Improved immune responses and safety of foot-and-mouth disease vaccine containing immunostimulating components in pigs

Background@#The quality of a vaccine depends strongly on the effects of the adjuvants applied simultaneously with the antigen in the vaccine. The adjuvants enhance the protective effect of the vaccine against a viral challenge. Conversely, oil-type adjuvants leave oil residue inside the bodies of the injected animals that can produce a local reaction in the muscle. The longterm immunogenicity of mice after vaccination was examined. ISA206 or ISA15 oil adjuvants maintained the best immunity, protective capability, and safety among the oil adjuvants in the experimental group. @*Objectives@#This study screened the adjuvant composites aimed at enhancing foot-andmouth disease (FMD) immunity. The C-type lectin or toll-like receptor (TLR) agonist showed the most improved protection rate. @*Methods@#Experimental vaccines were fabricated by mixing various known oil adjuvants and composites that can act as immunogenic adjuvants (gel, saponin, and other components) and examined the enhancement effect on the vaccine. @*Results@#The water in oil (W/O) and water in oil in water (W/O/W) adjuvants showed better immune effects than the oil in water (O/W) adjuvants, which have a small volume of oil component. The W/O type left the largest amount of oil residue, followed by W/O/W and O/W types. In the mouse model, intramuscular inoculation showed a better protection rate than subcutaneous inoculation. Moreover, the protective effect was particularly weak in the case of inoculation in fatty tissue. The initial immune reaction and persistence of long-term immunity were also confirmed in an immune reaction on pigs. @*Conclusions@#The new experimental vaccine with immunostimulants produces improved immune responses and safety in pigs than general oil-adjuvanted vaccines.

Stable Expression of Bovine Integrin Beta-6 Increases Susceptibility of Goat Kidney Cell Line to Foot-and-mouth Disease Virus

The integrins αvβ1, αvβ3, αvβ6, and αvβ8 are known to be the natural receptors of foot-and-mouth disease virus (FMDV). Among them, integrin αvβ6 is considered a major receptor for FMDV. We performed protein expression of full-length bovine integrins αv, β3, and β6 and confirmed the high efficiency of bovine αvβ6 as the FMDV receptor in FMDV non-permissive SW 480 cells. Next, we established the black goat kidney (BGK) cell line, stably expressing bovine integrin β6 (BGK-β6-4). We observed that BGK-β6-4 cells had significantly enhanced sensitivity to FMDV compared with that of BGK cells (P<0.05). In addition, BGK-β6-4 cells had equal or higher sensitivity to several serotypes of FMDV compared with that of other FMDV permissive cell lines, such as BHK-21 and IBRS-2. In conclusion, we established a promising novel goat cell line, BGK-β6-4, which can be used to isolate or culture FMDV. Furthermore, the BGK-β6-4 cell line may serve as a promising tool for studying integrin αvβ6 receptor functions.

New foot-and-mouth disease vaccine, O JC-R, induce complete protection to pigs against SEA topotype viruses occurred in South Korea, 2014–2015

Foot-and-mouth disease (FMD) is an acute epidemic that spreads rapidly among cattle and pigs. In 2014, in Korea, despite enforced vaccination, the type O Southeast Asia (SEA) topotype viruses (Mya-98 lineage) infected mainly cattle and pigs simultaneously, thereby causing enormous damage. If a vaccine that is completely protective against this FMD virus is developed and used, it can become a very important preventive measure in Asia, which is where this type of virus mainly circulates. The SEA topotype has been steadily evolving and transforming into new variations since it became epidemic in Asia. Therefore, it became necessary to develop a new vaccine that could provide protection against the FMD virus strain that was responsible for the 2014–2015 outbreak in Korea. This study aimed to develop a vaccine that would provide complete protection against the SEA topotype FMD virus to control sporadic FMD outbreaks, which occur despite the enforcement of vaccination, and to completely prevent virus shedding, thereby preventing the virus from spreading. The vaccine candidate virus developed in this study showed low pathogenicity and can be distinguished from the wild-type FMD virus strain. The developed vaccine was able to protect mice from SEA and Middle East–South Asia topotype virus strains and induced high titers of antibodies against both virus strains in pigs, thereby confirming the sufficiency of its protective function. In particular, the results of the SEA topotype virus challenge test in pigs revealed that perfect immunity was created in the vaccinated pigs, without virus shedding and viremia.

