Comparison of different inactivation methods on the stability of Indian vaccine strains of foot and mouth disease virus

Protein characterization of an Indonesian isolate of foot and mouth disease virus inactivated with formaldehyde and binary ethylenimine

BACKGROUND AND AIM

Foot-and-mouth disease (FMD) is a highly contagious viral disease of cloven-footed animals. It is a major threat to livestock production worldwide, causing significant economic losses. Inactivation of FMD virus (FMDV) is crucial for vaccine development and control of outbreaks. However, traditional inactivation methods can sometimes damage the viral protein, affecting vaccine efficacy. Therefore, finding new inactivating agents that effectively inactivate the virus while preserving the integrity of its proteins is an important research area. This study investigated the optimal materials (0.04% formaldehyde, 0.001 M binary ethylenimine [BEI], or a combination) for inactivating and preserving the specific molecular weight of Serotype O FMDV protein.

MATERIALS AND METHODS

This study used serotype O FMDV isolated from several areas of East Java. The virus was inoculated into baby hamster kidney-21 cells, and the titer was calculated using the TCID50 Assay. The virus was inactivated using 0.04% formaldehyde, 0.001 M BEI, or a combination of 0.04% formaldehyde and 0.001 M BEI. Inactive viral proteins were characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western blotting.

RESULTS

Serotype O FMDV can be inactivated using 0.04% formaldehyde while preserving specific FMDV proteins, specifically VP0 and VP3 with a molecular weight (MW) of 36 kDa and VP3 with a MW of 24 kDa. Serotype O FMDV can be inactivated by 0.001 M BEI while preserving specific FMDV proteins, specifically VP0 with a MW of 35 kDa, VP3 with a MW of 28 kDa, and VP1 with a MW of 23 kDa. FMDV serotype O can be inactivated using a combination of 0.04% formaldehyde and 0.001 M BEI while preserving specific FMDV proteins, specifically VP0 and VP3 with a MW of 36 kDa and VP3 with a MW of 24 kDa.

CONCLUSION

This study found that 0.04% formaldehyde, alone or in combination with 0.001 M BEI, was effective for inactivating and preserving the specific molecular weight of Serotype O FMDV protein. The limitation of this study was the inactivations of the virus have not yet been tested for their potency on experimental animals. Further research is warranted to investigate the inactivation kinetics of these materials, including their potency on experimental animals. Additionally, a comparison of the inactivation rates between 0.04% formaldehyde alone and the combination with BEI would help to determine the optimal inactivation agent for future applications.

Inactivation of an Indonesian isolate of foot-and-mouth disease virus using formaldehyde

BACKGROUND AND AIM

Foot-and-mouth disease (FMD) is a highly contagious viral disease that endangers livestock and the environment with significant economic consequences. This study aimed to validate the inactivation of the Indonesian isolate of foot-and-mouth disease virus (FMDV) with various formaldehyde concentration.

MATERIALS AND METHODS

The experiment started with FMDV being adapted on BHK-21 cells until cytopathic effects (CPE) appeared. The biological titer of the virus was determined using the 50% tissue culture infectious dose (TCID50) assay. The virus was inactivated by exposing the isolate to different formaldehyde (FA) concentrations (0.025%, 0.05%, 0.1%, and 0.2%) at 37°C for 24 h, and residual infectivity was assessed using CPE scoring of reinoculated BHK-21 cells.

RESULTS

72 h post-inoculation, the virulence of the FMDV isolate was indicated by complete CPE on BHK-21 monolayer cells, with a TCID50 value of 109/mL; CPE scoring did not signify significant differences (p < 0.05) among 0.025%, 0.05%, 0.1%, 0.2% FA, and the negative control. All treatment groups showed significant differences (p < 0.05) from the positive control (C+). FA concentrations inactivated the FMDV isolate under the given conditions. 0.025% and 0.05% FA continued to display CPE through the third passage, while 0.2% FA did not significantly differ from 0.1% FA (p > 0.05). 0.1% FA is the optimal concentration for safely and effectively inactivating FMDV.

CONCLUSION

All of the formaldehyde concentrations can completely inactivate the FMDV isolate, with the most optimal and safe concentration being 0.1%.

