Recent Field Isolates Research Articles

Genetic relatedness between recent field isolate strain of LSDV and other field and vaccinal strains based on GPCR, ORF095 and ORF103 genes in Egypt 2020

Genetic relatedness between recent field isolate strain of LSDV and other field and vaccinal strains based on GPCR, ORF095 and ORF103 genes in Egypt 2020

In-silico vaccine matching and its validation through in-vivo immune protection analysis for imported and indigenous vaccines against recent field isolate of avian influenza H9N2

In-silico vaccine matching and its validation through in-vivo immune protection analysis for imported and indigenous vaccines against recent field isolate of avian influenza H9N2

Determination of protection provided by two modified live bovine herpesvirus-1 vaccines against bovine herpesvirus-1 conjunctivitis in calves

A study was performed in 2 phases to determine the ability of 2 different modified live (MLV) bovine herpesvirus-1 (BoHV-1)vaccines to protect against conjunctivitis caused by a recent field isolate of BoHV-1. In phase I, BoHV-1 isolates were used todetermine the ability of the isolates to cause conjunctivitis and to establish a challenge model for phase II. Fifteen calves wererandomly assigned to 1 of 3 groups: 5 calves received 5 mL containing 107 tissue culture infectious dose (TCID)50/mL of BoHV-1adminisered intraocularly (topically) for 2 days, 5 calves received 5 mL of inoculum consisting of 107TCID50/mL of BoHV-1 administered intranasally for 2 days, and 5 calves served as unchallenged sentinels and received phosphatebuffered saline, 5 mL administered by the intranasal and 5 mL by the intraocular route for 2 days. All 15 calves developedpyrexia (rectal temperature greater than 103.5°F (39.7°C)), were BoHV-1 virus isolation positive from ocular swabsand 10/15 calves had increased ocular discharge and conjunctivitis. In phase II, 10 calves were intranasally vaccinated witha MLV BoHV-1, 10 calves were parenterally vaccinated with a MLV BoHV-1, and 5 calves were unvaccinated. All 25 calveswere challenged by receiving 5 mL ntraocularly of 107 TCID50/mL of BoHV-1 for 2 consecutive days. Following challenge, calves were examined daily, and blood (serum), nasal swabs, and conjunctival swab samples were obtained on study days 0, 3-7, 10, 14 and 28. Both vaccines significantly decreased post challenge ocular lesions, clinical scores, and quantity of virus isolated.

Genetic characterization and phylogenetic analysis of foot and mouth disease virus vaccine strains and recent field isolate

Foot and Mouth Disease (FMD) control is a national and regional responsibility. FMD outbreaks were detected in three farms in Port-Said Governorate in 2020, although animals in these farms were vaccinated with the local polyvalent inactivated vaccine. Samples from tongue epithelium and vesicular fluid were collected from these farms, where FMDV isolation was performed on BHK-21 cell culture. Viral RNA was extracted from the virus isolates, and vaccine strains were then screened for FMDV using conventional Reverse transcriptase polymerase chain reaction. The substitution rates and phylogenetic relationship between the field isolate and the vaccine strains were determined using DNA sequence and bioinformatics analyses. The results illustrate that the sequence analysis for the 1D region of FMDV field isolate was serotype A‑Africa topotype, Genotype IV, and closely related to isolated A‑Africa topotype Genotype IV by Animal Health Research Institute, 2020 with nucleotide similarity ranging from 97.1% to 99.74%, and revealing genetic variation of 5.63-7.88% from previously Egyptian isolated A‑Africa topotype, Genotype IV in 2016 and 2018. High genetic variations were determined from the locally used vaccine strain serotype A of the Asia topotype, lineage Iran‑05, in the major antigenic sites of the VP1 region with a nucleotide difference of 26.34%. Depending on these findings, the Veterinary Serum and Vaccine Research Institute produced an emergency inactivated monovalent vaccine using the newly isolated strain, and we recommended adding it to the subsequent prepared vaccine batches.

