Viral vector vaccines protect cockatiels from inflammatory lesions after heterologous parrot bornavirus 2 challenge infection

Negative-Strand RNA Virus-Vectored Vaccines

Vectored RNA vaccines offer a variety of possibilities to engineer targeted vaccines. They are cost-effective and safe, but replication competent, activating the humoral as well as the cellular immune system.This chapter focuses on RNA vaccines derived from negative-strand RNA viruses from the order Mononegavirales with special attention to Newcastle disease virus-based vaccines and their generation. It shall provide an overview on the advantages and disadvantages of certain vector platforms as well as their scopes of application, including an additional section on experimental COVID-19 vaccines.

Experimental pathogenesis of aquatic bird bornavirus 1 in Pekin ducks

Aquatic bird bornavirus 1 (ABBV-1) is a neurotropic virus that causes persistent infection in the nervous system of wild waterfowl. This study evaluated whether Pekin ducks, the most common waterfowl raised worldwide, are susceptible to ABBV-1 infection and associated disease. Groups of Pekin ducks were inoculated with ABBV-1 through the intracranial (IC; n, 32), intramuscular (IM; n, 30), and choanal (CH; n, 30) routes. Controls (CO; n, 29) received carrier only. At 1, 12, and 21 weeks postinfection (wpi), 7-14 birds were euthanized to assess virus distribution and lesions. Infection rates in the IC and IM groups were over 70%, while only 4 ducks in the CH group became infected. Neurological signs were observed in 8 ducks only, while over 25% of IC and IM birds had encephalitis and/or myelitis. Seroconversion was highest in the IC and IM groups, and mucosal ABBV-1 RNA shedding was most frequent in the IC group (53%). None of the fertile eggs laid during the experiment tested positive for ABBV-1 RNA. This study shows that Pekin ducks are permissive to ABBV-1 infection and partly susceptible to associated disease. While mucosal shedding may be an important route of transmission, congenital infection appears unlikely.

Factors Influencing Vertical Transmission of Psittacine Bornavirus in Cockatiels (Nymphicus hollandicus)

The transmission of parrot bornavirus is still not fully understood. Although horizontal transmission through wounds can be one route, vertical transmission is still discussed. PaBV RNA and PaBV antigen were detected in psittacine embryos, but isolation of the virus failed, raising doubts about this route. In this study, cockatiels were infected either as adults (adult group) or during the first 6 days after hatching (juvenile group) and raised until sexual maturity to breed and lay eggs. A total of 92 eggs (adult group: 49, juvenile group: 43) were laid and incubated until day 17. The embryos and yolk samples were examined by RT-PCR for PaBV RNA and by infectivity assay for infectious virus. In the adult group, 14/31 embryos (45.2%) and 20/39 (51%) of the yolk samples demonstrated PaBV RNA in the PCR. Isolation of PaBV was not possible in any embryo of this group, but it was achieved in six yolk samples from one female. Anti-PaBV antibodies were detected in the yolk samples after seroconversion of all female parents. In the juvenile group, 22/29 embryos (74.9%) were positive for PaBV RNA. In 9/21 embryos (42.9%), PaBV isolation was possible. PaBV RNA was detected in 100% and infectious virus in 41% of the yolk samples. Anti-PaBV antibodies were detected in all yolk samples. For the first time, successful vertical transmission of PaBV was proven, but it seems to depend on the age when the parent birds are infected. Therefore, the age of the bird at time of infection may be an important factor in the occurrence of vertical transmission.

Vaccination against Borna Disease: Overview, Vaccine Virus Characterization and Investigation of Live and Inactivated Vaccines

