Evidence for widespread infection of African bats with Crimean-Congo hemorrhagic fever-like viruses

Approaching the complexity of Crimean-Congo hemorrhagic fever virus serology: A study in swine

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne zoonotic orthonairovirus of public health concern and widespread geographic distribution. Several animal species are known to seroconvert after infection with CCHFV without showing clinical symptoms. The commercial availability of a multi-species ELISA has led to an increase in recent serosurveillance studies as well as in the range of species reported to be exposed to CCHFV in the field, including wild boar (Sus scrofa). However, development and validation of confirmatory serological tests for swine based on different CCHFV antigens or test principles are hampered by the lack of defined control sera from infected and non-infected animals. For the detection of anti-CCHFV antibodies in swine, we established a swine-specific in-house ELISA using a panel of swine sera from CCHFV-free regions and regions with reported CCHFV circulation. We initially screened more than 700 serum samples from wild boar and domestic pigs and observed a correlation of ≃67% between the commercial and the in-house test. From these sera, we selected a panel of 60 samples that were further analyzed in a newly established indirect immunofluorescence assay (iIFA) and virus neutralization test. ELISA-non-reactive samples tested negative. Interestingly, only a subset of samples reactive in both ELISA and iIFA displayed CCHFV-neutralizing antibodies. The observed partial discrepancy between the tests may be explained by different test sensitivities, antibody cross-reactivities or suggests that the immune response to CCHFV in swine is not necessarily associated with eliciting neutralizing antibodies. Overall, this study highlights that meaningful CCHFV serology in swine, and possibly other species, should involve the performance of multiple tests and careful interpretation of the results.

Tick-borne viruses and their risk to public health in the Caribbean: Spotlight on bats as reservoirs in Cuba

In recent decades, tick-borne diseases (TBDs) have surged and expanded globally due to factors like changes in human activities, land use patterns, and climate change, and it have been associated with the emergence of zoonotic diseases. Cuba faces the impact of ticks on human health and the economy. Although Cuba has studied TBDs extensively for the past 50 years, focus on tick-borne viral pathogens affecting humans remains scant. Despite TBDs not currently being a major health concern in Cuba, factors like inadequate clinician awareness, climate conditions, global tick emergence, and evidence of zoonotic pathogens in ticks underscore the importance of enhanced TBD surveillance in the country. Here we revised the available information on ticks as vectors of pathogenic viruses to humans, spotlighting bats as potential reservoirs of tick-borne viruses (TBVs). Ticks on bats have gained interest as potential reservoirs of pathogenic viruses to humans in Cuba and worldwide. Understanding their role in maintaining viruses and their potential transmission to humans is crucial for the implementation of surveillance and control programs to reduce the risk of tick-borne viral diseases and public health management.

Interferon-induced protein with tetratricopeptide repeats 5 of black fruit bat (Pteropus alecto) displays a broad inhibition of RNA viruses

Bats are natural host reservoirs and have adapted a unique innate immune system that permits them to host many viruses without exhibiting symptoms. Notably, bat interferon stimulated genes (ISGs) have been shown to play antiviral roles. Interferon induced protein with tetratricopeptide repeats 5 (IFIT5) is a well-characterised ISG in humans with antiviral activities against negative-sense RNA viruses via inhibiting viral transcription. Here, we aim to investigate if Pteropus alecto (pa) IFIT5 (paIFIT5) possess the ability to inhibit negative-sense RNA viruses. Initially, gene syntenic and comparative structural analyses of multiple animals highlighted a high level of similarity between Pteropus alecto and human IFIT5 proteins. Our results showed that paIFIT5 was significantly inducible by viral and dsRNA stimulation. Transient overexpression of paIFIT5 inhibited the replication of vesicular stomatitis virus (VSV). Using minireplicon and transcription reporter assays, we demonstrated the ability of paIFIT5 specifically to inhibit H17N10 polymerase activity. Mechanistically, we noticed that the antiviral potential of paIFIT5 against negative sense RNA viruses was retributed to its interaction with 5'ppp containing RNA. Taken together, these findings highlight the genetic and functional conservation of IFIT5 among mammals.

