A novel gE-deleted pseudorabies virus (PRV) provides rapid and complete protection from lethal challenge with the PRV variant emerging in Bartha-K61-vaccinated swine population in China

The currently used Bartha-K61 strain is a very safe and effective vaccine against pseudorabies (PR) and has played a critical role in the control and eradication of PR worldwide. Since late 2011, however, PR reemerged among Bartha-K61-vaccinated pig population in many regions in China. Our previous studies demonstrated that the Bartha-K61 vaccine was unable to provide complete protection from the challenge with the PRV TJ strain (PRVTJ), a representative emerging PRV variant that was isolated from a Bartha-K61-immunized pig farm in Tianjin, China. Here, we generated a gE-deleted PRV, named as rPRVTJ-delgE, based on PRVTJ and evaluated its safety and immunogenicity in pigs. Our results showed that groups of piglets (n = 5) immunized with 10³, 10⁴ or 10⁵ TCID₅₀ rPRVTJ-delgE did not exhibit clinical signs following immunization and challenge and were protected clinically and virologically from the lethal challenge with PRVTJ as early as 1 week post-immunization, in contrast with the incomplete protection provided by the Bartha-K61 vaccine. These indicate that rPRVTJ-delgE is a promising candidate vaccine for updating Bartha-K61 for the control of the currently epidemic PR in China.     

Construction of a triple gene-deleted Chinese Pseudorabies virus variant and its efficacy study as a vaccine candidate on suckling piglets

New-emerging variants of Pseudorabies virus (PRV) compromise the protection provided by current vaccines and cause the death of all ages of vaccinated pigs since 2011. New vaccines based on current circulating PRV strain are needed to control the spread of disease since the variants are antigenically different from classical strains of virus. In this study, a TK/gE/gI triple gene-deleted PRV derived from current circulating field isolate was generated by using bacterial artificial chromosome techniques, and the rescued virus showed similar growth properties in vitro to its parent strain but reduced plaque size. To evaluate it as vaccine candidate, 9 day-old pigs were vaccinated and challenged with a virulent PRV variant. The results showed that vaccination can generate high level of protective gB-specific antibodies after vaccination and provide complete protection to the viral challenge. By contrast, the unvaccinated piglets all died within 6 days after viral challenge. Therefore, the TK/gE/gI triple gene-deleted PRV could be a promising vaccine candidate to control the wide spreading of PR variants in China.     

Pseudorabies Virus Variant in Bartha-K61–Vaccinated Pigs,China, 2012

The widely used pseudorabies virus (PRV) Bartha-K61 vaccine has played a key role in the eradication of PRV. Since late 2011, however, a disease characterized by neurologic symptoms and a high number of deaths among newborn piglets has occurred among Bartha-K61–vaccinated pigs on many farms in China. Clinical samples from pigs on 15 farms in 6 provinces were examined. The PRV gE gene was detectable by PCR in all samples, and sequence analysis of the gE gene showed that all isolates belonged to a relatively independent cluster and contained 2 amino acid insertions. A PRV (named HeN1) was isolated and caused transitional fever in pigs. In protection assays, Bartha-K61 vaccine provided 100% protection against lethal challenge with SC (a classical PRV) but only 50% protection against 4 challenges with strain HeN1. The findings suggest that Bartha-K61 vaccine does not provide effective protection against PRV HeN1 infection.     

An interferon inducing porcine reproductive and respiratory syndrome virus vaccine candidate elicits protection against challenge with the heterologous virulent type 2 strain VR-2385 in pigs

