Genome Sequence of a Bornavirus Recovered from an African Garter Snake (Elapsoidea loveridgei)

In Vitro Characterization and Antiviral Susceptibility of Ophidian Serpentoviruses

Ophidian serpentoviruses, positive-sense RNA viruses in the order Nidovirales, are important infectious agents of both captive and free-ranging reptiles. Although the clinical significance of these viruses can be variable, some serpentoviruses are pathogenic and potentially fatal in captive snakes. While serpentoviral diversity and disease potential are well documented, little is known about the fundamental properties of these viruses, including their potential host ranges, kinetics of growth, environmental stability, and susceptibility to common disinfectants and viricides. To address this, three serpentoviruses were isolated in culture from three unique PCR-positive python species: Ball python (Python regius), green tree python (Morelia viridis), and Stimson's python (Antaresia stimsoni). A median tissue culture infectious dose (TCID₅₀) was established to characterize viral stability, growth, and susceptibility. All isolates showed an environmental stability of 10-12 days at room temperature (20 °C). While all three viruses produced variable peak titers on three different cell lines when incubated at 32 °C, none of the viruses detectably replicated at 35 °C. All viruses demonstrated a wide susceptibility to sanitizers, with 10% bleach, 2% chlorhexidine, and 70% ethanol inactivating the virus in one minute and 7% peroxide and a quaternary ammonium solution within three minutes. Of seven tested antiviral agents, remdesivir, ribavirin, and NITD-008, showed potent antiviral activity against the three viruses. Finally, the three isolates successfully infected 32 unique tissue culture cell lines representing different diverse reptile taxa and select mammals and birds as detected by epifluorescent immunostaining. This study represents the first characterization of in vitro properties of growth, stability, host range, and inactivation for a serpentovirus. The reported results provide the basis for procedures to mitigate the spread of serpentoviruses in captive snake colonies as well as identify potential non-pharmacologic and pharmacologic treatment options for ophidian serpentoviral infections.

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.

Two novel bornaviruses identified in colubrid and viperid snakes

We present the complete genome sequences of Caribbean watersnake bornavirus (CWBV) and Mexican black-tailed rattlesnake bornavirus (MRBV), which we identified in archived raw transcriptomic read data of a Caribbean watersnake (Tretanorhinus variabilis) and a Mexican black-tailed rattlesnake (Crotalus molossus nigrescens), respectively. The genomes of CWBV and MRBV have a length of about 8,900 nucleotides and comprise the complete coding regions and the untranslated regions. The overall genomic makeup and predicted gene content is typical for members of the genus Orthobornavirus within the family Bornaviridae. Alternative splicing was detected for the L and M genes. Based on a phylogenetic analysis of all viral proteins, we consider both viruses to be members of a single novel species within the genus Orthobornavirus. Both viruses form a distinct outgroup to all currently known orthobornaviruses. Based on the novel virus genomes, we furthermore identified closely related endogenous bornavirus-like nucleoprotein sequences in transcriptomic data of veiled chameleons (Chamaeleo calyptratus) and a common lancehead (Bothrops atrox).

New World camelids are sentinels for the presence of Borna disease virus

Borna disease (BD), a frequently fatal neurologic disorder caused by Borna disease virus 1 (BoDV-1), has been observed for decades in horses, sheep, and other mammals in certain regions of Europe. The bicoloured white-toothed shrew (Crocidura leucodon) was identified as a persistently infected species involved in virus transmission. Recently, BoDV-1 attracted attention as a cause of fatal encephalitis in humans. Here, we report investigations on BoDV-1-infected llamas from a farm in a BD endemic area of Switzerland, and alpacas from holdings in a region of Germany where BD was last seen in the 1960s but not thereafter. All New World camelids showed apathy and abnormal behaviour, necessitating euthanasia. Histologically, severe non-suppurative meningoencephalitis with neuronal Joest-Degen inclusion bodies was observed. BoDV-1 was confirmed by immunohistology, RT-qPCR, and sequencing in selected animals. Analysis of the llama herd over 20 years showed that losses due to clinically suspected BD increased within the last decade. BoDV-1 whole-genome sequences from one Swiss llama and one German alpaca and-for comparison-from one Swiss horse and one German shrew were established. They represent the first published whole-genome sequences of BoDV-1 clusters 1B and 3, respectively. Our analysis suggests that New World camelids may have a role as a sentinel species for BoDV-1 infection, even when symptomatic cases are lacking in other animal species.