Needleless intradermal vaccination for foot-and-mouth disease induced granuloma-free effective protection in pigs

Vaccination is one of the most effective ways of controlling and preventing foot-and-mouth disease (FMD) outbreaks. The effective prevention of this disease requires the use of high-quality vaccines to meet the criteria that enable customers to use them simply. The administration of FMD vaccines containing oil-based adjuvants in pigs can induce the formation of granuloma in the muscle of the vaccinated, which makes these vaccines a less preferable option. Therefore, it is important to establish an FMD vaccine and vaccine delivery tool that offers better immunity and safer application. This study compared the immune responses of intramuscular and needleless intradermal vaccination in pigs. When the same amount of an FMD virus (FMDV) antigen was administered to pigs, both the intradermally and intramuscularly vaccinated groups were protected completely against a challenge of the homologous FMDV, but the intramuscularly vaccinated group showed an overall higher level of neutralizing antibodies. Importantly, the formation of granuloma in muscle could be excluded in the intradermally vaccinated group. Of the oil-based adjuvants selected in this study, ISA 207 was effective in eliciting immunogenicity in intradermal vaccination. In conclusion, a new vaccine formula can be chosen for the delivery of intradermal route to exclude the possibility of local reactions in the muscle and generate protective immunity against an FMDV challenge.

Synergistic effect of ribavirin and vaccine for protection during early infection stage of foot-and-mouth disease

In many countries, vaccines are used for the prevention of foot-and-mouth disease (FMD). However, because there is no protection against FMD immediately after vaccination, research and development on antiviral agents is being conducted to induce protection until immunological competence is produced. This study tested whether well-known chemicals used as RNA virus treatment agents had inhibitory effects on FMD viruses (FMDVs) and demonstrated that ribavirin showed antiviral effects against FMDV in vitro/in vivo. In addition, it was observed that combining the administration of the antiviral agents orally and complementary therapy with vaccines synergistically enhanced antiviral activity and preserved the survival rate and body weight in the experimental animals. Antiviral agents mixed with an adjuvant were inoculated intramuscularly along with the vaccines, thereby inhibiting virus replication after injection and verifying that it was possible to induce early protection against viral infection prior to immunity being achieved through the vaccine. Finally, pigs treated with antiviral agents and vaccines showed no clinical signs and had low virus excretion. Based on these results, it is expected that this combined approach could be a therapeutic and preventive treatment for early protection against FMD.

Control of type O foot-and-mouth disease by vaccination in Korea, 2014–2015

On December 3, 2014, a type O foot-and-mouth disease (FMD) outbreak began in Korea. Although vaccinations were administered, FMD cases increased steadily for five months, and reached 185 cases by April 2015. Most of the affected animals were pigs, which are vulnerable to vaccination. The FMD virus belonged to the South-East Asia (SEA) topotype that had been observed three times in Korea between April 2010 and July 2014. However, the FMD virus isolated in December 2014 had a unique feature; that is, partial deletion of the 5′ non-coding region, a deletion not seen in previous SEA topotype isolates identified in Korea. We conclude that this outbreak included the introduction of a new FMD strain to Korea, and that Korea was now affected by genetically similar FMD virus strains that are related to those from neighboring countries.

Immune responses in pigs and cattle vaccinated with half-volume foot-and-mouth disease vaccine

With the current commercial foot-and-mouth disease vaccine, inoculating twice increases the formation of denatured meat due to granuloma or residual adjuvant at the injection site in pigs, resulting in economic loss. Therefore, we investigated protective antibody levels after reducing the amount of adjuvant in the vaccine. Field applicability of the experimental vaccine, made with a new adjuvant ISA 201, was tested by vaccinating farm animals with half-volume doses (1 mL/animal) of commercial vaccine and monitoring their immunogenicity. Among pigs, the group that received a half-volume dose showed similar or higher titers of structural protein antibody and neutralizing antibody than those receiving the standard dose (2 mL). In pigs, the durable effects of antibody titer of the reduced vaccine volume did not diminish up to the time of slaughter. Among cattle, boosting with a second 1 mL vaccine increased virus neutralizing antibody for the protective effects. The boosting effects were more marked in cattle than in pigs. The immune responses differed between species with the effect of the half-volume vaccination being lower in cattle than in pigs. In conclusion, the immune response to the half-volume vaccine was similar to that from the standard volume vaccine in pigs, but not in cattle.