Development and validation of multiplex PCR based molecular serotyping of Salmonella serovars associated with poultry in India

Salmonella species are Gram-negative bacteria with more than 2600 serovars. Among these serovars, many are associated with various diseases in livestock and humans. White Kauffman Le-Minor (WKL) serotyping scheme applies specific serum to determine the serovars of Salmonella. Recent studies have applied molecular methods for serovar predictions. These methods include PCR, hybridization and sequence data to detect/predict serovar-specific genetic elements. Among these, PCR is a robust method if the unique genetic element is already known. Within this context, also involving novel primers, two multiplex PCR assays were standardized to detect six important Salmonella serovars viz. Typhimurium, Enteritidis, Kentucky, Infantis, Virchow and Gallinarum associated with poultry in India. The developed PCR assays showed targeted serovar specificity. Serial dilution experiments of both kit-based and crude lysate DNA preparations indicated similar applicability of both methods for testing from pure cultures. Further the developed assays were validated with 25 recent field isolates to confirm the applicability in routine diagnosis. The PCR assay could predict all the targeted serovars (17/25) with 100% specificity (CI-95%; 0.63–1). Molecular serotyping can reduce the number of serum used in comparison to the conventional serotyping which involves more random application of serum.

Protective immunity in broiler chickens elicited by live commercial coccidia vaccines (LCV) against recent field isolates and vaccines

Use of live commercial coccidia vaccines (LCV) have proven to be important for control of coccidiosis in broilers, however LCV from different companies can vary. The objectives of this study were to measure the level of protection provided by five LCV against homologous and heterologous challenges at 20, 26 and 33 days of age and measure the level of protozoa parasite infection for each isolate in coccidia naïve chickens via wet mount smears. A Randomized Complete Block design with six vaccine treatments (a non-vaccinated, Con and vaccines A-E) was used. The dependent variables were weight gain and microscopic parasitic scores (MS). Vaccination was performed via coarse spray (d0). Birds were challenged on 20, 26, and 33 d of age with 3-5 field isolates and a homologous antigen. Four to five birds were challenged for each field isolate and homologous antigen. MS were determined 6 d post challenge. The d 26-32 and d 33-39 average gains of the Con treated broilers were lower (P ≤0.05) compared to the gain of broilers from the LCV treatments. The MS of the birds that were immunized with vaccines C, D, and E and challenged on d 20 with E. tenlla were 96, 83, and 92% numerically reduced, however this reduction was not significant. Similar results of MS were detected from the d 26 and 33 challenges. The average gain of broilers may be improved when LCV are used, however protection varies depending on Eimeria species challenged and the age of the broilers.

Estimating evolutionary changes between highly passaged and original parental lumpy skin disease virus strains.

Research into the phylogenetic relationships of lumpy skin disease virus (LSDV) strains was long overlooked, partially due to its original restricted distribution to sub-Saharan Africa. However, recent incursions into northern latitudes, and a rapid spread causing major economic losses worldwide, have intensified additional research on the disease and the causative virus. This study delineates the phylogeny of LSDV in the context of full genome sequences of strains recovered in the field, as well as strains highly passaged in cell culture. We sequenced the oldest known field strain to date (isolate LSDV/Haden/RSA/1954 [South Africa] recovered from an outbreak in 1954), a recent field isolate (LSDV/280-KZN/RSA/2018 [South Africa] sequenced directly from blood during an outbreak in 2018) and strain LSDV/Russia/Dagestan-75 (a high-passaged cell culture strain derived from the field strain, LSDV/Russia/Dagestan/2015 [Russia]). Sequence analysis placed the field strain LSDV/Haden/RSA/1954 in the same cluster (cluster 1.1) with attenuated Neethling-type commercial vaccine viruses, with eight SNP differences, discrediting the previously held hypothesis that cluster 1.1 vaccine strains were derived from cluster 1.2 field viruses via the process of attenuation between them. In contrast, the recent LSDV/280-KZN/RSA/2018 isolate grouped with other recent field isolates in cluster 1.2, providing evidence that cluster 1.1 strains were displaced by cluster 1.2 strains in South Africa. Based on the field isolates between 1954 and 2018, the substitution rate of 7.4×10-6 substitutions/site/year was established, with mutations occurring in either synonymous sites or intergenic regions. This is the first evolutionary metric recorded for LSDV. Comparing the genome sequences of high-passage strains of LSDV showed that propagation in vitro without animal host selective pressure generates mainly non-synonymous SNPs in virus-replication genes. These results improve our understanding of LSDV evolution and demonstrate that the population dynamics of circulating isolates is not constant, with LSDV associated with different genetic clusters dominating the landscape during specific periods in time.

