Bat flight and zoonotic viruses

Bat-Borne Coronaviruses in Jordan and Saudi Arabia: A Threat to Public Health?

Emerging infectious diseases are of great concern to public health, as highlighted by the ongoing coronavirus disease 2019 (COVID-19) pandemic. Such diseases are of particular danger during mass gathering and mass influx events, as large crowds of people in close proximity to each other creates optimal opportunities for disease transmission. The Hashemite Kingdom of Jordan and the Kingdom of Saudi Arabia are two countries that have witnessed mass gatherings due to the arrival of Syrian refugees and the annual Hajj season. The mass migration of people not only brings exotic diseases to these regions but also brings new diseases back to their own countries, e.g., the outbreak of MERS in South Korea. Many emerging pathogens originate in bats, and more than 30 bat species have been identified in these two countries. Some of those bat species are known to carry viruses that cause deadly diseases in other parts of the world, such as the rabies virus and coronaviruses. However, little is known about bats and the pathogens they carry in Jordan and Saudi Arabia. Here, the importance of enhanced surveillance of bat-borne infections in Jordan and Saudi Arabia is emphasized, promoting the awareness of bat-borne diseases among the general public and building up infrastructure and capability to fill the gaps in public health preparedness to prevent future pandemics.

An Overview of the Crystallized Structures of the SARS-CoV-2

Many research teams all over the world focus their research on the SARS-CoV-2, the new coronavirus that causes the so-called COVID-19 disease. Most of the studies identify the main protease or 3C-like protease (Mpro/3CLpro) as a valid target for large-spectrum inhibitors. Also, the interaction of the human receptor angiotensin-converting enzyme 2 (ACE2) with the viral surface glycoprotein (S) is studied in depth. Structural studies tried to identify the residues responsible for enhancement/weaken virus-ACE2 interactions or the cross-reactivity of the neutralizing antibodies. Although the understanding of the immune system and the hyper-inflammatory process in COVID-19 are crucial for managing the immediate and the long-term consequences of the disease, not many X-ray/NMR/cryo-EM crystals are available. In addition to 3CLpro, the crystal structures of other nonstructural proteins offer valuable information for elucidating some aspects of the SARS-CoV-2 infection. Thus, the structural analysis of the SARS-CoV-2 is currently mainly focused on three directions-finding Mpro/3CLpro inhibitors, the virus-host cell invasion, and the virus-neutralizing antibody interaction.

MR1-Restricted T Cells with MAIT-like Characteristics Are Functionally Conserved in the Pteropid Bat Pteropus alecto

Bats are reservoirs for a large number of viruses which have potential to cause major human disease outbreaks, including the current coronavirus disease 2019 (COVID-19) pandemic. Major efforts are underway to understand bat immune response to viruses, whereas much less is known about their immune responses to bacteria. In this study, MR1-restricted T (MR1T) cells were detected through the use of MR1 tetramers in circulation and tissues of Pteropus alecto (Pa) bats. Pa MR1T cells exhibited weak responses to MR1-presented microbial metabolites at resting state. However, following priming with MR1-presented agonist they proliferated, upregulated critical transcription factors and cytolytic proteins, and gained transient expression of Th1/17-related cytokines and antibacterial cytotoxicity. Collectively, these findings show that the Pa bat immune system encompasses an abundant and functionally conserved population of MR1T cells with mucosal-associated invariant T-like characteristics, suggesting that MR1 and MR1T cells also play a significant role in bat immune defense.

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MR1T cells are present in Pa bats and react to MR1-presented microbial metabolites

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Pa MR1T cells upregulate Prf and MAIT-associated TFs upon culture with MR1 agonists

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Upon stimulation, Pa MR1T cells rapidly and transiently express TNF and IL-17

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Pa MR1T cells kill E. coli and MR1 agonist-pulsed cells in an MR1-dependent manner

On the Evolution of Virulent Zoonotic Viruses in Bats

Ideas formulated by Paul Ewald about the “evolution of virulence” are used to explain why bats, more often than other mammals, are a reservoir of virulent viruses, and why many of these viruses severely affect other mammals, including humans, but are apparently less pathogenic for bats. Potential factors contributing to bat viruses often being zoonotic are briefly discussed.

Evolution of Flight Muscle Contractility and Energetic Efficiency

The powered flight of animals requires efficient and sustainable contractions of the wing muscles of various flying species. Despite their high degree of phylogenetic divergence, flight muscles in insects and vertebrates are striated muscles with similarly specialized sarcomeric structure and basic mechanisms of contraction and relaxation. Comparative studies examining flight muscles together with other striated muscles can provide valuable insights into the fundamental mechanisms of muscle contraction and energetic efficiency. Here, we conducted a literature review and data mining to investigate the independent emergence and evolution of flight muscles in insects, birds, and bats, and the likely molecular basis of their contractile features and energetic efficiency. Bird and bat flight muscles have different metabolic rates that reflect differences in energetic efficiencies while having similar contractile machinery that is under the selection of similar natural environments. The significantly lower efficiency of insect flight muscles along with minimized energy expenditure in Ca2+ handling is discussed as a potential mechanism to increase the efficiency of mammalian striated muscles. A better understanding of the molecular evolution of myofilament proteins in the context of physiological functions of invertebrate and vertebrate flight muscles can help explore novel approaches to enhance the performance and efficiency of skeletal and cardiac muscles for the improvement of human health.

Possibility for reverse zoonotic transmission of SARS-CoV-2 to free-ranging wildlife: A case study of bats

The COVID-19 pandemic highlights the substantial public health, economic, and societal consequences of virus spillover from a wildlife reservoir. Widespread human transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) also presents a new set of challenges when considering viral spillover from people to naïve wildlife and other animal populations. The establishment of new wildlife reservoirs for SARS-CoV-2 would further complicate public health control measures and could lead to wildlife health and conservation impacts. Given the likely bat origin of SARS-CoV-2 and related beta-coronaviruses (β-CoVs), free-ranging bats are a key group of concern for spillover from humans back to wildlife. Here, we review the diversity and natural host range of β-CoVs in bats and examine the risk of humans inadvertently infecting free-ranging bats with SARS-CoV-2. Our review of the global distribution and host range of β-CoV evolutionary lineages suggests that 40+ species of temperate-zone North American bats could be immunologically naïve and susceptible to infection by SARS-CoV-2. We highlight an urgent need to proactively connect the wellbeing of human and wildlife health during the current pandemic and to implement new tools to continue wildlife research while avoiding potentially severe health and conservation impacts of SARS-CoV-2 "spilling back" into free-ranging bat populations.

Suppressed anti-inflammatory heat shock response in high-risk COVID-19 patients: lessons from basic research (inclusive bats), light on conceivable therapies

The major risk factors to fatal outcome in COVID-19 patients, i.e., elderliness and pre-existing metabolic and cardiovascular diseases (CVD), share in common the characteristic of being chronic degenerative diseases of inflammatory nature associated with defective heat shock response (HSR). The molecular components of the HSR, the principal metabolic pathway leading to the physiological resolution of inflammation, is an anti-inflammatory biochemical pathway that involves molecular chaperones of the heat shock protein (HSP) family during homeostasis-threatening stressful situations (e.g., thermal, oxidative and metabolic stresses). The entry of SARS coronaviruses in target cells, on the other hand, aggravates the already-jeopardized HSR of this specific group of patients. In addition, cellular counterattack against virus involves interferon (IFN)-mediated inflammatory responses. Therefore, individuals with impaired HSR cannot resolve virus-induced inflammatory burst physiologically, being susceptible to exacerbated forms of inflammation, which leads to a fatal "cytokine storm". Interestingly, some species of bats that are natural reservoirs of zoonotic viruses, including SARS-CoV-2, possess an IFN-based antiviral inflammatory response perpetually activated but do not show any sign of disease or cytokine storm. This is possible because bats present a constitutive HSR that is by far (hundreds of times) more intense and rapid than that of human, being associated with a high core temperature. Similarly in humans, fever is a physiological inducer of HSR while antipyretics, which block the initial phase of inflammation, impair the resolution phase of inflammation through the HSR. These findings offer a rationale for the reevaluation of patient care and fever reduction in SARS, including COVID-19.

