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

Abstract

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 10^5.0 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.

Keywords: Bait; ERAGS-GFP; Immunologyy; Rabies; Raccoon dogs.

Fig. 1. Formulation of the ERAGS-GFP bait vaccine: approximately 20 g of the ERAGS-GFP bait vaccine is sealed within a polyethylene film sachet and is placed inside a rectangular block (27 mm × 27 mm × 12 mm).

ERAGS-GFP, recombinant rabies virus expressing green fluorescent protein.

Fig. 2. Identification of the nucleotide sequence of the rabies virus G gene of the ERAGS-GFP strain that has undergone 5 back passages in mice. The nucleotide sequences (TCC, 637-639, GAA, 1054-1056) corresponding to 2 amino acids of the G gene associated with the pathogenicity of the rabies virus remained unchanged even after 5 back passages.

G, glycoprotein; ERAGS-GFP, recombinant rabies virus expressing green fluorescent protein.

Fig. 3. Determination of the minimum effective dose of the ERAGS-GFP strain in polyethylene film bag.

ERAGS-GFP, recombinant rabies virus expressing green fluorescent protein; VNA, virus neutralizing antibody; TCID₅₀, 50% tissue culture infectious dose. ^*p<0.05.

Fig. 4. Comparison of the uptake rate of the two types of rabies bait vaccines administered to raccoon dogs.

ERAGS-GFP, recombinant rabies virus expressing green fluorescent protein; V-RG, rabies virus glycoprotein gene.

Fig. 5. Immunogenicity (A) and duration of immunity (B) after administration of two types of the rabies bait vaccine to raccoon dogs.

^*p<0.02, ^**p<0.05.