Comparative study between lumpy skin disease virus and sheep pox virus vaccines against recent field isolate of lumpy skin disease virus

Lumpy Skin Disease (LSD) is a vector born disease of cattle, caused by Lumpy Skin Disease Virus (LSDV), there is antigenic relationship between LSDV, Sheeppox virus (SPPV) and Goat pox virus GTPV within a genus Capripoxvirus, accordingly it can be used homologous or heterologous Capripoxvirus strains for vaccination of cattle against LSD. This study compare the efficacy of live attenuated Neethling LSDV vaccine and live attenuated Romanian SSPV Vaccine against recent circulating LSDV field isolate. The evaluation was done in calves as the main host of LSD, through using three different batches for each vaccine type. Experimental calf groups were vaccinated with vaccines batches, and after 21 days serum samples were collected for evaluation of humoral immune response by using SNT and commercial ELISA technique, then the vaccinated calves were challenged by virulent LSDV field isolate. The results of SNT for vaccinated calves by LSDV vaccines indicated mean neutralizing antibody titer 1.2, 1.6 and1.5 log10 for the batches 1, 2 and 3 respectively, while vaccinated calves by SPPV vaccines indicated 1.05, 1.05 and 1.5 log10 for the batches 1,2 and 3 respectively; the ELISA mean sample to positive (S/P) percentage for the vaccine batches 1, 2 and 3 of LSDV were 40, 45 and 42% respectively and for SPPV vaccine batches 1,2 and 3 were 35, 37 and 40 % respectively, the challenge test indicated mean difference titer for the groups of calves vaccinated with LSDV vaccine were 4.2, 4.5 and 3.8 log10 and for groups vaccinated with SPPV vaccine were 2.6, 2 and 2.65 log10 respectively, it was concluded that potential using of Neethling LSDV vaccine against LSD is superior for combating and prevention of the lumpy skin disease.

Genetic diversity and different cross-neutralization capability of porcine circovirus type 2 isolates recently circulating in South Korea

BackgroundPorcine circovirus type 2 (PCV2) is a small single-stranded DNA virus and a primary cause of PCV-associated diseases (PCVAD) that result insubstantial economic loss for swine farms. Between 2016 and 2018, PCV2 field viruses were isolated from PCVAD-affected swine farms in South Korea and investigated for genetic and antigenic heterogeneity.ResultsThe genetic analysis of ORF2 showed that the genotype of the Korean PCV2 field isolates has been rapidly shifted from PCV2a or 2b to mutant PCV2b known as PCV2d with 82.6 to 100% amino acid sequence similarity. PCV2-specific monoclonal antibodies (mAbs) demonstrated variable antigen-binding activity to four representative Korean PCV2 field isolates [QIA215 (PCV2a), QIA418 (PCV2b), QIA169 (PCV2d), and QIA244 (PCV2d)] without genotype specificity, and one mAb showed neutralization activity to QIA215. In a cross-virus neutralization assay using anti-PCV2 sera of pigs and guinea pigs injected with a commercial vaccine and the Korean PCV2 field isolates, the anti-porcine sera of a commercial vaccine had high neutralization activity against QIA215 and QIA418 with statistically lower activity against PCV2d viruses. Anti-guinea pig sera of QIA215, QIA418, QIA169, and a commercial vaccine had high neutralization activity against all of the viruses with significantly lower activity against QIA244. Importantly, anti-guinea pig sera of QIA244 had high neutralization activity against all of the viruses.ConclusionsThis study confirmed genetic and antigenic diversity among recent PCV2 field isolates in Korean swine farms, and the strain-based difference in virus neutralization capability should be considered for more effective control by vaccination.