Robust evidence for bats as reservoir hosts is lacking in most African virus studies: a review and call to optimize sampling and conserve bats

Africa experiences frequent emerging disease outbreaks among humans, with bats often proposed as zoonotic pathogen hosts. We comprehensively reviewed virus-bat findings from papers published between 1978 and 2020 to evaluate the evidence that African bats are reservoir and/or bridging hosts for viruses that cause human disease. We present data from 162 papers (of 1322) with original findings on (1) numbers and species of bats sampled across bat families and the continent, (2) how bats were selected for study inclusion, (3) if bats were terminally sampled, (4) what types of ecological data, if any, were recorded and (5) which viruses were detected and with what methodology. We propose a scheme for evaluating presumed virus-host relationships by evidence type and quality, using the contrasting available evidence for Orthoebolavirus versus Orthomarburgvirus as an example. We review the wording in abstracts and discussions of all 162 papers, identifying key framing terms, how these refer to findings, and how they might contribute to people's beliefs about bats. We discuss the impact of scientific research communication on public perception and emphasize the need for strategies that minimize human-bat conflict and support bat conservation. Finally, we make recommendations for best practices that will improve virological study metadata.

Baseline of Physiological Body Temperature and Hematological Parameters in Captive Rousettus aegyptiacus and Eidolon helvum Fruit Bats

The discovery of bats as reservoir hosts for a number of highly pathogenic zoonotic agents has led to an increasing interest of infectious disease research in experimental studies with bats. Therefore, we established breeding colonies of Rousettus aegyptiacus and Eidolon helvum fruit bats, which both have been identified as reservoir hosts for relevant zoonotic disease agents, such as Marburg virus and Lagos bat virus. Since 2013, individuals of both species have been recruited to the Friedrich-Loeffler-Institut (FLI) from zoological gardens in Europe, to where these species had been introduced from the wild several decades ago. The aviaries have been designed according to national recommendations published by the Federal Ministry of Agriculture. Under these conditions, both species have been reproducing for years. To better understand the physiology of these animals, and to generate baseline knowledge for infection experiments, we monitored the body core temperatures of R. aegyptiacus bats in the aviaries, and found a circadian variation between 34°C and 41.5°C. We also determined the hematological parameters of both species, and detected specific differences between both bat species. For values of clinical chemistry, no correlation to age or sex was observed. However, species-specific differences were detected since ALT, BUN and CREA were found to be significantly higher in R. aegyptiacus and GLU and TP were significantly higher in E. helvum bats. A higher hematocrit, hemoglobin and red blood cell level was observed in subadult R. aegyptiacus, with hemoglobin and red blood cells also being significantly increased compared to E. helvum. Lymphocytes were found to be the dominant white blood cells in both species and are higher in female E. helvum. Neutrophil granulocytes were significantly higher in E. helvum bats. This underlines the necessity to define baseline profiles for each bat species prior to their use in experimental challenge.

Interaction between Old World fruit bats and humans: From large scale ecosystem services to zoonotic diseases

The Old World tropical and subtropical frugivorous bat genus Rousettus (Pteropodidae) contains species with broad distributions, as well as those occurring in restricted geographical areas, particularly islands. Herein we review the role of Rousettus as a keystone species from a global "One Health" approach and related to ecosystem functioning, zoonotic disease and public health. Rousettus are efficient at dispersing seeds and pollinating flowers; their role in forest regeneration is related to their ability to fly considerable distances during nightly foraging bouts and their relatively small body size, which allows them to access fruits in forested areas with closed vegetation. Rousettus are also reservoirs for various groups of pathogens (viruses, bacteria, fungi, protozoa), which, by definition, are infectious agents causing disease. The study of day roosts of different species of Rousettus and the successful establishment of captive breeding colonies have provided important details related to the infection dynamics of their associated pathogens. Large-scale conversion of forested areas into agricultural landscapes has increased contact between humans and Rousettus, therefore augmenting the chances of infectious agent spillover. Many crucial scientific details are still lacking related to members of this genus, which have direct bearing on the prevention of emerging disease outbreaks, as well as the conservation of these bats. The public should be better informed on the capacity of fruit bats as keystone species for large scale forest regeneration and in spreading pathogens. Precise details on the transmission of zoonotic diseases of public health importance associated with Rousettus should be given high priority.