Fruit bats in flight: a look into the movements of the ecologically important Eidolon helvum in Tanzania

BACKGROUND

Many ecologically important plants are pollinated or have their seeds dispersed by fruit bats, including the widely distributed African straw-colored fruit bats (Eidolon helvum). Their ability to fly long distances makes them essential for connecting plant populations across fragmented landscapes. While bats have been implicated as a reservoir of infectious diseases, their role in disease transmission to humans is not well understood. In this pilot study, we tracked E. helvum to shed light on their movement patterns in Tanzania and possible contact with other species.

METHODS

Tracking devices were deployed on 25 bats captured in the Morogoro Municipal and Kilombero District area near the Udzungwa Mountains of Tanzania. Nightly flight patterns, areas corresponding to foraging bouts and feeding roosts, and new day roosts were determined from bat movement data and characterized according to their proximity to urban built-up and protected areas. Sites for additional environmental surveillance using camera traps were identified via tracking data to determine species coming in contact with fruits discarded by bats.

RESULTS

Tracking data revealed variability between individual bat movements and a fidelity to foraging areas. Bats were tracked from one to six nights, with a mean cumulative nightly flight distance of 26.14 km (min: 0.33, max: 97.57) based on data from high-resolution GPS tags. While the majority of their foraging locations were in or near urban areas, bats also foraged in protected areas, of which the Udzungwa Mountains National Park was the most frequented. Camera traps in fruit orchards frequented by tracked bats showed the presence of multiple species of wildlife, with vervet monkeys (Chlorocebus pygerythrus) observed as directly handling and eating fruit discarded by bats.

CONCLUSIONS

Because we observed multiple interactions of animals with fruits discarded by bats, specifically with vervet monkeys, the possibility of disease spillover risk exists via this indirect pathway. With flight distances of up to 97 km, however, the role of E. helvum in the seed dispersal of plants across both protected and urban built-up areas in Tanzania may be even more important, especially by helping connect increasingly fragmented landscapes during this Anthropocene epoch.

White-nose syndrome: A novel dermatomycosis of biologic interest and epidemiologic consequence

Over the past 10 years, the environmental and veterinary communities have sounded alarms over an insidious keratinophilous fungus, Pseudogymnoascus destructans, that has decimated populations of bats (yes, bats, chiropterans) throughout North America and, most recently, Northern China and Siberia. We as dermatologists may find this invasive keratinophilous fungus of particular interest, as its method of destruction is disruption of the homeostatic mechanism of the bat wing integument. Although it is unlikely that this pathogen will become an infectious threat to humans, its environmental impact will likely affect us all, especially as recent data have shown upregulation of naturally occurring coronaviruses in coinfected bats. Dermatologists are familiar with keratinophilous dermatophyte infections, but these rarely cause serious morbidity in individual patients and never cause crisis on a population basis. This contribution describes the effects of P destructans on both the individual and the population basis. Bringing the white-nose syndrome to the attention of human dermatologists and skin scientists may invite transfer of expertise in understanding the disease, its pathophysiology, epidemiology, treatment, and prevention.

How virus size and attachment parameters affect the temperature sensitivity of virus binding to host cells: Predictions of a thermodynamic model for arboviruses and HIV

Virus binding to host cells involves specific interactions between viral (glyco)proteins (GP) and host cell surface receptors (Cr) (protein or sialic acid (SA)). The magnitude of the enthalpy of association changes with temperature according to the change in heat capacity (ΔCp) on GP/Cr binding, being little affected for avian influenza virus (AIV) haemagglutinin (HA) binding to SA (ΔCp = 0 kJ/mol/K) but greatly affected for HIV gp120 binding to CD4 receptor (ΔCp = -5.0 kJ/mol/K). A thermodynamic model developed here predicts that values of ΔCp from 0 to ~-2.0 kJ/mol/K have relatively little impact on the temperature sensitivity of the number of mosquito midgut cells with bound arbovirus, while intermediate values of ΔCp of ~-3.0 kJ/mol/K give a peak binding at a temperature of ~20 °C as observed experimentally for Western equine encephalitis virus. More negative values of ΔCp greatly decrease arbovirus binding at temperatures below ~20 °C. Thus to promote transmission at low temperatures, arboviruses may benefit from ΔCp ~ 0 kJ/mol/K as for HA/SA and it is interesting that bluetongue virus binds to SA in midge midguts. Large negative values of ΔCp as for HIV gp120:CD4 diminish binding at 37 °C. Of greater importance, however, is the decrease in entropy of the whole virus (ΔSa_immob) on its immobilisation on the host cell surface. ΔSa_immob presents a repulsive force which the enthalpy-driven GP/Cr interactions weakened at higher temperatures struggle to overcome. ΔSa_immob is more negative (less favourable) for larger diameter viruses which therefore show diminished binding at higher temperatures than smaller viruses. It is proposed that small size phenotype through a less negative ΔSa_immob is selected for viruses infecting warmer hosts thus explaining the observation that virion volume decreases with increasing host temperature from 0 °C to 40 °C in the case of dsDNA viruses. Compared to arboviruses which also infect warm-blooded vertebrates, HIV is large at 134 nm diameter and thus would have a large negative ΔSa_immob which would diminish its binding at human body temperature. It is proposed that prior non-specific binding of HIV through attachment factors takes much of the entropy loss for ΔSa_immob so enhancing subsequent specific gp120:CD4 binding at 37 °C. This is consistent with the observation that HIV attachment factors are not essential but augment infection. Antiviral therapies should focus on increasing virion size, for example through binding of zinc oxide nanoparticles to herpes simplex virus, hence making ΔSa_immob more negative, and thus reducing binding affinity at 37 °C.

Using Surveillance of Animal Bite Patients to Decipher Potential Risks of Rabies Exposure From Domestic Animals and Wildlife in Brazil

Direct contact with domestic animals and wildlife is linked to zoonotic spillover risk. Patients presenting with animal-bite injuries provide a potentially valuable source of surveillance data on rabies viruses that are transmitted primarily by animal bites. Here, we used passive surveillance data of bite patients to identify areas with high potential risk of rabies transmission to humans across Brazil, a highly diverse and populous country, where rabies circulates in a range of species. We analyzed one decade of bite patient data from the national health information system (SINAN) comprising over 500,000 patients attending public health facilities after being bitten by a domestic or wild animal. Our analyses show that, between 2008 and 2016, patients were mostly bitten by domestic dogs (average annual dog bite patients: 502,043 [436,391-544,564], annual incidence per state: 258 dog bites/100,000 persons) and cats (76,512 [56,588-97,580] cat bites, 41 cat bites/100,000/year), but bites from bats (4,172 [3,351-5,365] bat bites, 2.3/100,000/year), primates (3,320 [3,013-3,710] primate bites, 2.0/100,000/year), herbivores (1,908 [1,492-2,298] herbivore bites, 0.9/100,000/year) and foxes (883 [609-1,086] fox bites, 0.6/100,000/year) were also considerable. Incidence of bites due to dogs and herbivores remained relatively stable over the last decade. In contrast bites by cats and bats increased while bites by primates and foxes decreased. Bites by wild animals occurred in all states but were more frequent in the North and Northeast of Brazil, with over 3-fold differences in incidence between states across all animal groups. Most bites reported from domestic animals and wildlife occurred in urban settings (71%), except for bites from foxes, which were higher in rural settings (57%). Based upon the Ministry of Health guidelines, only half of patients received the correct Post-Exposure Prophylaxis following a bite by a suspect rabid animal. We identified areas and species of high-risk for potential zoonotic transmission of rabies in Brazil and reveal that, despite increasing human encroachment into natural ecosystems, only patients reporting bites by bats increased. Our study calls for future research to identity the socio-ecological factors underlying bites and the preventive measures needed to reduce their incidence and potential risk of rabies transmission.