Selected Emerging Infectious Diseases of Squamata: An Update

This article details emerging infectious diseases that have devastating impacts on captive and wild squamates. Treatment advances have been attempted for Cryptosporidium infections in squamates. Gram-positive bacteria, Devriesea agamarum and Austwickia chelonae, are contributing to severe disease in captive and now in wild reptiles, some critically endangered. Nannizziposis, Paranannizziopsis, and Ophidiomyces continue to cause fatal disease as primary pathogens in wild and captive populations of squamates and sphenodontids. Nidovirus, bornavirus, paramyxovirus, sunshine virus, and arenavirus have emerged to be significant causes of neurorespiratory disease in snakes. Controlled studies evaluating environmental stability, disinfection, transmission control, and treatment are lacking.

A fixed moderate-dose combination of tiletamine+zolazepam outperforms midazolam in induction of short-term immobilization of ball pythons (Python regius)

Laboratory animals are commonly anesthetized to prevent pain and distress and to provide safe handling. Anesthesia procedures are well-developed for common laboratory mammals, but not as well established in reptiles. We assessed the performance of intramuscularly injected tiletamine (dissociative anesthetic) and zolazepam (benzodiazepine sedative) in fixed combination (2 mg/kg and 3 mg/kg) in comparison to 2 mg/kg of midazolam (benzodiazepine sedative) in ball pythons (Python regius). We measured heart and respiratory rates and quantified induction parameters (i.e., time to loss of righting reflex, time to loss of withdrawal reflex) and recovery parameters (i.e., time to regain righting reflex, withdrawal reflex, normal behavior). Mild decreases in heart and respiratory rates (median decrease of <10 beats per minute and <5 breaths per minute) were observed for most time points among all three anesthetic dose groups. No statistically significant difference between the median time to loss of righting reflex was observed among animals of any group (p = 0.783). However, the withdrawal reflex was lost in all snakes receiving 3mg/kg of tiletamine+zolazepam but not in all animals of the other two groups (p = 0.0004). In addition, the time for animals to regain the righting reflex and resume normal behavior was longer in the drug combination dose groups compared to the midazolam group (p = 0.0055). Our results indicate that midazolam is an adequate sedative for ball pythons but does not suffice to achieve reliable immobilization or anesthesia, whereas tiletamine+zolazepam achieves short-term anesthesia in a dose-dependent manner.

Divergent bornaviruses from Australian carpet pythons with neurological disease date the origin of extant Bornaviridae prior to the end-Cretaceous extinction

Tissue samples from Australian carpet pythons (Morelia spilota) with neurological disease were screened for viruses using next-generation sequencing. Coding complete genomes of two bornaviruses were identified with the gene order 3'-N-X-P-G-M-L, representing a transposition of the G and M genes compared to other bornaviruses and most mononegaviruses. Use of these viruses to search available vertebrate genomes enabled recognition of further endogenous bornavirus-like elements (EBLs) in diverse placental mammals, including humans. Codivergence patterns and shared integration sites revealed an ancestral laurasiatherian EBLG integration (77 million years ago [MYA]) and a previously identified afrotherian EBLG integration (83 MYA). The novel python bornaviruses clustered more closely with these EBLs than with other exogenous bornaviruses, suggesting that these viruses diverged from previously known bornaviruses prior to the end-Cretaceous (K-Pg) extinction, 66 MYA. It is possible that EBLs protected mammals from ancient bornaviral disease, providing a selective advantage in the recovery from the K-Pg extinction. A degenerate PCR primer set was developed to detect a highly conserved region of the bornaviral polymerase gene. It was used to detect 15 more genetically distinct bornaviruses from Australian pythons that represent a group that is likely to contain a number of novel species.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): Borna disease

Borna disease has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of Borna disease to be listed, Article 9 for the categorisation of Borna disease according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to Borna disease. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, Borna disease cannot be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL because there was no compliance on criterion 5 A(v). Consequently, the assessment on compliance of Borna disease with the criteria as in Annex IV of the AHL, for the application of the disease prevention and control rules referred to in Article 9(1) is not applicable, as well as which animal species can be considered to be listed for Borna disease according to Article 8(3) of the AHL.

