A genetically modified rabies vaccine (ERAGS) induces protective immunity in dogs and cattle

Protective antibody response in Korean raccoon dogs (Nyctereutes procynoide koreensis) administered a new rabies bait vaccine containing the ERAGS-GFP strain

Purpose

Rabies is a deadly zoonotic disease affecting many mammals, including humans. Oral rabies bait vaccines induce an immune response without direct inoculation, and are crucial for controlling rabies in wildlife. This study evaluated the safety and immunogenicity of a new rabies bait vaccine containing a recombinant rabies virus expressing green fluorescent protein (ERAGS-GFP) in wild raccoon dogs.

Materials and Methods

To confirm the safety of the ERAGS-GFP vaccine, reversion to virulence was evaluated in 1-day-old suckling mice. The uptake, minimum effective dose, and immunogenicity of the bait vaccine were assessed in raccoon dogs, as was the persistence of post-vaccine immunity. Serum rabies virus neutralizing antibody (VNA) titers were measured using fluorescent antibody virus neutralization.

Results

No adverse effects were noted in mice, guinea pigs, dogs, or raccoon dogs administered the ERAGS-GFP vaccine orally during the test period. The glycoprotein gene of the ERAGS-GFP strain remained unchanged after five reverse passages in 1-day-old mice. Uptake of the bait vaccine was 75.8% in raccoon dogs. The minimum effective dose was at least 105.0 TCID50/mL. Forty-three raccoon dogs administered the ERAGS-GFP bait vaccine developed an average VNA titer of 4.23 IU/mL 28 days post-administration. Protective antibody levels were maintained for 4 months.

Conclusion

The ERAGS-GFP bait vaccine showed high uptake and strong immunogenicity in raccoon dogs, and protective antibody levels were maintained for at least 4 months. These results indicate the vaccine's potential for effective rabies control in wildlife, which can reduce the risk of transmission to humans and domestic animals.

The roles of rabies virus structural proteins in immune evasion and implications for vaccine development

Rabies is a zoonotic infectious disease that targets the nervous system of human and animals and has about 100% fatality rate without treatment. Rabies virus is a bullet-like viral particle composed of five structural proteins, including nucleoprotein (N), phosphorylated protein (P), matrix protein (M), glycoprotein (G), and large subunit (L) of RNA-dependent RNA polymerase. These multifunctional viral proteins also play critical roles in the immune escape by inhibiting specific immune responses in the host, resulting in massive replication of the virus in the nervous system and abnormal behaviors of patients such as brain dysfunction and hydrophobia, which ultimately lead to the death of patients. Herein, the role of five structural proteins of rabies virus in the viral replication and immune escape and its implication for the development of vaccines were systemically reviewed, so as to shed light on the understanding of pathogenic mechanism of rabies virus.

Whole-Cell Vaccine Preparation: Options and Perspectives

Vaccines are biological preparations to elicit a specific immune response in individuals against the targetted microorganisms. The use of vaccines has caused the near eradication of many critical diseases and has had an everlasting impact on public health at a relatively low cost. Most of the vaccines developed today are based on techniques which were developed a long time ago. In the beginning, vaccines were prepared from tissue fluids obtained from infected animals or people, but at present, the scenario has changed with the development of vaccines from live or killed whole microorganisms and toxins or using genetic engineering approaches. Considerable efforts have been made in vaccine development, but there are still many diseases that need attention, and new technologies are being developed in vaccinology to combat them. In this chapter, we discuss different approaches for vaccine development, including the properties and preparation of whole-cell vaccines.

Generation of a recombinant rabies virus expressing green fluorescent protein for a virus neutralization antibody assay

BACKGROUND

Fluorescent antibody virus neutralization (FAVN) test is a standard assay for quantifying rabies virus-neutralizing antibody (VNA) in serum. However, a safer rabies virus (RABV) should be used in the FAVN assay. There is a need for a new method that is economical and time-saving by eliminating the immunostaining step.

OBJECTIVES

We aimed to improve the traditional FAVN method by rescuing and characterizing a new recombinant RABV expressing green fluorescent protein (GFP).

METHODS

A new recombinant RABV expressing GFP designated as ERAGS-GFP was rescued using a reverse genetic system. Immuno-fluorescence assay, peroxidase-linked assay, electron microscopy and reverse transcription polymerase chain reaction were performed to confirm the recombinant ERAGS-GFP virus as a RABV expressing the GFP gene. The safety of ERAGS-GFP was evaluated in 4-week-old mice. The rabies VNA titers were measured and compared with conventional FAVN and FAVN-GFP tests using VERO cells.

RESULTS

The virus propagated in VERO cells was confirmed as RABV expressing GFP. The ERAGS-GFP showed the highest titer (10^8.0 TCID₅₀/mL) in VERO cells at 5 days post-inoculation, and GFP expression persisted until passage 30. The body weight of 4-week-old mice inoculated intracranially with ERAGS-GFP continued to increase and the survival rate was 100%. In 62 dog sera, the FAVN-GFP result was significantly correlated with that of conventional FAVN (r = 0.95).

CONCLUSIONS

We constructed ERAGS-GFP, which could replace the challenge virus standard-11 strain used in FAVN test.

Strategies to maintain Korea's animal rabies non-occurrence status

Endemic animal rabies causes >99% of all human rabies cases; elimination of animal rabies reduces the rate of human infections. The most recent animal rabies cases in the Gangwon and Gyeonggi provinces of Korea occurred in November 2012 and February 2013, respectively. Here we explore ways to ensure that Korea remains animal rabies non-occurrence. The government must prevent rabies recurrence by vaccinating dogs, distributing bait vaccine in regions with a high rabies risk, performing laboratory-based surveillance, preventing the flow of rabies-suspect animals from neighboring countries, and enhancing border quarantine. As has already been shown in several developed countries, careful and ongoing rabies control will allow Korea to remain animal rabies-free.