positivity five weeks after the second vaccination, before declining again; NS2-3-specific antibodies were detected in one serum sample and one milk sample from two heifers in this group. A pooled milk sample from each vaccine group tested negative by both ELISAS 12 weeks after the second vaccination.     

Humoral Immune Response and Assessment of Vaccine Virus Shedding in Calves Receiving Modified Live Virus Vaccines Containing Bovine Herpesvirus‐1 and Bovine Viral Diarrhoea Virus 1a

Susceptible calves were administered modified live virus (MLV) vaccines containing bovine herpesvirus‐1 (BHV1) and bovine viral diarrhoea type 1 (BVDV1a) strains intramuscularly, with one vaccine containing both MLV and inactivated BHV‐1 and inactivated BVDV1a. There was no evidence of transmission of vaccine (BHV‐1 and BVDV1a) strains to susceptible non‐vaccinated controls commingled with vaccinates. No vaccinates had detectable BHV‐1 in peripheral blood leucocytes (PBL) after vaccination. Each of three vaccines containing an MLV BVDV1a strain caused a transient BVDV vaccine induced viremia in PBL after vaccination, which was cleared as the calves developed serum BVDV1 antibodies. The vaccine containing both MLV and inactivated BHV‐1 induced serum BHV‐1 antibodies more rapid than MLV BHV‐1 vaccine. Two doses of MLV BHV‐1 (days 0 and 28) in some cases induced serum BHV‐1 antibodies to higher levels and greater duration than one dose.     

Comparative serological response in calves to eight commercial vaccines against infectious bovine rhinotracheitis, parainfluenza-3, bovine respiratory syncytial, and bovine viral diarrhea viruses

A field trial was conducted to compare the serological responses in calves to eight commercial vaccines against infectious bovine rhinotracheitis virus (IBRV), parainfluenza-3 virus (PI3V), bovine respiratory syncytial virus (BRSV), and/or bovine viral diarrhea virus (BVDV). Calves given IBRV, P13V, BRSV, and BVDV vaccines had significantly higher antibodies to these viruses than unvaccinated controls; however, serological responses to killed BVDV vaccines were low. Calves with preexisting antibodies to IBRV, PI3V, BRSV, and the Singer strain of BVDV had lower seroconversion rates following vaccination than calves that were seronegative initially.

Serological responses in calves to IBRV, PI3V, BRSV, and BVDV differed among various commercial vaccines. Antibody titers to IBRV were higher in calves vaccinated with modified-live IBRV vaccines than in those vaccinated with killed IBRV vaccines. Following double vaccination with modified-live IBRV and PI3V vaccines, seroconversion rates and antibody titers to IBRV and PI3V were higher in calves vaccinated intramuscularly than in those vaccinated intranasally. Calves given Cattlemaster 4 had significantly higher titers to BRSV and PI3V, and lower titers to BVDV, than calves given Cattlemaster 3, suggesting that the addition of BRSV to Cattlemaster 4 caused some interaction among antigens.

     

Use of a blocking ELISA for antibodies to equine influenza virus as a test to distinguish between naturally infected and vaccinated horses: proof of concept studies

An important consideration in the selection of a vaccine during the Australian equine influenza (EI) outbreak in 2007 was the ability to differentiate between infected and vaccinated animals (DIVA). A blocking enzyme-linked immunosorbent assay (bELISA) targeted for the nucleoprotein of influenza A viruses was developed to differentiate between naturally infected horses and horses vaccinated with the ProteqFlu? vaccine, which only induces a response to viral haemagglutinin. This bELISA assay met the DIVA requirements and was used extensively during the EI control and eradication programs and 'proof of freedom' testing.     

Functional analysis of antibody responses of feedlot cattle to bovine respiratory syncytial virus following vaccination with mixed vaccines.