The pathogenesis of proventricular dilatation disease

Bornaviruses cause neurologic diseases in several species of birds, especially parrots, waterfowl and finches. The characteristic lesions observed in these birds include encephalitis and gross dilatation of the anterior stomach — the proventriculus. The disease is thus known as proventricular dilatation disease (PDD). PDD is characterized by extreme proventricular dilatation, blockage of the passage of digesta and consequent death by starvation. There are few clinical resemblances between this and the bornaviral encephalitides observed in mammals. Nevertheless, there are common virus-induced pathogenic pathways shared across this disease spectrum that are explored in this review. Additionally, a review of the literature relating to gastroparesis in humans and the control of gastric mobility in mammals and birds points to several plausible mechanisms by which bornaviral infection may result in extreme proventricular dilatation.

Taxonomy of the order Mononegavirales: update 2016

In 2016, the order Mononegavirales was emended through the addition of two new families (Mymonaviridae and Sunviridae), the elevation of the paramyxoviral subfamily Pneumovirinae to family status (Pneumoviridae), the addition of five free-floating genera (Anphevirus, Arlivirus, Chengtivirus, Crustavirus, and Wastrivirus), and several other changes at the genus and species levels. This article presents the updated taxonomy of the order Mononegavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV).

Reporter-Expressing, Replicating-Competent Recombinant Arenaviruses

Several arenaviruses cause hemorrhagic fever (HF) disease in humans and pose an important public health problem in their endemic regions. To date, no Food and Drug Administration (FDA)-licensed vaccines are available to combat human arenavirus infections, and current anti-arenaviral drug therapy is limited to an off-label use of ribavirin that is only partially effective. The development of arenavirus reverse genetic approaches has provided investigators with a novel and powerful approach for the study of arenavirus biology including virus–host interactions underlying arenavirus induced disease. The use of cell-based minigenome systems has allowed examining the cis- and trans-acting factors involved in arenavirus replication and transcription, as well as particle assembly and budding. Likewise, it is now feasible to rescue infectious arenaviruses containing predetermined mutations in their genomes to investigate virus-host interactions and mechanisms of pathogenesis. The use of reverse genetics approaches has also allowed the generation of recombinant arenaviruses expressing additional genes of interest. These advances in arenavirus molecular genetics have also facilitated the implementation of novel screens to identify anti-arenaviral drugs, and the development of novel strategies for the generation of arenavirus live-attenuated vaccines. In this review, we will summarize the current knowledge on reporter-expressing, replicating-competent arenaviruses harboring reporter genes in different locations of the viral genome and their use for studying and understanding arenavirus biology and the identification of anti-arenaviral drugs to combat these important human pathogens.

Reverse Genetics Approaches to Control Arenavirus

Several arenavirus cause hemorrhagic fever disease in humans and pose a significant public health problem in their endemic regions. To date, no licensed vaccines are available to combat human arenavirus infections, and anti-arenaviral drug therapy is limited to an off-label use of ribavirin that is only partially effective. The development of arenavirus reverse genetics approaches provides investigators with a novel and powerful approach for the investigation of the arenavirus molecular and cell biology. The use of cell-based minigenome systems has allowed examining the cis- and trans-acting factors involved in arenavirus replication and transcription and the identification of novel anti-arenaviral drug targets without requiring the use of live forms of arenaviruses. Likewise, it is now feasible to rescue infectious arenaviruses entirely from cloned cDNAs containing predetermined mutations in their genomes to investigate virus-host interactions and mechanisms of pathogenesis, as well as to facilitate screens to identify anti-arenaviral drugs and development of novel live-attenuated arenavirus vaccines. Recently, reverse genetics have also allowed the generation of tri-segmented arenaviruses expressing foreign genes, facilitating virus detection and opening the possibility of implementing live-attenuated arenavirus-based vaccine vector approaches. Likewise, the development of single-cycle infectious, reporter-expressing, arenaviruses has provided a new experimental method to study some aspects of the biology of highly pathogenic arenaviruses without the requirement of high-security biocontainment required to study HF-causing arenaviruses. In this chapter we summarize the current knowledge on arenavirus reverse genetics and the implementation of plasmid-based reverse genetics techniques for the development of arenavirus vaccines and vaccine vectors.

