Bats and Viruses: Current Research and Future Trends | Book
Caister Academic Press
and Martin Schwemmle2
1Virology, Research Center for Tropical Diseases (CIET), University of Costa Rica, San José, Costa Rica; 2Institute of Virology, Medical Center, University of Freiburg, Germany
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Bats act as reservoirs for over 200 viruses, many of which cause severe, often life-threatening, diseases in humans, livestock and wildlife. Examples include rabies virus, SARS and MERS coronaviruses and Ebola virus. Surprisingly many of these viruses cause asymptomatic infections in bats. In fact it has been postulated that these viral infections may even confer a benefit (as yet unknown) to the bat host. Research into the molecular and cellular biology of the virus-host interaction and studies on the immune systems of the bat hosts are providing new insights into these fascinating viruses and are essential first steps for the development of novel strategies for the prevention of bat-borne zoonotic infections.
In this multi-authored volume, international experts review the current hot-topics in this field. Chapters have extensive reference sections that should encourage readers to pursue each subject in greater detail. The book opens with an introductory chapter that is followed by six chapters (chapters 2-7) reviewing different important families of bat-borne viruses. The following two chapters (chapters 8-9) focus on the bat immune system. Chapters 9-12 cover in vitro isolation, in vivo models and metagenomics for viral discovery in bats. The book closes with a fascinating look at the special ability of bats to act as reservoirs for so many different types of viruses.
This book is an invaluable reference source of timely information for students, virologists, immunologists, medical and veterinary professionals, and scientists working on bat-borne diseases. It is also highly recommended for all university libraries.
Table of contents
1. Bats and Viruses: Introduction
Eugenia Corrales-Aguilar and Martin Schwemmle
Bats are flying mammals of the order Chiroptera. Second to rodents, they have extremely high species richness with more than 1300 species described so far. Owing to their lifestyle, bats possess several interesting characteristics. But all these characteristics do not eclipse one that has been frequently emphasised lately, their potential link with human diseases, and mainly those caused by zoonotic viruses. More than 200 viruses have been isolated from or detected in bats so far. These viruses belong to 27 different virus families, denoting an astonishing diversity and suggesting that their detection is not a serendipitous event. In this book, current knowledge about bats as hosts of viruses (suspected, accidental, or definite), bats as models for infection, and bat immunology is summarised and discussed. A collection of experts from all around the world provide information about the many viral families involved, or suspected to be involved, in human zoonotic diseases. All topics reviewed here reflect current knowledge, which allows us to fully appreciate the extent and complexity of the relationship between bats and viruses. We can make use of all these observations to deepen our understanding of this ecological interaction and how we can prevent (or be prepared for) viral emergence.
2. Bats and Flaviviruses
Andres Moreira-Soto and Eugenia Corrales-Aguilar
Bats have been associated as reservoir hosts of viruses of public health importance, such as SARS or henipaviruses. However, for flaviviruses, viruses that are mainly transmitted by arthropod vectors, the link has been difficult to prove. This comprehensive review of the literature analyses in vitro and in vivo experiments, as well as viral isolation and molecular and serological detection of flaviviruses in bats. Later, findings involving and/or excluding bats as hosts, reservoirs or even their putative involvement in the flaviviral transmission cycles are discussed. These confounding discoveries prime to a much needed multidisciplinary approach to prove or disprove the role of bats as hosts for these viruses and to finally clarify if they do play an important role in their transmission cycles.