Ornithodoros (Pavlovskyella) ticks associated with a Rickettsia sp. in Pakistan

Background

Soft ticks (Ixodida: Argasidae) are medically important ectoparasites that mainly feed on birds and mammals, which play a key role in their geographic distribution and dispersion. Despite their importance, studies on soft ticks are scarce for many regions and countries of the world, including Pakistan.

Methods

In this study, 2330 soft ticks—179 larvae (7.7%), 850 nymphs (36.4%), 711 males (30.5%) and 590 females (25.3%)—were collected from animal shelters in 18 locations within five districts of Khyber Pakhtunkhwa, Pakistan. A subset of the collected ticks was processed for DNA extraction and polymerase chain reaction (PCR) for the amplification of tick 12S ribosomal DNA (rDNA), 16S rDNA and cytochrome c oxidase subunit I (cox1), and rickettsial 16S rDNA gene fragments. The obtained sequences were used for the construction of a phylogenetic tree.

Results

All the specimens were morphologically identified as Ornithodoros, and were morphologically similar to Ornithodoros tholozani. The genus was confirmed by sequencing partial 12S rDNA, 16S rDNA and cox1 gene fragments. Additionally, a Rickettsia sp. was detected in some of the collected ticks by PCR targeting 16S rDNA. The morphological relatedness of the tick specimens with O. tholozani was confirmed by phylogenetic analysis, in which the Ornithodoros sp. clustered with Ornithodoros tholozani and Ornithodoros verrucosus, both of which belong to the subgenus Pavlovskyella and have been previously reported from Israel, Ukraine and Iran. The phylogenetic tree also indicated that the Ornithodoros sp. from Pakistan corresponds to an undetermined species. Furthermore, the associated Rickettsia sp. grouped with the limoniae group of Rickettsia species previously reported from Argas japonicus ticks from China.

Conclusions

This is the first molecular study of an Ornithodoros species from Pakistan. Further studies are essential to confirm its identity and possible pathogenicity with regard to its associated microorganisms in the studied region.

Graphical abstract

Genetic Characterization of Rift Valley Fever Virus in Insectivorous Bats, Egypt

Background: The endemic character of Rift Valley fever (RVF) disease points toward an interepidemic reservoir. Although not yet identified, bats and rodents may be implicated in RVF virus (RVFV) epidemiology. In this study, we investigated the putative role of Egyptian frugivorous and insectivorous bats in RVFV epidemiology in Egypt. Methods: From 2019 to 2021, 200 bats of two different species from six Egyptian governorates were tested for phleboviruses using real-time RT-PCR (rRT-PCR) and sequence analysis. Results: Screening through rRT-PCR showed evidence of the RVFV genome only in insectivorous bats. Partial sequence and phylogenetic analysis based on S and M genome segments showed that these viruses are genetically similar to those circulating (clade A) in livestock and humans during previously reported RVFV outbreaks in 1977/78 and 2003 in Egypt. Conclusions: Our molecular data suggest that the bat Pipistrellus deserti could play a role in RVFV ecology in Egypt.

Seroprevalence and Risk Factors of Crimean-Congo Hemorrhagic Fever in Cattle of Smallholder Farmers in Central Malawi

