Detection of classical swine fever virus (CSFV) E2 and Erns antibody (IgG, IgA) in oral fluid specimens from inoculated (ALD strain) or vaccinated (LOM strain) pigs

Enhancement of systemic virus-specific T lymphocyte responses in pigs supplemented with algae-derived β-glucan

Algae-derived β-glucan has been widely used as a feed additive in the swine industry. The supplementation of β-glucan aims to improve growth performance and modulate the immunity of pigs. However, the potential effects of supplementing β-glucan from algae on immune responses in pigs-specifically antigen-specific immunity-must be determined. In this study, the effects of algae-derived β-glucan supplementation on growth performance, virus neutralising antibody and virus-specific T lymphocytes responses were investigated in pigs. Piglets (n=112 per treatment) were assigned to three treatments including non-supplemented group (control), β-glucan 100 g/ton supplemented group (BG100), and β-glucan 200 g/ton supplemented group (BG200). In this study, production performance of pigs was not found to be different between the experimental groups. Pigs supplemented with β-glucan exhibited high levels of classical swine fever virus (CSFV)-specific producing T lymphocytes and neutralising antibody titer, compared to the control group. Interestingly, supplementation of β-glucan significantly enhanced porcine reproductive and respiratory syndrome virus (PRRSV)-specific interferon-gamma (IFN-γ) producing T lymphocytes, including CD4+, CD8+, and CD4+CD8+ T lymphocyte subpopulations. Moreover, PRRS modified live vaccine (MLV) viremia was reduced in earlier for β-glucan-supplemented pigs compared to the control group. The findings indicate that the algae-derived β-glucan possesses biological potential as an immunomodulatory substance to enhance antiviral immunity, which may contribute to disease resistance in pigs.

Development of a dual immunochromatographic test strip to detect E2 and Erns antibodies against classical swine fever

Background

It is essential to consider a practical antibody test to successfully implement marker vaccines and validate vaccination efficacy against classical swine fever virus (CSFV). The test should include a serological antibody assay, combined with a tool for differentiating infected from vaccinated animals (DIVA). The immunochromatographic test strip (ICS) has been exclusively designed for detecting CSFV E2 antibodies while lacking in detecting Erns antibodies, which can be employed and satisfy DIVA strategy. This study developed a novel ICS for detecting CSFV E2/Erns dual-antibody. The effectiveness of ICS in evaluating the DIVA capability of two novel chimeric pestivirus vaccine candidates was assessed.

Methods

Recombinant E2 or Erns protein was transiently expressed in the plant benthamiana using Agrobacterium tumefaciens. ICS was subsequently assembled, and goat anti-rabbit IgG and recombinant CSFV E2 or Erns protein were plated onto the nitrocellulose membrane as control and test lines, respectively. The sensitivity and specificity of ICS were evaluated using sera with different neutralizing antibody titers or positive for antibodies against CSFV and other pestiviruses. The coincidence rates for detecting E2 and Erns antibodies between ICS and commercial enzyme-linked immunosorbent assay (ELISA) kits were also computed. ICS performance for DIVA capability was evaluated using sera from pigs vaccinated with conventional vaccine or chimeric vaccine candidates.

Results

E2 and Erns proteins were successfully expressed in N. benthamiana-produced recombinant proteins. ICS demonstrated high sensitivity in identifying CSFV E2 and Erns antibodies, even at the low neutralizing antibody titers. No cross-reactivity with antibodies from other pestiviruses was confirmed using ICS. There were high agreement rates of 93.0 and 96.5% between ICS and two commercial ELISA kits for E2 antibody testing. ICS also achieved strong coincidence rates of 92.9 and 89.3% with two ELISA kits for Erns antibody detection. ICS confirmed the absence of CSFV Erns-specific antibodies in sera from pigs vaccinated with chimeric vaccine candidates.

Conclusion

E2 and Erns proteins derived from the plant showed great potential and can be used to engineer a CSFV E2/Erns dual-antibody ICS. The ICS was also highly sensitive and specific for detecting CSFV E2 and Erns antibodies. Significantly, ICS can fulfill the DIVA concept by incorporating chimeric vaccine candidates.