Achieving consistent protection by vaccinating pigs against porcine reproductive and respiratory syndrome virus (PRRSV) remains difficult. Recently, an interferon-inducing PRRSV vaccine candidate strain A2MC2 was demonstrated to be attenuated and induced neutralizing antibodies. The objective of this study was to determine the efficacy of passage 90 of A2MC2 (A2P90) to protect pigs against challenge with moderately virulent PRRSV strain VR-2385 (92.3% nucleic acid identity with A2MC2) and highly virulent atypical PRRSV MN184 (84.5% nucleic acid identity with A2MC2). Forty 3-week old pigs were randomly assigned to five groups including a NEG-CONTROL group (non-vaccinated, non-challenged), VAC-VR2385 (vaccinated, challenged with strain VR-2385), VR2385 (challenged with strain VR-2385), VAC-MN184 (vaccinated, challenged with strain MN184) and a MN184 group (challenged with MN184 virus). Vaccination was done at 3 weeks of age followed by challenge at 8 weeks of age. No viremia was detectable in any of the vaccinated pigs; however, by the time of challenge, 15/16 vaccinated pigs had seroconverted based on ELISA and had neutralizing antibodies against a homologous strain with titers ranging from 8 to 128. Infection with VR-2385 resulted in mild-to-moderate clinical disease and lesions. For VR-2385 infected pigs, vaccination significantly lowered PRRSV viremia and nasal shedding by 9 days post challenge (dpc), significantly reduced macroscopic lung lesions, and significantly increased the average daily weight gain compared to the non-vaccinated pigs. Infection with MN184 resulted in moderate-to-severe clinical disease and lesions regardless of vaccination status; however, vaccinated pigs had significantly less nasal shedding by dpc 5 compared to non-vaccinated pigs. Under the study conditions, the A2P90 vaccine strain was attenuated without detectable shedding, improved weight gain, and offered protection to the pigs challenged with VR-2385 by reduction of virus load and macroscopic lung lesions. Further work is needed to investigate different vaccination and challenge protocols, including routes, doses, timing and strains.     

Induction of protective immunity in swine by immunization with live attenuated recombinant pseudorabies virus expressing the capsid precursor encoding regions of foot-and-mouth disease virus

Foot-and-mouth disease (FMD) causes morbidity to livestock and serious economic consequences to its associated industry and therefore it is necessary to develop a safe and efficient vaccine to prevent or control this disease. A recombinant live attenuated virus vaccine, designated PRV-P1, was generated by insertion of an expression cassette containing CMV promoter, FMDV P1 gene and SV 40 poly-A into the gG gene region of a live attenuated pseudorabies virus vaccine strain (TK⁻/gG⁻/LacZ⁺). To determine the induction of protective immunity, 16 FMDV and PRV seronegative white swine were randomly divided into four groups and immunized intramuscularly. The parental virus (TK⁻/gG⁻/LacZ⁺) was injected into three pigs, the recombinant virus PRV-P1 into five pigs and commercial FMD-inactivated vaccine into five pigs, with PBS (negative control) into three pigs. All animals were immunized again 4 weeks later to boost the immune response and challenged with virulent type O FMDV O/ES/2001 strain 4 weeks after the second immunization. Results showed PRV-P1 vaccinated pigs induced high-level neutralizing antibody response to both FMDV and PRV, and strong CTL response against FMD antigen activation. Three of five pigs were completely protected against challenge with FMDV, one pig minimally protected and the other one had increased protection but not complete. However, one pig vaccinated with commercial FMD vaccine developed constant pyrexia. Average levels of antibodies against non-structural 3ABC proteins were significantly lower and efficacy on inhibition of FMDV replication was much increased in swine vaccinated with PRV-P1 than those immunized with commercial FMD vaccine after FMDV challenge. Our results showed that the recombinant PRV-P1 can induce not only humoral and cell-mediated immune responses but also partial protection against FMDV challenge, making it a good candidate for future development of the FMD vaccine.     

Cross-protective efficacy of engineering serotype A foot-and-mouth disease virus vaccine against the two pandemic strains in swine

Foot-and-mouth disease (FMD) is a highly contagious vesicular disease that affects domestic and wild cloven-hoofed animals worldwide. Recently, a series of outbreaks of type A FMDV occurred in Southeast Asian countries, China, the Russia Federation, Mongolia, Kazakhstan and South Korea. The FMD virus (A/GDMM/CHA/2013) from China's Guangdong province (2013) is representative of those responsible for the latest epidemic, and has low amino acid identity (93.9%) in VP1 protein with the epidemic strain A/WH/CHA/09 from Wuhan, China in 2009. Both of isolates belong to the Sea-97 genotype of ASIA topotype. Therefore, the application of a new vaccine strain with cross-protective efficacy is of fundamental importance to control the spread of the two described pandemic strains. A chimeric strain rA/P1-FMDV constructed by our lab previously through replacing the P1 gene in the vaccine strain O/CHA/99 with that from the epidemic stain A/WH/CHA/09, has been demonstrated to exhibit good growth characteristics in culture, and the rA/P1-FMDV inactivated vaccine can provide protection against epidemic strain A/WH/CHA/09 in cattle. However, it is still unclear whether the vaccine produces efficient protection against the new pandemic strain (A/GDMM/CHA/2013). Here, vaccine matching and pig 50% protective dose (PD₅₀) tests were performed to assess the vaccine potency. The vaccine matching test showed cross-reactivity of sera from full dose vaccine vaccinated pigs with A/WH/CHA/09 and A/GDMM/CHA/2013 isolates, with average r₁ values of 0.94 ± 0.12 and 0.68 ± 0.06 (r₁ ≥ 0.3), which indicates that the rA/P1-FMDV vaccine is likely to confer good cross-protection against the two isolates. When challenged with two pandemic isolates A/WH/CHA/09 and A/GDMM/CHA/2013 strain, the vaccine achieved 12.51 PD₅₀ and 10.05 PD₅₀ per dose (2.8 μg), respectively. The results indicated that the rA/P1-FMDV inactivated vaccine could protect pigs against both A/WH/CHA/09 and A/GDMM/CHA/2013 pandemic isolates.     