(1) Background: Vaccination of horses and sheep against Borna disease (BD) was common in endemic areas of Germany in the 20th century but was abandoned in the early 1990s. The recent occurrence of fatal cases of human encephalitis due to Borna disease virus 1 (BoDV-1) has rekindled the interest in vaccination. (2) Methods: The full genomes of the BD live vaccine viruses "Dessau" and "Giessen" were sequenced and analyzed for the first time. All vaccination experiments followed a proof-of-concept approach. Dose-titration infection experiments were performed in rabbits, based on both cell culture- and brain-derived viruses at various doses. Inactivated vaccines against BD were produced from concentrated cell culture supernatants and investigated in rabbits and horses. The BoDV-1 live vaccine "Dessau" was administered to horses and antibody profiles were determined. (3) Results: The BD live vaccine viruses "Dessau" and "Giessen" belong to clusters 3 and 4 of BoDV-1. Whereas the "Giessen" virus does not differ substantially from field viruses, the "Dessau" virus shows striking differences in the M gene and the N-terminal part of the G gene. Rabbits infected with high doses of cell-cultured virus developed neutralizing antibodies and were protected from disease, whereas rabbits infected with low doses of cell-cultured virus, or with brain-derived virus did not. Inactivated vaccines were administered to rabbits and horses, following pre-defined vaccination schemes consisting of three vaccine doses of either adjuvanted or nonadjuvanted inactivated virus. Their immunogenicity and protective efficacy were compared to the BD live vaccine "Dessau". Seventy per cent of horses vaccinated with the BD live vaccine "Dessau" developed neutralizing antibodies after vaccination. (4) Conclusion: Despite a complex evasion of immunological responses by bornaviruses, some vaccination approaches can protect against clinical disease. For optimal effectiveness, vaccines should be administered at high doses, following vaccination schemes consisting of three vaccine doses as basic immunization. Further investigations are necessary in order to investigate and improve protection against infection and to avoid side effects.

Pathogenicity of Avian Polyomaviruses and Prospect of Vaccine Development

Polyomaviruses are nonenveloped icosahedral viruses with a double-stranded circular DNA containing approximately 5000 bp and 5–6 open reading frames. In contrast to mammalian polyomaviruses (MPVs), avian polyomaviruses (APVs) exhibit high lethality and multipathogenicity, causing severe infections in birds without oncogenicity. APVs are classified into 10 major species: Adélie penguin polyomavirus, budgerigar fledgling disease virus, butcherbird polyomavirus, canary polyomavirus, cormorant polyomavirus, crow polyomavirus, Erythrura gouldiae polyomavirus, finch polyomavirus, goose hemorrhagic polyomavirus, and Hungarian finch polyomavirus under the genus Gammapolyomavirus. This paper briefly reviews the genomic structure and pathogenicity of the 10 species of APV and some of their differences in terms of virulence from MPVs. Each gene’s genomic size, number of amino acid residues encoding each gene, and key biologic functions are discussed. The rationale for APV classification from the Polyomavirdae family and phylogenetic analyses among the 10 APVs are also discussed. The clinical symptoms in birds caused by APV infection are summarized. Finally, the strategies for developing an effective vaccine containing essential epitopes for preventing virus infection in birds are discussed. We hope that more effective and safe vaccines with diverse protection will be developed in the future to solve or alleviate the problems of viral infection.

Avian Bornavirus Research—A Comprehensive Review

Avian bornaviruses constitute a genetically diverse group of at least 15 viruses belonging to the genus Orthobornavirus within the family Bornaviridae. After the discovery of the first avian bornaviruses in diseased psittacines in 2008, further viruses have been detected in passerines and aquatic birds. Parrot bornaviruses (PaBVs) possess the highest veterinary relevance amongst the avian bornaviruses as the causative agents of proventricular dilatation disease (PDD). PDD is a chronic and often fatal disease that may engulf a broad range of clinical presentations, typically including neurologic signs as well as impaired gastrointestinal motility, leading to proventricular dilatation. It occurs worldwide in captive psittacine populations and threatens private bird collections, zoological gardens and rehabilitation projects of endangered species. In contrast, only little is known about the pathogenic roles of passerine and waterbird bornaviruses. This comprehensive review summarizes the current knowledge on avian bornavirus infections, including their taxonomy, pathogenesis of associated diseases, epidemiology, diagnostic strategies and recent developments on prophylactic and therapeutic countermeasures.

A New Multiplex Real-Time RT-PCR for Simultaneous Detection and Differentiation of Avian Bornaviruses

Avian bornaviruses were first described in 2008 as the causative agents of proventricular dilatation disease (PDD) in parrots and their relatives (Psittaciformes). To date, 15 genetically highly diverse avian bornaviruses covering at least five viral species have been discovered in different bird orders. Currently, the primary diagnostic tool is the detection of viral RNA by conventional or real-time RT-PCR (rRT-PCR). One of the drawbacks of this is the usage of either specific assays, allowing the detection of one particular virus, or of assays with a broad detection spectrum, which, however, do not allow for the simultaneous specification of the detected virus. To facilitate the simultaneous detection and specification of avian bornaviruses, a multiplex real-time RT-PCR assay was developed. Whole-genome sequences of various bornaviruses were aligned. Primers were designed to recognize conserved regions within the overlapping X/P gene and probes were selected to detect virus species-specific regions within the target region. The optimization of the assay resulted in the sensitive and specific detection of bornaviruses of Psittaciformes, Passeriformes, and aquatic birds. Finally, the new rRT-PCR was successfully employed to detect avian bornaviruses in field samples from various avian species. This assay will serve as powerful tool in epidemiological studies and will improve avian bornavirus detection.