The World Goes Bats: Living Longer and Tolerating Viruses

For centuries, people believed that bats possessed sinister powers. Bats are thought to be ancestral hosts to many deadly viruses affecting humans including Ebola, rabies, and most recently SARS-CoV-2 coronavirus. However, bats themselves tolerate these viruses without ill effects. The second power that bats have is their longevity. Bats live much longer than similar-sized land mammals. Here we review how bats' ability to control inflammation may be contributing to their longevity. The underlying mechanisms may hold clues to developing new treatments for age-related diseases. Now may be the time to use science to exploit the secret powers of bats for human benefit.

Implications of SARS-CoV-2 Mutations for Genomic RNA Structure and Host microRNA Targeting

The SARS-CoV-2 virus is a recently-emerged zoonotic pathogen already well adapted to transmission and replication in humans. Although the mutation rate is limited, recently introduced mutations in SARS-CoV-2 have the potential to alter viral fitness. In addition to amino acid changes, mutations could affect RNA secondary structure critical to viral life cycle, or interfere with sequences targeted by host miRNAs. We have analysed subsets of genomes from SARS-CoV-2 isolates from around the globe and show that several mutations introduce changes in Watson-Crick pairing, with resultant changes in predicted secondary structure. Filtering to targets matching miRNAs expressed in SARS-CoV-2-permissive host cells, we identified ten separate target sequences in the SARS-CoV-2 genome; three of these targets have been lost through conserved mutations. A genomic site targeted by the highly abundant miR-197-5p, overexpressed in patients with cardiovascular disease, is lost by a conserved mutation. Our results are compatible with a model that SARS-CoV-2 replication within the human host is constrained by host miRNA defences. The impact of these and further mutations on secondary structures, miRNA targets or potential splice sites offers a new context in which to view future SARS-CoV-2 evolution, and a potential platform for engineering conditional attenuation to vaccine development, as well as providing a better understanding of viral tropism and pathogenesis.

Snapshot of the evolution and mutation patterns of SARS-CoV-2

The COVID-19 pandemic is the most important public health threat in recent history. Here we study how its causal agent, SARS-CoV-2, has diversified genetically since its first emergence in December 2019. We have created a pipeline combining both phylogenetic and structural analysis to identify possible human-adaptation related mutations in a data set consisting of 4,894 SARS-CoV-2 complete genome sequences. Although the phylogenetic diversity of SARS-CoV-2 is low, the whole genome phylogenetic tree can be divided into five clusters/clades based on the tree topology and clustering of specific mutations, but its branches exhibit low genetic distance and bootstrap support values. We also identified 11 residues that are high-frequency substitutions, with four of them currently showing some signal for potential positive selection. These fast-evolving sites are in the non-structural proteins nsp2, nsp5 (3CL-protease), nsp6, nsp12 (polymerase) and nsp13 (helicase), in accessory proteins (ORF3a, ORF8) and in the structural proteins N and S. Temporal and spatial analysis of these potentially adaptive mutations revealed that the incidence of some of these sites was declining after having reached an (often local) peak, whereas the frequency of other sites is continually increasing and now exhibit a worldwide distribution. Structural analysis revealed that the mutations are located on the surface of the proteins that modulate biochemical properties. We speculate that this improves binding to cellular proteins and hence represents fine-tuning of adaptation to human cells. Our study has implications for the design of biochemical and clinical experiments to assess whether important properties of SARS-CoV-2 have changed during the epidemic.

Bat-borne virus diversity, spillover and emergence

Most viral pathogens in humans have animal origins and arose through cross-species transmission. Over the past 50 years, several viruses, including Ebola virus, Marburg virus, Nipah virus, Hendra virus, severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory coronavirus (MERS-CoV) and SARS-CoV-2, have been linked back to various bat species. Despite decades of research into bats and the pathogens they carry, the fields of bat virus ecology and molecular biology are still nascent, with many questions largely unexplored, thus hindering our ability to anticipate and prepare for the next viral outbreak. In this Review, we discuss the latest advancements and understanding of bat-borne viruses, reflecting on current knowledge gaps and outlining the potential routes for future research as well as for outbreak response and prevention efforts.

The influence of bat ecology on viral diversity and reservoir status

Repeated emergence of zoonotic viruses from bat reservoirs into human populations demands predictive approaches to preemptively identify virus-carrying bat species. Here, we use machine learning to examine drivers of viral diversity in bats, determine whether those drivers depend on viral genome type, and predict undetected viral carriers. Our results indicate that bat species with longer life spans, broad geographic distributions in the eastern hemisphere, and large group sizes carry more viruses overall. Life span was a stronger predictor of deoxyribonucleic acid viral diversity, while group size and family were more important for predicting ribonucleic acid viruses, potentially reflecting broad differences in infection duration. Importantly, our models predict 54 bat species as likely carriers of zoonotic viruses, despite not currently being considered reservoirs. Mapping these predictions as a proportion of local bat diversity, we identify global regions where efforts to reduce disease spillover into humans by identifying viral carriers may be most productive.

Bat-borne viruses in Africa: a critical review

In Africa, bat-borne zoonoses emerged in the past few decades resulting in large outbreaks or just sporadic spillovers. In addition, hundreds of more viruses are described without any information on zoonotic potential. We discuss important characteristics of bats including bat biology, evolution, distribution and ecology that not only make them unique among most mammals but also contribute to their potential as viral reservoirs. The detection of a virus in bats does not imply that spillover will occur and several biological, ecological and anthropogenic factors play a role in such an event. We summarize and critically analyse the current knowledge on African bats as reservoirs for corona-, filo-, paramyxo- and lyssaviruses. We highlight that important information on epidemiology, bat biology and ecology is often not available to make informed decisions on zoonotic spillover potential. Even if knowledge gaps exist, it is still important to recognize the role of bats in zoonotic disease outbreaks and implement mitigation strategies to prevent exposure to infectious agents including working safely with bats. Equally important is the crucial role of bats in various ecosystem services. This necessitates a multidisciplinary One Health approach to close knowledge gaps and ensure the development of responsible mitigation strategies to not only minimize risk of infection but also ensure conservation of the species.

Structural and Biochemical Characterization of the nsp12-nsp7-nsp8 Core Polymerase Complex from SARS-CoV-2

The ongoing global pandemic of coronavirus disease 2019 (COVID-19) has caused a huge number of human deaths. Currently, there are no specific drugs or vaccines available for this virus (SARS-CoV-2). The viral polymerase is a promising antiviral target. Here, we describe the near-atomic-resolution structure of the SARS-CoV-2 polymerase complex consisting of the nsp12 catalytic subunit and nsp7-nsp8 cofactors. This structure highly resembles the counterpart of SARS-CoV with conserved motifs for all viral RNA-dependent RNA polymerases and suggests a mechanism of activation by cofactors. Biochemical studies reveal reduced activity of the core polymerase complex and lower thermostability of individual subunits of SARS-CoV-2 compared with SARS-CoV. These findings provide important insights into RNA synthesis by coronavirus polymerase and indicate adaptation of SARS-CoV-2 toward humans with a relatively lower body temperature than the natural bat hosts.