Crimean-Congo hemorrhagic fever virus (CCHFV) is endemic in Africa, Asia, and Eastern Europe where it circulates among animals and ticks causing sporadic outbreaks in humans. Although CCHF is endemic in sub-Saharan Africa, epidemiological information is lacking in many countries, including Malawi. To assess the risk of CCHF in Malawi, we conducted an epidemiological study in cattle reared by smallholder livestock farmers in central Malawi. A cross-sectional study was conducted in April 2020 involving seven districts, four from Kasungu and three from Lilongwe Agriculture Development Divisions. A structured questionnaire was administered to farmers to obtain demographic, animal management, and ecological risk factors data. Sera were collected from randomly selected cattle and screened for CCHF virus (CCHFV) specific antibodies using a commercial ELISA kit. Ticks were collected from cattle and classified morphologically to species level. An overall CCHFV seropositivity rate of 46.9% (n = 416; 95% CI: 42.0–51.8%) was observed. The seropositivity was significantly associated with the age of cattle (p < 0.001), sex (p < 0.001), presence of ticks in herds (p = 0.01), district (p = 0.025), and type of grazing lands (p = 0.013). Five species of ticks were identified, including Hyalomma truncatum, a known vector of CCHFV. Ticks of the species Hyalomma truncatum were not detected in two districts with the highest seroprevalence for CCHF and vector competency must be further explored in the study area. To our knowledge, this is the first report of serologic evidence of the presence of CCHV among smallholder cattle in central Malawi. This study emphasizes the need for continued monitoring of CCHFV infection among livestock, ticks, and humans for the development of data-based risk mitigation strategies.

Update on Potentially Zoonotic Viruses of European Bats

Bats have been increasingly gaining attention as potential reservoir hosts of some of the most virulent viruses known. Numerous review articles summarize bats as potential reservoir hosts of human-pathogenic zoonotic viruses. For European bats, just one review article is available that we published in 2014. The present review provides an update on the earlier article and summarizes the most important viruses found in European bats and their possible implications for Public Health. We identify the research gaps and recommend monitoring of these viruses.

Epidemiology of Crimean-Congo Hemorrhagic Fever (CCHF) in Africa-Underestimated for Decades

Crimean-Congo hemorrhagic fever (CCHF) is endemic in Africa, but the epidemiology remains to be defined. Using a broad database search, we reviewed the literature to better define CCHF evidence in Africa. We used a One Health approach to define the impact of CCHF by reviewing case reports, human and animal serology, and records of CCHF virus (CCHFV) isolations (1956-mid-2020). In addition, published and unpublished collection data were used to estimate the geographic distribution of Hyalomma ticks and infection vectors. We implemented a previously proposed classification scheme for organizing countries into five categories by the level of evidence. From January 1, 1956 to July 25, 2020, 494 CCHF cases (115 lethal) were reported in Africa. Since 2000, nine countries (Kenya, Mali, Mozambique, Nigeria, Senegal, Sierra Leone, South Sudan, Sudan, and Tunisia) have reported their first CCHF cases. Nineteen countries reported CCHF cases and were assigned level 1 or level 2 based on maturity of their surveillance system. Thirty countries with evidence of CCHFV circulation in the absence of CCHF cases were assigned level 3 or level 4. Twelve countries for which no data were available were assigned level 5. The goal of this review is to inform international organizations, local governments, and healthcare professionals about shortcomings in CCHF surveillance in Africa to assist in a movement toward strengthening policy to improve CCHF surveillance.

The virome of German bats: comparing virus discovery approaches

Bats are known to be reservoirs of several highly pathogenic viruses. Hence, the interest in bat virus discovery has been increasing rapidly over the last decade. So far, most studies have focused on a single type of virus detection method, either PCR, virus isolation or virome sequencing. Here we present a comprehensive approach in virus discovery, using all three discovery methods on samples from the same bats. By family-specific PCR screening we found sequences of paramyxoviruses, adenoviruses, herpesviruses and one coronavirus. By cell culture we isolated a novel bat adenovirus and bat orthoreovirus. Virome sequencing revealed viral sequences of ten different virus families and orders: three bat nairoviruses, three phenuiviruses, one orbivirus, one rotavirus, one orthoreovirus, one mononegavirus, five parvoviruses, seven picornaviruses, three retroviruses, one totivirus and two thymoviruses were discovered. Of all viruses identified by family-specific PCR in the original samples, none was found by metagenomic sequencing. Vice versa, none of the viruses found by the metagenomic virome approach was detected by family-specific PCRs targeting the same family. The discrepancy of detected viruses by different detection approaches suggests that a combined approach using different detection methods is necessary for virus discovery studies.