Genomic Mining Reveals Deep Evolutionary Relationships between Bornaviruses and Bats

Bats globally harbor viruses in order Mononegavirales, such as lyssaviruses and henipaviruses; however, little is known about their relationships with bornaviruses. Previous studies showed that viral fossils of bornaviral origin are embedded in the genomes of several mammalian species such as primates, indicative of an ancient origin of exogenous bornaviruses. In this study, we mined the available 10 bat genomes and recreated a clear evolutionary relationship of endogenous bornaviral elements and bats. Comparative genomics showed that endogenization of bornaviral elements frequently occurred in vesper bats, harboring EBLLs (endogenous bornavirus-like L elements) in their genomes. Molecular dating uncovered a continuous bornavirus-bat interaction spanning 70 million years. We conclude that better understanding of modern exogenous bornaviral circulation in bat populations is warranted.

Coding-complete sequencing classifies parrot bornavirus 5 into a novel virus species

In this study, we determined the sequence of the coding region of an avian bornavirus detected in a blue-and-yellow macaw (Ara ararauna) with pathological/histopathological changes characteristic of proventricular dilatation disease. The genomic organization of the macaw bornavirus is similar to that of other bornaviruses, and its nucleotide sequence is nearly identical to the available partial parrot bornavirus 5 (PaBV-5) sequences. Phylogenetic analysis showed that these strains formed a monophyletic group distinct from other mammalian and avian bornaviruses and in calculations performed with matrix protein coding sequences, the PaBV-5 and PaBV-6 genotypes formed a common cluster, suggesting that according to the recently accepted classification system for bornaviruses, these two genotypes may belong to a new species, provisionally named Psittaciform 2 bornavirus.

Taxonomic reorganization of the family Bornaviridae

Knowledge of bornaviruses has expanded considerably during the last decade. A possible reservoir of mammalian Borna disease virus has been identified, divergent bornaviruses have been detected in birds and reptiles, and endogenous bornavirus-like elements have been discovered in the genomes of vertebrates of several species. Previous sequence comparisons and alignments have indicated that the members of the current family Bornaviridae are phylogenetically diverse and are not adequately classified in the existing bornavirus taxonomy supported by the International Committee on Taxonomy of Viruses (ICTV). We provide an update of these analyses and describe their implications for taxonomy. We propose retaining the family name Bornaviridae and the genus Bornavirus but reorganizing species classification. PAirwise Sequence Comparison (PASC) of bornavirus genomes and Basic Local Alignment Search Tool (BLAST) comparison of genomic and protein sequences, in combination with other already published phylogenetic analyses and known biological characteristics of bornaviruses, indicate that this genus should include at least five species: Mammalian 1 bornavirus (classical Borna disease virus and divergent Borna disease virus isolate No/98), Psittaciform 1 bornavirus (avian/psittacine bornaviruses 1, 2, 3, 4, 7), Passeriform 1 bornavirus (avian/canary bornaviruses C1, C2, C3, LS), Passeriform 2 bornavirus (estrildid finch bornavirus EF), and Waterbird 1 bornavirus (avian bornavirus 062CG). This classification is also in line with biological characteristics of these viruses and their vertebrate hosts. A snake bornavirus, proposed to be named Loveridge's garter snake virus 1, should be classified as a member of an additional species (Elapid 1 bornavirus), unassigned to a genus, in the family Bornaviridae. Avian bornaviruses 5, 6, MALL, and another "reptile bornavirus" ("Gaboon viper virus") should stay unclassified until further information becomes available. Finally, we propose new virus names and abbreviations when necessary to achieve clear differentiation and unique identification.