Diversity of Astroviruses Circulating in Humans, Bats, and Wild Birds in Egypt

Astroviruses belong to Astroviridae family which includes two main genera: Mamastroviruses that infect mammals, and Avastroviruses that infect avian hosts. Bats and wild birds are considered among the natural reservoirs for astroviruses. Infections in humans are associated with severe gastroenteritis, especially among children. We conducted surveillance for astroviruses in bats, wild birds, and humans in Egypt. Our results indicated relatively high prevalence of astroviruses in those hosts. Phylogenetic analysis revealed diversity of these viruses within hosts. Detected human viruses showed similarity with classic and variant human astroviruses, as well as similarity with animal-origin viruses. Viruses in bats were dispersed, with similarities to other bat viruses as well as other mammalian, including human, viruses. Wild bird viruses varied and were related to other avastroviruses, as well as human astroviruses. Our results indicate that astroviruses are common in bats, wild birds, and humans in Egypt, with a wide gene pool. Potential cross-species transmission may be occurring but should be verified by further surveillance and molecular studies.

Diverse Functions of Polyamines in Virus Infection

As obligate intracellular parasites, viruses rely on host cells for the building blocks of progeny viruses. Metabolites such as amino acids, nucleotides, and lipids are central to viral proteins, genomes, and envelopes, and the availability of these molecules can restrict or promote infection. Polyamines, comprised of putrescine, spermidine, and spermine in mammalian cells, are also critical for virus infection. Polyamines are small, positively charged molecules that function in transcription, translation, and cell cycling. Initial work on the function of polyamines in bacteriophage infection illuminated these molecules as critical to virus infection. In the decades since early virus-polyamine descriptions, work on diverse viruses continues to highlight a role for polyamines in viral processes, including genome packaging and viral enzymatic activity. On the host side, polyamines function in the response to virus infection. Thus, viruses and hosts compete for polyamines, which are a critical resource for both. Pharmacologically targeting polyamines, tipping the balance to favor the host and restrict virus replication, holds significant promise as a broad-spectrum antiviral strategy.

Genetic evolution analysis of 2019 novel coronavirus and coronavirus from other species

The Corona Virus Disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a Public Health Emergency of International Concern. However, so far, there are still controversies about the source of the virus and its intermediate host. Here, we found the novel coronavirus was closely related to coronaviruses derived from five wild animals, including Paguma larvata, Paradoxurus hermaphroditus, Civet, Aselliscus stoliczkanus and Rhinolophus sinicus, and was in the same branch of the phylogenetic tree. However, genome and ORF1a homology show that the virus is not the same coronavirus as the coronavirus derived from these five animals, whereas the virus has the highest homology with Bat coronavirus isolate RaTG13.

Whole genome sequence analysis of cell culture-adapted rotavirus A strains from chicken

Rotavirus A (RVA) is a major cause of gastroenteritis in humans and mammalian animals, and has also been abundantly detected in avian species. Avian RVA infection is associated with diarrhea, reduced growth and increased mortality, leading to economic losses in the poultry industry. Avian RVA forms a unique genetic clade within the whole RVA species. However, up to now, only a few full-length avian RVA genomes have been published and only a small number of avian RVA strains have been adapted to grow in cell culture for subsequent studies. Here, the four cell culture-adapted chicken RVA strains 02V0002G3, 04V0027G6, 05V0500F6 and 06V0661G1 were characterized in more detail. Transmission electron microscopy of the viruses derived from culture supernatant showed a typical triple-layered morphology of rotavirus particles; in addition, strain 06V0661G1 showed a high proportion of double-layered particles. The (nearly) complete genome sequences of the viruses were determined using next-generation sequencing (NGS). The resulting sequences were compared to full-length or partial sequences of the strains previously determined using Sanger sequencing; and a few nucleotide mismatches, some of them resulting in amino acid substitutions, were identified. The genomes of strains 02V0002G3, 04V0027G6 and 05V0500F6 were closely related to each other showing a G19-P[30]-I11-R6-C6-M7-A16-N6-T8-E10-H8 genotype constellation. Strain 06V0661G1 carries the VP4 genotype P[31] in the same genetic backbone like the other strains. However, further sequence analysis showed that the genes of this strain, especially that encoding NSP3, clustered more separately from the other strains in phylogenetic trees. The characterized cell culture-adapted chicken RVA strains may be useful for future studies investigating genetic diversity and replication of avian rotaviruses, as well as for the development of vaccines and diagnostic tools.