A Review on Emerging Infectious Diseases Prioritized Under the 2018 WHO Research and Development Blueprint: Lessons from the Indian Context

Objective: This review describes the current scenario of a priority group of emerging infectious diseases (EIDs) listed by World Health Organization (WHO), and their main determinants and drivers for the emergence/spread of the diseases. The gaps and strategies developed by India to meet the WHO guidelines on the effective control of epidemic-prone diseases and outbreaks are also presented in the review. Methods: Epidemiologic information of EIDs, namely Crimean-Congo hemorrhagic fever (CCHF), Ebola and Marburg viruses (EboV and MarV), Zika virus (ZIKAV), Rift Valley fever (RVF), Middle East respiratory syndrome, severe acute respiratory syndrome (SARS), Nipah and Hendra virus (NiV and HeV), and Lassa fever virus (LASV), was drawn from international and national electronic databases to assess the situation. A brief view on the novel coronavirus disease 2019 (COVID-19) in India is also included. Results: There are no reports for human infection of EboV, MarV, RVF, and LASV in India. CCHF, SARS, ZIKAV, and NiV have been involved in outbreaks in eight states of India, while COVID-19 is currently reported from majority of states. India has deeply strengthened its surveillance and response system of outbreaks and epidemic-prone diseases. Conclusions: Despite its enormous improvements made in the anticipation of such threats, still more efforts are needed in sensitization of populations as well as hospital management in the context to EIDs, as addressed in the review. Furthermore, there is still a need for more research and development activities to efficiently control EIDs.

ISG15 overexpression compensates the defect of Crimean-Congo hemorrhagic fever virus polymerase bearing a protease-inactive ovarian tumor domain

Crimean-Congo Hemorrhagic Fever virus (CCHFV; family Nairoviridae) is an extremely pathogenic member of the Bunyavirales order. Previous studies have shown that the N-terminal domain of the CCHFV polymerase (L) contains an ovarian tumor-type protease (OTU) domain with the capability to remove both ubiquitin and ISG15 molecules from proteins. The approximately 200 amino acids-long OTU domain, if ectopically expressed, can interfere with both the induction of antiviral type I interferons (IFN) as well as the IFN-stimulated signaling. A OTU protease mutant (C40A), by contrast, was inactive in that respect. However, the effect of the OTU protease activity in the context of the full-length L protein (approximately 4000 amino acids) is only poorly characterized, and recombinant CCHFV with the C40A mutation could not be rescued. Here, we employed transcriptionally active virus-like particles (tc-VLPs) to investigate the interaction between the L-embedded OTU protease and the IFN system. Our data show a cis requirement of the OTU protease for optimal CCHFV polymerase activity in human HuH-7 cells. The L-embedded OTU did not influence IFN signaling, the sensitivity to IFN, or IFN induction. Moreover, the attenuation of OTU C40A-mutated L could not be relieved by inactivating the IFN response, but after overexpression of conjugation-competent ISG15 the polymerase activity recovered to wild-type levels. Consequently, ISG15 was used to produce OTU-deficient tc-VLPs, a potential vaccine candidate. Our data thus indicate that in the context of full-length L the OTU domain is important for the regulation of CCHFV polymerase by ISG15.

Tick-transmitted Crimean-Congo Hemorrhagic Fever virus (CCHFV) causes a serious and potentially fatal disease in humans. The CCHFV polymerase possesses an N-terminal ovarian tumor-type protease (OTU) domain that cleaves ubiquitin and ISG15 modifiers from target proteins. Previous studies demonstrated that the ectopically expressed OTU domain can inhibit antiviral type I interferon responses. Hence, cleavage-negative OTU mutants of virus or transcriptionally active virus-like particles (tc-VLPs) are expected to exhibit elevated immunogenicity and would be candidates for a live vaccine. For unknown reasons, however, recombinant virus with just the OTU minus mutation cannot be generated. Using tc-VLPs, we show that in human HuH-7 cells the activity of the OTU minus polymerase is reduced by more than 80%. Curiously, the attenuation could not be compensated by inactivating the interferon system or by adding the OTU domain in trans. However, a complete reversion of the OTU minus phenotype was achieved by transcomplementation with ISG15, whereas the other OTU substrate, ubiquitin, had no such positive influence. Our data thus indicate a role of cis OTU in CCHFV polymerase regulation that is independent of an anti-interferon activity but connected to ISG15. Transcomplementation with ISG15 may be a means to rescue the OTU minus CCHV vaccine candidate.

