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

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.

A Global Perspective on Oral Vaccination of Wildlife against Rabies

The long-term mitigation of human-domestic animal-wildlife conflicts is complex and difficult. Over the last 50 yr, the primary biomedical concepts and actualized collaborative global field applications of oral rabies vaccination to wildlife serve as one dramatic example that revolutionized the field of infectious disease management of free-ranging animals. Oral vaccination of wildlife occurred in diverse locales within Africa, Eurasia, the Middle East, and North America. Although rabies is not a candidate for eradication, over a billion doses of vaccine-laden baits distributed strategically by hand, at baiting stations, or via aircraft, resulted in widespread disease prevention, control, or local disease elimination among mesocarnivores. Pure, potent, safe, and efficacious vaccines consisted of either modified-live, highly attenuated, or recombinant viruses contained within attractive, edible baits. Since the late 1970s, major free-ranging target species have included coyotes (Canis latrans), foxes (Urocyon cinereoargenteus; Vulpes vulpes), jackals (Canis aureus; Lupulella mesomelas), raccoons (Procyon lotor), raccoon dogs (Nyctereutes procyonoides), and skunks (Mephitis mephitis). Operational progress has occurred in all but the latter species. Programmatic evaluations of oral rabies vaccination success have included: demonstration of biomarkers incorporated within vaccine-laden baits in target species as representative of bait contact; serological measurement of the induction of specific rabies virus neutralizing antibodies, indicative of an immune response to vaccine; and most importantly, the decreasing detection of rabies virus antigens in the brains of collected animals via enhanced laboratory-based surveillance, as evidence of management impact. Although often conceived mistakenly as a panacea, such cost-effective technology applied to free-ranging wildlife represents a real-world, One Health application benefiting agriculture, conservation biology, and public health. Based upon lessons learned with oral rabies vaccination of mesocarnivores, opportunities for future extension to other taxa and additional diseases will have far-reaching, transdisciplinary benefits.

Characterization and pathogenicity of a naturally reassortant and recombinant infectious bursal disease virus in China

Infectious bursal disease virus (IBDV), an Avibirnavirus, is the pathogen of infectious bursal disease, which is a severely immunosuppressive disease in 3-15-week-old chickens. Different phenotypes of IBDV, including classical, variant, very virulent (vv) and attenuated IBDV, have been reported in many chicken-rearing countries worldwide. Here, we isolated and identified a naturally reassortant and recombinant IBDV (designated GXB02) from 20-day-old chickens with clinicopathological changes of infectious bursal disease (IBD) in Guangxi Province, China. Whole genomic sequencing showed that the strain GXB02 simultaneously has both reassortant and recombinant characteristics with segments A and B being derived from recombinant intermediate vaccine strain and classic strains of IBDV. Segment A of strain GXB02 was incorporated into the skeleton of an intermediate IBDV vaccine strain (W2512), where the breakpoints of two recombinant events located at nucleotide positions 1468 and 1648 were replaced by reassortant vvIBDV (PK2) and vvIBDV (D6948) of segment A, respectively. We used this GXB02 strain to inoculate 21-day-old specific-pathogen-free chickens to evaluate its pathogenicity. Strain GXB02 has clinicopathologic characteristics of IBD with severe bursal lesions, as evidenced by necrosis, depletion of lymphocytes, and follicle atrophy, indicating that reassortment with classical strains in segment B or/and recombination with very virulent strains increased pathogenicity of the strain GXB02 in chickens. These findings provide important insights into the genetic exchange between classic and attenuated strains of IBDV with two recombinant events occurring at the intermediate derivative segment A with vvIBDV strains, thereby increasing the difficulty of prevention and control of IBD due to novel reassortant-recombinant strains.