A commercial porcine circovirus (PCV) type 2a-based vaccine reduces PCV2d viremia and shedding and prevents PCV2d transmission to naïve pigs under experimental conditions

Porcine circovirus type 2 (PCV2) vaccination has been effective in protecting pigs from clinical disease and today is used extensively. Recent studies in vaccinated populations indicate a major PCV2 genotype shift from the predominant PCV2 genotype 2b towards 2d. The aims of this study were to determine the ability of the commercial inactivated PCV2a vaccine Circovac® to protect pigs against experimental challenge with a 2013 PCV2d strain and prevent transmission. Thirty-eight pigs were randomly divided into four groups with 9–10 pigs per group: NEG (sham-vaccinated, sham-challenged), VAC (PCV2a-vaccinated, sham-challenged), VAC + CHAL (PCV2a-vaccinated and PCV2d-challenged), and CHAL (sham-vaccinated, PCV2d-challenged). Vaccination was done at 3 weeks of age using Circovac® according to label instructions. The CHAL and VAC + CHAL groups were challenged with PCV2d at 7 weeks of age and all pigs were necropsied 21 days post-challenge (dpc). The VAC-CHAL pigs seroconverted to PCV2 by 21 days post vaccination (dpv). At PCV2d challenge on 28 dpv, 3/9 VAC and 1/9 VAC + CHAL pigs were seropositive. NEG pigs remained seronegative for the duration of the study. Vaccination significantly reduced PCV2d viremia (VAC + CHAL) at dpc 14 and 21, PCV2d fecal shedding at dpc 14 and 21 and PCV2d nasal shedding at dpc 7, 14 and 21 compared to CHAL pigs. Vaccination significantly reduced mean PCV2 antigen load in lymph nodes in VAC + CHAL pigs compared to CHAL pigs. When pooled serum or feces collected from VAC + CHAL and CHAL pigs at dpc 21 were used to expose single-housed PCV2 naïve pigs, a pooled fecal sample from CHAL pigs contained infectious PCV2 whereas this was not the case for VAC + CHAL pigs suggesting reduction of PCV2d transmission by vaccination. Under the study conditions, the PCV2a-based vaccine was effective in reducing PCV2d viremia, tissue loads, shedding and transmission indicating that PCV2a vaccination should be effective in PCV2d-infected herds.     

Efficacy and safety of simultaneous vaccination with two modified live virus vaccines against porcine reproductive and respiratory syndrome virus types 1 and 2 in pigs

The objective of the study was to compare responses of pigs vaccinated with a PRRS MLV vaccine against PRRSV-1 or PRRSV-2 with the responses of pigs vaccinated simultaneously with both vaccines. Furthermore, the efficacy of the two PRRSV MLV vaccination strategies was assessed following challenge. The experimental design included four groups of 4-weeks old SPF-pigs. On day 0 (DPV0), groups 1–3 (N = 18 per group) were vaccinated with modified live virus vaccines (MLV) containing PRRSV-1 virus (VAC-T1), PRRSV-2 virus (VAC-T2) or both (VAC-T1T2). One group was left unvaccinated (N = 12). On DPV 62, the pigs from groups 1–4 were mingled in new groups and challenged (DPC 0) with PRRSV-1, subtype 1, PRRSV-1, subtype 2 or PRRSV-2. On DPC 13/14 all pigs were necropsied. Samples were collected after vaccination and challenge. PRRSV was detected in all vaccinated pigs and the majority of the pigs were positive until DPV 28, but few of the pigs were still viremic 62 days after vaccination. Virus was detected in nasal swabs until DPV 7–14. No overt clinical signs were observed after challenge. PRRSV-2 vaccination resulted in a clear reduction in viral load in serum after PRRSV-2 challenge, whereas there was limited effect on the viral load in serum following challenge with the PRRSV-1 strains. Vaccination against PRRSV-1 had less impact on viremia following challenge. The protective effects of simultaneous vaccination with PRRSV Type 1 and 2 MLV vaccines and single PRRS MLV vaccination were comparable. None of the vaccines decreased the viral load in the lungs at necropsy. In conclusion, simultaneous vaccination with MLV vaccines containing PRRSV-1 and PRRSV-2 elicited responses comparable to single vaccination and the commercial PRRSV vaccines protected only partially against challenge with heterologous strains. Thus, simultaneous administration of the two vaccines is an option in herds with both PRRSV types.     