Virus- and Interferon Alpha-Induced Transcriptomes of Cells from the Microbat Myotis daubentonii

Antiviral interferons (IFN-alpha/beta) are possibly responsible for the high tolerance of bats to zoonotic viruses. Previous studies focused on the IFN system of megabats (suborder Yinpterochiroptera). We present statistically robust RNA sequencing (RNA-seq) data on transcriptomes of cells from the “microbat” Myotis daubentonii (suborder Yangochiroptera) responding at 6 and 24 h to either an IFN-inducing virus or treatment with IFN. Our data reveal genes triggered only by virus, either in both humans and Myotis (CCL4, IFNL3, CH25H), or exclusively in Myotis (STEAP4). Myotis cells also express a series of conserved IFN-stimulated genes (ISGs) and an unusually high paralog number of the antiviral ISG BST2 (tetherin) but lack several ISGs that were described for megabats (EMC2, FILIP1, IL17RC, OTOGL, SLC24A1). Also, in contrast to megabats, we detected neither different IFN-alpha subtypes nor an unusually high baseline expression of IFNs. Thus, Yangochiroptera microbats, represented by Myotis, may possess an IFN system with distinctive features.

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Virus- and IFN-responsive transcriptomes of the microbat Myotis daubentonii

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CCL4, IFNL3, CH25H, STEAP4 are IFNB-like genes triggered by virus only

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Microbats encode more paralogs of BST2 (tetherin) than any other mammal

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Clear differences between the IFN systems of microbats and megabats

Can Bats Serve as Reservoirs for Arboviruses?

Bats are known to harbor and transmit many emerging and re-emerging viruses, many of which are extremely pathogenic in humans but do not cause overt pathology in their bat reservoir hosts: henipaviruses (Nipah and Hendra), filoviruses (Ebola and Marburg), and coronaviruses (SARS-CoV and MERS-CoV). Direct transmission cycles are often implicated in these outbreaks, with virus shed in bat feces, urine, and saliva. An additional mode of virus transmission between bats and humans requiring further exploration is the spread of disease via arthropod vectors. Despite the shared ecological niches that bats fill with many hematophagous arthropods (e.g. mosquitoes, ticks, biting midges, etc.) known to play a role in the transmission of medically important arboviruses, knowledge surrounding the potential for bats to act as reservoirs for arboviruses is limited. To this end, a comprehensive literature review was undertaken examining the current understanding and potential for bats to act as reservoirs for viruses transmitted by blood-feeding arthropods. Serosurveillance and viral isolation from either free-ranging or captive bats are described in relation to four arboviral groups (Bunyavirales, Flaviviridae, Reoviridae, Togaviridae). Further, ecological associations between bats and hematophagous viral vectors are characterized (e.g. bat bloodmeals in mosquitoes, ingestion of mosquitoes by bats, etc). Lastly, knowledge gaps related to hematophagous ectoparasites (bat bugs and bed bugs (Cimicidae) and bat flies (Nycteribiidae and Streblidae)), in addition to future directions for characterization of bat-vector-virus relationships are described.