Performance of a Differentiation of Infected from Vaccinated Animals (DIVA) Classical Swine Fever Virus (CSFV) Serum and Oral Fluid Erns Antibody AlphaLISA Assay

Classical swine fever virus (CSFV) is an OIE-listed disease that requires effective surveillance tools for its detection and control. The aim of this study was to develop and evaluate the diagnostic performance of a novel CSFV Erns IgG AlphaLISA for both serum and oral fluid specimens that would likewise be compatible with the use of CSFV E2 DIVA vaccines. Test performance was evaluated using a panel of well-characterized serum (n = 760) and individual (n = 528) or pen-based (n = 30) oral fluid samples from four groups of animals: (1) negative controls (n = 60 pigs); (2) inoculated with ALD strain wild-type CSFV (n = 30 pigs); (3) vaccinated with LOM strain live CSFV vaccine (n = 30 pigs); and (4) vaccinated with live CSFV marker vaccine on commercial farms (n = 120 pigs). At a cutoff of S/P ≥ 0.7, the aggregate estimated diagnostic sensitivities and specificities of the assay were, respectively, 97.4% (95% CI 95.9%, 98.3%) and 100% for serum and 95.4% (95% CI 92.9%, 97.0%) and 100% for oral fluid. The Erns IgG antibody AlphaLISA combined DIVA capability with solid diagnostic performance, rapid turnaround, ease of use, and compatibility with both serum and oral fluid specimens.

Evidence of Horse Exposure to Anaplasma phagocytophilum, Borrelia burgdorferi, and Leishmania infantum in Greece through the Detection of IgG Antibodies in Serum and in an Alternative Diagnostic Sample-The Saliva

Among the various zoonotic pathogens that infect horses, Anaplasma phagocytophilum, Borrelia spp. and Leishmania spp. have gained scientific interest, and relevant molecular and serological studies in horses have been conducted worldwide. Moreover, human and veterinary medicine have extensively applied alternatives to serum diagnostic samples-such as saliva-for detecting pathogens or antibodies. In this study, we investigated the exposure of horses in Greece to A. phagocytophilum, B. burgdorferi, and L. infantum, and we assessed the diagnostic accuracy of saliva compared to serum in detecting IgG antibodies against the abovementioned pathogens. Paired saliva and serum samples were collected from 317 horses from different regions in Greece. The paired samples were examined using the indirect fluorescent antibody test (IFAT) for detecting IgG antibodies against A. phagocytophilum, B. burgdorferi, and L. infantum. Sensitivity, specificity, positive likelihood ratio (PLR), and negative likelihood ratio (NLR) were determined to assess the validity of saliva as an alternative to serum. The receiver operating characteristic (ROC) curve revealed that the optimal cut-off value for detecting antibodies against all the examined pathogens in saliva was 1/10. Higher seropositivity rates were found for B. burgdorferi (15.14%) and A. phagocytophilum (14.19%) compared to L. infantum (1.26%). The detection of IgG antibodies using IFAT in saliva samples had a good test performance compared to serum. The two sample types had a substantial to almost perfect agreement. Although the sensitivity was moderate (70.83-75.56%) in all cases, the specificity was almost perfect to perfect (99.63-100%). This study provides the first evidence that horses in Greece are exposed to A. phagocytophilum and B. burgdorferi and confirms that the seroprevalence of L. infantum in horses in Greece remains low. Our findings suggest that saliva sampling coupled with IFAT could be successfully applied for detecting IgG antibodies against these important zoonotic pathogens in large-scale epidemiological studies in horses, at the population level, as an alternative to serum.