The antibody response of cattle to bovine respiratory syncytial virus (BRSV) immunization was investigated using 4 different commercially available mixed vaccines. Forty, 5-6 month old, beef calves, randomly assigned to groups of 10, were vaccinated on day 0 and 21 with 1 of 3 inactivated vaccines, (3 groups), or a modified live virus (MLV) vaccine. BRSV-specific antibody responses were measured prior to vaccination and on day 35 by using an enzyme linked immunosorbent assay (ELISA), virus neutralization assay (VN), a fusion inhibition assay (FI); and responses were also measured for their ability to facilitate antibody dependent, complement mediated cytotoxicity (ADCMC) of BRSV infected cells. Sera from day 35 were, in addition, analyzed by use of an IgG1, IgG2 isotype specific ELISA. All vaccines induced significant increases in BRSV specific IgG antibody as measured by ELISA, but only one inactivated and the MLV vaccine induced significant increases in VN titers. Fusion inhibiting antibody titers were low or undetected in calves vaccinated with the inactivated vaccines. Vaccination with modified live virus induced significantly higher titers of fusion inhibiting antibodies, which are considered to be most highly correlated with protection. The VN to ELISA and FI to ELISA ratio of the calves that received MLV vaccine were significantly greater than the calves receiving the 3 inactivated vaccines. Vaccination with MLV induced the highest IgG2/IgG1 ratio. This difference was small, and only significant relative to 2 of the inactivated vaccine groups, which were not significantly different from each other. The higher proportion of IgG2 isotype in the MLV sera was not associated with lower ADCMC, a function not attributed to this isotype. The VN and FI titers, but not the ELISA value of the sera, were most predictive of ADCMC. The inactivation processes apparently alter epitopes and affect the induction of functional antibodies.     

Sensitive glycoprotein gIII blocking ELISA to distinguish between pseudorabies (Aujeszky's disease)-infected and vaccinated pigs.

A blocking enzyme-linked immunosorbent assay (ELISA) test has been developed to distinguish pseudorabies virus (PRV) (Aujeszky's disease virus) -infected pigs from those immunized with a glycoprotein g92 (gIII) deletion mutant, PRV (dlg92dltk) [OMNIMARK-PRV]. This blocking ELISA test utilizes an anti-PRV gIII monoclonal antibody (mAbgIII)-horseradish peroxidase (HRPO) conjugate, TMB for color development and a cloned PRVg92 (gIII) antigen to coat wells of microtiter test plates. Undiluted sera are used to block the binding of the mAbgIII-HRPO conjugate to the antigen. The gIII blocking ELISA is specific and has a sensitivity comparable to screening ELISA and latex agglutination tests. PRV-negative sera and sera from pigs vaccinated once, twice, or four times with the gIII-negative vaccine all showed negative S/N values of greater than 0.70 (S/N defined as the optical density at 630 nm of test sera/optical density at 630 nm of negative control sera). Sera from PRV-infected herds, sera from pigs experimentally infected with virulent PRV, and sera from pigs vaccinated with modified-live or inactivated gIII+ vaccines were positive for gIII antibodies (S/N less than 0.7). Sera from pigs experimentally infected with 200 PFU virulent PRV seroconverted to gIII+ antibodies 7-10 days postinfection. Sera from pigs vaccinated with gpX- and gI- vaccines seroconverted to gIII+ antibodies 7-8 days after vaccination. The gIII antibodies persisted after gIII+ vaccinated for at least 376 days postvaccination. Sera from pigs protected by vaccination with PRV (dlg92dltk) and then challenge exposed to virulent PRV at 21 days postvaccination showed gIII+ antibodies by 14 days postchallenge. The specificity and sensitivity of the gIII blocking ELISA assay was further demonstrated on the United States Department of Agriculture-National Veterinary Services Laboratory (USDA-NVSL) sera from the 1988 PRV check set and the 1989 gIII PRV check set by comparing the gIII blocking ELISA assay with virus neutralization, screening/verification ELISA and latex agglutination assays.     