Immunogenicity and protective efficacy of a single-dose live non-pathogenic Escherichia coli oral vaccine against F4-positive enterotoxigenic Escherichia coli challenge in pigs

Enterotoxigenic Escherichia coli strains expressing F4 (K88) fimbriae (F4-ETEC) are one of the most important causes of post-weaning diarrhea (PWD) in pigs. F4, a major antigen, plays an important role in the early steps of the infection. Herein, the efficacy of a live oral vaccine consisting of a non-pathogenic E. coli strain expressing F4 for protection of pigs against PWD was evaluated. Three blinded, placebo-controlled, block design, parallel-group confirmatory experiments were conducted, using an F4-ETEC PWD challenge model, each with a different vaccination-challenge interval (3, 7, and 21 days). The pigs were vaccinated via the drinking water with a single dose of the Coliprotec® F4 vaccine one day post-weaning. Efficacy was assessed by evaluating diarrhea, clinical observations, intestinal fluid accumulation, weight gain, intestinal colonization and fecal shedding of F4-ETEC. The immune response was evaluated by measuring serum and intestinal F4-specific antibodies. The administration of the vaccine resulted in a significant reduction of the incidence of moderate to severe diarrhea, ileal colonization by F4-ETEC, and fecal shedding of F4-ETEC after the heterologous challenge at 7 and 21 days post-vaccination. The 7-day onset of protection was associated with an increase of serum anti-F4 IgM whereas the 21-day duration of protection was associated with an increase of both serum anti-F4 IgM and IgA. Significant correlations between levels of serum and intestinal secretory anti-F4 antibodies were detected. Maternally derived F4-specific serum antibodies did not interfere with the vaccine efficacy. The evaluation of protection following a challenge three days after vaccination showed a reduction of the severity and the duration of diarrhea and of fecal shedding of F4-ETEC. The 7-day onset and the 21-day duration of protection induced by Coliprotec® F4 vaccine administered once in drinking water to pigs of at least 18 days of age were confirmed by protection against F4-ETEC and induction of F4-specific protective immunity.     

The protective effect of a Schistosoma japonicum Chinese strain 23 kDa plasmid DNA vaccine in pigs is enhanced with IL-12

The schistosome integral membrane protein Sm/Sj23 was initially shown to induce protection in mice as a synthetic peptide vaccine and further, as a plasmid DNA vaccine to induce protection in mice, sheep and water buffalo. In this study we asked if we could induce protection against challenge infection in pigs against Schistosoma japonicum by vaccinating them with a plasmid DNA vaccine encoding the S. japonicum Chinese strain 23 kDa membrane protein. Further, we asked if we could enhance protective efficacy of this vaccine by the addition of IL-12. We compared vaccination with SjC23 plasmid DNA alone or with IL-12 plasmid DNA in pigs. Pigs were immunized three times at three weekly intervals. Thirty Chinese Songjang native pigs were divided into three groups. In group A, each pig was immunized with 500 μg of SjC23 plasmid DNA by intramuscular (i.m.) injection in both buttocks. In group B each pig was immunized with 500 μg of SjC23 plasmid DNA, and 500 μg of each of pcDNA3.1-p35 and 500 μg of pcDNA3.1-p40 DNA by i.m. injection. In group C each pig was immunized with 500 μg of pcDNA3.1 as the control. Thirty days post-vaccination, pigs were challenged with S. japonicum cercariae and adult and egg burdens and granuloma size determined 45 days post-challenge. The results showed that worm reduction rates in SjC23 group compared with control group were 29.2% and in the SjC23 + IL-12 group reduced 58.6%. Similarly the female worm reduction rates were 50.8 and 58.8%, the hepatic egg reduction rates were 48.2 and 56.4%, and the mean square measure reduction rates of hepatic egg granulomas were 48.6 and 44.4%, the mean diameter reduction rates of granulomas were 27.6 and 22.8% in pigs vaccinated with SjC23 or SjC23 + IL-12 compared to plasmid vaccinated pigs, respectively. Analysis of sera from pigs vaccinated with SjC23 showed that 4 of 10 pigs had anti-Sj23 antibody responses; with 5 of 10 pigs positive for anti-Sj23 in the SjC23+IL-12 group. These results suggest that vaccination with Sj23 DNA vaccine induces not only a significant reduction in worm and egg burdens, but also significantly reduces the size of egg granulomas, thus is also anti-pathology.     