Mating Competitiveness of Transgenic Aedes aegypti (Diptera: Culicidae) Males Against Wild-Type Males Reared Under Simulated Field Conditions.

Efforts directed at genetic modification of mosquitoes for population control or replacement are highly dependent on the initial mating success of transgenic male mosquitoes following their release into natural populations. Adult mosquito phenotypes are influenced by the environmental conditions experienced as larvae. Semifield studies conducted to date have not taken that under consideration when testing male mating fitness, and have compared mating success of males reared under identical environmental conditions. We performed pairwise mating challenges between males from a genetically modified laboratory strain (BF2) versus males from a recent Trinidad field isolate of Aedes aegypti (L.), a major vector of multiple arboviruses. We utilized larval density and nutrition to simulate environmental stress experienced by the Trinidad males and females. Our results indicated that environmental stress during larval development negatively influenced the competitiveness and reproductive success of males from the Trinidad population when paired with optimum reared BF2 males. Small (0.027 m3) and large (0.216 m3) trials were conducted wherein stressed or optimum Trinidad males competed with optimum BF2 males for mating with stressed Trinidad females. When competing with stress reared Trinidad males, optimum reared BF2 males were predominant in matings with stress reared Trinidad females, and large proportions of these females mated with males of both strains. When competing with optimum reared Trinidad males, no difference in mating success was observed between them and BF2 males, and frequencies of multiple matings were low. Our results indicate that future mating competition studies should incorporate appropriate environmental conditions when designing mating fitness trials of genetically modified males.

Efficacy of The Turkey Herpes virus-IBDV Vector Vaccine Against Recent Egyptian Very Virulent IBDV in Commercial Layers

The infectious bursal disease virus (IBDv) is widespread in poultry flocks all around the world. During the period between 2016- 2017, 22 IBD outbreaks were investigated in El-Minoufiya Governorate in different chicken sectors (11 broilers, 7 commercial layer pullets and 4 native baladi varieties). The disease occurred at 23-42 days of age. The mortality ranged between 3-9 % in commercial broilers farms, 5.8-12% in native breed varieties and 5-10 % in commercial layer replacement pullets. Two hundred one-day-old commercial male layer chicks was used for assessment of protection obtained after vaccination with HVT-IBDV vector vaccine Vaxxitek against challenged with vvIBDV local field isolate Lay./Men.Egypt/17 at 46th-day of age. Maternal derived antibodies (MDA) was followed up by ELISA to determine MA waning and the suitable age of chicks for IBDV vaccination and/or challenge. Chicks divided into 4 groups of (50 birds/ of each), G1 (vaccinated with HVT-IBD vector vaccine at 1 day old of age and non-challeneged) and G2 (vaccinated with HVT-IBDV at one-day of age and challenged with vvIBDV local field isolate Lay./Men.Egypt/017 at 46-day of age), G3 (non- vac-cinated and non-challenged) and G4 (non-vaccinated and challenged chickens). Our results revealed that the mortality percentage of commercial male layer chickens chal-lenged with recent vvIBDV local field isolate lay./Men.Egypt/017 was (0%) in G2, while in G4 was (90%), at 7-days post challenge. The highest bursa body ratio observed was (5.32 and 5.31) in non- vaccinated and non-challenged birds (G3) and birds vac-cinated with the VAXXITEK HVT-IBDv vaccine (G1). Conclusion, the recombinant VAXXITEK HVT-IBDv vaccine has provided protection for commercial male layer chicks against challenge with recent vvIBDv isolate. Vaccination with vector vaccine in en-demic areas with vvIBDV, protect against mortality, partially against bursal atrophy and decreases immunosuppressive effect of vvIBDV.

