Bats host the most virulent-but not the most dangerous-zoonotic viruses

Zoonotic assemblages A and B of Giardia duodenalis in Chiroptera from Brazilian Amazon biome

Bats are important reservoirs and spreaders of pathogens. Giardia duodenalis is a globally important protozoan that infects humans and other mammals with considerable public health burden, particularly on the child development. Based on genetic variation and host specificity, G. duodenalis is categorized into eight genotypes/assemblages A-H. Assemblages A and B are widespread globally and are associated with human and animal disease. There is evidence of Giardia in the bat feces from diverse geographic regions, but the G. duodenalis assemblages are unknown, which is a key point for the One Health view. Here, we successfully amplified the BG/GDH/DIS3/HCMP2/HCMP3 targets of G. duodenalis from five bat species captured in the Brazilian Amazon biome revealing the presence of zoonotic G. duodenalis assemblages A and B in the feces of these flying mammals. Our study reveals that bats may play a role in transmission of zoonotic G. duodenalis, at least in this biome.

Bats generate lower affinity but higher diversity antibody responses than those of mice, but pathogen-binding capacity increases if protein is restricted in their diet

Bats are reservoirs of many zoonotic viruses that are fatal in humans but do not cause disease in bats. Moreover, bats generate low neutralizing antibody titers in response to experimental viral infection, although more robust antibody responses have been observed in wild-caught bats during times of food stress. Here, we compared the antibody titers and B cell receptor (BCR) diversity of Jamaican fruit bats (Artibeus jamaicensis; JFBs) and BALB/c mice generated in response to T-dependent and T-independent antigens. We then manipulated the diet of JFBs and challenged them with H18N11 influenza A-like virus or a replication incompetent Nipah virus VSV (Nipah-riVSV). Under standard housing conditions, JFBs generated a lower avidity antibody response and possessed more BCR mRNA diversity compared to BALB/c mice. However, withholding protein from JFBs improved serum neutralization in response to Nipah-riVSV and improved serum antibody titers specific to H18 but reduced BCR mRNA diversity.

Disease tolerance as immune defense strategy in bats: One size fits all?

Bats are natural reservoirs for zoonotic pathogens, yet the determinants of microbial persistence as well as the specific functionality of their immune system remain largely enigmatic. Their propensity to harbor viruses lethal to humans and/or livestock, mostly in absence of clinical disease, makes bats stand out among mammals. Defending against pathogens relies on avoidance, resistance, and/or tolerance strategies. In bats, disease tolerance has recently gained increasing attention as a prevailing host defense paradigm. We here summarize the current knowledge on immune responses in bats in the context of infection with zoonotic agents and discuss concepts related to disease tolerance. Acknowledging the wide diversity of bats, the broad spectrum of bat-associated microbial species, and immune-related knowledge gaps, we identify research priorities necessary to provide evidence-based proofs for disease tolerance in bats. Since disease tolerance relies on networks of biological processes, we emphasize that investigations beyond the immune system, using novel technologies and computational biology, could jointly advance our knowledge about mechanisms conferring bats reservoir abilities. Although disease tolerance may not be the "one fit all" defense strategy, deciphering disease tolerance in bats could translate into novel therapies and inform prevention of spillover infections to humans and livestock.

Multispecies interactions and the community context of the evolution of virulence

Pairwise host-parasite relationships are typically embedded in broader networks of ecological interactions, which have the potential to shape parasite evolutionary trajectories. Understanding this 'community context' of pathogen evolution is vital for wildlife, agricultural and human systems alike, as pathogens typically infect more than one host-and these hosts may have independent ecological relationships. Here, we introduce an eco-evolutionary model examining ecological feedback across a range of host-host interactions. Specifically, we analyse a model of the evolution of virulence of a parasite infecting two hosts exhibiting competitive, mutualistic or exploitative relationships. We first find that parasite specialism is necessary for inter-host interactions to impact parasite evolution. Furthermore, we find generally that increasing competition between hosts leads to higher shared parasite virulence while increasing mutualism leads to lower virulence. In exploitative host-host interactions, the particular form of parasite specialization is critical-for instance, specialization in terms of onward transmission, host tolerance or intra-host pathogen growth rate lead to distinct evolutionary outcomes under the same host-host interactions. Our work provides testable hypotheses for multi-host disease systems, predicts how changing interaction networks may impact virulence evolution and broadly demonstrates the importance of looking beyond pairwise relationships to understand evolution in realistic community contexts.