Update on Avian Bornavirus and Proventricular Dilatation Disease: Diagnostics, Pathology, Prevalence, and Control

Avian bornavirus (ABV) is a neurotropic virus that can cause gastrointestinal and/or neurologic signs of disease in birds. The disease process is called proventricular dilatation disease (PDD). The characteristic lesions observed in birds include encephalitis and gross dilatation of the proventriculus. ABV is widely distributed in captive and wild bird populations. Most birds infected do not show clinical signs of disease. This article is an update of the Veterinary Clinics of North America article from 2013: Avian Bornavirus and Proventricular Dilatation Disease: Diagnostics, Pathology, Prevalence, and Control.

Update on immunopathology of bornavirus infections in humans and animals

Knowledge on bornaviruses has expanded tremendously during the last decade through detection of novel bornaviruses and endogenous bornavirus-like elements in many eukaryote genomes, as well as by confirmation of insectivores as reservoir species for classical Borna disease virus 1 (BoDV-1). The most intriguing finding was the demonstration of the zoonotic potential of lethal human bornavirus infections caused by a novel bornavirus of different squirrel species (variegated squirrel 1 bornavirus, VSBV-1) and by BoDV-1 known as the causative agent for the classical Borna disease in horses and sheep. Whereas a T cell-mediated immunopathology has already been confirmed as key disease mechanism for infection with BoDV-1 by experimental studies in rodents, the underlying pathomechanisms remain less clear for human bornavirus infections, infection with other bornaviruses or infection of reservoir species. Thus, an overview of current knowledge on the pathogenesis of bornavirus infections focusing on immunopathology is given.

Newcastle Disease Virus as a Vaccine Vector for 20 Years: A Focus on Maternally Derived Antibody Interference

It has been 20 years since Newcastle disease virus (NDV) was first used as a vector. The past two decades have witnessed remarkable progress in vaccine generation based on the NDV vector and optimization of the vector. Protective antigens of a variety of pathogens have been expressed in the NDV vector to generate novel vaccines for animals and humans, highlighting a great potential of NDV as a vaccine vector. More importantly, the research work also unveils a major problem restraining the NDV vector vaccines in poultry, i.e., the interference from maternally derived antibody (MDA). Although many efforts have been taken to overcome MDA interference, a lack of understanding of the mechanism of vaccination inhibition by MDA in poultry still hinders vaccine improvement. In this review, we outline the history of NDV as a vaccine vector by highlighting some milestones. The recent advances in the development of NDV-vectored vaccines or therapeutics for animals and humans are discussed. Particularly, we focus on the mechanisms and hypotheses of vaccination inhibition by MDA and the efforts to circumvent MDA interference with the NDV vector vaccines. Perspectives to fill the gap of understanding concerning the mechanism of MDA interference in poultry and to improve the NDV vector vaccines are also proposed.

Avian Bornaviral Ganglioneuritis: Current Debates and Unanswered Questions

Avian bornaviral ganglioneuritis, often referred to as parrot wasting disease, is associated with a newly discovered avian virus from the taxonomic family Bornaviridae. Research regarding the pathogenesis and treatment for this disease is ongoing, with implications for understanding other emerging human and nonhuman diseases, as well as the health and ecology of wildlife. At this time, numerous questions remain unanswered regarding the transmission of the disease, best practices for diagnostic sampling and testing, and whether currently used drug therapies are effective or harmful for afflicted birds. The pathogenesis of the disease also remains unclear with many birds showing resistance to the effects of the virus and being able to remain clinically unaffected for years, while other birds succumb to its effects. New research findings regarding avian bornaviral ganglioneuritis are discussed and important as yet unanswered questions are identified.