Molecular characteristics and pathogenicity analysis of QX-like avian infectious bronchitis virus isolated in China in 2017 and 2018

ABSTRACTProportions of QX-like genotype infectious bronchitis virus (IBV) isolates have increased over time. Here, to better understand the epidemiology and pathogenicity of IBV in China and control the spread of infectious bronchitis (IB), we conducted sequence analyses and examined the pathogenicity of 5 field isolates from diseased flocks in 2017 and 2018. Sequence analyses revealed that all the 5 strains, as well as many recent field isolates from other researchers, belonged to the QX-like IBV genotype, which were distantly related to commercial vaccine strains. Viral pathogenicity experiments showed that the isolates caused high morbidity and severe ciliostasis in chickens, although they caused milder lethality. This provides further evidence that QX-like IBV emergence remains a major problem in the poultry industry, and information on IBV epidemiology and pathogenicity may help to control IB.

Effector gene reshuffling involves dispensable mini-chromosomes in the wheat blast fungus.

Newly emerged wheat blast disease is a serious threat to global wheat production. Wheat blast is caused by a distinct, exceptionally diverse lineage of the fungus causing rice blast disease. Through sequencing a recent field isolate, we report a reference genome that includes seven core chromosomes and mini-chromosome sequences that harbor effector genes normally found on ends of core chromosomes in other strains. No mini-chromosomes were observed in an early field strain, and at least two from another isolate each contain different effector genes and core chromosome end sequences. The mini-chromosome is enriched in transposons occurring most frequently at core chromosome ends. Additionally, transposons in mini-chromosomes lack the characteristic signature for inactivation by repeat-induced point (RIP) mutation genome defenses. Our results, collectively, indicate that dispensable mini-chromosomes and core chromosomes undergo divergent evolutionary trajectories, and mini-chromosomes and core chromosome ends are coupled as a mobile, fast-evolving effector compartment in the wheat pathogen genome.

Efficacy of Prepared Oil Inactivated Pigeon Paramyxo Vaccine

Control of pigeon paramyxo virus infection relays on the production of a vaccine that is able to protect the birds from the lethal virulent infection as well as reducing shedding level to prevent virus circulation in the environment. In the current study inactivated vaccine was prepared from the recent field isolate (PPMV-1 YA/14) which is extensively characterized and identified. The vaccine was prepared in two formulas. The aluminum hydroxide gel (given S/C and I/M) and the oil adjuvanted formula. Evaluation of the 2 formulas revealed that the gel-based formula gave a higher antibody titer than the oil-based preparation during the course of the vaccination period and after challenge. The cellular immune response was also evaluated by the QRT-PCR analysis of the IFN-γ transcripts and it was found that the oil-based formula gave a high fold change than the gel-based formula although it was not reflected in decreasing the shedding level. Studying the shedding level by the EID50 or QRT-PCR of the cloacal swaps after challenge revealed that the gel-based formula administrated S/C gave lesser degree of shedding than the oil-based formula. In conclusion the gel-based formula of the vaccine prepared from the recent characterized PPMV-1 YA/14 isolate could protect pigeon from lethal infection with the virulent virus and could reduce but not eliminate the shedding level.

Endoperoxide-based compounds: cross-resistance with artemisinins and selection of a Plasmodium falciparum lineage with a K13 non-synonymous polymorphism