History is repeating itself: Probable zoonotic spillover as the cause of the 2019 novel Coronavirus Epidemic

Pathogen transmission from a vertebrate animal to a human, also known as zoonotic spillover, represents a global public health burden, which while associated with multiple outbreaks, still remains a poorly understood phenomenon. Coronaviruses, like influenza viruses, circulate in nature in various animal species. Alpha-coronaviruses and beta-coronaviruses can infect mammals and gamma-coronaviruses and delta-coronaviruses tend to infect birds, but some of them can also be transmitted to mammals. Although still preliminary, current data suggest that bats are the most probable initial source of the current 2019 novel CoV (2019nCoV) outbreak, that begun on December 2019 in Wuhan, China, apparently spreading from a "wet market" to multiple cities and provinces in China. This epidemic of 2019nCoV, already reaching more than 6,000 cases to-day (end of January 2020) (>90% in China), will not be the last one linked to zoonotic spillover events.

What do studies in wild mammals tell us about human emerging viral diseases in Mexico?

Multiple species of viruses circulate in wild mammals, some of them potentially causing zoonosis. Most of the suspected viral zoonotic diseases affecting human patients remain unidentified with regard to their aetiological agent. The aim of this study is to summarize the state of knowledge of the viral richness associated with wild mammals in Mexico throughout 1900-2018 and their relationship with human cases. We compiled two databases, one of them containing all available published studies on potentially zoonotic viruses in wild mammals and another with human cases related to zoonotic viruses. The database on wild mammals covers the period of 1900-2018; the human case database spans 2000-2013. We calculated the richness of viral potential zoonotic agents and evaluated their geographical distribution. We found 262 records of 42 potential zoonotic viral species associated with 92 wild mammal species in 28 states across Mexico. Records of human viral cases were only found in 29 states, which did not overlap with the reports in wild mammals. We detected 25.6% (42/164) of viral zoonotic agents reported worldwide. This analysis opens a relevant topic of discussion for public health attention.

Insights into the Host Specificity of Mosquito-Borne Flaviviruses Infecting Wild Mammals

Mosquito-borne flaviviruses (MBFVs) are of public and animal health concern because they cause millions of human deaths annually and impact domestic animals and wildlife globally. MBFVs are phylogenetically divided into two clades, one is transmitted by Aedes mosquitoes (Ae-MBFVs) associated with mammals and the other by Culex mosquitoes (Cx-MBFVs) associated with birds. However, this assumption has not been evaluated. Here, we synthesized 79 published reports of MBFVs from wild mammals, estimating their host. Then, we tested whether the host specificity was biased to sampling and investigation efforts or to phylogenetic relationships using a viral phylogenetic tree drawn from analyzing whole flavivirus genomes obtained in GenBank. We found in total 18 flaviviruses, nine related to Aedes spp. and nine to Culex spp. infecting 129 mammal species. Thus, this supports that vectors are transmitting MBFV across available host clades and that ornithophilic mosquitoes are readily infecting mammals. Although most of the mosquito species are generalists in their host-feeding preferences, we also found a certain degree of MBFV's specificity, as most of them infect closely related mammal species. The present study integrates knowledge regarding MBFVs, and it may help to understand their transmission dynamics between viruses, vectors, and mammal hosts.

Codon Usage in the Iflaviridae Family Is Not Diverse Though the Family Members Are Isolated from Diverse Host Taxa