Detection, characterization, and phylogenetic analysis of novel astroviruses from endemic Malagasy fruit bats

Bats (order: Chiroptera) are known to host a diverse range of viruses, some of which present a human public health risk. Thorough viral surveillance is therefore essential to predict and potentially mitigate zoonotic spillover. Astroviruses (family: Astroviridae) are an understudied group of viruses with a growing amount of indirect evidence for zoonotic transfer. Astroviruses have been detected in bats with significant prevalence and diversity, suggesting that bats may act as important astrovirus hosts. Most astrovirus surveillance in wild bat hosts has, to date, been restricted to single-gene PCR detection and concomitant Sanger sequencing; additionally, many bat species and many geographic regions have not yet been surveyed for astroviruses at all. Here, we use metagenomic Next Generation Sequencing (mNGS) to detect astroviruses in three species of Madagascar fruit bats, Eidolon dupreanum, Pteropus rufus, and Rousettus madagascariensis. We detect numerous partial sequences from all three species and one near-full length astrovirus sequence from Rousettus madagascariensis, which we use to characterize the evolutionary history of astroviruses both within bats and the broader mammalian clade, Mamastrovirus. Taken together, applications of mNGS implicate bats as important astrovirus hosts and demonstrate novel patterns of bat astrovirus evolutionary history, particularly in the Southwest Indian Ocean region.

A meta-analysis on global change drivers and the risk of infectious disease

Anthropogenic change is contributing to the rise in emerging infectious diseases, which are significantly correlated with socioeconomic, environmental and ecological factors1. Studies have shown that infectious disease risk is modified by changes to biodiversity2-6, climate change7-11, chemical pollution12-14, landscape transformations15-20 and species introductions21. However, it remains unclear which global change drivers most increase disease and under what contexts. Here we amassed a dataset from the literature that contains 2,938 observations of infectious disease responses to global change drivers across 1,497 host-parasite combinations, including plant, animal and human hosts. We found that biodiversity loss, chemical pollution, climate change and introduced species are associated with increases in disease-related end points or harm, whereas urbanization is associated with decreases in disease end points. Natural biodiversity gradients, deforestation and forest fragmentation are comparatively unimportant or idiosyncratic as drivers of disease. Overall, these results are consistent across human and non-human diseases. Nevertheless, context-dependent effects of the global change drivers on disease were found to be common. The findings uncovered by this meta-analysis should help target disease management and surveillance efforts towards global change drivers that increase disease. Specifically, reducing greenhouse gas emissions, managing ecosystem health, and preventing biological invasions and biodiversity loss could help to reduce the burden of plant, animal and human diseases, especially when coupled with improvements to social and economic determinants of health.

Building a pathway to One Health surveillance and response in Asian countries

To detect and respond to emerging diseases more effectively, an integrated surveillance strategy needs to be applied to both human and animal health. Current programs in Asian countries operate separately for the two sectors and are principally concerned with detection of events that represent a short-term disease threat. It is not realistic to either invest only in efforts to detect emerging diseases, or to rely solely on event-based surveillance. A comprehensive strategy is needed, concurrently investigating and managing endemic zoonoses, studying evolving diseases which change their character and importance due to influences such as demographic and climatic change, and enhancing understanding of factors which are likely to influence the emergence of new pathogens. This requires utilisation of additional investigation tools that have become available in recent years but are not yet being used to full effect. As yet there is no fully formed blueprint that can be applied in Asian countries. Hence a three-step pathway is proposed to move towards the goal of comprehensive One Health disease surveillance and response.