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Cryo-EM structure of SARS-CoV-2 nsp12-nsp7-nsp8 core polymerase complex

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The core complex of SARS-CoV-2 has lower enzymatic activity than SARS-CoV

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SARS-CoV-2 nsp7-8-12 subunits are less thermostable than the SARS-CoV counterpart

Selection of viral variants during persistent infection of insectivorous bat cells with Middle East respiratory syndrome coronavirus

Coronaviruses that cause severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) are speculated to have originated in bats. The mechanisms by which these viruses are maintained in individuals or populations of reservoir bats remain an enigma. Mathematical models have predicted long-term persistent infection with low levels of periodic shedding as a likely route for virus maintenance and spillover from bats. In this study, we tested the hypothesis that bat cells and MERS coronavirus (CoV) can co-exist in vitro. To test our hypothesis, we established a long-term coronavirus infection model of bat cells that are persistently infected with MERS-CoV. We infected cells from Eptesicus fuscus with MERS-CoV and maintained them in culture for at least 126 days. We characterized the persistently infected cells by detecting virus particles, protein and transcripts. Basal levels of type I interferon in the long-term infected bat cells were higher, relative to uninfected cells, and disrupting the interferon response in persistently infected bat cells increased virus replication. By sequencing the whole genome of MERS-CoV from persistently infected bat cells, we identified that bat cells repeatedly selected for viral variants that contained mutations in the viral open reading frame 5 (ORF5) protein. Furthermore, bat cells that were persistently infected with ΔORF5 MERS-CoV were resistant to superinfection by wildtype virus, likely due to reduced levels of the virus receptor, dipeptidyl peptidase 4 (DPP4) and higher basal levels of interferon in these cells. In summary, our study provides evidence for a model of coronavirus persistence in bats, along with the establishment of a unique persistently infected cell culture model to study MERS-CoV-bat interactions.

Viral zoonotic risk is homogenous among taxonomic orders of mammalian and avian reservoir hosts

Identifying whether novel human viruses disproportionately originate from certain animal groups could inform risk-based allocations of research and surveillance effort. Whether such “special reservoirs” exist remains controversial. We show that the proportion of viruses that infect humans varies minimally across reservoir taxonomic orders. Instead, the number of human-infecting viruses increases proportionately to the total number of viruses maintained by each reservoir group, which is in turn explained by the number of animal species within each group. This supports a host-neutral explanation for observed variation in the number of zoonoses among animal groups, such that traits of animal orders are unlikely to produce viruses that disproportionately threaten humans. These findings refine strategies to identify high-risk viruses prior to their emergence.

The notion that certain animal groups disproportionately maintain and transmit viruses to humans due to broad-scale differences in ecology, life history, and physiology currently influences global health surveillance and research in disease ecology, virology, and immunology. To directly test whether such “special reservoirs” of zoonoses exist, we used literature searches to construct the largest existing dataset of virus–reservoir relationships, consisting of the avian and mammalian reservoir hosts of 415 RNA and DNA viruses along with their histories of human infection. Reservoir host effects on the propensity of viruses to have been reported as infecting humans were rare and when present were restricted to one or two viral families. The data instead support a largely host-neutral explanation for the distribution of human-infecting viruses across the animal orders studied. After controlling for higher baseline viral richness in mammals versus birds, the observed number of zoonoses per animal order increased as a function of their species richness. Animal orders of established importance as zoonotic reservoirs including bats and rodents were unexceptional, maintaining numbers of zoonoses that closely matched expectations for mammalian groups of their size. Our findings show that variation in the frequency of zoonoses among animal orders can be explained without invoking special ecological or immunological relationships between hosts and viruses, pointing to a need to reconsider current approaches aimed at finding and predicting novel zoonoses.

Positive Selection of a Serine Residue in Bat IRF3 Confers Enhanced Antiviral Protection

Compared with other mammals, bats harbor more zoonotic viruses per species and do not demonstrate signs of disease on infection with these viruses. To counteract infections with viruses, bats have evolved enhanced mechanisms to limit virus replication and immunopathology. However, molecular and cellular drivers of antiviral responses in bats largely remain an enigma. In this study, we demonstrate that a serine residue in IRF3 is positively selected for in multiple bat species. IRF3 is a central regulator of innate antiviral responses in mammals. Replacing the serine residue in bat IRF3 with the human leucine residue decreased antiviral protection in bat cells, whereas the addition of this serine residue in human IRF3 significantly enhanced antiviral protection in human cells. Our study provides genetic and functional evidence for enhanced IRF3-mediated antiviral responses in bats and adds support to speculations that bats have positively selected for multiple adaptations in their antiviral immune responses.

Between roost contact is essential for maintenance of European bat lyssavirus type-2 in Myotis daubentonii bat reservoir: 'The Swarming Hypothesis'

Many high-consequence human and animal pathogens persist in wildlife reservoirs. An understanding of the dynamics of these pathogens in their reservoir hosts is crucial to inform the risk of spill-over events, yet our understanding of these dynamics is frequently insufficient. Viral persistence in a wild bat population was investigated by combining empirical data and in-silico analyses to test hypotheses on mechanisms for viral persistence. A fatal zoonotic virus, European Bat lyssavirus type 2 (EBLV-2), in Daubenton’s bats (Myotis daubentonii) was used as a model system. A total of 1839 M. daubentonii were sampled for evidence of virus exposure and excretion during a prospective nine year serial cross-sectional survey. Multivariable statistical models demonstrated age-related differences in seroprevalence, with significant variation in seropositivity over time and among roosts. An Approximate Bayesian Computation approach was used to model the infection dynamics incorporating the known host ecology. The results demonstrate that EBLV-2 is endemic in the study population, and suggest that mixing between roosts during seasonal swarming events is necessary to maintain EBLV-2 in the population. These findings contribute to understanding how bat viruses can persist despite low prevalence of infection, and why infection is constrained to certain bat species in multispecies roosts and ecosystems.

Recurrent evolution of extreme longevity in bats

Bats live longer than similar-sized mammals, but the number of lineages that have independently evolved extreme longevity has not previously been determined. Here we reconstruct the evolution of size-corrected longevity on a recent molecular phylogeny and find that at least four lineages of bats have lifespans more than fourfold those of similar-sized placental mammals, with the ancestral bat projected to live 2.6 times as long. We then evaluate a series of phylogenetic generalized least-squares models containing up to nine variables hypothesized to influence extrinsic mortality. These analyses reveal that body mass and hibernation predict longevity. Among hibernators, longevity is predicted by the absolute value of the median latitude of the species range and cave use, while cave use and lack of sexual dimorphism predict longevity among non-hibernators. The importance of torpor in extending lifespan is further supported by the one lineage with extreme longevity that does not hibernate but exhibits flexible thermoregulation, the common vampire bat. We propose several potential mechanisms that may enable bats to live so long, and suggest that the ability to tolerate a wide range of body temperatures could be important for surviving viral or other pathogen infections.

Nipah virus: epidemiology, pathology, immunobiology and advances in diagnosis, vaccine designing and control strategies - a comprehensive review

Nipah (Nee-pa) viral disease is a zoonotic infection caused by Nipah virus (NiV), a paramyxovirus belonging to the genus Henipavirus of the family Paramyxoviridae. It is a biosafety level-4 pathogen, which is transmitted by specific types of fruit bats, mainly Pteropus spp. which are natural reservoir host. The disease was reported for the first time from the Kampung Sungai Nipah village of Malaysia in 1998. Human-to-human transmission also occurs. Outbreaks have been reported also from other countries in South and Southeast Asia. Phylogenetic analysis affirmed the circulation of two major clades of NiV as based on currently available complete N and G gene sequences. NiV isolates from Malaysia and Cambodia clustered together in NiV-MY clade, whereas isolates from Bangladesh and India clusterered within NiV-BD clade. NiV isolates from Thailand harboured mixed population of sequences. In humans, the virus is responsible for causing rapidly progressing severe illness which might be characterized by severe respiratory illness and/or deadly encephalitis. In pigs below six months of age, respiratory illness along with nervous symptoms may develop. Different types of enzyme-linked immunosorbent assays along with molecular methods based on polymerase chain reaction have been developed for diagnostic purposes. Due to the expensive nature of the antibody drugs, identification of broad-spectrum antivirals is essential along with focusing on small interfering RNAs (siRNAs). High pathogenicity of NiV in humans, and lack of vaccines or therapeutics to counter this disease have attracted attention of researchers worldwide for developing effective NiV vaccine and treatment regimens.