The recombinant Erns and truncated E2-based indirect enzyme-linked immunosorbent assays to distinguishably test specific antibodies against classical swine fever virus and bovine viral diarrhea virus

Background

Classical swine fever (CSF) virus is the causative agent of an economically important, highly contagious disease of pigs. CSFV is genetically and serologically related to bovine viral diarrhea virus (BVDV). BVDV infection in pigs can mimic CSF clinical signs, which cause difficulty in differentiation. Serological test for detection of virus specific antibodies is a valuable tool for diagnosis and surveillance of CSFV and BVDV infections in animals. The aim of this study was to develop the CSFV Erns and BVDV tE2 -based ELISAs to distinguishably test specific antibodies against CSFV and BVDV.

Methods

The CSFV Erns and truncated E2 (tE2, residues 690–865) of BVDV were expressed in E. coli and purified by Ni–NTA affinity chromatography, respectively. Employing Erns or tE2 protein as diagnostic antigen, indirect ELISAs were developed to distinguishably test specific antibodies against CSFV and BVDV. The specificity and sensitivity of ELISAs were evaluated using a panel of virus specific sera of pigs, immunized rabbits and immunized mice. A total 150 clinical serum samples from farm pigs were measured by the developed ELISAs and compared with virus neutralizing test (VNT).

Results

Indirect ELISA was established based on recombinant CSFV Erns or BVDV tE2 protein, respectively. No serological cross-reaction between antibodies against CSFV and BVDV was observed in sera of immunized rabbits, immunized mice or farm pigs by detections of the Erns and tE2 -based ELISAs. Compared to VNT, the CSFV Erns -based ELISA displayed a high sensitivity (93.3%), specificity (92.0%) and agreement rate (92.7%), and the sensitivity, specificity and agreement rate of BVDV tE2 -based ELISA was 92.3%, 95.2% and 94.7%, respectively.

Conclusion

The newly developed ELISAs are highly specific and sensitive and would be valuable tools for serological diagnosis for CSFV and BVDV infections.

Immunogenicity of the recombinant adenovirus fusion-expressing E0-E2 gene of the classical swine fever virus

Adenovirus vector vaccines have been the mainstream research direction of CSF vaccines, due to the replication deficiency of adenovirus vectors, achieving double effects with the safety of inactivated vaccines and the efficacy of live vaccines. Therefore, the E0 and E2 genes were expressed by an adenovirus vector, a recombinant adenovirus E0-E2 (rAd-E0-E2) vaccine was constructed, and the minimum immunization dose and immune duration period were determined in this study. Forty healthy piglets were randomly divided into 8 groups (n = 5). Groups 1 ~ 5 were used to determine the minimum immunization dose, and 5 groups were inoculated with rAd-E0-E2 at different immune doses. Serum was collected at 7 d and 14 d after immunization to detect CSFV antibodies by ELISA, and piglets were challenged at 7 d post immunization. Groups 6 ~ 8 were immunized with 1 dose of rAd-E0-E2, the CSFV live attenuated vaccine C strain and saline to identify the immune duration period. Serum was collected at different time points after immunization, CSFV antibodies were detected by ELISA, and piglets were challenged at 8 months post immunization. Meanwhile, temperature, clinical symptoms and pathology were observed. The results of groups 1 ~ 5 showed that 1 piglet was protected after challenge, and 4 piglets exhibited high fever retention, typical CSFV symptoms and tissue lesions in the 1/50 dose group, whereas no clinical symptoms were observed in the 1/10 dose, 1/5 dose or 1 dose groups with 5/5 protection after challenge. The minimum dose was determined as 1/10 dose. The results of groups 6 ~ 8 showed that all piglets survived after challenge, but the antibody level of the rAd-E0-E2 strain was higher than that of the C strain at 8 months post immunization, and all piglets in the negative group developed the disease process after challenge. Overall, the minimum immunization dose of rAd-E0-E2 was 1/10 dose (3.16 × 10^6.0 IFU) and the minimum immune dose was determined to be 1 dose (3.16 × 10^7.0 IFU) to achieve the expected effects. The immune duration period of piglets immunized with 1 dose of rAd-E0-E2 was at least 8 months.