Humoral immune response and assessment of vaccine virus shedding in calves receiving modified live virus vaccines containing bovine herpesvirus-1 and bovine viral diarrhoea virus 1a

Susceptible calves were administered modified live virus (MLV) vaccines containing bovine herpesvirus-1 (BHV1) and bovine viral diarrhoea type 1 (BVDV1a) strains intramuscularly, with one vaccine containing both MLV and inactivated BHV-1 and inactivated BVDV1a. There was no evidence of transmission of vaccine (BHV-1 and BVDV1a) strains to susceptible non-vaccinated controls commingled with vaccinates. No vaccinates had detectable BHV-1 in peripheral blood leucocytes (PBL) after vaccination. Each of three vaccines containing an MLV BVDV1a strain caused a transient BVDV vaccine induced viremia in PBL after vaccination, which was cleared as the calves developed serum BVDV1 antibodies. The vaccine containing both MLV and inactivated BHV-1 induced serum BHV-1 antibodies more rapid than MLV BHV-1 vaccine. Two doses of MLV BHV-1 (days 0 and 28) in some cases induced serum BHV-1 antibodies to higher levels and greater duration than one dose.     

An efficient peptide-based ELISA for differentiating fowl adenovirus 4–infected chickens from vaccinated chickens

Fowl adenovirus serotype 4 (FAdV4), the causative agent of hepatitis-hydropericardium syndrome (HPS), has caused major economic losses to the poultry industry worldwide. Although inactivated vaccines have been deployed widely against FAdV4, a DIVA (differentiating infected from vaccinated animals) test specific for FAdV4 has not been available. We synthesized an immunogenic peptide, corresponding to regions 66–88 aa of the 22K nonstructural protein of FAdV4, and used the peptide as coating antigen to develop an indirect ELISA for a DIVA test specific to FAdV4. Specificity analysis showed that the ELISA only reacted with sera against FAdV4, and not with sera against other pathogens tested. Moreover, the ELISA could effectively differentiate FAdV4–infected chickens from vaccinated chickens. In a test of sera from experimentally infected chickens, the ELISA had 95% and 85% concordance with an indirect immunofluorescence assay (indirect IFA) and a commercial ELISA, respectively, and the concordance was 80.5% between the ELISA and the indirect IFA in detecting clinical infection samples. Our peptide-based ELISA provides an efficient DIVA test for FAdV4 in clinical samples.     

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.     

Transmission of Bovine viral diarrhea virus 1b to susceptible and vaccinated calves by exposure to persistently infected calves

Bovine viral diarrhea virus (BVDV) persistently infected (PI) calves represent significant sources of infection to susceptible cattle. The objectives of this study were to determine if PI calves transmitted infection to vaccinated and unvaccinated calves, to determine if BVDV vaccine strains could be differentiated from the PI field strains by subtyping molecular techniques, and if there were different rates of recovery from peripheral blood leukocytes (PBL) versus serums for acutely infected calves. Calves PI with BVDV1b were placed in pens with nonvaccinated and vaccinated calves for 35 d. Peripheral blood leukocytes, serums, and nasal swabs were collected for viral isolation and serology. In addition, transmission of Bovine herpes virus 1 (BHV-1), Parainfluenza-3 virus (PI-3V), and Bovine respiratory syncytial virus (BRSV) was monitored during the 35 d observation period. Bovine viral diarrhea virus subtype 1b was transmitted to both vaccinated and nonvaccinated calves, including BVDV1b seronegative and seropositive calves, after exposure to PI calves. There was evidence of transmission by viral isolation from PBL, nasal swabs, or both, and seroconversions to BVDV1b. For the unvaccinated calves, 83.2% seroconverted to BVDV1b. The high level of transmission by PI calves is illustrated by seroconversion rates of nonvaccinated calves in individual pens: 70% to 100% seroconversion to the BVDV1b. Bovine viral diarrhea virus was isolated from 45 out of 202 calves in this study. These included BVDV1b in ranch and order buyer (OB) calves, plus BVDV strains identified as vaccinal strains that were in modified live virus (MLV) vaccines given to half the OB calves 3 d prior to the study. The BVDV1b isolates in exposed calves were detected between collection days 7 and 21 after exposure to PI calves. Bovine viral diarrhea virus was recovered more frequently from PBL than serum in acutely infected calves. Bovine viral diarrhea virus was also isolated from the lungs of 2 of 7 calves that were dying with pulmonary lesions. Two of the calves dying with pneumonic lesions in the study had been BVDV1b viremic prior to death. Bovine viral diarrhea virus 1b was isolated from both calves that received the killed or MLV vaccines. There were cytopathic (CP) strains isolated from MLV vaccinated calves during the same time frame as the BVDV1b isolations. These viruses were typed by polymerase chain reaction (PCR) and genetic sequencing, and most CP were confirmed as vaccinal origin. A BVDV2 NCP strain was found in only 1 OB calf, on multiple collections, and the calf seroconverted to BVDV2. This virus was not identical to the BVDV2 CP 296 vaccine strain. The use of subtyping is required to differentiate vaccinal strains from the field strains. This study detected 2 different vaccine strains, the BVDV1b in PI calves and infected contact calves, and a heterologous BVDV2 subtype brought in as an acutely infected calf. The MLV vaccination, with BVDV1a and BVDV2 components, administered 3 d prior to exposure to PI calves did not protect 100% against BVDV1b viremias or nasal shedding. There were other agents associated with the bovine respiratory disease signs and lesions in this study including Mannheimia haemolytica, Mycoplasma spp., PI-3V, BRSV, and BHV-1.     