Recombinant Modified Vaccinia Virus Ankara (MVA) Vaccines Efficiently Protect Cockatiels Against Parrot Bornavirus Infection and Proventricular Dilatation Disease

Parrot bornaviruses (PaBVs) are the causative agents of proventricular dilatation disease (PDD), a chronic and often fatal neurologic disorder in Psittaciformes. The disease is widely distributed in private parrot collections and threatens breeding populations of endangered species. Thus, immunoprophylaxis strategies are urgently needed. In previous studies we demonstrated a prime-boost vaccination regime using modified vaccinia virus Ankara (MVA) and Newcastle disease virus (NDV) constructs expressing the nucleoprotein and phosphoprotein of PaBV-4 (MVA/PaBV-4 and NDV/PaBV-4, respectively) to protect cockatiels (Nymphicus hollandicus) against experimental challenge infection. Here we investigated the protective effect provided by repeated immunization with either MVA/PaBV-4, NDV/PaBV-4 or Orf virus constructs (ORFV/PaBV-4) individually. While MVA/PaBV-4-vaccinated cockatiels were completely protected against subsequent PaBV-2 challenge infection and PDD-associated lesions, the course of the challenge infection in NDV/PaBV-4- or ORFV/PaBV-4-vaccinated birds did not differ from the unvaccinated control group. We further investigated the effect of vaccination on persistently PaBV-4-infected cockatiels. Remarkably, subsequent immunization with MVA/PaBV-4 and NDV/PaBV-4 neither induced obvious immunopathogenesis exacerbating the disease nor reduced viral loads in the infected birds. In summary, we demonstrated that vaccination with MVA/PaBV-4 alone is sufficient to efficiently prevent PaBV-2 challenge infection in cockatiels, providing a suitable vaccine candidate against avian bornavirus infection and bornavirus-induced PDD.

Monitoring of free-ranging and captive Psittacula populations in Western Europe for avian bornaviruses, circoviruses and polyomaviruses

Avian pathogens such as bornaviruses, circoviruses and polyomaviruses are widely distributed in captive collections of psittacine birds worldwide and can cause fatal diseases. In contrast, only little is known about their presence in free-ranging psittacines and their impact on these populations. Rose-ringed parakeets (Psittacula krameri) and Alexandrine parakeets (Psittacula eupatria) are non-native to Europe, but have established stable populations in parts of Western Europe. From 2012-2017, we surveyed free-ranging populations in Germany and France as well as captive Psittacula individuals from Germany and Spain for avian bornavirus, circovirus and polyomavirus infections. Samples from two out of 469 tested free-ranging birds (0.4%; 95% confidence interval [CI-95]: 0.1-1.5%) were positive for beak and feather disease virus (BeFDV), whereas avian bornaviruses and polyomaviruses were not detected in the free-ranging populations. In contrast, avian bornaviruses and polyomaviruses, but not circoviruses were detected in captive populations. Parrot bornavirus 4 (PaBV-4) infection was detected by RT-PCR in four out of 210 captive parakeets (1.9%; CI-95: 0.7-4.8%) from four different holdings in Germany and Spain and confirmed by detection of bornavirus-reactive antibodies in two of these birds. Three out of 160 tested birds (1.9%; CI-95: 0.5-5.4%) possessed serum antibodies directed against budgerigar fledgling disease virus (BuFDV). PaBV-4 and BuFDV were also detected in several psittacines of a mixed holding in Germany, which had been in contact with free-ranging parakeets. Our results demonstrate that Psittacula parakeets are susceptible to common psittacine pathogens and their populations in Western Europe are exposed to these viruses. Nevertheless, the prevalence of avian bornaviruses, circoviruses and polyomaviruses in those populations is very low.RESEARCH HIGHLIGHTS Psittacula parakeets are susceptible to bornavirus, circovirus and polyomavirus infection.Introduced Psittacula populations in Europe have been exposed to these viruses.Nevertheless, they may be absent or present at only low levels in free-ranging Psittacula populations.Free-ranging populations in Europe pose a minor threat of transmitting these viruses to captive Psittaciformes.