Structure of interferon-stimulated gene product 15 (ISG15) from the bat species Myotis davidii and the impact of interdomain ISG15 interactions on viral protein engagement

Bats have long been observed to be the hosts and the origin of numerous human diseases. Bats, like all mammals, rely on a number of innate immune mechanisms to combat invading pathogens, including the interferon type I, II and III responses. Ubiquitin-like interferon-stimulated gene product 15 (ISG15) is a key modulator of these interferon responses. Within these pathways, ISG15 can serve to stabilize host proteins modulating innate immune responses and act as a cytokine. Post-translational modifications of viral proteins introduced by ISG15 have also been observed to directly affect the function of numerous viral proteins. Unlike ubiquitin, which is virtually identical across all animals, comparison of ISG15s across species reveals that they are relatively divergent, with sequence identity dropping to as low as ∼58% among mammals. In addition to serving as an obstacle to the zoonotic transmission of influenza, these ISG15 species-species differences have also long been shown to have an impact on the function of viral deISGylases. Recently, the structure of the first nonhuman ISG15, originating from mouse, suggested that the structures of human ISG15 may not be reflective of other species. Here, the structure of ISG15 from the bat species Myotis davidii solved to 1.37 Å resolution is reported. Comparison of this ISG15 structure with those from human and mouse not only underscores the structural impact of ISG15 species-species differences, but also highlights a conserved hydrophobic motif formed between the two domains of ISG15. Using the papain-like deISGylase from Severe acute respiratory syndrome coronavirus as a probe, the biochemical importance of this motif in ISG15-protein engagements was illuminated.

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.

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.

Translating Predictions of Zoonotic Viruses for Policymakers

Recent outbreaks of Ebola virus disease and Zika virus disease highlight the need for disseminating accurate predictions of emerging zoonotic viruses to national governments for disease surveillance and response. Although there are published maps for many emerging zoonotic viruses, it is unknown if there is agreement among different models or if they are concordant with national expert opinion. Therefore, we reviewed existing predictions for five high priority emerging zoonotic viruses with national experts in Cameroon to investigate these issues and determine how to make predictions more useful for national policymakers. Predictive maps relied primarily on environmental parameters and species distribution models. Rift Valley fever virus and Crimean-Congo hemorrhagic fever virus predictions differed from national expert opinion, potentially because of local livestock movements. Our findings reveal that involving national experts could elicit additional data to improve predictions of emerging pathogens as well as help repackage predictions for policymakers.

Virome analysis of two sympatric bat species (Desmodus rotundus and Molossus molossus) in French Guiana

Environmental disturbances in the Neotropics (e.g., deforestation, agriculture intensification, urbanization) contribute to an increasing risk of cross-species transmission of microorganisms and to disease outbreaks due to changing ecosystems of reservoir hosts. Although Amazonia encompasses the greatest diversity of reservoir species, the outsized viral population diversity (virome) has yet to be investigated. Here, through a metagenomic approach, we identified 10,991 viral sequences in the saliva and feces of two bat species, Desmodus rotundus (hematophagous), trapped in two different caves surrounded by primary lowland forest, and Molossus molossus (insectivorous), trapped in forest and urban habitats. These sequences are related to 51 viral families known to infect a wide range of hosts (i.e., bacteria, plants, insects and vertebrates). Most viruses detected reflected the diet of bat species, with a high proportion of plant and insect-related viral families for M. molossus and a high proportion of vertebrate-related viral families for D. rotundus, highlighting its influence in shaping the viral diversity of bats. Lastly, we reconstructed the phylogenetic relationships for five vertebrate-related viral families (Nairoviridae, Circoviridae, Retroviridae, Herpesviridae, Papillomaviridae). The results showed highly supported clustering with other viral sequences of the same viral family hosted by other bat species, highlighting the potential association of viral diversity with the host’s diet. These findings provide significant insight into viral bat diversity in French Guiana belonging to the Amazonian biome and emphasize that habitats and the host’s dietary ecology may drive the viral diversity in the bat communities investigated.