A novel live attenuated anthrax spore vaccine based on an acapsular Bacillus anthracis Sterne strain with mutations in the htrA,lef and cya genes

We recently reported the development of a novel, next-generation, live attenuated anthrax spore vaccine based on disruption of the htrA (High Temperature Requirement A) gene in the Bacillus anthracis Sterne veterinary vaccine strain. This vaccine exhibited a highly significant decrease in virulence in murine, guinea pig and rabbit animal models yet preserved the protective value of the parental Sterne strain. Here, we report the evaluation of additional mutations in the lef and cya genes, encoding for the toxin components lethal factor (LF) and edema factor (EF), to further attenuate the SterneΔhtrA strain and improve its compatibility for human use. Accordingly, we constructed seven B. anthracis Sterne-derived strains exhibiting different combinations of mutations in the htrA, cya and lef genes. The various strains were indistinguishable in growth in vitro and in their ability to synthesise the protective antigen (PA, necessary for the elicitation of protection). In the sensitive murine model, we observed a gradual increase (ΔhtrA < ΔhtrAΔcya < ΔhtrAΔlef < ΔhtrAΔlefΔcya) in attenuation – up to 10⁸-fold relative to the parental Sterne vaccine strain. Most importantly, all various SterneΔhtrA derivative strains did not differ in their ability to elicit protective immunity in guinea pigs. Immunisation of guinea pigs with a single dose (10⁹ spores) or double doses (>10⁷ spores) of the most attenuated triple mutant strain SterneΔhtrAlef^MUTΔcya induced a robust immune response, providing complete protection against a subsequent respiratory lethal challenge. Partial protection was observed in animals vaccinated with a double dose of as few as 10⁵ spores. Furthermore, protective immune status was maintained in all vaccinated guinea pigs and rabbits for at least 40 and 30 weeks, respectively.     

A effective DNA vaccine against diverse genotype J infectious hematopoietic necrosis virus strains prevalent in China

Infectious hematopoietic necrosis virus (IHNV) is the most important pathogen threatening the aquaculture of salmonid fish in China. In this study, a DNA vaccine, designated pIHNch-G, was constructed with the glycoprotein (G) gene of a Chinese IHNV isolate SD-12 (also called Sn1203) of genotype J. The minimal dose of vaccine required, the expression of the Mx-1 gene in the muscle (vaccine delivery site) and anterior kidney, and the titers of the neutralizing antibodies produced were used to evaluate the vaccine efficacy. To assess the potential utility of the vaccine in controlling IHNV throughout China, the cross protective efficacy of the vaccine was determined by challenging fish with a broad range of IHNV strains from different geographic locations in China. A single 100 ng dose of the vaccine conferred almost full protection to rainbow trout fry (3 g) against waterborne or intraperitoneal injection challenge with IHNV strain SD-12 as early as 4 days post-vaccination (d.p.v.), and significant protection was still observed at 180 d.p.v. Intragenogroup challenges showed that the DNA vaccine provided similar protection to the fish against all the Chinese IHNV isolates tested, suggesting that the vaccine can be widely used in China. Mx-1 gene expression was significantly upregulated in the muscle tissue (vaccine delivery site) and anterior kidney in the vaccinated rainbow trout at both 4 and 7 d.p.v. Similar levels of neutralizing antibodies were determined with each of the Chinese IHNV strains at 60 and 180 d.p.v. This DNA vaccine should play an important role in the control of IHN in China.     