Novel foot-and-mouth disease virus in Korea, July-August 2014

Despite nation-wide immunization with O, A, and Asia 1 type vaccines in Republic of Korea, foot-and-mouth disease type O occurred again in July 2014 after three years and three months. This virus was a Mya-98 strain of the Southeast Asian topotype and was most similar to the identified type that circulated in East Asia in 2014. This was new virus with the deletion of 23 amino acids in 3A/3B1 region and low pathogenic property.

Antigenic properties and virulence of foot-and-mouth disease virus rescued from full-length cDNA clone of serotype O, typical vaccine strain

We cloned the full-length cDNA of O Manisa, the virus for vaccinating against foot-and-mouth disease. The antigenic properties of the virus recovered from the cDNA were similar to those of the parental virus. Pathogenesis did not appear in the pigs, dairy goats or suckling mice, but neutralizing antibodies were raised 5-6 days after the virus challenge. The utilization of O Manisa as a safe vaccine strain will increase if recombinant viruses can be manipulated by inserting or removing a marker gene for differential serology or replacing the protective gene from another serotype.

Human Adenovirus Type 5 as a Delivery Vector is Not Neutralized in Field Serum Samples of Cattle, Pig, and Goat of Republic of Korea

Human adenovirus type 5 (hAd5) vectors have been demonstrated to be useful vehicles for gene expressions in animals. However, it has not been reported whether hAd5 transduction might be hampered in the sera of livestock animals in Republic of Korea. We collected 205 samples of livestock animals, such as pig (n=84), cattle (n=84), and goat (n=37) in Korea. The neutralizing antibody (NAb) titers to hAd5 virus were less than 15 in most of samples. Only 8% of goat samples had a NAb titer of 15 or 30. Thus, we showed that hAd5 virus was not neutralized in sera from cattle, pig, and goat, and suggest that the hAd5 vector could be used for the effective delivery of vaccines or proteins in livestock animals in the field.

Genetic diversity of porcine reproductive and respiratory syndrome virus in Korea

The high genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) has been an obstacle to developing an effective vaccine for porcine reproductive and respiratory syndrome (PRRS). This study was performed to assess the degree of genetic diversity among PRRSVs from Korean pig farms where wasting and respiratory syndrome was observed from 2005 to 2009. Samples from 786 farms were tested for the presence of PRRSV using reverse transcription PCR protocol. A total of 117 farms were positive for type 1 PRRSV while 198 farms were positive for type 2. Nucleotide sequences encoding the open reading frame (ORF) 5 were analyzed and compared to those of various published PRRSV isolates obtained worldwide. Sequence identity of the ORF 5 in the isolates was 81.6~100% for type 1 viruses and 81.4~100% for type 2 viruses. Phylogenetic analysis of the ORF 5 sequences showed that types 1 and 2 PRRSVs from Korea were mainly classified into three and four clusters, respectively. The analyzed isolates were distributed throughout the clusters independent of the isolation year or geographical origin. In conclusion, our results indicated that the genetic diversity of PRRSVs from Korean pig farms is high and has been increasing over time.

Adenovirus Expressing Human Interferon Inhibits Replication of Foot and Mouth Disease Virus and Reduces Fatal Rate in Mice

Interferon is an important cytokine that plays a critical role in the initial host defense against viral infection. Recombinant human adenoviruses expressing human interferon-alpha (Ad-HIFNalpha) or pig interferon-beta fused with interleukin-18 (Ad-PIFNbeta-IL18) were constructed and used to induce an early protective response against foot and mouth disease (FMD). To analyze the antiviral effect, bovine thyroid and porcine kidney IBRS-2 cells and ICR mice were treated with Ad-HIFNalpha, Ad-PIFNbeta-IL18, and cocktail of Ad-HIFNalpha and Ad-PIFNbeta-IL18. The survival rate of suckling mice was monitored after foot and mouth disease virus (FMDV) challenge following intra-peritoneal (IP) administration of appropriate adenovirus. Indirect antigen ELISA was performed to evaluate inhibition of FMDV replication following challenge with the FMDV O, A, or Asia 1 serotypes in vitro. These recombinant adenoviruses reduced the replication of FMDV in susceptible cells, thereby decreasing the fatality in mice, suggesting that they can be a useful control method for the early protection against FMD infection in livestock after field trial.