Determination of Optimal Antigen Yield and Virus Inactivation Conditions for the Production of the Candidate Foot-and-Mouth Disease Recombinant Vaccine Strain Asia1 Shamir-R in a Bioreactor

Since the foot-and-mouth disease (FMD) outbreak in South Korea in 2010-2011, vaccination policies utilizing inactivated FMD vaccines composed of types O and A have been implemented nationwide. However, because type Asia1 occurred in North Korea in 2007 and intermittently in neighboring countries, the risk of type Asia1 introduction cannot be ruled out. This study evaluated the antigen yield and viral inactivation kinetics of the recombinant Asia1 Shamir vaccine strain (Asia1 Shamir-R). When Asia1 Shamir-R was proliferated in shaking flasks (1 L), a 2 L bioreactor (1 L), and a wave bioreactor (25 L), the antigen yields were 7.5 μg/mL, 5.2 μg/mL, and 3.8 μg/mL, respectively. The optimal FMDV inactivation conditions were 2 mM BEI at 26 °C and 1.0 mM BEI at 37 °C. There was no antigen loss due to BEI treatment, and only a decrease in antigen levels was observed during storage. The sera from pigs immunized with antigen derived from a bioreactor exhibited a neutralizing antibody titer of approximately 1/1000 against Asia1 Shamir and Asia1/MOG/05 viruses; therefore, Asia1 Shamir-R is expected to provide sufficient protection against both viruses. If an FMD vaccine production facility is established, this Asia1 Shamir-R can be employed for domestic antigen banks in South Korea.

Evaluation of Foot-and-Mouth Disease (FMD) Virus Asia1 Genotype-V as an FMD Vaccine Candidate: Study on Vaccine Antigen Production Yield and Inactivation Kinetics

South Korea has experienced outbreaks of foot-and-mouth disease (FMD) of serotypes O and A, leading to nationwide vaccination with a bivalent vaccine. Since the FMD virus (FMDV) Asia1 group-V genotype occurred in North Korea in 2007, an Asia1/MOG/05 vaccine strain belonging to the Asia1 group-V genotype was developed using a genetic recombination method (Asia1/MOG/05-R). This study aimed to evaluate the antigen productivity and viral inactivation kinetics of Asia1/MOG/05-R to assess its commercial viability. The antigen yield of Asia1/MOG/05-R produced in flasks and bioreactors was approximately 4.0 μg/mL. Binary ethylenimine (BEI) inactivation kinetics of Asia1/MOG/05-R showed that 2 mM and 1.0 mM BEI treatment at 26 °C and 37 °C, respectively, resulted in a virus titer <10-7 TCID50/mL within 24 h, meeting the inactivation kinetics criteria. During incubation at 26 °C and 37 °C, 10% antigen loss occurred, but not due to BEI treatment. When pigs were inoculated twice with the Asia1/MOG/05-R antigen, the virus neutralization titer increased to approximately 1:1000; therefore, it can sufficiently protect against Asia1/MOG/05-R and Asia1 Shamir viruses. The Asia1/MOG/05-R will be useful as a vaccine strain for domestic antigen banks.

Efficacy of Binary Ethylenimine in the Inactivation of Foot-and-Mouth Disease Virus for Vaccine Production in South Korea

Foot-and-mouth disease (FMD) vaccines must be produced in a biosafety level 3 facility, so the FMD virus (FMDV) must be completely inactivated after amplification. The inactivation kinetics of FMDV during vaccine antigen production were assessed by evaluating whether the viral titer dropped below 10^-7 TCID₅₀/mL within 24 h of binary ethyleneimine (BEI) treatment. This study dealt with four FMD vaccine candidate strains for the efficacy of BEI treatment at different concentrations and temperatures to determine the optimal inactivation condition of each virus. Two domestic isolates, O/SKR/Boeun/2017 (O BE) and A/SKR/Yeoncheon/2017 (A YC), and two recombinant viruses, PAK/44/2008 (O PA-2) and A22/Iraq/24/64 (A22 IRQ), were investigated. The O BE and A22 IRQ required 2 mM BEI at 26 °C and 0.5 mM BEI at 37 °C for complete inactivation. The O PA-2 and A YC required 2 mM BEI at 26 °C and 1 mM BEI at 37 °C. Crucially, the yield of FMD virus particles (146S) in the viral infection supernatant was higher (>4.0 µg/mL) than those previously reported; additionally, there was little antigen loss, even after 24 h of treatment with 3 mM BEI. Overall, it is considered economical to produce FMD vaccines using these four kinds of viruses; therefore, these candidate strains will be prioritized for the manufacture of FMD vaccines in South Korea.