3. Alphavirus and Its Vertebrate Hosts
Alphaviruses are positive-sense single-stranded RNA arthropod-borne zoonotic arboviruses, which belong to the family Togaviridae. Geographically, alphaviruses have a near worldwide distribution and around 30 species have been described. Antigenic and evolutionary patterns classify alphaviruses into ten antigenic complexes and show association with reservoir and human disease. Clinically, alphaviruses are associated with a range of diseases, including mild febrile disease, rash and encephalitis, but sometimes results are fatal. Recent studies of 'dengue-like' illness in Latin America have revealed that many alphaviruses such as Venezuelan equine encephalitis, Madariaga, Mayaro and chikungunya viruses are misdiagnosed as dengue; diagnosis based on only signs and symptoms is even more complicated in areas where these viruses circulate simultaneously. In nature, alphaviruses are maintained in enzootic sylvatic cycles that involve a vertebrate host and enzootic vectors. However, altered host and mosquito ranges have been reported during alphavirus emergence and major epidemics. Epidemiological and serological evidence suggest that several species of mammals could serve as enzootic reservoirs and potential amplifiers of alphaviruses in nature. This chapter describes the current state of alphavirus reservoirs, with a focus on major alphaviruses, namely VEEV, MADV, EEEV and CHIKV, and future implication of alphavirus ecological studies for outbreak investigation and control.
4. Bat Influenza A-like Viruses
Gert Zimmer, Veronika Götz, Kevin Ciminski, Sebastian Giese and Martin Schwemmle
Influenza A viruses (IAV) are highly contagious pathogens that can cause considerable mortality and morbidity in animals and humans. Until recently it had been believed that all IAV subtypes circulate in aquatic waterfowl; however, this understanding has recently been challenged with the discovery of two novel influenza A-like virus sequences in faeces from fruit-eating bats in Central and South America. Overall, these two new subtypes, provisionally designated H17N10 and H18N11, share many features with conventional IAVs, yet their surface glycoproteins lack the canonical receptor-binding and -destroying activity of the classical haemagglutinin and neuraminidase proteins, respectively. The identification of two novel IAV subtypes in combination with their currently unknown receptor raised the question of their potential zoonotic risk. Here, we summarize recent progress in the characterisation of these viruses.
5. Bats and Coronaviruses
Susanna K.P. Lau, Antonio C.P. Wong, Hayes K.H. Luk and Patrick C.Y. Woo
Before the SARS epidemic, bats were not known to harbour any coronaviruses (CoVs). After the discovery of SARSr-CoV in horseshoe bats in 2005, more than 35 Alphacoronaviruses and Betacoronaviruses have been discovered and analysed from various bat species in both suborders Yinpterochiroptera and Yangochiroptera globally in the last 13 years. These discoveries have led to a revision of the classification of CoVs and marked improvement of our understanding of the phylogeny and evolution of CoVs. A number of bat CoVs, such as Tylonyteris bat coronavirus HKU4 and Pipistrellus bat coronavirus HKU5, were found to be closely related to MERS-CoV. Interspecies jumping events have been observed between bats and other mammals, such as Rhinolophus bat coronavirus HKU2 between Chinese horseshoe bat and pigs, resulting in outbreaks. New CoV discoveries provide a solid foundation and evolutionary model to study this family of viruses, which has been associated with two major outbreaks, SARS and MERS, in the first two decades of this millennium. In the next decade, with the help of ever-changing robust technologies, we will be able to further understand the mechanistic pathways of pathogenesis and develop antiviral agents and vaccines for CoV infections.
6. Genetic Diversity and Geographic Distribution of Bat-borne Hantaviruses
Satoru Arai and Richard Yanagihara
The recent discovery that multiple species of shrews and moles (order Eulipotyphla, families Soricidae and Talpidae) from Europe, Asia, Africa and/or North America harbour genetically distinct viruses belonging to the family Hantaviridae (order Bunyavirales) has prompted a further exploration of their host diversification. In analysing thousands of frozen, RNAlater®-preserved and ethanol-fixed tissues from bats (order Chiroptera) by reverse transcription polymerase chain reaction (RT-PCR), ten hantaviruses have been detected to date in bat species belonging to the suborder Yinpterochiroptera (families Hipposideridae, Pteropodidae and Rhinolophidae) and the suborder Yangochiroptera (families Emballonuriade, Nycteridae and Vespertilionidae). Of these, six hantaviruses are from Asia (Xuân Sơn virus and Đakrông virus in Vietnam; Láibīn virus in China and Myanmar; Huángpí virus and Lóngquán virus in China; and Quezon virus in the Philippines); three are from Africa (Mouyassué virus in Côte d'Ivoire and Ethiopia; Magboi virus in Sierra Leone; and Makokou virus in Gabon); and one from Europe (Brno virus in the Czech Republic). Molecular identification of many more bat-borne hantaviruses is expected. However, thus far, none of these newfound viruses has been isolated in cell culture and it is unclear if they cause infection or disease in humans. Future research must focus on myriad unanswered questions about the genetic diversity and geographic distribution, as well as the pathogenic potential, of bat-borne viruses of the family Hantaviridae.