Identification of a novel adenovirus in liver tissue sample of the Great Himalayan leaf-nosed bat (Hipposideros armiger)

Bats are important reservoirs for many zoonotic viruses. To explore and monitor potential novel viruses carried by bats, 21 liver samples of bats (Hipposideros armiger) were collected from Yunnan Province in southern China. Only one (4.8%) of all models was detected with adenovirus. The whole genome strain obtained by the viral metagenomics method combined with PCR was temporarily named YN01. The complete genome of YN01 was 37,676 bp, with a G + C content of 55.20% and 28 open reading frames. Phylogenetic analysis indicated that the strain YN01 can be classified as genus Mastadenovirus and was the most similar to the adenovirus isolated from Rhinolophus sinicus in China in 2016. The analysis is needed to verify the possibility of cross-species transmission. This virological investigation has increased our understanding of the ecology of bat-borne viruses in this area and provided a reference for possible future infectious diseases.

Sex differences and individual variability in the captive Jamaican fruit bat (Artibeus jamaicensis) intestinal microbiome and metabolome

The intestinal microbiome plays an important role in mammalian health, disease, and immune function. In light of this function, recent studies have aimed to characterize the microbiomes of various bat species, which are noteworthy for their roles as reservoir hosts for several viruses known to be highly pathogenic in other mammals. Despite ongoing bat microbiome research, its role in immune function and disease, especially the effects of changes in the microbiome on host health, remains nebulous. Here, we describe a novel methodology to investigate the intestinal microbiome of captive Jamaican fruit bats (Artibeus jamaicensis). We observed a high degree of individual variation in addition to sex- and cohort-linked differences. The intestinal microbiome was correlated with intestinal metabolite composition, possibly contributing to differences in immune status. This work provides a basis for future infection and field studies to examine in detail the role of the intestinal microbiome in antiviral immunity.

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.

Pteropus vampyrus TRIM40 Is an Interferon-Stimulated Gene That Antagonizes RIG-I-like Receptors

Nipah virus (NiV; genus: Henipavirus; family: Paramyxoviridae) naturally infects Old World fruit bats (family Pteropodidae) without causing overt disease. Conversely, NiV infection in humans and other mammals can be lethal. Comparing bat antiviral responses with those of humans may illuminate the mechanisms that facilitate bats' tolerance. Tripartite motif proteins (TRIMs), a large family of E3-ubiquitin ligases, fine-tune innate antiviral immune responses, and two human TRIMs interact with Henipavirus proteins. We hypothesize that NiV infection induces the expression of an immunosuppressive TRIM in bat, but not human cells, to promote tolerance. Here, we show that TRIM40 is an interferon-stimulated gene (ISG) in pteropodid but not human cells. Knockdown of bat TRIM40 increases gene expression of IFNβ, ISGs, and pro-inflammatory cytokines following poly(I:C) transfection. In Pteropus vampyrus, but not human cells, NiV induces TRIM40 expression within 16 h after infection, and knockdown of TRIM40 correlates with reduced NiV titers as compared to control cells. Bats may have evolved to express TRIM40 in response to viral infections to control immunopathogenesis.

The global risk of infectious disease emergence from giant land snail invasion and pet trade

BACKGROUND

Pathogen outbreaks mostly originate from animals, but some species are more likely to trigger epidemics. The giant land snail (Lissachatina fulica) is a widespread invader, a popular exotic pet, and a notorious vector of the rat lungworm, causing eosinophilic meningitis in humans. However, a comprehensive assessment of the risks of disease outbreak associated with this species is lacking.

METHODS

We assessed and mapped the risk of disease transmission associated with the invasion and pet trade of L. fulica. First, we conducted a review of the scientific literature to list all known L. fulica parasites and pathogens and query host-pathogen databases to identify their potential mammalian hosts. Then, to assess the potential for L. fulica to spread globally, we modelled its suitable climatic conditions and tested whether, within climatically suitable areas, the species tended to occur near humans or not. Finally, we used social media data to map L. fulica possession as an exotic pet and to identify human behaviours associated with increased risk of disease transmission.