All iflavirus members belong to the unique genus, Iflavirus, of the family, Iflaviridae. The host taxa and sequence identities of these viruses are diverse. A codon usage bias, maintained by a balance between selection, mutation, and genetic drift, exists in a wide variety of organisms. We characterized the codon usage patterns of 44 iflavirus genomes that were isolated from the classes, Insecta, Arachnida, Mammalia, and Malacostraca. Iflaviruses lack a strong codon usage bias when they are evaluated using an effective number of codons. The odds ratios of the majority of dinucleotides are within the normal range. However, the dinucleotides at the 1st-2nd codon positions are more biased than those at the 2nd-3rd codon positions. Plots of effective numbers of codons, relative neutrality analysis, and PR2 bias analysis all indicate that selection pressure dominates mutations in shaping codon usage patterns in the family, Iflaviridae. When these viruses were grouped into their host taxa, we found that the indices, including the nucleotide composition, effective number of codons, relative synonymous codon usage, and the influencing factors behind the codon usage patterns, all show that there are non-significant differences between the six host-taxa-groups. Our results disagree with our assumption that diverse viruses should possess diverse codon usage patterns, suggesting that the nucleotide composition and codon usage in the family, Iflaviridae, are not host taxa-specific signatures.

Sample descriptors linked to metagenomic sequencing data from human and animal enteric samples from Vietnam

There is still limited information on the diversity of viruses co-circulating in humans and animals. Here, we report data obtained from a large field collection of enteric samples taken from humans, pigs, rodents and other mammal hosts in Vietnam between 2012 and 2016. Each of 2100 stool or rectal swab samples was subjected to virally-enriched agnostic metagenomic sequencing; the short read sequence data are accessible from the European Nucleotide Archive (ENA). We link the sequence data to metadata on host type and demography and geographic location, distinguishing hospital patients, members of a cohort identified as a high risk of zoonotic infections (e.g. abattoir workers, rat traders) and animals. These data are suitable for further studies of virus diversity and virus discovery in humans and animals from Vietnam and to identify viruses found in multiple hosts that are potentially zoonotic.

Complete Genome Sequence of Parainfluenza Virus 5 (PIV5) from a Sunda Pangolin (Manis javanica) in China

We report here the complete genome sequence of the parainfluenza virus PIV5-GD18 strain, isolated from a wild Sunda pangolin (Manis javanica) in China in 2017. It was 15,246 nucleotides with four nucleotides substitutions, which resulted in four changes of amino acid that were found only in PIV5-GD18, which further broadens the PIV5 infection host spectrum and will aid in our understanding of the complete genome sequence of PIV5 in different hosts.

Faecal Virome Analysis of Wild Animals from Brazil

The Brazilian Cerrado fauna shows very wide diversity and can be a potential viral reservoir. Therefore, the animal's susceptibility to some virus can serve as early warning signs of potential human virus diseases. Moreover, the wild animal virome of this biome is unknown. Based on this scenario, high-throughput sequencing contributes a robust tool for the identification of known and unknown virus species in this environment. In the present study, faeces samples from cerrado birds (Psittacara leucophthalmus, Amazona aestiva, and Sicalis flaveola) and mammals (Didelphis albiventris, Sapajus libidinosus, and Galictis cuja) were collected at the Veterinary Hospital, University of Brasília. Viral nucleic acid was extracted, submitted to random amplification, and sequenced by Illumina HiSeq platform. The reads were de novo assembled, and the identities of the contigs were evaluated by Blastn and tblastx searches. Most viral contigs analyzed were closely related to bacteriophages. Novel archaeal viruses of the Smacoviridae family were detected. Moreover, sequences of members of Adenoviridae, Anelloviridae, Circoviridae, Caliciviridae, and Parvoviridae families were identified. Complete and nearly complete genomes of known anelloviruses, circoviruses, and parvoviruses were obtained, as well as putative novel species. We demonstrate that the metagenomics approach applied in this work was effective for identification of known and putative new viruses in faeces samples from Brazilian Cerrado fauna.

Investigation about the Occurrence of Transmission Cycles of Arbovirus in the Tropical Forest, Amazon Region

Because of its ecological characteristics, the Caxiuanã National Forest (FLONA) is a potential area of arbovirus circulation. The present study aimed to investigate the occurrence of arbovirus transmission cycles at FLONA de Caxiuanã. Five field trips were performed to capture mosquitoes and sylvatic vertebrates. For these vertebrates, we attempted viral isolation by cell monolayer inoculation from blood, and hemagglutination inhibition and further seroneutralization assays from sera. For mosquitoes, we performed tests of viral genome detection. A total of 338 vertebrates were captured, and the greatest representative was birds (251/74.26%). A total of 16,725 mosquitoes were captured, distributed among 56 species. There were no viruses isolated by newborn mouse inoculation. Among birds, antibodies against Ilheus virus were the most prevalent. Catu virus, Caraparu virus, and Mucambo virus were the most prevalent among mammals and reptiles. Fragments of Mucambo virus, Ilheus virus, Bussuquara virus, and Rocio virus genome were detected in a pool of mosquito samples. These results of the study suggest the occurrence of arbovirus transmission cycles in the FLONA of Caxiuanã. The proximity of human populations with elements, involved in transmission cycles, makes surveillance necessary in this population to avoid dispersion of arboviruses to naïve locations.

