Utilisation of Chimeric Lyssaviruses to Assess Vaccine Protection against Highly Divergent Lyssaviruses

Taiwan Bat Lyssavirus: In Vitro and In Vivo Assessment of the Ability of Rabies Vaccine-Derived Antibodies to Neutralise a Novel Lyssavirus

Rabies is a neglected tropical disease. The prototype virus, the rabies virus, still causes tens of thousands of human fatalities annually. Rabies is one member of the genus Lyssavirus. The burden of other lyssaviruses is unclear. The continued emergence of novel lyssaviruses means that assessment of vaccine efficacy against these viruses is critical, as standard rabies vaccines are not efficacious against all lyssaviruses. Taiwan bat lyssavirus (TWBLV) was first reported in 2018 following isolation from Japanese house bats. Since the initial detection and genetic characterisation, no attempts have been made to antigenically define this virus. Due to the inaccessibility of the wildtype isolate, the successful generation of a live recombinant virus, cSN-TWBLV, is described, where the full-length genome clone of the RABV vaccine strain, SAD-B19, was constructed with the glycoprotein of TWBLV. In vitro and in vivo characterization of cSN-TWBLV was undertaken and demonstrated evidence for cross-neutralisation of cSN-TWBLV with phylogroup I -specific sera and rabies virus standard sera. For neutralisation equivalent to 0.5 IU/mL of WHO and World Organisation of Animal Health (WOAH) sera against CVS, 0.5 IU/mL of WOAH sera and 2.5 IU/mL of WHO sera were required to neutralise cSN-TWBLV. In addition, specific sera for ARAV and EBLV-1 exhibited the highest neutralising antibody titres against cSN-TWBLV, compared to other phylogroup I-specific sera.

Bat and Lyssavirus Exposure among Humans in Area that Celebrates Bat Festival, Nigeria, 2010 and 2013

Using questionnaires and serologic testing, we evaluated bat and lyssavirus exposure among persons in an area of Nigeria that celebrates a bat festival. Bats from festival caves underwent serologic testing for phylogroup II lyssaviruses (Lagos bat virus, Shimoni bat virus, Mokola virus). The enrolled households consisted of 2,112 persons, among whom 213 (10%) were reported to have ever had bat contact (having touched a bat, having been bitten by a bat, or having been scratched by a bat) and 52 (2%) to have ever been bitten by a bat. Of 203 participants with bat contact, 3 (1%) had received rabies vaccination. No participant had neutralizing antibodies to phylogroup II lyssaviruses, but >50% of bats had neutralizing antibodies to these lyssaviruses. Even though we found no evidence of phylogroup II lyssavirus exposure among humans, persons interacting with bats in the area could benefit from practicing bat-related health precautions.

Assessing Rabies Vaccine Protection against a Novel Lyssavirus, Kotalahti Bat Lyssavirus

Rabies is a fatal encephalitis caused by an important group of viruses within the Lyssavirus genus. The prototype virus, rabies virus, is still the most commonly reported lyssavirus and causes approximately 59,000 human fatalities annually. The human and animal burden of the other lyssavirus species is undefined. The original reports for the novel lyssavirus, Kotalahti bat lyssavirus (KBLV), were based on the detection of viral RNA alone. In this report we describe the successful generation of a live recombinant virus, cSN-KBLV; where the full-length genome clone of RABV vaccine strain, SAD-B19, was constructed with the glycoprotein of KBLV. Subsequent in vitro characterisation of cSN-KBLV is described here. In addition, the ability of a human rabies vaccine to confer protective immunity in vivo following challenge with this recombinant virus was assessed. Naïve or vaccinated mice were infected intracerebrally with a dose of 100 focus-forming units/30 µL of cSN-KBLV; all naïve mice and 8% (n = 1/12) of the vaccinated mice succumbed to the challenge, whilst 92% (n = 11/12) of the vaccinated mice survived to the end of the experiment. This report provides strong evidence for cross-neutralisation and cross-protection of cSN-KBLV using purified Vero cell rabies vaccine.

Lyssavirus Vaccine with a Chimeric Glycoprotein Protects across Phylogroups

Rabies is nearly 100% lethal in the absence of treatment, killing an estimated 59,000 people annually. Vaccines and biologics are highly efficacious when administered properly. Sixteen rabies-related viruses (lyssaviruses) are similarly lethal, but some are divergent enough to evade protection from current vaccines and biologics, which are based only on the classical rabies virus (RABV). Here we present the development and characterization of LyssaVax, a vaccine featuring a structurally designed, functional chimeric glycoprotein (G) containing immunologically important domains from both RABV G and the highly divergent Mokola virus (MOKV) G. LyssaVax elicits high titers of antibodies specific to both RABV and MOKV Gs in mice. Immune sera also neutralize a range of wild-type lyssaviruses across the major phylogroups. LyssaVax-immunized mice are protected against challenge with recombinant RABV and MOKV. Altogether, LyssaVax demonstrates the utility of structural modeling in vaccine design and constitutes a broadened lyssavirus vaccine candidate.