Evolution and Antiviral Specificities of Interferon-Induced Mx Proteins of Bats against Ebola, Influenza, and Other RNA Viruses

Bats serve as a reservoir for various, often zoonotic viruses, including significant human pathogens such as Ebola and influenza viruses. However, for unknown reasons, viral infections rarely cause clinical symptoms in bats. A tight control of viral replication by the host innate immune defense might contribute to this phenomenon. Transcriptomic studies revealed the presence of the interferon-induced antiviral myxovirus resistance (Mx) proteins in bats, but detailed functional aspects have not been assessed. To provide evidence that bat Mx proteins might act as key factors to control viral replication we cloned Mx1 cDNAs from three bat families, Pteropodidae, Phyllostomidae, and Vespertilionidae. Phylogenetically these bat Mx1 genes cluster closely with their human ortholog MxA. Using transfected cell cultures, minireplicon systems, virus-like particles, and virus infections, we determined the antiviral potential of the bat Mx1 proteins. Bat Mx1 significantly reduced the polymerase activity of viruses circulating in bats, including Ebola and influenza A-like viruses. The related Thogoto virus, however, which is not known to infect bats, was not inhibited by bat Mx1. Further, we provide evidence for positive selection in bat Mx1 genes that might explain species-specific antiviral activities of these proteins. Together, our data suggest a role for Mx1 in controlling these viruses in their bat hosts.IMPORTANCE Bats are a natural reservoir for various viruses that rarely cause clinical symptoms in bats but are dangerous zoonotic pathogens, like Ebola or rabies virus. It has been hypothesized that the interferon system might play a key role in controlling viral replication in bats. We speculate that the interferon-induced Mx proteins might be key antiviral factors of bats and have coevolved with bat-borne viruses. This study evaluated for the first time a large set of bat Mx1 proteins spanning three major bat families for their antiviral potential, including activity against Ebola virus and bat influenza A-like virus, and we describe here their phylogenetic relationship, revealing patterns of positive selection that suggest a coevolution with viral pathogens. By understanding the molecular mechanisms of the innate resistance of bats against viral diseases, we might gain important insights into how to prevent and fight human zoonotic infections caused by bat-borne viruses.

Biochemical and Structural Insights into the Preference of Nairoviral DeISGylases for Interferon-Stimulated Gene Product 15 Originating from Certain Species

The regulation of the interferon type I (IFN-I) response has been shown to rely on posttranslational modification by ubiquitin (Ub) and Ub-like interferon-stimulated gene product 15 (ISG15) to stabilize, or activate, a variety of IFN-I signaling and downstream effector proteins. Unlike Ub, which is almost perfectly conserved among eukaryotes, ISG15 is highly divergent, even among mammals. Since zoonotic viruses rely on viral proteins to recognize, or cleave, ISG15 conjugates in order to evade, or suppress, innate immunity, the impact of ISG15 biodiversity on deISGylating proteases of the ovarian tumor family (vOTU) from nairoviruses was evaluated. The enzymatic activities of vOTUs originating from the Crimean-Congo hemorrhagic fever virus, Erve virus, and Nairobi sheep disease virus were tested against ISG15s from humans, mice, shrews, sheep, bats, and camels, which are mammalian species known to be infected by nairoviruses. This along with investigation of binding by isothermal titration calorimetry illustrated significant differences in the abilities of nairovirus deISGylases to accommodate certain species of ISG15. To investigate the molecular underpinnings of species preferences of these vOTUs, a structure was determined to 2.5 Å for a complex of Erve virus vOTU protease and a mouse ISG15 domain. This structure revealed the molecular basis of Erve virus vOTU's preference for ISG15 over Ub and the first structural insight into a nonhuman ISG15. This structure also revealed key interactions, or lack thereof, surrounding three amino acids that may drive a viral deISgylase to prefer an ISG15 from one species over that of another.

IMPORTANCE

Viral ovarian tumor domain proteases (vOTUs) are one of the two principal classes of viral proteases observed to reverse posttranslational modification of host proteins by ubiquitin and interferon-stimulated gene product 15 (ISG15), subsequently facilitating downregulation of IFN-I signaling pathways. Unlike the case with ubiquitin, the amino acid sequences of ISG15s from various species are notably divergent. We illustrate that vOTUs have clear preferences for ISG15s from certain species. In addition, these observations are related to the molecular insights acquired via the first X-ray structure of the vOTU from the Erve nairovirus in complex with the first structurally resolved nonhuman ISG15. This information implicates certain amino acids that drive the preference of vOTUs for ISG15s from certain species.