Novel pseudorabies virus variant with defects in TK,gE and gI protects growing pigs against lethal challenge

One of the distinct features of the emerging Chinese pseudorabies virus (PRV) variant is its ability to cause severe neurological signs and high mortality in growing pigs in Bartha-K61-vaccinated pig farms. Either single- or multiple-gene-deleted live vaccine candidates have been developed; however, none was evaluated thoroughly in growing pigs. Here, we generated rSMXΔgI/gEΔTK, an attenuated PRV variant with defects in TK, gI and gE genes. The growth kinetics of the attenuated virus was similar to the wild type (wt) strain. It was safe for 1-day-old piglets. Twenty one-day-old weaned pigs were immunized intramuscularly either with 10^6.0 TCID₅₀ of rSMXΔgI/gEΔTK or one dose of commercial Bartha-K61 vaccine, or with DMEM, and were challenged intranasally with 10^7.0 TCID₅₀ wt virus at 28 days post vaccination. rSMXΔgI/gEΔTK elicited higher level neutralization antibody against both PRV variant SMX and Bartha-K61 strain, while Bartha-K61 vaccine elicited lower neutralization activity of antibody against SMX. After challenge, all pigs in rSMXΔgI/gEΔTK group survived without any clinical signs, while unvaccinated group showed 100% mortality, and Bartha-K61 group showed severe respiratory symptoms and 3 out of 5 pigs exhibited severe neurological signs. Pigs in rSMXΔgI/gEΔTK group gained significantly higher body weight and diminished viral excretion titer and period, compared with Bartha-K61 group. Furthermore, the safety and efficacy of rSMXΔgI/gEΔTK was also evaluated in sheep and compared with local vaccine in growing pigs. These data suggest that the attenuated strain rSMXΔgI/gEΔTK is a promising live marker vaccine candidate for PR control in the context of emerging PRV variants.     

Efficacy of the oral rabies virus vaccine strain SPBN GASGAS in foxes and raccoon dogs

To test the immunogenicity and efficacy of a new oral rabies virus vaccine strain SPBN GASGAS in wildlife target species, one group of foxes and two groups of raccoon dogs were offered a bait containing 1.7 ml of the vaccine (10^6.6 FFU/ml; 10^6.8 FFU/dose) and subsequently challenged approximately 180 days later with a fox rabies virus isolate. One group of raccoon dogs (n = 30) received the same challenge dose (10^0.7 MICLD₅₀/ml) as the red foxes (n = 29). The other group with raccoon dogs (n = 28) together with 8 animals that received the vaccine dose by direct instillation into the oral cavity (DIOC) were infected with a 40-fold higher dose of the challenge virus (10^2.3 MICLD₅₀/ml). All but one of the 29 vaccinated foxes survived the challenge infection; meanwhile all 12 control foxes succumbed to rabies. Twenty-eight of 30 vaccinated raccoon dogs challenged with the same dose survived the infection, however only six of 12 control animals succumbed. When the higher challenge dose was administered, all 12 control animals died from rabies and all 36 vaccinated animals (28 baited plus 8 DIOC) survived. Blood samples were collected at different time points post vaccination and examined by both RFFIT and ELISA. The kinetics of the measured immune response was similar for both species, although in RFFIT slightly higher values were observed in foxes than in raccoon dogs. However, the immune response as measured in ELISA was identical for both species. The oral rabies virus vaccine SPBN GASGAS meets the efficacy requirements for live rabies virus vaccines as laid down by the European Pharmacopoeia.     

Multiple efficacy studies of an adenovirus-vectored foot-and-mouth disease virus serotype A24 subunit vaccine in cattle using homologous challenge

The safety and efficacy of an experimental, replication-deficient, human adenovirus-vectored foot-and-mouth disease virus (FMDV) serotype A24 Cruzeiro capsid-based subunit vaccine (AdtA24) was examined in eight independent cattle studies. AdtA24 non-adjuvanted vaccine was administered intramuscularly to a total of 150 steers in doses ranging from approximately 1.0 × 10⁸ to 2.1 × 10¹¹ particle units per animal. No detectable local or systemic reactions were observed after vaccination. At 7 days post-vaccination (dpv), vaccinated and control animals were challenged with FMDV serotype A24 Cruzeiro via the intradermal lingual route. Vaccine efficacy was measured by FMDV A24 serum neutralizing titers and by protection from clinical disease and viremia after challenge. The results of eight studies demonstrated a strong correlation between AdtA24 vaccine dose and protection from clinical disease (R² = 0.97) and viremia (R² = 0.98). There was also a strong correlation between FMDV A24 neutralization titers on day of challenge and protection from clinical disease (R² = 0.99). Vaccination with AdtA24 enabled differentiation of infected from vaccinated animals (DIVA) as demonstrated by the absence of antibodies to the FMDV nonstructural proteins in vaccinates prior to challenge. Lack of AdtA24 vaccine shedding after vaccination was indicated by the absence of neutralizing antibody titers to both the adenovector and FMDV A24 Cruzeiro in control animals after co-mingling with vaccinated cattle for three to four weeks. In summary, a non-adjuvanted AdtA24 experimental vaccine was shown to be safe, immunogenic, consistently protected cattle at 7 dpv against direct, homologous FMDV challenge, and enabled differentiation of infected from vaccinated cattle prior to challenge.     