Apparent resolution of parrot bornavirus infection in cockatiels (Nymphicus hollandicus)

Parrot bornavirus (PaBV), the etiologic agent of proventricular dilatation disease (PDD), is a major cause of concern in the avian health community. Within an infected flock, some birds will develop PDD and succumb to disease, while others remain healthy. Until now, there has been no study describing the results of long-term infection in apparently healthy carriers. For the last 5 years, the Schubot Exotic Bird Health Center at Texas A&M University has monitored individual PaBV shedding data in a flock of 66 naturally infected cockatiels. Of these birds, 53 were detected shedding PaBV4 in their droppings by reverse transcriptase polymerase chain reaction on at least one occasion. However, the prevalence of shedding declined over time, with the last positive cloacal swab being in October 2013. To determine whether the decline and eventual lack of shedding was an indication of virus elimination, seven previously shedding birds were euthanized and necropsied in 2016. Neither any gross lesion of PDD was observed nor was there any evidence of PDD or bornaviral encephalitis detected by histopathology. All tissues tested were negative for the presence of PaBV by reverse transcriptase polymerase chain reaction and immunohistochemistry. Thus, there was no evidence of an ongoing, productive infection in these birds. There are two possible explanations for these results. One possibility is that the birds were previously infected and have subsequently eliminated the virus. Alternatively, there may have been as few as three truly infected birds in the flock and the transient detection of PaBV in the droppings of other birds may simply be a "pass-through" phenomenon.

Avian Vaccination: Current Options and Strategies

Researchers have generated an array of potential avian antiviral vaccines. However, vaccine and viral complexity, small profit margins, the cost of development and manufacturing, and the small population at risk relegate most avian vaccine use to commercial species. Some vaccines designed for use in nonavian species are used to prevent or ameliorate disease in exotic and companion birds. This article highlights newly developed vaccines that may be used in exotic and pet birds. Information pertinent to vaccine choice and strategy is provided, including disease lethality, species affected, and previous knowledge regarding vaccine safety and efficacy. Other avian species of concern are also included.

Avian Ganglioneuritis in Clinical Practice

Avian ganglioneuritis (AG) comprises one of the most intricate pathologies in avian medicine and is researched worldwide. Avian bornavirus (ABV) has been shown to be a causative agent of proventricular dilatation disease in birds. The avian Bornaviridae represent a genetically diverse group of viruses that are widely distributed in captive and wild populations around the world. ABV and other infective agents are implicated as a cause of the autoimmune pathology that leads to AG, similar to human Guillain Barrè syndrome. Management of affected birds is beneficial and currently centered at reducing neurologic inflammation, managing secondary complications, and providing nutritional support.

Studies on immunity and immunopathogenesis of parrot bornaviral disease in cockatiels

We have demonstrated that vaccination of cockatiels (Nymphicus hollandicus) with killed parrot bornavirus (PaBV) plus recombinant PaBV-4 nucleoprotein (N) in alum was protective against disease in birds challenged with a virulent bornavirus isolate (PaBV-2). Unvaccinated birds, as well as birds vaccinated after challenge, developed gross and histologic lesions typical of proventricular dilatation disease (PDD). There was no evidence that vaccination either before or after challenge made the infection more severe. Birds vaccinated prior to challenge largely remained free of disease, despite the persistence of the virus in many organs. Similar results were obtained when recombinant N, in alum, was used for vaccination. In some rodent models, Borna disease is immune mediated thus we did an additional study whereby cyclosporine A was administered to unvaccinated birds starting 1day prior to challenge. This treatment also conferred complete protection from disease, but not infection.

From nerves to brain to gastrointestinal tract: A time-based study of parrot bornavirus 2 (PaBV-2) pathogenesis in cockatiels (Nymphicus hollandicus)

Parrot bornaviruses (PaBVs) are the causative agents of proventricular dilatation disease, however key aspects of its pathogenesis, such as route of infection, viral spread and distribution, and target cells remain unclear. Our study aimed to track the viral spread and lesion development at 5, 10, 20, 25, 35, 40, 60, 80, 95 and 114 dpi using histopathology, immunohistochemistry, and RT-PCR. After intramuscular inoculation of parrot bornavirus 2 (PaBV-2) in the pectoral muscle of cockatiels, this virus was first detected in macrophages and lymphocytes in the inoculation site and adjacent nerves, then reached the brachial plexus, centripetally spread to the thoracic segment of the spinal cord, and subsequently invaded the other spinal segments and brain. After reaching the central nervous system (CNS), PaBV-2 centrifugally spread out the CNS to the ganglia in the gastrointestinal (GI) system, adrenal gland, heart, and kidneys. At late points of infection, PaBV-2 was not only detected in nerves and ganglia but widespread in the smooth muscle and/or scattered epithelial cells of tissues such as crop, intestines, proventriculus, kidneys, skin, and vessels. Despite the hallmark lesion of PaBVs infection being the dilation of the proventriculus, our results demonstrate PaBV-2 first targets the CNS, before migrating to peripheral tissues such as the GI system.