Towards rabies elimination in the Asia-Pacific region: From theory to practice

Rabies is a major neglected zoonotic disease and causes a substantial burden in the Asian region. Currently, Pacific Oceania is free of rabies but enzootic areas throughout southeast Asia represent a major risk of disease introduction to this region. On September 25-26, 2019, researchers, government officials and related stakeholders met at an IABS conference in Bangkok, Thailand to engage on the topic of human rabies mediated by dogs. The objective of the meeting was focused upon snowballing efforts towards achieving substantial progress in rabies prevention, control and elimination within Asia by 2030, and thereby to safeguard the Pacific region. Individual sessions focused upon domestic animal, wildlife and human vaccination; the production and evaluation of quality, safety and efficacy of existing rabies biologics; and the future development of new products. Participants reviewed the progress to date in eliminating canine rabies by mass vaccination, described supportive methods to parenteral administration by oral vaccine application, considered updated global and local approaches at human prophylaxis and discussed the considerable challenges ahead. Such opportunities provide continuous engagement on disease management among professionals at a trans-disciplinary level and promote new applied research collaborations in a modern One Health context.

Current status of human rabies prevention: remaining barriers to global biologics accessibility and disease elimination

Introduction: Rabies is a serious, neglected tropical disease. Zoonotic agents are RNA viruses (Genus Lyssavirus, Family Rhabdoviridae), global in distribution. As an acute, progressive, incurable encephalitis, rabies has the highest case fatality of any infectious disease. Warm-blooded vertebrates are susceptible hosts. Major mammalian reservoirs include mesocarnivores and bats. Given wildlife perpetuation, rabies is not eradicable, but is preventable and controllable, especially under newly available international guidelines. Areas covered: Literature review over the past 5 years reveals development of sensitive, specific diagnostic tests and safe and highly effective human and veterinary vaccines. Yet, tens of thousands of human fatalities occur annually, usually in Africa and Asia, primarily after canine exposure. Human and domestic animal vaccination, before or after exposure, is the single greatest preventative strategy following a rabid animal bite. Expert opinion: Significant progress occurred during the twenty-first century regarding vaccine development, doses, and schedules. Remaining barriers to widespread rabies vaccination include an inter-related set of economic, cultural, social, educational, ecological and technological factors. A basic understanding of local and regional root causes of cases historically allows for broader accessibility to vaccination in a trans-disciplinary fashion to meet the global elimination of human rabies caused via dogs (GEHRD) by 2030.

Rabies: Current Preventive Strategies

Desensitization to rabies is a result of successfully eliminating canine rabies in the United States, which occurred in 2007; however, the need for mandatory rabies vaccination in pets remains. Rabies cases are rare in comparison with other vaccine-preventable diseases in companion animals; however, because it is a zoonotic disease with the highest case fatality rate of any infectious disease demands the establishment of strict laws for disease prevention. Preventive strategies include addressing current concerns in consideration of disease surveillance, appropriate vaccination recommendations, and local regulations protecting public health.

Priorities in applied research to ensure programmatic success in the global elimination of canine rabies

The elimination of human rabies mediated by dogs is attainable in concept, based upon current sensitive and specific diagnostic methods, existing safe and effective human and veterinary vaccines and a sound virological, pathological and epidemiological understanding of the disease. Globally, all developed countries achieved this goal. Regionally, major progress occurred throughout the Americas. However, less advancement is evident in Africa and Asia. Our objective was to concentrate upon those salient improvements to extant tools and methods over the next five years which could assist and simplify the task for both those developing countries that have already begun the process, as well as other localities in the earlier stages of consideration. We considered several categories of applied research which could be accomplished in the short term, based upon the available scientific evidence and recent recommendations from subject matter experts and key opinion leaders, focused upon perceived major limitations to prior program success. Areas of concentration included: laboratory-based surveillance, pathogen detection and characterization; human rabies prophylaxis; veterinary biologics; implementation of canine vaccination; and oral vaccination of free-ranging community dogs. Further real-time application in these core areas with proven techniques and technology would simplify attaining not only the global goal focused subtly upon human mortality, but the actual elimination of canine rabies as well.

Foot and mouth disease vaccine strain selection: current approaches and future perspectives

INTRODUCTION

Lack of cross protection between foot and mouth disease (FMD) virus (FMDV) serotypes as well as incomplete protection between some subtypes of FMDV affect the application of vaccine in the field. Further, the emergence of new variant FMD viruses periodically makes the existing vaccine inefficient. Consequently, periodical vaccine strain selection either by in vivo methods or in vitro methods become an essential requirement to enable utilization of appropriate and efficient vaccines.

AREAS COVERED

Here we describe the cross reactivity of the existing vaccines with the global pool of circulating viruses and the putative selected vaccine strains for targeting protection against the two major circulating serotype O and A FMD viruses for East Africa, the Middle East, South Asia and South East Asia.

EXPERT COMMENTARY

Although in vivo cross protection studies are more appropriate methods for vaccine matching and selection than in vitro neutralization test or ELISA, in the face of an outbreak both in vivo and in vitro methods of vaccine matching are not easy, and time consuming. The FMDV capsid contains all the immunogenic epitopes, and therefore vaccine strain prediction models using both capsid sequence and serology data will likely replace existing tools in the future.