Vaccination with a live attenuated Acinetobacter baumannii deficient in thioredoxin provides protection against systemic Acinetobacter infection

Multi-drug resistant Acinetobacter baumannii (MDR-Ab), an opportunistic pathogen associated with nosocomial and combat related infections, has a high mortality due to its virulence and limited treatment options. Deletion of the thioredoxin gene (TrxA) from a clinical isolate of MDR-Ab resulted in a 100-fold increase in 50% lethal dose (LD₅₀) in a systemic challenge murine model. Thus, we investigated the potential use of this attenuated strain as a live vaccine against MDR-Ab. Mice were vaccinated by subcutaneous (s.c.) injection of 2 × 10⁵ CFU of the ΔtrxA mutant, boosted 14 days later with an equivalent inoculum, and then challenged 30 days post-vaccination by i.p. injection with 10 LD₅₀ of the wild type (WT) Ci79 strain. Efficacy of vaccination was evaluated by monitoring MDR-Ab specific antibody titers and cytokine production, observing pathology and organ burdens after WT challenge, and measuring levels of serum pentraxin-3, a molecular correlate of A. baumannii infection severity, before and after challenge. Mice vaccinated with ΔtrxA were fully protected against the lethal challenge of WT. However, minimal immunoglobulin class switching was observed with IgM predominating. Spleens harvested from vaccinated mice exhibited negligible levels of IL-4, IFN-γ and IL-17 production when stimulated with UV-inactivated WT Ci79. Importantly, tissues obtained from vaccinated mice displayed reduced pathology and organ burden compared to challenged non-vaccinated mice. Additionally, serum pentraxin-3 concentrations were not increased 24 h after challenge in vaccinated mice, correlating with reduction of WT MDR-Ab infection in ΔtrxA immunized mice. Furthermore, passive immunization with ΔtrxA-immune sera provided protection against lethal systemic Ci79 challenge. Collectively, the defined live attenuated ΔtrxA strain is a vaccine candidate against emerging MDR Acinetobacter infection.     

A commercial PCV2a-based vaccine significantly reduces PCV2b transmission in experimental conditions

Transmission characteristics of PCV2 have been compared between vaccinated and non-vaccinated pigs in experimental conditions. Twenty-four Specific Pathogen Free (SPF) piglets, vaccinated against PCV2 at 3 weeks of age (PCV2a recombinant CAP protein-based vaccine), were inoculated at 15 days post-vaccination with a PCV2b inoculum (6 ⋅ 10⁵ TCID₅₀), and put in contact with 24 vaccinated SPF piglets during 42 days post-inoculation. Those piglets were shared in six replicates of a contact trial involving 4 inoculated piglets mingled with 4 susceptible SPF piglets. Two replicates of a similar contact trial were made with non-vaccinated pigs. Non vaccinated animals received a placebo at vaccination time and were inoculated the same way and at the same time as the vaccinated group. All the animals were monitored twice weekly using quantitative real-time PCR and ELISA for serology until 42 days post-inoculation. The frequency of infection and the PCV2 genome load in sera of the vaccinated pigs were significantly reduced compared to the non-vaccinated animals. The duration of infectiousness was significantly different between vaccinated and non-vaccinated groups (16.6 days [14.7;18.4] and 26.6 days [22.9;30.4] respectively). The transmission rate was also considerably decreased in vaccinated pigs (β = 0.09 [0.05–0.14] compared to β = 0.19 [0.11–0.32] in non-vaccinated pigs). This led to an estimated reproduction ratio of 1.5 [95% CI 0.8 – 2.2] in vaccinated animals versus 5.1 [95% CI 2.5 – 8.2] in non-vaccinated pigs when merging data of this experiment with previous trials carried out in same conditions.     