Fetal protection against continual exposure to bovine viral diarrhea virus following administration of a vaccine containing an inactivated bovine viral diarrhea virus fraction to cattle

OBJECTIVE: To evaluate the efficacy of a commercially available killed bovine viral diarrhea virus (BVDV) vaccine to protect against fetal infection in pregnant cattle continually exposed to cattle persistently infected with the BVDV. ANIMALS: 60 crossbred beef heifers and 4 cows persistently infected with BVDV. PROCEDURES: Beef heifers were allocated to 2 groups. One group was vaccinated twice (21-day interval between the initial and booster vaccinations) with a commercially available vaccine against BVDV, and the other group served as nonvaccinated control cattle. Estrus was induced, and the heifers were bred. Pregnancy was confirmed by transrectal palpation. Four cows persistently infected with BVDV were housed with 30 pregnant heifers (15 each from the vaccinated and nonvaccinated groups) from day 52 to 150 of gestation. Fetuses were then harvested by cesarean section and tested for evidence of BVDV infection. RESULTS: 1 control heifer aborted after introduction of the persistently infected cows. Bovine viral diarrhea virus was isolated from 14 of 14 fetuses obtained via cesarean section from control heifers but from only 4 of 15 fetuses obtained via cesarean section from vaccinated heifers; these proportions differed significantly. CONCLUSIONS AND CLINICAL RELEVANCE: A commercially available multivalent vaccine containing an inactivated BVDV fraction significantly reduced the risk of fetal infection with BVDV in heifers continually exposed to cattle persistently infected with BVDV. However, not all vaccinated cattle were protected, which emphasizes the need for biosecurity measures and elimination of cattle persistently infected with BVDV in addition to vaccination within a herd.     

Kinetics and persistence of neutralizing antibodies against bovine viral diarrhea virus-1 and -2 and border disease virus after two step vaccination of cattle

The aim of the study was the assessment of rise and persistence of neutralizing antibodies (nAb) to bovine viral diarrhea virus (BVDV) and border disease virus (BDV) after a two step vaccination using an inactivated BVDV/BDV (Mucobovin) and a modified live BVDV vaccine (Vacoviron). In a first experiment eight heifers were kept in isolation and were serologically surveyed regularly over a three year period after vaccination. The same experiment was done with 80 vaccinated cattle kept under field conditions. Neutralizing antibody titres were monitored using homologous as well as heterologous BVDV and one BDV strain, respectively. Maximum titres were obtained two to three months after vaccination. During the three years of monitoring the antibody titres decreased but never fell below the detection limit. This slow antibody regression demonstrates that a single two step vaccination elicited high nAb titres which persist over at least three years. These results might serve as a decision tool when considering the necessity and time of revaccination of cattle, which have been vaccinated using the two step method.     