Serosurveillance for Japanese encephalitis virus in wild birds captured in Korea

Climate change induced by recent global warming may have a significant impact on vector-borne and zoonotic diseases. For example, the distribution of Japanese encephalitis virus (JEV) has expanded into new regions. We surveyed the levels of hemagglutination-inhibition (HI) antibodies against JEV (Family Flaviviridae, genus Flavivirus) in wild birds captured in Korea. Blood samples were collected from 1,316 wild birds including the following migratory birds: Oceanodroma castro (n = 4), Anas formosa (n = 7), Anas penelope (n = 20), Fulica atra (n = 30), Anas acuta (n = 89), Anas crecca (n = 154), Anas platyrhynchos (n = 214), Aix galericulata (n = 310), and Anas poecilorhyncha (n = 488). All were captured in 16 locations in several Korea provinces between April 2007 and December 2009. Out of the 1,316 serum samples tested, 1,141 (86.7%) were positive for JEV. Wild birds captured in 2009 had a higher seroprevalence of ant-JEV antibodies than those captured in 2007. Wild birds with an HI antibody titer of 1 : 1,280 or higher accounted for 21.2% (280/1,316) of the animals tested. These findings indicated that wild birds from the region examined in our study have been exposed to JEV and may pose a high risk for introducing a new JEV genotype into Korea.

Selection of a Less Pathogenic BVDV Strain for the Construction of Avirulent Chimeric Pestivirus

To select a less pathogenic bovine viral diarrhea virus (BVDV) strain for the construction of chimeric pestivirus harboring classical swine fever virus (CSFV) E2 gene, five Korean BVDV isolates (four type 1 isolates and a type 2 isolate) were evaluated for their pathological and biological properties with respect to porcine infection. Each of five groups of 100-day-old pigs was inoculated intranasally with one of the five BVDV isolates. No clinical sign or leukopenia was observed in any pig throughout the duration of the experiment, but viruses were detected in blood, nasal discharges and postmortem samples using RT-PCR. These results indicated that although the five BVD viruses could infect pigs, they did not cause clinically apparent symptoms. Because of its proper infection dynamics shown in this preliminary animal study and its fast growth rate and quick CPE in cell culture, one isolate (KD26-1) was chosen among the five isolates to test its virulence and immunogenic properties in 40-day-old piglets. Neither clinical sign nor pathological lesion was observed in 40-day-old piglets during the course of infection of isolate KD26-1. The first neutralizing antibodies were detectable 14 days post-inoculation (PI) and increased to 1:128~1:256 28 days PI. A BVDV specific gene was detectable by RT-PCR in tonsil, spleen, inguinal lymph node and brain until 14 days PI. According to this study, it can be concluded that isolate KD26-1 has little pathological effect in pigs and is a candidate for construction of chimeric pestivirus harboring CSFV E2 gene.

Selection of a Less Pathogenic BVDV Strain for the Construction of Avirulent Chimeric Pestivirus

To select a less pathogenic bovine viral diarrhea virus (BVDV) strain for the construction of chimeric pestivirus harboring classical swine fever virus (CSFV) E2 gene, five Korean BVDV isolates (four type 1 isolates and a type 2 isolate) were evaluated for their pathological and biological properties with respect to porcine infection. Each of five groups of 100-day-old pigs was inoculated intranasally with one of the five BVDV isolates. No clinical sign or leukopenia was observed in any pig throughout the duration of the experiment, but viruses were detected in blood, nasal discharges and postmortem samples using RT-PCR. These results indicated that although the five BVD viruses could infect pigs, they did not cause clinically apparent symptoms. Because of its proper infection dynamics shown in this preliminary animal study and its fast growth rate and quick CPE in cell culture, one isolate (KD26-1) was chosen among the five isolates to test its virulence and immunogenic properties in 40-day-old piglets. Neither clinical sign nor pathological lesion was observed in 40-day-old piglets during the course of infection of isolate KD26-1. The first neutralizing antibodies were detectable 14 days post-inoculation (PI) and increased to 1:128~1:256 28 days PI. A BVDV specific gene was detectable by RT-PCR in tonsil, spleen, inguinal lymph node and brain until 14 days PI. According to this study, it can be concluded that isolate KD26-1 has little pathological effect in pigs and is a candidate for construction of chimeric pestivirus harboring CSFV E2 gene.