Noninvasive strategies for surveillance of swine viral diseases: a review

In view of the intensive development of the swine industry, monitoring and surveillance of infectious diseases require low-cost, effective, and representative population sampling methods. We present herein the state of knowledge, to date, in the use of alternative strategies in the monitoring of swine health. Blood sampling, the most commonly used method in veterinary medicine to obtain samples for monitoring swine health, is labor-intensive and expensive, which has resulted in a search for alternative sampling strategies. Oral fluid (OF) is a good alternative to serum for pooled sample analysis, especially for low-prevalence pathogens. Detection of viral nucleic acids or antiviral antibodies in OF is used to detect numerous viruses in the swine population. Meat juice is used as an alternative to serum in serologic testing. Processing fluid obtained during processing of piglets (castration and tail-docking) may also be used to detect viruses. These matrices are simple, safe, cost-effective, and allow testing of many individuals at the same time. The latest methods, such as snout swabs and udder skin wipes, are also promising. These alternative samples are easy to acquire, and do not affect animal welfare negatively.

Guidelines for oral fluid-based surveillance of viral pathogens in swine

Recent decades have seen both rapid growth and extensive consolidation in swine production. As a collateral effect, these changes have exacerbated the circulation of viruses and challenged our ability to prevent, control, and/or eliminate impactful swine diseases. Recent pandemic events in human and animal health, e.g., SARS-CoV-2 and African swine fever virus, highlight the fact that clinical observations are too slow and inaccurate to form the basis for effective health management decisions: systematic processes that provide timely, reliable data are required. Oral fluid-based surveillance reflects the adaptation of conventional testing methods to an alternative diagnostic specimen. The routine use of oral fluids in commercial farms for PRRSV and PCV2 surveillance was first proposed in 2008 as an efficient and practical improvement on individual pig sampling. Subsequent research expanded on this initial report to include the detection of ≥23 swine viral pathogens and the implementation of oral fluid-based surveillance in large swine populations (> 12,000 pigs). Herein we compile the current information regarding oral fluid collection methods, testing, and surveillance applications in swine production.

Sensing the classical swine fever virus with molecularly imprinted polymer on quartz crystal microbalance

Classical swine fever (CSF) is a highly contagious and fatal viral disease in pigs caused by the virus of the same name (classical swine fever virus – CSFV). Economical reasons dictate the need for rapid early detection of this pathogen. Herein we report on a sensor for CSFV detection based on a quartz crystal microbalance (QCM) making use of molecularly imprinted polymer (MIP) as the receptor. It relies on a copolymer comprising acrylamide (AAM), methacrylic acid (MAA), methyl methacrylate (MMA), and n-vinylpyrrolidone (VP). SEM images of CSFV MIP reveal cavities on the polymer surface with an average diameter of d = 59 nm, which correlates well with the dimensions of CSFV particles. QCM sensor measurements yield concentration-dependent CSFV sensor responses resulting in LOD = 1.7 μg/mL, LOQ = 5.1 μg/mL and R² = 0.9963. Furthermore, CSFV-MIP sensors selectively bind CSFV with selectivity factors of 2 over porcine respiratory and reproductive virus (PRRSV) and 62 over pseudorabies virus (PRV), respectively. Finally, sensor responses turned out fully reversible.

Molecular detection of porcine reproductive and respiratory syndrome virus, porcine circovirus 2 and hepatitis E virus in oral fluid compared to their detection in faeces and serum

Background

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), Porcine Circovirus Type 2 (PCV2) and Hepatitis E virus (HEV) are common and economically important viral disease causative agents detected in pig oral fluid (OF), faeces and serum at some infection stages. The purpose of this study was to detect PRRSV, PCV2 and HEV on six pig farms to determine which of the three sample types, OF, faeces or serum is appropriate for the diagnosis of these viruses in different pig categories.

The following pig categories were included: 5 weeks-old (w/o), 7 w/o, 9 w/o, 11 w/o weaners, fatteners and breeding sows. Pursuant to the preliminary detection of each pathogen at the selected farms, OF samples, faeces, serum pools and 10 individual sera were examined, using PCR, for each age category. If any of the viruses were found in pools of faeces and OF, then faeces and OF from positive farms were tested separately for each pig category. The viral nucleic acids were detected using RT-PCR, PCR and real-time RT-PCR, for PRRSV, PCV2 and HEV respectively.