RESULTS

Lissachatina fulica can carry at least 36 pathogen species, including two-thirds that can infect humans. The global invasion of L. fulica is climatically limited to tropical areas, but the species is strongly associated with densely populated areas where snails are more likely to enter in contact with humans. In temperate countries, however, climatic conditions should prevent L. fulica's spread. However, we show that in Europe, giant snails are popular exotic pets and are often handled with direct skin contact, likely increasing the risk of pathogen transmission to their owners.

CONCLUSIONS

It is urgent to raise public awareness of the health risks associated with L. fulica in both tropical countries and Europe and to regulate its trade and ownership internationally. Our results highlight the importance of accounting for multiple types of human-wildlife interactions when assessing risks of infectious disease emergence. Furthermore, by targeting the species most likely to spread pathogens, we show that it is possible to rapidly identify emerging disease risks on a global scale, thus guiding timely and appropriate responses.

Reservoir host immunology and life history shape virulence evolution in zoonotic viruses

The management of future pandemic risk requires a better understanding of the mechanisms that determine the virulence of emerging zoonotic viruses. Meta-analyses suggest that the virulence of emerging zoonoses is correlated with but not completely predictable from reservoir host phylogeny, indicating that specific characteristics of reservoir host immunology and life history may drive the evolution of viral traits responsible for cross-species virulence. In particular, bats host viruses that cause higher case fatality rates upon spillover to humans than those derived from any other mammal, a phenomenon that cannot be explained by phylogenetic distance alone. In order to disentangle the fundamental drivers of these patterns, we develop a nested modeling framework that highlights mechanisms that underpin the evolution of viral traits in reservoir hosts that cause virulence following cross-species emergence. We apply this framework to generate virulence predictions for viral zoonoses derived from diverse mammalian reservoirs, recapturing trends in virus-induced human mortality rates reported in the literature. Notably, our work offers a mechanistic hypothesis to explain the extreme virulence of bat-borne zoonoses and, more generally, demonstrates how key differences in reservoir host longevity, viral tolerance, and constitutive immunity impact the evolution of viral traits that cause virulence following spillover to humans. Our theoretical framework offers a series of testable questions and predictions designed to stimulate future work comparing cross-species virulence evolution in zoonotic viruses derived from diverse mammalian hosts.

An immediate way to lower pandemic risk: (not) seizing the low-hanging fruit (bat)

What is the least that humanity can do to mitigate the risks of future pandemics, to prevent worldwide surges in human deaths, illness, and suffering-and more waves of multitrillion US dollar impacts on the global economy? The issues around our consumption and trading of wildlife are diverse and complex, with many rural communities being dependent on wild meat for their nutritional needs. But bats might be one taxonomic group that can be successfully eliminated from the human diet and other uses, with minimal costs or inconvenience to the vast majority of the 8 billion people on Earth. The order Chiroptera merits genuine respect given all that these species contribute to human food supplies through pollination services provided by the frugivores and to disease risk mitigation delivered by insectivorous species. The global community missed its chance to stop SARS-CoV and SARS-CoV-2 from emerging-how many more times will humanity allow this cycle to repeat? How long will governments ignore the science that is in front of them? It's past time for humans to do the least that can be done. A global taboo is needed whereby humanity agrees to leave bats alone, not fear them or try to chase them away or cull them, but to let them have the habitats they need and live undisturbed by humans.

A cross-sectional survey on fruit bat-human interaction in Pakistan; one health perspective

OBJECTIVE

Several factors, such as residential area topography, population density, and lack of infrastructure, were hypothesized to contribute toward respondents' knowledge, attitude, and practice regarding disease transmission. The present study was designed to investigate the knowledge, attitudes, and perception of human-fruit bat interaction by student respondents located in ten districts within the Punjab and Khyber Pakhtunkhwa provinces in Pakistan.

METHOD

A cross-sectional survey was conducted by trained enumerators in academic institutions using a structured questionnaire among student respondents (n = 1466), living in two topographically distinct (Mountainous and Plain) residential regions of the Punjab and Khyber Pakhtunkhwa (KPK) provinces in Pakistan regarding their history of bat encounters.