Owing to the emergence of multiresistant Plasmodium falciparum parasites in Southeast Asia, along with the impressive decrease in the efficacy of the endoperoxide compound artemisinin and of artemisinin-based combination therapies, the development of novel antimalarial drugs or combinations is required. Although several antiplasmodial molecules, such as endoperoxide-based compounds, are in advanced research or development, we do not know whether resistance to artemisinin derivatives might impact the efficacy of these new compounds. To address this issue, the antiplasmodial efficacy of trioxaquines, hybrid endoperoxide-based molecules, was explored, along with their ability to select in vitro resistant parasites under discontinuous and dose-escalating drug pressure. The in vitro susceptibilities of artemisinin- and trioxaquine-resistant laboratory strains and recent Cambodian field isolates were evaluated by different phenotypic and genotypic assays. Trioxaquines tested presented strong cross-resistance with artemisinin both in the artemisinin-resistant laboratory F32-ART5 line and in Cambodian field isolates. Trioxaquine drug pressure over 4 years led to the in vitro selection of the F32-DU line, which is resistant to trioxaquine and artemisinin, similar to the F32-ART lineage. F32-DU whole genome sequencing (WGS) revealed that resistance to trioxaquine was associated with the same non-synonymous mutation in the propeller domain of the K13 protein (M476I) that was found in the F32-ART lineage. These worrisome results indicate the risk of cross-resistance between artemisinins and endoperoxide-based antiplasmodial drugs in the development of the K13 mutant parasites and question the usefulness of these molecules in the future therapeutic arsenal.

Larval stress alters dengue virus susceptibility in Aedes aegypti (L.) adult females

In addition to genetic history, environmental conditions during larval stages are critical to the development, success and phenotypic fate of the Aedes aegypti mosquito. In particular, previous studies have shown a strong genotype-by-environment component to adult mosquito body size in response to optimal vs stressed larval conditions. Here, we expand upon those results by investigating the effects of larval-stage crowding and nutritional limitation on the susceptibility of a recent field isolate of Aedes aegypti to dengue virus serotype-2. Interestingly, female mosquitoes from larvae subjected to a stressed regime exhibited significantly reduced susceptibility to disseminated dengue infection 14days post infection compared to those subjected to optimal regimes. Short term survivorship post-infected blood feeding was not significantly different. As with body size, dengue virus susceptibility of a mosquito population is determined by a combination of genetic and environmental factors and is likely maintained by balancing selection. Here, we provide evidence that under different environmental conditions, the innate immune response of field-reared mosquitoes exhibits a large range of phenotypic variability with regard to dengue virus susceptibility. Further, as with body size, our results suggest that mosquitoes reared under optimal laboratory conditions, as employed in all mosquito-pathogen studies to date, may not always be realistic proxies for natural populations.

Isolation, identification, and hexon gene characterization of fowl adenoviruses from a contaminated live Newcastle disease virus vaccine

To investigate the possible causes of the massive spread of fowl adenovirus (FAdV) infection among chickens in recent years in China, 32 batches of live-virus vaccines were tested for contamination with FAdV by PCR. Among these, 1 live Newcastle disease virus (NDV) vaccine of the LaSota strain was demonstrated to be positive for contamination. The amplified hexon gene exhibited 99.8% identity with a recent Chinese field isolate (JSJ13) of FAdV-4. The positive LaSota vaccine was first neutralized with anti-NDV serum and then inoculated into specific pathogen-free embryos at embryonic day 5 through the yolk sac for isolation of the contaminated FAdV. The same hexon gene bands were amplified from extracted DNA of the liver tissues and chicken embryo allantoic fluid of the inoculated embryos, indicating the replication and isolation of the FAdV-4 virus strain that had contaminated the vaccine. This represents the first report of FAdV-4 contamination in a live vaccine for poultry in China. These findings suggest that contamination of live vaccine might represent one of the most important causes of massive outbreaks of FAdV infection among chickens and indicate that FAdV should therefore be included in the regular monitoring list for the detection of exogenous viral contamination of attenuated vaccines for poultry.

Development of the full-length cDNA clones of two porcine epidemic diarrhea disease virus isolates with different virulence.