7. Bat Polyomaviruses: A Challenge to the Strict Host-Restriction Paradigm within the Mammalian Polyomaviridae
Michael J. Carr, Gabriel Gonzalez, Emma C. Teeling and Hirofumi Sawa
Polyomaviruses (PyVs), family Polyomaviridae, are highly stable, circular, dsDNA viruses, which exhibit strict host-specificity, particularly in mammals, with cross-species transmission events leading to productive infection considered to be rare or non-existent. PyVs have, however, been identified in a diverse range of vertebrates (mammals, birds, reptiles, amphibians and fish) and now, with the recent discovery in invertebrate species, including insects and arachnids, an ancient association with metazoan life is clear. Previous PyV studies in insectivorous and frugivorous bat species from across the globe have identified significant diversity and high rates of positivity (> 20 %) using exclusively molecular (PCR-based) approaches in bats sampled from North, Central and South America, Africa, Indonesia, New Zealand and China. No culture isolates of bat PyVs currently exist and the shortage of immortalised bat cell lines and the paucity of surveillance data in the literature from much of the Eurasian continent is striking and efforts should be made to address this dearth of knowledge in the future. In our previous studies of horseshoe bat (Rhinolophus) species in Zambia, we have provided evidence of host-switching of PyVs in mammals for the first time, indicative of a greater capacity for cross-species transmission events in the particularly speciose mammalian order Chiroptera. Our findings have implications for studies of polyomaviral evolution and, also, for the investigation of zoonotic transmission events involving high-consequence pathogens in bat hosts.
8. Innate Immunity in Bats
Christopher F. Basler
Bats are reservoir hosts for several viruses that cause severe disease in humans, raising the question as to whether bats have unique innate antiviral immune responses. There are three classes of interferons (IFN) type I, II and III, with type I and type III IFNs serving as a rapid innate antiviral response that up-regulates interferon stimulated genes, to control virus replication. Activation of type I and type III IFN expression is mediated by pattern recognition receptors, which detect products of virus replication and initiate downstream signaling. Genome sequencing and transcriptional profiling studies indicate that the major components of the type I, II and III IFN systems are intact in bats. There is evidence for constitutive IFN-α expression in at least some bats and a corresponding higher baseline expression of some interferon stimulated genes (ISGs), which perhaps influences how bats tolerate infection. Furthermore, viruses that use bats as reservoir hosts have evolved mechanisms to suppress bat IFN responses. There is also emerging evidence for altered inflammation in bats. Future functional studies should further clarify how the bat innate immune system and viruses interact.
9. Immune (Adaptive) Response in Bats
Bats naturally harbour a variety of viruses. Some of these viruses could infect humans and lead to deadly diseases but cause no clinical symptoms in bats. The ability of bats to coexist with viruses may be explained by their ability to quickly control viral replication, as well as having a good tolerance to viral diseases. The human immune system consists of innate and adaptive immunity. The adaptive immune responses, mediated mainly by T-cell-mediated immune response and B cells responses, are pathogen-specific and long lasting. The development of bat adaptive immunity has been unbalanced, with the majority of studies focusing on antibody responses. As natural harbourers of viruses, it is probable that bats maintain strong antibody reactions. Here, we summarised the findings from bat adaptive immunity studies. We found bat antibody responses against viral infection may not be as important as initially thought. In fact, early interferon response and cell-mediated immunity may play major antiviral roles; however, these are poorly studied in bats. The purpose of this chapter is to provide an update of the knowledge about bat adaptive immune responses, and also to foster future studies in this area.