Experimental quantification of transmission of genetically engineered pseudorabies virus

There is concern that live pseudorabies virus (PRV) vaccine or PRV vector vaccine strains may spread from vaccinated to unvaccinated pigs. Moreover, it is feared that recombining PRV vaccine strains with related vaccine or wild-type strains may lead to spread and survival of recombinant PRV. To learn more about to what extent different PRV vaccine strains could spread we used a previously described experimental model to study the transmission of intranasally inoculated PRV mutant strains under experimental conditions. We used PRV strains that lacked glycoprotein E (gE) or thymidine kinase (TK), and a PRV vector vaccine (gE⁻, TK⁻, gG⁻) that expresses the glycoprotein E1 (E1) of hog cholera virus. In addition, we investigated whether intranasally co-inoculated gE-negative and gE-positive PRV strains competed in transmission among pigs. The extent of transmission was estimated using the reproduction ratio R. This ratio has a threshold property; when R1, the infection can spread; when R<1, the infection will disappear. We found that R for a gE-negative strain was 10.1, and R for a TK-negative strain was 5. Furthermore, the R for the vector vaccine (gE⁻, TK⁻, gG⁻) expressing E1 was 0.18, and did not differ significantly from the R for the control strain without E1. The R of gE-negative strain was significantly 1 (P=0.0005). Co-inoculation with a gE-positive field strain did not prevent the transmission of a gE-negative strain. This study shows that a small-scale experiment can be used to estimate the transmission of genetically engineered organisms in their host species. The results of this study indicate that the deletion of ge alone or TK alone is not enough to prevent spread of PRV among susceptible pigs, and that transmission of gE-negative PRV is not firmly limited by co-presence of a gE-positive strain.     

Early protection in sheep against intratypic heterologous challenge with serotype O foot-and-mouth disease virus using high-potency,emergency vaccine

In 2009–2011, spread of a serotype O foot-and-mouth disease virus (FMDV) belonging to the South East Asia topotype led to the culling of over 3.5 million cattle and pigs in Japan and Korea. The O1 Manisa vaccine (belonging to the Middle East-South Asian topotype) was used at high potency in Korea to limit the expansion of the outbreak. However, no data are available on the spread of this virus or the efficacy of the O1 Manisa vaccine against this virus in sheep. In this study, the early protection afforded with a high potency (>6 PD₅₀) FMD O1 Manisa vaccine against challenge with the O/SKR/2010 virus was tested in sheep. Sheep (n = 8) were vaccinated 4 days prior to continuous direct-contact challenge with donor sheep. Donor sheep were infected with FMDV O/SKR/2010 by coronary band inoculation 24 h prior to contact with the vaccinated animals, or unvaccinated controls (n = 4). Three of the four control sheep became infected, two clinically. All eight O1 Manisa vaccinated sheep were protected from clinical disease. None had detectable antibodies to FMDV non-structural proteins (3ABC), no virus was isolated from nasal swabs, saliva or oro-pharyngeal fluid and none became carriers. Using this model of challenge, sheep were protected against infection as early as 4 days post vaccination.     

Efficacy of a new bivalent vaccine of porcine circovirus type 2 and Mycoplasma hyopneumoniae (Fostera™ PCV MH) under experimental conditions

The objective of this study was to evaluate the efficacy of a new bivalent vaccine (Fostera™ PCV MH, Zoetis) of porcine circovirus type 2 (PCV2) and Mycoplasma hyopneumoniae in growing pigs under experimental conditions. A total of 80 pigs were randomly divided into 8 groups (10 pigs per group). The pigs were administered the bivalent vaccine intramuscularly as a 2.0 mL dose at 21 days of age based on the manufacturer's instructions. Three weeks after vaccination, the pigs were inoculated with either PCV2 (intranasal route) or M. hyopneumoniae (intratracheal route) or both. Regardless of the type of inoculation, vaccinated pigs after challenge exhibited effective reduction of clinical signs, PCV2 viremia levels and mycoplasma nasal shedding, and lung and lymphoid lesion when compared to unvaccinated challenged pigs. Vaccinated challenged pigs had significantly higher (P < 0.05) levels of PCV2-specific neutralizing antibodies, and numbers of PCV2-and M. hyopneumoniae-specific interferon-γ secreting cells compared to unvaccinated challenged pigs. This study demonstrates that the bivalent vaccine is able to protect pigs against either PCV2 or M. hyopneumoniae infection or both based on clinical, microbiological, immunological, and pathological evaluation.