RESULTS

Our study revealed that 71.4% of the 1466 respondents had observed bats in their geographic region. 21% of our survey respondents reported bat bites incidents over their lifetime, but only 40% actively sought medical care for wound management despite reporting they had a close family member that had contracted rabies (27-35%). Our generalized linear models (GLMs) highlighted that a respondent residing in a residential region had a greater association with reporting a suspected bat bite over their lifetime and reported rabies victims in both near and extended family members (OR = -0,85, p-value = 0.03, 95% CI). This appeared to be due to delaying consulting a doctor or medical facility for treatment following a suspected bat bite in the topographic residential group as compared to the respondents in the provincial residential group (OR 1.12, p-value = 0.04, 95% CI).

CONCLUSION

Our findings indicate the necessity of a One Health comprehensive surveillance system in Pakistan for emerging and re-emerging zoonotic pathogens in Pteropodidae.

Role of Brazilian bats in the epidemiological cycle of potentially zoonotic pathogens

Bats (Chiroptera) are flying mammals of great biodiversity and habits. These characteristics contribute for them being natural reservoirs and part of the epidemiological cycle of several potentially zoonotic pathogens, such as viruses, protozoa, fungi and bacteria. Brazil hosts approximately 15% of the world's bat diversity, with 181 distinct species, 68 genera and 9 families. About 60% of infectious diseases in humans are of zoonotic origin and, in the last decades, the detection of zoonotic pathogens in bats and their environment has been reported, such as Rabies virus (RABV) and Histoplasma capsulatum. Thus, the aim of this work was to review the reports of zoonotic pathogens associated with bats in Brazil in the past ten years. We reviewed the main pathogenic microorganisms described and the species of bats most frequently involved in the epidemiological cycles of these zoonotic agents. The obtained data show an upward trend in the detection of zoonotic pathogens in Brazilian bats, such as RABV, Bartonella sp., Histoplasma capsulatum and Leishmania spp., with emphasis on the bat species Artibeus lituratus, Carollia perspicillata, Desmodus rotundus and Molossus molossus. These findings highlight the importance of monitoring bat-associated microrganisms to early identify pathogens that may threaten bat populations, including potentially zoonotic microrganisms, emphasizing the importance of the One Health approach to prevent and mitigate the risks of the emergence of zoonotic diseases.

The Virome of Bats Inhabiting Brazilian Biomes: Knowledge Gaps and Biases towards Zoonotic Viruses

Bats host a large variety of viruses, including some that may infect other vertebrates and humans. Research on bat-borne viruses attracted significant attention in recent years mainly due to epizootics caused by viruses having bats as hosts. The characterization of the viral communities of bats was then prioritized, but despite increasing efforts, there are large disparities in the geographical ranges covered and the methodologies employed around the world. As a result, large gaps remain in our current understanding of bat viromes and their role in disease emergence. This is particularly true for megadiverse regions in Latin America. This review aims to summarize the current understanding about bat viruses that inhabit Brazilian biomes, one of the most bat species-rich and diverse regions of the globe. Taking into account all known bat-associated viral families studied in Brazilian biomes, we found that almost half of all bat species (86/181 species) were not investigated for viruses at all. Moreover, only a small fraction of viral lineages or families have been studied more in depth, usually employing targeted methods with limited power to characterize a broad virus diversity. Additionally, these studies relied on limited spatiotemporal sampling and small sample sizes. Therefore, our current understanding of bat viral communities in the Brazilian biomes is limited and biased at different levels, limiting zoonotic risk assessments of bat-borne viruses. Considering these limitations, we propose strategies to bridge the existing gaps in the near future. IMPORTANCE Bat-borne viruses have attracted much attention due to zoonotic outbreaks with large consequences to humans. Because of that, virus characterization in bats has been prioritized in tropical regions of the globe. However, bat-virus research in Latin America and particularly in Brazil, which are among the most bat species-rich regions of the world, are highly biased toward zoonotic viruses and known bat reservoir species. These results have direct implication for virus studies in general but also for new zoonotic virus and spillover events characterization. The limited knowledge we currently have about the virome of Brazilian bats drastically limits any broad assessment of zoonotic viruses they carry and calls for coordinated and large-scale studies to fill this crucial knowledge gap.