Safety and efficacy of an E2 glycoprotein subunit vaccine produced in mammalian cells to prevent experimental infection with bovine viral diarrhoea virus in cattle

Bovine viral diarrhea (BVD) infection caused by bovine viral diarrhea virus (BVDV), a Pestivirus of the Flaviviridae family, is an important cause of morbidity, mortality and economical losses in cattle worldwide. E2 protein is the major glycoprotein of BVDV envelope and the main target for neutralising antibodies (NAbs). Different studies on protection against BVDV infection have focused on E2, supporting its putative use in subunit vaccines. A truncated version of type 1a BVDV E2 (tE2) expressed in mammalian cells was used to formulate an experimental oleous monovalent vaccine. Immunogenicity was studied through immunisation of guinea pigs and followed by trials in cattle. Calves of 8-12?months were vaccinated, twice with a 4?week interval, with either a tE2 subunit vaccine (n?=?8), a whole virus inactivated vaccine (n?=?8) or left untreated as negative control group (n?=?8). Four weeks after the last immunisation the animals were experimentally challenged intranasally with a non-cythopathic BVDV strain. Following challenge, BVDV was isolated from all unvaccinated animals, while 6 out of 8 animals vaccinated with tE2 showed complete virological protection indicating that the tE2 vaccine presented a similar performance to a satisfactory whole virus inactivated vaccine.     

Antigen quantification as in vitro alternative for potency testing of inactivated viral poultry vaccines

Routine batch control of licensed inactivated viral vaccines for poultry usually includes a potency assay as a measure of vaccine efficacy. Potency assays often consist of vaccination-challenge experiments in the target species or in laboratory animals. Instead of measuring the protection of vaccinated animals against virulent pathogens, the serological response after vaccination can be quantified for some vaccines. In vitro antigen quantification assays would be attractive alternatives for the current potency assays because the time and costs involved could be greatly reduced and animal use could be avoided. Such in vitro assays will only be acceptable when the correlation between results and efficacy or potency has been demonstrated convincingly. The results of our studies on antigen quantification assays indicate that, in principle, quantification of viral antigens from inactivated oil-adjuvanted vaccines is feasible and reproducible using specially developed antigen capture ELISAs in combination with specific software for statistical analysis of the ELISA data. We have developed methods to quantify the haemagglutination-neuraminidase (HN) and fusion (F) proteins of Newcastle disease virus (NDV), the viral protein 3 (VP3) of the infectious bursal disease virus (IBDV), and the spike-1 (S1) protein of the infectious bronchitis virus (IBV). Vaccination experiments with inactivated ND vaccines indicate that the in vitro quantified HN- or F-proteins of NDV are reliable indicators of the serological response after vaccination.     

Presence of antibodies to non-structural proteins of foot-and-mouth disease virus in repeatedly vaccinated cattle

For the purpose of removing infected animals by detecting humoral immune responses to non-structural proteins of the foot-and-mouth disease (FMD) virus, antibodies induced by contaminated residual non-structural proteins contained in less pure FMD vaccine can be problematic for serological screening. The aim of the present study was to measure the possible presence of antibodies against these non-structural proteins in repeatedly vaccinated calves and beef cattle. Five imported FMD vaccines were examined using two commercial ELISA kits, UBI FMDV NS EIA and Ceditest FMDV-NS, for serological testing. After five doses of vaccination, the serum of one calf tested positive, and two vaccines induced a significant increase in anti-3ABC antibodies in calves. This finding demonstrated that a positive reaction to non-structural proteins due to impurities in the FMD vaccine was detectable using commercial tests. A low percentage of field sera sampled from beef cattle in Kinmen also tested positive, but the key factor resulting in the positive reactions could not be positively identified based on our data.