Full-Length Genomic RNA of Foot-and-Mouth Disease Virus Is Infectious for Cattle by Injection

Safe sample transport is of great importance for infectious diseases diagnostics. Various treatments and buffers are used to inactivate pathogens in diagnostic samples. At the same time, adequate sample preservation, particularly of nucleic acids, is essential to allow an accurate laboratory diagnosis. For viruses with single-stranded RNA genomes of positive polarity, such as foot-and-mouth disease virus (FMDV), however, naked full-length viral RNA can itself be infectious. In order to assess the risk of infection from inactivated FMDV samples, two animal experiments were performed. In the first trial, six cattle were injected with FMDV RNA (isolate A22/IRQ/24/64) into the tongue epithelium. All animals developed clinical disease within two days and FMDV was reisolated from serum and saliva samples. In the second trial, another group of six cattle was exposed to FMDV RNA by instilling it on the tongue and spraying it into the nose. The animals were observed for 10 days after exposure. All animals remained clinically unremarkable and virus isolation as well as FMDV genome detection in serum and saliva were negative. No transfection reagent was used for any of the animal inoculations. In conclusion, cattle can be infected by injection with naked FMDV RNA, but not by non-invasive exposure to the RNA. Inactivated FMDV samples that contain full-length viral RNA carry only a negligible risk of infecting animals.

Validation of a binary ethylenimine (BEI) inactivation procedure for biosafety treatment of foot-and-mouth disease viruses (FMDV), vesicular stomatitis viruses (VSV), and swine vesicular disease virus (SVDV)

Binary ethylenimine (BEI) has been widely used as a virucide to inactivate viruses. For regulatory exclusion of a select agent, the United States Federal Select Agent Program (FSAP) requires an inactivation procedure that renders a select agent non-viable but allows the select agent to retain antigenic characteristics for future use must be validated, and the inactivated agent must be confirmed by a viability testing. In this curve-based validation study, we examined impacts of BEI concentration, treatment temperature, and time on our in-house inactivation procedures of Foot-and-Mouth Disease Virus (FMDV), Vesicular Stomatitis Virus (VSV), and Swine Vesicular Disease Virus (SVDV). The inactivation efficacy was confirmed by virus titration and 3 consecutive blind passages on the monolayers of susceptible cells. A linear correlation between the virus titer reduction and BEI concentration, treatment time, and temperature was established. The results confirmed our in-house BEI inactivation procedure of two doses of 1.5 mM BEI treatment at 37 °C, 1st dose for 24 h, then 2nd dose for 6 more hours for a total of 30 h BEI contact time, can ensure complete inactivation of FMDV, VSV, and SVDV.

An effective inactivant based on singlet oxygen-mediated lipid oxidation implicates a new paradigm for broad-spectrum antivirals

Emerging viral pathogens cause substantial morbidity and pose a severe threat to health worldwide. However, a universal antiviral strategy for producing safe and immunogenic inactivated vaccines is lacking. Here, we report an antiviral strategy using the novel singlet oxygen (¹O₂)-generating agent LJ002 to inactivate enveloped viruses and provide effective protection against viral infection. Our results demonstrated that LJ002 efficiently generated ¹O₂ in solution and living cells. Nevertheless, LJ002 exhibited no signs of acute toxicity in vitro or in vivo. The ¹O₂ produced by LJ002 oxidized lipids in the viral envelope and consequently destroyed the viral membrane structure, thus inhibiting the viral and cell membrane fusion necessary for infection. Moreover, the ¹O₂-based inactivated pseudorabies virus (PRV) vaccine had no effect on the content of the viral surface proteins. Immunization of mice with LJ002-inactiviated PRV vaccine harboring comparable antigen induced more neutralizing antibody responses and efficient protection against PRV infection than conventional formalin-inactivated vaccine. Additionally, LJ002 inactivated a broad spectrum of enveloped viruses. Together, our results may provide a new paradigm of using broad-spectrum, highly effective inactivants functioning through ¹O₂-mediated lipid oxidation for developing antivirals that target the viral membrane fusion process.

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LJ002 efficiently generates ¹O₂ in solution and living cells.