A comprehensive annotation and differential expression analysis of short and long non-coding RNAs in 16 bat genomes

Although bats are increasingly becoming the focus of scientific studies due to their unique properties, these exceptional animals are still among the least studied mammals. Assembly quality and completeness of bat genomes vary a lot and especially non-coding RNA (ncRNA) annotations are incomplete or simply missing. Accordingly, standard bioinformatics pipelines for gene expression analysis often ignore ncRNAs such as microRNAs or long antisense RNAs. The main cause of this problem is the use of incomplete genome annotations. We present a complete screening for ncRNAs within 16 bat genomes. NcRNAs affect a remarkable variety of vital biological functions, including gene expression regulation, RNA processing, RNA interference and, as recently described, regulatory processes in viral infections. Within all investigated bat assemblies, we annotated 667 ncRNA families including 162 snoRNAs and 193 miRNAs as well as rRNAs, tRNAs, several snRNAs and lncRNAs, and other structural ncRNA elements. We validated our ncRNA candidates by six RNA-Seq data sets and show significant expression patterns that have never been described before in a bat species on such a large scale. Our annotations will be usable as a resource (rna.uni-jena.de/supplements/bats) for deeper studying of bat evolution, ncRNAs repertoire, gene expression and regulation, ecology and important host–virus interactions.

Viral networks and detection of potential zoonotic viruses in bats and rodents: A worldwide analysis

Bats and rodents are recognized to host a great diversity of viruses and several important viral zoonoses, but how this viral diversity is structured and how viruses are connected, shared and distributed among host networks is not well understood. To address this gap in knowledge, we compared the associative capacity of the host-virus networks in rodents and bats with the identification of those viruses with zoonotic potential. A virus database, detected by molecular methods, was constructed in the two taxonomic groups. We compiled 5,484 records: 825 in rodents and 4,659 in bats. We identified a total of 173 and 166 viruses, of which 53 and 40 are zoonotic viruses, in rodents and bats, respectively. Based on a network theory, a non-directed bipartite host-virus network was built for each group. Subsequently, the networks were collapsed to represent the connections among hosts and viruses. We identified both discrete and connected communities. We observed a greater degree of connectivity in bat viruses and more discrete communities in rodents. The Coronaviridae recorded in bats have the highest values of degree, betweenness and closeness centralities. In rodents, higher degree positions were distributed homogeneously between viruses and hosts. At least in our database, a higher proportion of rodent viruses were zoonotic. Rodents should thus not be underestimated as important reservoirs of zoonotic disease. We found that viruses were more frequently shared among bats than in rodents. Network theory can reveal some macroecological patterns and identify risks that were previously unrecognized. For example, we found that parvovirus in megabats and Gbagroube virus in rodents may represent a zoonotic risk due to the proximity to humans and other zoonotic viruses. We propose that epidemiological surveillance programmes should consider the connectivity of network actors as a measure of the risks of dispersion and transmission.

Identification of Diverse Bat Alphacoronaviruses and Betacoronaviruses in China Provides New Insights Into the Evolution and Origin of Coronavirus-Related Diseases

Outbreaks of severe acute respiratory syndrome (SARS) in 2002, Middle East respiratory syndrome in 2012 and fatal swine acute diarrhea syndrome in 2017 caused serious infectious diseases in humans and in livestock, resulting in serious public health threats and huge economic losses. All such coronaviruses (CoVs) were confirmed to originate from bats. To continuously monitor the epidemic-related CoVs in bats, virome analysis was used to classify CoVs from 831 bats of 15 species in Yunnan, Guangxi, and Sichuan Provinces between August 2016 and May 2017. We identified 11 CoV strains from 22 individual samples of four bat species. Identification of four alpha-CoVs from Scotophilus kuhlii in Guangxi, which was closely related to a previously reported bat CoV and porcine epidemic diarrhea virus (PEDV), revealed a bat-swine lineage under the genus Alphacoronavirus. A recombinant CoV showed that the PEDV probably originated from the CoV of S. kuhlii. Another alpha-CoV, α-YN2018, from Rhinolophus sinicus in Yunnan, suggested that this alpha-CoV lineage had multiple host origins, and α-YN2018 had recombined with CoVs of other bat species over time. We identified five SARS-related CoVs (SARSr-CoVs) in Rhinolophus bats from Sichuan and Yunnan and confirmed that angiotensin-converting enzyme 2 usable SARSr-CoVs were continuously circulating in Rhinolophus spp. in Yunnan. The other beta-CoV, strain β-GX2018, found in Cynopterus sphinx of Guangxi, represented an independently evolved lineage different from known CoVs of Rousettus and Eonycteris bats. The identification of diverse CoVs here provides new genetic data for understanding the distribution and source of pathogenic CoVs in China.

Isolation and characterization of trypanosomatids, including Crithidia mellificae, in bats from the Atlantic Forest of Rio de Janeiro, Brazil

We studied infection by Trypanosomatidae in bats captured in two areas with different degradation levels in the Atlantic Forest of Rio de Janeiro state: Reserva Ecológica de Guapiaçu (REGUA) and Estação Fiocruz Mata Atlântica (EFMA). Furthermore, we evaluated whether the diversity of trypanosomatids changes according to bat diversity and the different levels of preservation in the region. The results showed no influence of the level of preservation on bat species richness (15 and 14 species, respectively), with similar chiropterofauna and higher abundance of two common fruit-eating bat species in the tropics: Carollia perspicillata and Artibeus lituratus. Of the 181 bat specimens analyzed by LIT/Schneider hemoculture, we detected 24 infected individuals (13%), including one positive Sturnira lilium individual that was also positive by fresh blood examination. Molecular characterization using nested PCR targeting the 18 SSU rRNA-encoding gene fragment showed similar trypanosomatid infection rates in bats from the two areas: 15% in REGUA and 11% in EFMA (p = 0.46). Trypanosoma dionisii was the most frequently detected parasite (54%), followed by T. cruzi DTUs TcI and TcIV and Trypanosoma sp., in Neotropical phyllostomid bats (RNMO63 and RNMO56); mixed infections by T. dionisii/T. cruzi TcIII and T. dionisii/T. cruzi TcI were also observed. The T. cruzi DTUs TcI and TcIV are the genotypes currently involved in cases of acute Chagas disease in Brazil, and T. dionisii was recently found in the heart tissue of an infected child. Surprisingly, we also describe for the first time Crithidia mellificae, a putative monoxenous parasite from insects, infecting a vertebrate host in the Americas. Bats from the Atlantic Forest of Rio de Janeiro state harbor a great diversity of trypanosomatids, maintaining trypanosomatid diversity in this sylvatic environment.

High basal heat-shock protein expression in bats confers resistance to cellular heat/oxidative stress

Bats, unique among mammals with powered flight, have many species with the longest size-proportionate lifespan of all mammals. Evolutionary adaptations would have been required to survive the elevated body temperatures during flight. Heat shock protein (HSP), highly conserved master regulators of cell stress, expression was examined across tissues and various cell lines in bats. Basal expression level of major HSPs (HSP70 and HSP90) is significantly higher in two different bat species compared to other mammals. This HSP expression could be a bat-unique, key factor to modulate cellular stress and death. Consequently, bat cells survive prolonged heat treatment, along with other stress stimuli, in a HSP-dependent manner, whereas other mammalian cells succumbed. This suggests HSP expression in bats could be an important adaption to intrinsic metabolic stresses like flight and therefore an important model to study stress resilience and longevity in general.