Investigation of the Virome and Characterization of Issyk-Kul Virus from Swedish Myotis brandtii Bats

Bats are reservoirs for many different viruses, including some that can be transmitted to and cause disease in humans and/or animals. However, less is known about the bat-borne viruses circulating in Northern European countries such as in Sweden. In this study, saliva from Myotis brandtii bats, collected from south-central Sweden, was analyzed for viruses. The metagenomic analysis identified viral sequences belonging to different viral families, including, e.g., Nairoviridae, Retroviridae, Poxviridae, Herpesviridae and Siphoviridae. Interestingly, through the data analysis, the near-complete genome of Issyk-Kul virus (ISKV), a zoonotic virus within the Nairoviridae family, was obtained, showing 95-99% protein sequence identity to previously described ISKVs. This virus is believed to infect humans via an intermediate tick host or through contact with bat excrete. ISKV has previously been found in bats in Europe, but not previously in the Nordic region. In addition, near full-length genomes of two novel viruses belonging to Picornavirales order and Tymoviridae family were characterized. Taken together, our study has not only identified novel viruses, but also the presence of a zoonotic virus not previously known to circulate in this region. Thus, the results from these types of studies can help us to better understand the diversity of viruses circulating in bat populations, as well as identify viruses with zoonotic potential that could possibly be transmitted to humans.

Reproduction, seasonal morphology, and juvenile growth in three Malagasy fruit bats

The island nation of Madagascar is home to three endemic species of Old World fruit bat in the family Pteropodidae: Pteropus rufus, Eidolon dupreanum, and Rousettus madagascariensis, all three of which are IUCN Red Listed under some category of threat. Delineation of seasonal limits in the reproductive calendar for threatened mammals can inform conservation efforts by clarifying parameters used in population viability models, as well as elucidate understanding of the mechanisms underpinning pathogen persistence in host populations. Here, we define the seasonal limits of a staggered annual birth pulse across the three species of endemic Madagascar fruit bat, known reservoirs for viruses of high zoonotic potential. Our field studies indicate that this annual birth pulse takes place in September/October for P. rufus, November for E. dupreanum, and December for R. madagascariensis in central-eastern Madagascar where the bulk of our research was concentrated. Juvenile development periods vary across the three Malagasy pteropodids, resulting in near-synchronous weaning of pups for all species in late January-February at the height of the fruiting season for this region. We here document the size range in morphological traits for the three Malagasy fruit bat species, with P. rufus and E. dupreanum among the larger of pteropodids globally and R. madagascariensis among the smaller. All three species demonstrate subtle sexual dimorphism with males being larger than females. We explore seasonal variation in adult body condition by comparing observed body mass with body mass predicted by forearm length, demonstrating that pregnant females add weight during staggered gestation periods and males lose weight during the nutritionally deficit Malagasy winter. Finally, we quantify forearm, tibia, and ear length growth rates in juvenile bats, demonstrating both faster growth and more protracted development times for P. rufus as compared with E. dupreanum and R. madagascariensis. The longer development period for the already-threatened P. rufus further undermines the conservation status of this species as human hunting is particularly detrimental to population viability during reproductive periods. Our work highlights the importance of longitudinal field studies in collecting critical data for mammalian conservation efforts and human public health alike.

Highly Diverse Arenaviruses in Neotropical Bats, Brazil

We detected arenavirus RNA in 1.6% of 1,047 bats in Brazil that were sampled during 2007-2011. We identified Tacaribe virus in 2 Artibeus sp. bats and a new arenavirus species in Carollia perspicillata bats that we named Tietê mammarenavirus. Our results suggest that bats are an underrecognized arenavirus reservoir.