Results

PRRSV and HEV were detected on one farm and PCV2 on three others, positive results being more often obtained from the OF than from the faeces of the same animals. Ten individual serum samples from pigs from the same group of animals were also tested. The viruses were detected in almost all individual sera and OF in the same pig category with some exceptions: PRRSV was detected in the OF of fatteners but was absent in their sera; on Farm 2, PCV2 was detected in sera of 11 w/o pigs and fatteners but absent in group samples of their OF and, vice versa, in case of 9 w/o animals; HEV was detected in the OF of the youngest, 5 w/o weaners and absent in sera of the same age group.

Conclusions

The primary finding of the study is that OF is a welfare-friendly, non-invasive and highly efficient matrix for pathogen detection, thus evidencing the usefulness of pig OF as a matrix in which each of the three viruses considered can be detected with the highest probability.

Detection of antibodies to Toxoplasma gondii in oral fluid from pigs

Toxoplasma gondii-infected pigs play a major role as a source of infection for humans and detection of high-risk herds is essential to implement control measures at the farm level. The aim of this study was to determine whether oral fluid (OF) could be used as a matrix to detect antibodies against T. gondii in infected pigs by immunoblot (IB). For this, OF from experimentally inoculated sows (n = 8) (serial samples) and naturally exposed group-housed fatteners (n = 42 groups, one sample/group) were analysed for IgG and IgA against T. gondii-SAG1 antigen by IB. Simultaneously, each animal was serologically tested for anti-T. gondii IgG by ELISA. Specific IgG was detected in the sera of all inoculated sows from 2 to 3 weeks post inoculation (pi) and in 3.4 to 92% of the pigs in 13 out of 42 groups. Experimentally inoculated sows showed positive OF-IB results for IgA (100%) and IgG (87.5%) at 1.5 weeks pi and continued yielding positive results for IgA (87.5-75%) and IgG (50%) until 4 weeks pi; however, from 8 weeks pi the frequency of detection of both isotypes was lower, despite constantly positive IgG values in serum-ELISA. Interestingly, consecutive daily samplings for 4 days at 13 and 30 weeks pi showed inconsistent results for some sows, showing that the antibody concentration in OF is prone to timely variations. Pooled OF from groups with 91 and 92% of seropositive pigs yielded positive IB results for IgG and IgA. Fattener groups with ≤13% of seropositive pigs gave negative IB results to both isotypes. Our results showed that antibodies to T. gondii can be detected in OF from infected pigs, and that IgA seems to be a more adequate target than IgG. Although OF does not seem to be a robust matrix to assess the serological status for T. gondii in individual animals, this diagnostic approach represents an interesting non-invasive, low-cost and animal welfare friendly option as a screening method at the farm level to determine high exposure to T. gondii in the herd.

E2 and Erns isotype-specific antibody responses in serum and oral fluid after infection with classical swine fever virus (CSFV)

Oral fluid sampling for the detection of classical swine fever virus infection provides a relatively inexpensive method for conducting active CSF surveillance. The purpose of this study was to detect CSFV nucleic acid and antibody in serum and oral fluid samples in a group of 10 pigs infected with the moderate CSFV strain, Paderborn. Based on clinical signs, outcome, and other results, pigs were placed into one of three disease outcome groups; Acute, Chronic and Recovered. Oral fluid and serum samples were analyzed for the presence of CSFV nucleic acid along with E2 and E^rns surface protein-specific IgM, IgG and IgA responses. The results were summarized into a timeline of detection events beginning with the appearance of E2-IgM in serum (3 DPI) followed by CSFV nucleic acid in serum (6 DPI), CSFV nucleic acid in oral fluid (8 DPI), E2-IgG in serum (20 DPI), and E2-IgG in oral fluid (24 DPI). The results show that a combination of molecular and serological analyses of oral fluid can be incorporated into CSF surveillance.