The recently emerged highly virulent variants of porcine epidemic and diarrhea virus (PEDV) remain a huge threat to the worldwide swine industry. Here, we describe the development of a bacterial artificial chromosome (BAC) reverse genetics system for PEDV based on two recent Chinese field isolates, namely CHM2013 and BJ2011C. Phylogenetically, CHM2013 is closely related to the vaccine strain SM98 whereas the isolate BJ2011C belongs to the GIIb group, a cluster that contains many recent pandemic strains. The full-length cDNA clones of the two isolates were constructed into BAC under the control of CMV promoter. The rescued viruses rBJ2011C and rCHM2013 were found to replicate at the kinetics similar to their respective parental viruses in cell culture. When tested in the 2-day-old pig model, rBJ2011C caused severe diarrhea of piglets with extensive damages to the intestinal epithelium, leading to 100% fatality within 48 hours. In contrast, the rCHM2013-inoculated piglets all survived with only very minor tissue damage observed. Thus, we have successfully established a convenient platform for PEDV genome manipulation. This study also represents the first description of a DNA-launched reverse genetics system for the highly virulent PEDV.

Duration of immunity of a four-valent vaccine against bovine respiratory diseases

This study demonstrated the duration of immunity over 6 months of a vaccine against key bovine respiratory disease pathogens: Parainfluenza 3, Bovine Respiratory Syncytial Virus, Bovine Viral Diarrhoea and Mannheimia haemolytica. This was performed by challenge on colostrum-deprived calves at the age of 2 weeks. Recent European field isolates were used as challenge strains. Clinical signs and pathogen excretion or presence were monitored. Field relevance of the viral challenge strains was analysed using phylogenic analysis. Significant reduction of excretion of the 3 viruses in vaccinated animals was a consistent finding, demonstrating the efficacy of the vaccine. Reducing shedding is indeed key to interrupting the infection transmission chain and helping to achieve the protective effects of immunisation that extend beyond the individual. A significant reduction of clinical signs and lung lesions following the Mannheimia haemolytica challenge was also observed in vaccinated animals versus controls. Comparison of the challenge strains to an array of global and European strains, including recent ones, demonstrated a high genetic proximity, supporting the potential for the vaccine to maintain similar levels of efficacy in the field over a 6-month period post vaccination.

Efficacy of Suvaxyn CSF Marker (CP7_E2alf) in the presence of pre-existing antibodies against Bovine viral diarrhea virus type 1

Classical swine fever (CSF) is still one of the most important viral diseases of pigs worldwide and outbreaks are notifiable to the OIE. The different control options also include (emergency) vaccination, preferably with a vaccine that allows differentiation of infected from vaccinated animals (DIVA principle). Recently, the chimeric pestivirus “CP7_E2alf” (Suvaxyn® CSF Marker, Zoetis) was licensed as live attenuated marker vaccine by the European Medicines Agency (EMA). In the context of risk assessments for an emergency vaccination scenario, the question has been raised whether pre-existing anti-pestivirus antibodies, especially against the vaccine backbone Bovine viral diarrhea virus type 1 (BVDV-1), would interfere with “CP7_E2alf” vaccination and the accompanying DIVA diagnostics.To answer this question, a vaccination-challenge-trial was conducted with Suvaxyn® CSF Marker and the “gold-standard” of live-modified CSF vaccines C-strain (RIEMSER® Schweinepestvakzine) as comparator. Pre-existing antibodies against BVDV-1 were provoked in a subset of animals through intramuscular inoculation of a recent field isolate from Germany (two injections with an interval of 2weeks). Twenty-seven days after the first injection, intramuscular vaccination of pre-exposed and naïve animals with either “CP7_E2alf” or C-strain “Riems” was performed. Seven days later, all vaccinated animals and two additional controls were oro-nasally challenged with highly virulent CSF virus (CSFV) strain Koslov.It was demonstrated that pre-existing BVDV-1 antibodies do not impact on the efficacy of live attenuated vaccines against CSF. Both C-strain “Riems” and marker vaccine “CP7_E2alf” were able to confer full protection against highly virulent challenge seven days after vaccination. However, slight interference was seen with serological DIVA diagnostics accompanying the vaccination with CP7_E2alf. Amended sample preparation and combination of test systems was able to resolve most cases of false positive reactions. However, in such a co-infection scenario, optimization and embedding in a well-defined surveillance strategy is clearly needed.