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LJ002 oxidizes lipids in the viral envelope, thus inhibiting fusion between the virus and cell membrane.

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LJ002-inactivated PRV vaccine has no effect on the content of antigens on the viral surface.

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LJ002-inactivated PRV vaccine elicits a strong neutralizing antibody response.

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LJ002 can inactivate a broad spectrum of enveloped viruses.

In vitro antiviral efficacy of pleconaril and ribavirin on foot-and-mouth disease virus replication

Antiviral therapy is a promising strategy to control acute viral infections. FMDV causes an acute infection and the vaccination provides a protective immunity 7 days post immunization. If the infection is uncontained, then it affects the entire herd. In such circumstances, if antiviral drug is administered the infection can be checked in a herd. Ribavirin is known to cure persistently infected BHK21 cells with FMD virus. However, there have been no systematic studies on antiviral activity of ribavirin against FMDV at different time points with the application of ELISA, PCR or real-time PCR. Pleconaril is known to inhibit enteroviruses and rhinoviruses but has not been explored on FMDV. Hence, the present study evaluates the in vitro antiviral efficacy of pleconaril and ribavirin on FMDV replication. The maximum non-toxic concentrations (MNTC) of pleconaril and ribavirin for BHK21 cells respectively were 7.81 μg/50 μL and 15.62 μg/50 μL. Thus, drug concentrations below MNTC were tested for their antiviral activity against serial tenfold diluted FMDV O, A and Asia 1 serotypes. Pleconaril did not inhibit FMDV serotype O replication at 7.5 μg/50 μL based on CPE inhibition assay and this was further confirmed using sandwich ELISA, PCR/real-time PCR. On the other hand, ribavirin at 15.62 μg/50 μL inhibited the in vitro replication of FMDV O, A and Asia 1 and the inhibition was confirmed by serotype specific sandwich ELISA, PCR and real-time PCR assays. The inhibition was directly proportional to the concentration of ribavirin. Therefore, ribavirin could be explored for its in vivo efficacy as a potential therapeutic in the prevention of early spread of FMDV infection in a herd.

The efficacy of binary ethylenimine-inactivated vaccines of Gianyar-1/AK/2014 virulent strain in protecting chickens against Tabanan-1/ARP/2017 virulent Newcastle disease virus isolates

AIM

This study aimed to prepare binary ethylenimine (BEI)-inactivated virulent Newcastle disease virus (NDV) vaccine and to examine their ability to induce a protective antibody response in commercial chickens.

MATERIALS AND METHODS

A virulent NDV field isolate Gianyar-1/AK/2014 was propagated in chicken-embryonated eggs and was then inactivated with BEI at a concentration of 4 mM. Three groups of chickens with low-level (2 log2 hemagglutination inhibition [HI] units) maternally derived antibodies against NDV were then immunized with the BEI-inactivated vaccine. A commercial live vaccine (LaSota strain) was used as positive control, and phosphate-buffered saline (PBS) was used as negative control. A challenge experiment with a virulent NDV of Tabanan-1/ARP/2017 was performed at 3 weeks post-vaccination.

RESULTS

At 2 weeks post-immunization, the mean titers of antibodies against NDV in serum samples of chickens immunized with 0.2 mL of BEI-inactivated NDV (Group I), with live commercial NDV vaccine (Group II) and with PBS (Group III) were 3±0.94 log2 HI units, 4.9±0.99 log2 HI unit, and 0.0±0.0 HI units, respectively. At week 3 post-immunization, the mean titers of the antibodies for the three groups were 5±1.09 log2 HI units, 6.9±0.32 log2 HI units, and 0.00 HI units, respectively. The antibody titer induced by inactivated NDV Gianyar-1/AK/2014 isolates examined at 2 and 3 weeks post-vaccination was still at a significantly (p<0.01) lower level as compared to those induced by commercial life vaccine. However, the challenge test with virulent NDV of Tabanan 1/ARP/2017 isolates showed that all immunized chickens (Group I and II) survived without exhibiting any clinical sign post-challenge with the protection rates of 100%, whereas all chickens injected with PBS (Group III) died with clinical signs of ND.

CONCLUSION

This finding shows that the BEI-inactivated vaccines prepared using virulent NDV of Gianyar-1/AK/2014 strain was able to induce protective antibody response in chickens but still at a lower level than those induce by commercial live NDV vaccine.