The spleen morphophysiology of fruit bats

Spleen is one of the important lymphoid organs with wide variations of morphological and physiological functions according to species. Morphology and function of the spleen in bats, which are hosts to several viral strains without exhibiting clinical symptoms, remain to be fully elucidated. This study aims to examine the spleen morphology of fruit bats associated with their physiological functions. Spleen histological observations were performed in three fruit bats species: Cynopterus titthaecheilus (n = 9), Rousettus leschenaultii (n = 3) and Pteropus vampyrus (n = 3). The spleens of these fruit bats were surrounded by a thin capsule. Red pulp consisted of splenic cord and wide vascular space filled with blood. Ellipsoids in all three studied species were found numerously and adjacent to one another forming macrophages aggregates. White pulp consisted of periarteriolar lymphoid sheaths (PALS), lymphoid follicles and marginal zone. The lymphoid follicle contained a germinal centre and a tingible body macrophage that might reflect an active immune system. The marginal zone was prominent and well developed. This study reports some differences in spleen structure of fruit bats compared to other bat species previously reported and discusses possible physiological implications of the spleen based on its morphology.

Dengue Virus in Bats from Córdoba and Sucre, Colombia

Natural infection of dengue virus (DENV) in bats is an unexplored field in Colombia. To detect the presence of DENV in bats, a descriptive prospective study using a nonprobabilistic sampling was carried out; 286 bats in 12 sites were caught. Sample tissues of different animals were obtained; the RNA was obtained from tissues and a nested-RT-PCR was carried out and detected amplicons of 143 fragment of the NS5 gene were sequenced by the Sanger method. In nonhematophagous bats Carollia perspicillata and Phyllostomus discolor captured in Ayapel and San Carlos (Córdoba), respectively, an amplicon corresponding to NS5 was detected. The amplicons showed a high similarity with serotype-2 dengue virus (DENV-2). This is the first evidence of the DENV-2 genome in bats in from the Colombian Caribbean.

Differential Evolution of Antiretroviral Restriction Factors in Pteropid Bats as Revealed by APOBEC3 Gene Complexity

Bats have attracted attention in recent years as important reservoirs of viruses deadly to humans and other mammals. These infections are typically nonpathogenic in bats raising questions about innate immune differences that might exist between bats and other mammals. The APOBEC3 gene family encodes antiviral DNA cytosine deaminases with important roles in the suppression of diverse viruses and genomic parasites. Here, we characterize pteropid APOBEC3 genes and show that species within the genus Pteropus possess the largest and most diverse array of APOBEC3 genes identified in any mammal reported to date. Several bat APOBEC3 proteins are antiviral as demonstrated by restriction of retroviral infectivity using HIV-1 as a model, and recombinant A3Z1 subtypes possess strong DNA deaminase activity. These genes represent the first group of antiviral restriction factors identified in bats with extensive diversification relative to homologues in other mammals.

Nipah virus: epidemiology, pathology, immunobiology and advances in diagnosis, vaccine designing and control strategies - a comprehensive review

Nipah (Nee-pa) viral disease is a zoonotic infection caused by Nipah virus (NiV), a paramyxovirus belonging to the genus Henipavirus of the family Paramyxoviridae. It is a biosafety level-4 pathogen, which is transmitted by specific types of fruit bats, mainly Pteropus spp. which are natural reservoir host. The disease was reported for the first time from the Kampung Sungai Nipah village of Malaysia in 1998. Human-to-human transmission also occurs. Outbreaks have been reported also from other countries in South and Southeast Asia. Phylogenetic analysis affirmed the circulation of two major clades of NiV as based on currently available complete N and G gene sequences. NiV isolates from Malaysia and Cambodia clustered together in NiV-MY clade, whereas isolates from Bangladesh and India clusterered within NiV-BD clade. NiV isolates from Thailand harboured mixed population of sequences. In humans, the virus is responsible for causing rapidly progressing severe illness which might be characterized by severe respiratory illness and/or deadly encephalitis. In pigs below six months of age, respiratory illness along with nervous symptoms may develop. Different types of enzyme-linked immunosorbent assays along with molecular methods based on polymerase chain reaction have been developed for diagnostic purposes. Due to the expensive nature of the antibody drugs, identification of broad-spectrum antivirals is essential along with focusing on small interfering RNAs (siRNAs). High pathogenicity of NiV in humans, and lack of vaccines or therapeutics to counter this disease have attracted attention of researchers worldwide for developing effective NiV vaccine and treatment regimens.

Bat tolerance to viral infections

Inflammatory molecules evolved partly to protect hosts from viruses, but increasing evidence suggests that they cause disease pathology and chronic conditions, and play a role in aging. By mitigating these effects, bats are able to both tolerate viral infections and live well beyond expectations.

Frugivorous bats in the Colombian Caribbean region are reservoirs of the rabies virus

BACKGROUND

Bats are an important ecological group within ecosystems. The rabies virus is a Lyssavirus, and haematophagous bats are the principal reservoir; however, the virus has also been detected in non-haematophagous bats. The objective was to determine the rabies virus in non-haematophagous bats in the Colombian Caribbean region.

METHODS

In 2017, a cross-sectional study was carried out with a base-risk sampling in twelve geographic zones of the Colombian Caribbean area that included the main ecosystems of two departments. 286 bats were captured, which were euthanized with a pharmacological treatment following the ethical protocols of animal experimentation. The taxonomic identification was done with dichotomous keys. The necropsy was carried out at the capture site, and brain samples were kept in liquid nitrogen. The extraction of the RNA was carried out from the frozen brains with Trizol™; a fragment of 914 bp of the glycoprotein G of the rabies virus was amplified with RT-PCR. The amplicons were sequenced with the Sanger method.

RESULTS

Twenty-three genera of bats were identified, and, in two frugivorous, Artibeus lituratus and Artibeus planirostris, amplicons were obtained and sequenced as the rabies virus.

CONCLUSIONS

This is the first evidence of natural infection of the rabies virus in frugivorous bats in the Colombian Caribbean area; this result is important for the surveillance and control of rabies.

Enhanced Autophagy Contributes to Reduced Viral Infection in Black Flying Fox Cells

Bats are increasingly implicated as hosts of highly pathogenic viruses. The underlying virus⁻host interactions and cellular mechanisms that promote co-existence remain ill-defined, but physiological traits such as flight and longevity are proposed to drive these adaptations. Autophagy is a cellular homeostatic process that regulates ageing, metabolism, and intrinsic immune defense. We quantified basal and stimulated autophagic responses in black flying fox cells, and demonstrated that although black flying fox cells are susceptible to Australian bat lyssavirus (ABLV) infection, viral replication is dampened in these bat cells. Black flying fox cells tolerated prolonged ABLV infection with less cell death relative to comparable human cells, suggesting post-entry mechanisms interference with virus replication. An elevated basal autophagic level was observed and autophagy was induced in response to high virus doses. Pharmacological stimulation of the autophagy pathway reduced virus replication, indicating autophagy acts as an anti-viral mechanism. Enhancement of basal and virus-induced autophagy in bat cells connects related reports that long-lived species possess homeostatic processes that dampen oxidative stress and macromolecule damage. Exemplifying the potential that evolved cellular homeostatic adaptations like autophagy may secondarily act as anti-viral mechanisms, enabling bats to serve as natural hosts to an assortment of pathogenic viruses. Furthermore, our data suggest autophagy-inducing drugs may provide a novel therapeutic strategy for combating lyssavirus infection.