10. In Vitro Isolation of Bat Viruses Using Commercial and Bat-derived Cell Lines
M. Geldenhuys, J. Coertse, M. Mortlock and Wanda Markotter
Large viral diversities have been detected from bats using nucleic acid detection methods; however, cell culture isolation of this diversity has been less successful. Virus isolation attempts are limited by challenges that primarily include suitability of available cell lines, quality of infectious viral particles and high levels of biocontainment. In this chapter, we review bat-borne virus isolations in cell culture and factors that may assist in isolation. We review the cell lines that have been used for bat virus isolation, including those derived from non-bat hosts, which are often commercially available, as well as bat-derived cell lines. Additionally, reasons are examined for why specific viruses may be more readily isolated or why certain cell lines may be more useful than others. The chapter focuses on four viral families, namely the Corona-, Paramyxo-, Filo- and Rhabdoviridae; but briefly also mentions the Adeno-, Herpes-, Phenui-, Nairo-, Pox- and Reoviridae.
11. In Vivo Models of Infection
Chiroptera represents the second largest family of mammals, with more than 1200 species. Bats are reservoir, or suspected reservoir, hosts of several important human and livestock pathogens, including ebolaviruses, marburgviruses, SARS and MERS coronaviruses, Nipah and Hendra viruses, and rabies virus and other lyssaviruses. Hundreds of other viruses from many families have been detected in bats, principally via sequencing of viral genomes in samples, suggesting bats may be among the most important sources of zoonotic agents. Despite their importance, virtually nothing is known about infection dynamics in bats, nor how bat immune systems engage these viruses without apparent disease. These limitations are principally due to the lack of breeding colonies of bats, which limits experimental infection studies. Many challenges must be overcome to establish such colonies, including their high cost, requirement for specialised facilities, and competent animal care staff and veterinarians. In addition, the low fecundity of bats, with one to three offspring per year, depending on the species, constrains use of bats and can result in small experimental sample sizes. In recent years, several groups have begun to rectify this deficiency by establishing closed colonies of bats. These colonies will become valuable resources for the examination of bat-borne viruses and will shed light on viral ecology, bat immune responses, and mechanisms of disease resistance.
12. Metagenomics for Viral Discovery in Bats
M. Geldenhuys and Wanda Markotter
Metagenomics using high-throughput sequencing technologies can serve as powerful tools to investigate viral discovery in bats and define their virome diversity. Viral metagenomic research has been performed on several bat species in countries from nearly all continents, and the identification of diverse viral sequences has been phenomenal. Viral metagenomics is inherently faced with many limitations and challenges that need to be overcome before and after sequencing results on sequencing platforms are obtained. This chapter reviews the successes of viral discovery from bats using metagenomic approaches, discusses terminology, details the enrichment approaches utilised, describes the challenges encountered and lists several mitigation strategies for poor sequencing results that can be adopted.
13. Are Bats 'Special'?
Aaron T. Irving and Lin-Fa Wang
Although bats have been associated with viruses for more than a century, they have attracted increased attention in the last two decades as an important reservoir of many new viruses. This was largely because of the discovery of different highly lethal zoonotic viruses originating from bats, including Hendra, Nipah, SARS, MERS, Ebola and Marburg viruses, among many others as detailed in the previous chapters. Although the notion of bats as the natural reservoir is still being debated for some of these viruses, it is beyond any doubt that bats at least harbour viruses highly related to all of these. The research focus has largely shifted from 'Are bats a true reservoir?' to 'Are bats special?' In this chapter, a brief review will be provided on the various aspects supporting the observation that bats are special or unusual and, as such, an excellent host of many different viruses, many of which have proven spillover potential with high lethality in alternative hosts
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(EAN: 9781912530144 9781912530151 Subjects: [medical microbiology] [molecular microbiology] [virology] )