Studies on B Cells in the Fruit-Eating Black Flying Fox (Pteropus alecto)

The ability of bats to act as reservoir for viruses that are highly pathogenic to humans suggests unique properties and functional characteristics of their immune system. However, the lack of bat specific reagents, in particular antibodies, has limited our knowledge of bat's immunity. Here, we report a panel of cross-reactive antibodies against MHC-II, NK1.1, CD3, CD21, CD27, and immunoglobulin (Ig), that allows flow cytometry analysis of B, T and NK cell populations in two different fruit-eating bat species namely, Pteropus alecto and E. spelaea. Results confirmed predominance of T cells in the spleen and blood of bats, as previously reported by us. However, the percentages of B cells in bone marrow and NK cells in spleen varied greatly between wild caught P. alecto bats and E. spelaea colony bats, which may reflect inherent differences of their immune system or different immune status. Other features of bat B cells were investigated. A significant increase in sIg+ B cell population was observed in the spleen and blood from LPS-injected bats but not from poly I:C-injected bats, supporting T-independent polyclonal B cell activation by LPS. Furthermore, using an in vitro calcium release assay, P. alecto B cells exhibited significant calcium release upon cross-linking of their B cell receptor. Together, this work contributes to improve our knowledge of bat adaptive immunity in particular B cells.

Bat Research Networks and Viral Surveillance: Gaps and Opportunities in Western Asia

Bat research networks and viral surveillance are assumed to be at odds due to seemingly conflicting research priorities. Yet human threats that contribute to declines in bat populations globally also lead to increased transmission and spread of bat-associated viruses, which may pose a threat to global health and food security. In this review, we discuss the importance of and opportunities for multidisciplinary collaborations between bat research networks and infectious disease experts to tackle shared threats that jeopardize bat conservation as well as human and animal health. Moreover, we assess research effort on bats and bat-associated viruses globally, and demonstrate that Western Asia has limited published research and represents a gap for coordinated bat research. The lack of bat research in Western Asia severely limits our capacity to identify and mitigate region-specific threats to bat populations and detect interactions between bats and incidental hosts that promote virus spillover. We detail a regional initiative to establish the first bat research network in Western Asia (i.e., the Western Asia Bat Research Network, WAB-Net), with the aim of integrating ecological research on bats with virus surveillance to find “win-win” solutions that promote bat conservation and safeguard public and animal health across the region.

Dampened NLRP3-mediated inflammation in bats and implications for a special viral reservoir host

Bats are special in their ability to host emerging viruses. As the only flying mammal, bats endure high metabolic rates yet exhibit elongated lifespans. It is currently unclear whether these unique features are interlinked. The important inflammasome sensor, NLR family pyrin domain containing 3 (NLRP3), has been linked to both viral-induced and age-related inflammation. Here, we report significantly dampened activation of the NLRP3 inflammasome in bat primary immune cells compared to human or mouse counterparts. Lower induction of apoptosis-associated speck-like protein containing a CARD (ASC) speck formation and secretion of interleukin-1β in response to both 'sterile' stimuli and infection with multiple zoonotic viruses including influenza A virus (-single-stranded (ss) RNA), Melaka virus (PRV3M, double-stranded RNA) and Middle East respiratory syndrome coronavirus (+ssRNA) was observed. Importantly, this reduction of inflammation had no impact on the overall viral loads. We identified dampened transcriptional priming, a novel splice variant and an altered leucine-rich repeat domain of bat NLRP3 as the cause. Our results elucidate an important mechanism through which bats dampen inflammation with implications for longevity and unique viral reservoir status.

Immune System Modulation and Viral Persistence in Bats: Understanding Viral Spillover

Bats harbor a myriad of viruses and some of these viruses may have spilled over to other species including humans. Spillover events are rare and several factors must align to create the “perfect storm” that would ultimately lead to a spillover. One of these factors is the increased shedding of virus by bats. Several studies have indicated that bats have unique defense mechanisms that allow them to be persistently or latently infected with viruses. Factors leading to an increase in the viral load of persistently infected bats would facilitate shedding of virus. This article reviews the unique nature of bat immune defenses that regulate virus replication and the various molecular mechanisms that play a role in altering the balanced bat–virus relationship.

Handling Stress and Sample Storage Are Associated with Weaker Complement-Mediated Bactericidal Ability in Birds but Not Bats

Variation in immune defense influences infectious disease dynamics within and among species. Understanding how variation in immunity drives pathogen transmission among species is especially important for animals that are reservoir hosts for zoonotic pathogens. Bats, in particular, have a propensity to host serious viral zoonoses without developing clinical disease themselves. The immunological adaptations that allow bats to host viruses without disease may be related to their adaptations for flight (e.g., in metabolism and mediation of oxidative stress). A number of analyses report greater richness of zoonotic pathogens in bats than in other taxa, such as birds (i.e., mostly volant vertebrates) and rodents (i.e., nonvolant small mammals), but immunological comparisons between bats and these other taxa are rare. To examine interspecific differences in bacterial killing ability (BKA), a functional measure of overall constitutive innate immunity, we use a phylogenetic meta-analysis to compare how BKA responds to the acute stress of capture and to storage time of frozen samples across the orders Aves and Chiroptera. After adjusting for host phylogeny, sample size, and total microbe colony-forming units, we find preliminary evidence that the constitutive innate immune defense of bats may be more resilient to handling stress and storage time than that of birds. This pattern was also similar when we analyzed the proportion of nonnegative and positive effect sizes per species, using phylogenetic comparative methods. We discuss potential physiological and evolutionary mechanisms by which complement proteins may differ between species orders and suggest future avenues for comparative field studies of immunity between sympatric bats, birds, and rodents in particular.

Lowland grazing and Marburg virus disease (MVD) outbreak in Kween district, Eastern Uganda

BACKGROUND

Uganda is one of the few countries in Africa that has been experiencing outbreaks of viral hemorrhagic fevers such as Ebola, Marburg and Crimean-Congo Hemorrhagic fevers. In 2017 Uganda experienced a Marburg Virus Disease (MVD) outbreak with case fatality rate of 100% in Kween district. Although hunting for wild meat was linked to the MVD outbreak in Kween district, less was reported on the land use changes, especially the changing animal grazing practices in Kween district.

METHODS

Through Makerere University One Health graduate fellowship program with attachment to Uganda Red Cross Society, a study was conducted among the agricultural communities to elucidate the risk behaviors in Kween district that can be linked to the 2017 Marburg disease outbreak.

RESULTS

Results show that although a few elderly participants ascribed fatal causes (disobedience to gods, ancestors, and evil spirits) to the MVD outbreak during FGDs, majority of participants linked MVD to settling in caves (inhabited by Fruit Bats) during wet season as upper belts are extensively used for crop production leaving little space for animal grazing. Members also noted side activities like hunting for wild meat during this grazing period that could have predisposed them to Marburg Virus.

CONCLUSIONS

There is need to integrate One Health concepts within agricultural extension service provision in Uganda so as to enhance the management of such infectious diseases.

PRINCIPLES AND PATTERNS OF BAT MOVEMENTS: FROM AERODYNAMICS TO ECOLOGY

Movement ecology as an integrative discipline has advanced associated fields because it presents not only a conceptual framework for understanding movement principles but also helps formulate predictions about the consequences of movements for animals and their environments. Here, we synthesize recent studies on principles and patterns of bat movements in context of the movement ecology paradigm. The motion capacity of bats is defined by their highly articulated, flexible wings. Power production during flight follows a U-shaped curve in relation to speed in bats yet, in contrast to birds, bats use mostly exogenous nutrients for sustained flight. The navigation capacity of most bats is dominated by the echolocation system, yet other sensory modalities, including an iron-based magnetic sense, may contribute to navigation depending on a bat's familiarity with the terrain. Patterns derived from these capacities relate to antagonistic and mutualistic interactions with food items. The navigation capacity of bats may influence their sociality, in particular, the extent of group foraging based on eavesdropping on conspecifics' echolocation calls. We infer that understanding the movement ecology of bats within the framework of the movement ecology paradigm provides new insights into ecological processes mediated by bats, from ecosystem services to diseases.

Metagenomic Analysis of Samples from Three Bat Species Collected in the Amazon Rain Forest

We report here the sequencing of five microbiome samples collected from different bat species in the Amazon rain forest. All contigs matching virus sequences were assigned to members of the Retroviridae family, while the bacterial contigs matched several bacterial species mostly belonging to the Proteobacteria phylum.

We report here the sequencing of five microbiome samples collected from different bat species in the Amazon rain forest. All contigs matching virus sequences were assigned to members of the Retroviridae family, while the bacterial contigs matched several bacterial species mostly belonging to the Proteobacteria phylum.

Extreme temperature event and mass mortality of insectivorous bats

A mass mortality event involving Chaerephon plicatus and Taphozous theobaldi bats occurred during a heat wave in April 2016 in Cambodia. This was investigated to clarify the causes of the die-off and assess the risk to public health. Field evidences, clinical signs, and gross pathology findings were consistent with a heat stress hypothesis. However, the detection of a novel bat paramyxovirus raises questions about its role as a contributing factor or a coincidental finding. Systematic documentation of bat die-offs related to extreme weather events is necessary to improve understanding of the effect of changing weather patterns on bat populations and the ecosystem services they provide.

Arousal from hibernation and reactivation of Eptesicus fuscus gammaherpesvirus (EfHV) in big brown bats

Many viruses that cause serious and often fatal disease in humans have spilled over from bats. Recent evidence suggests that stress may enhance virus shedding by bats increasing the possibility of transmission to other species. To understand the reasons for spillover is therefore important to determine the molecular pathways that link stress to virus reactivation and shedding in bats. We recently isolated and characterized a gammaherpesvirus (Eptesicus fuscus herpesvirus, EfHV) autochthonous to North American big brown bats. Since herpesviruses are known to reactivate from latent infections in response to a wide variety of stressors, EfHV presents us with an opportunity to study how physiological, behavioural or environmental changes may influence the big brown bats' relationship with EfHV. To understand the biology of the virus and how the extended periods of torpor experienced by these bats during hibernation along with the stress of arousal might influence the virus-host relationship, we attempted to detect the virus in the blood of wild-caught non-hibernating bats as well as captive bats arising from hibernation. We compared the prevalence of EfHV in the blood (using PCR) and EfHV-specific antibodies (using ELISA) between captive hibernating bats and wild-caught non-hibernating bats. We detected EfHV only in the blood of captive hibernating bats (27.8% = 10/36) and not in wild-caught non-hibernating bats (0.0% = 0/43). In contrast, the EfHV-specific antibody titres were higher in the non-hibernating bats compared to the hibernating bats. Our study suggests that: (a) viral DNA in blood indicates reactivation from latency, (b) long periods of hibernation lead to suppression of immunity, (c) stress of arousal from hibernation reactivates the virus in bats with lower levels of anti-viral immunity (indicated by humoral immune response), and (d) levels of anti-viral immunity increase in non-hibernating bats following reactivation.

Predicting wildlife reservoirs and global vulnerability to zoonotic Flaviviruses

Flaviviruses continue to cause globally relevant epidemics and have emerged or re-emerged in regions that were previously unaffected. Factors determining emergence of flaviviruses and continuing circulation in sylvatic cycles are incompletely understood. Here we identify potential sylvatic reservoirs of flaviviruses and characterize the macro-ecological traits common to known wildlife hosts to predict the risk of sylvatic flavivirus transmission among wildlife and identify regions that could be vulnerable to outbreaks. We evaluate variability in wildlife hosts for zoonotic flaviviruses and find that flaviviruses group together in distinct clusters with similar hosts. Models incorporating ecological and climatic variables as well as life history traits shared by flaviviruses predict new host species with similar host characteristics. The combination of vector distribution data with models for flavivirus hosts allows for prediction of  global vulnerability to flaviviruses and provides potential targets for disease surveillance in animals and humans.

Productive Propagation of Rift Valley Fever Phlebovirus Vaccine Strain MP-12 in Rousettus aegyptiacus Fruit Bats

Rift Valley fever phlebovirus (RVFV), the causative agent of an emerging zoonotic disease in Africa and Arabia, can infect a variety of species, predominantly ruminants, camelids, and humans. While clinical symptoms are mostly absent in adult ruminants and camelids, RVFV infection may lead to a serious, sometimes fatal disease in humans. Virus transmissions between individuals and between species mainly occur through mosquito bites, but direct or even indirect contact with infectious materials may also result in infection. Although the main reservoir of the virus is not yet identified, small mammals such as rodents and bats may act as amplifying hosts. We therefore inoculated Rousettus aegyptiacus fruit bats that are abundant in northern Africa with the vaccine strain MP-12, in order to elucidate the general competence of this species for virus propagation and transmission. We were able to detect the RVFV genome in the spleen of each of these animals, and re-isolated the virus from the spleen and liver of some animals. Moreover, we were able to identify the Gc RVFV surface antigen in mild subacute multifocal necrotizing hepatic lesions of one bat which was sacrificed 7 days post exposure. These findings demonstrate that Rousettus aegyptiacus fruit bats can propagate RVFV.

White-nose syndrome is associated with increased replication of a naturally persisting coronaviruses in bats

Spillover of viruses from bats to other animals may be associated with increased contact between them, as well as increased shedding of viruses by bats. Here, we tested the prediction that little brown bats (Myotis lucifugus) co-infected with the M. lucifugus coronavirus (Myl-CoV) and with Pseudogymnoascus destructans (Pd), the fungus that causes bat white-nose syndrome (WNS), exhibit different disease severity, viral shedding and molecular responses than bats infected with only Myl-CoV or only P. destructans. We took advantage of the natural persistence of Myl-CoV in bats that were experimentally inoculated with P. destructans in a previous study. Here, we show that the intestines of virus-infected bats that were also infected with fungus contained on average 60-fold more viral RNA than bats with virus alone. Increased viral RNA in the intestines correlated with the severity of fungus-related pathology. Additionally, the intestines of bats infected with fungus exhibited different expression of mitogen-activated protein kinase pathway and cytokine related transcripts, irrespective of viral presence. Levels of coronavirus antibodies were also higher in fungal-infected bats. Our results suggest that the systemic effects of WNS may down-regulate anti-viral responses in bats persistently infected with M. lucifugus coronavirus and increase the potential of virus shedding.

Ebola Virus Maintenance: If Not (Only) Bats, What Else?

The maintenance mechanisms of ebolaviruses in African forest ecosystems are still unknown, but indirect evidences point at the involvement of some bat species. Despite intense research, the main bat-maintenance hypothesis has not been confirmed yet. The alternative hypotheses of a non-bat maintenance host or a maintenance community including, or not, several bat and other species, deserves more investigation. However, African forest ecosystems host a large biodiversity and abound in potential maintenance hosts. How does one puzzle out? Since recent studies have revealed that several bat species have been exposed to ebolaviruses, the common denominator to these hypotheses is that within the epidemiological cycle, some bats species must be exposed to the viruses and infected by these potential alternative hosts. Under this constraint, and given the peculiar ecology of bats (roosting behaviour, habitat utilisation, and flight mode), we review the hosts and transmission pathways that can lead to bat exposure and infection to ebolaviruses. In contrast to the capacity of bats to transmit ebolaviruses and other pathogens to many hosts, our results indicate that only a limited number of hosts and pathways can lead to the transmission of ebolaviruses to bats, and that the alternative maintenance host, if it exists, must be amongst them. A list of these pathways is provided, along with protocols to prioritise and investigate these alternative hypotheses. In conclusion, taking into account the ecology of bats and their known involvement in ebolaviruses ecology drastically reduces the list of potential alternative maintenance hosts for ebolaviruses. Understanding the natural history of ebolaviruses is a health priority, and investigating these alternative hypotheses could complete the current effort focused on the role of bats.