Diverse Mechanisms Underlie Enhancement of Enteric Viruses by the Mammalian Intestinal Microbiota

Over the past two decades, there has been tremendous progress in understanding the impact of the intestinal microbiota on mammalian metabolism, physiology, and immune development and function. There has also been substantial advancement in elucidating the interplay between commensal and pathogenic bacteria. Relatively more recently, researchers have begun to investigate the effect of the intestinal microbiota on viral pathogenesis. Indeed, a growing body of literature has reported that commensal bacteria within the mammalian intestinal tract enhance enteric virus infections through a variety of mechanisms. Commensal bacteria or bacterial glycans can increase the stability of enteric viruses, enhance virus binding to host receptors, modulate host immune responses in a proviral manner, expand the numbers of host cell targets, and facilitate viral recombination. In this review, we will summarize the current literature exploring these effects of the intestinal microbiota on enteric virus infections.

Exploring the Reservoir Hosts of Tick-Borne Encephalitis Virus

Tick-borne encephalitis virus (TBEV) is an important arbovirus, which is found across large parts of Eurasia and is considered to be a major health risk for humans. Like any other arbovirus, TBEV relies on complex interactions between vectors, reservoir hosts, and the environment for successful virus circulation. Hard ticks are the vectors for TBEV, transmitting the virus to a variety of animals. The importance of these animals in the lifecycle of TBEV is still up for debate. Large woodland animals seem to have a positive influence on virus circulation by providing a food source for adult ticks; birds are suspected to play a role in virus distribution. Bank voles and yellow-necked mice are often referred to as classical virus reservoirs, but this statement lacks strong evidence supporting their highlighted role. Other small mammals (e.g., insectivores) may also play a crucial role in virus transmission, not to mention the absence of any suspected reservoir host for non-European endemic regions. Theories highlighting the importance of the co-feeding transmission route go as far as naming ticks themselves as the true reservoir for TBEV, and mammalian hosts as a mere bridge for transmission. A deeper insight into the virus reservoir could lead to a better understanding of the development of endemic regions. The spatial distribution of TBEV is constricted to certain areas, forming natural foci that can be restricted to sizes of merely 500 square meters. The limiting factors for their occurrence are largely unknown, but a possible influence of reservoir hosts on the distribution pattern of TBE is discussed. This review aims to give an overview of the multiple factors influencing the TBEV transmission cycle, focusing on the role of virus reservoirs, and highlights the questions that are waiting to be further explored.

PB2 mutations arising during H9N2 influenza evolution in the Middle East confer enhanced replication and growth in mammals

Avian influenza virus H9N2 has been endemic in birds in the Middle East, in particular in Egypt with multiple cases of human infections since 1998. Despite concerns about the pandemic threat posed by H9N2, little is known about the biological properties of H9N2 in this epicentre of infection. Here, we investigated the evolutionary dynamics of H9N2 in the Middle East and identified phylogeny-associated PB2 mutations that acted cooperatively to increase H9N2 replication/transcription in human cells. The accumulation of PB2 mutations also correlated with an increase in H9N2 virus growth in the upper and lower airways of mice and in virulence. These mutations clustered on a solvent-exposed region in the PB2-627 domain in proximity to potential interfaces with host factors. These PB2 mutations have been found at high prevalence during evolution of H9N2 in the field, indicating that they have provided a selective advantage for viral adaptation to infect poultry. Therefore, continuous prevalence of H9N2 virus in the Middle East has generated a far more fit or optimized replication phenotype, leading to an expanded viral host range, including to mammals, which may pose public health risks beyond the current outbreaks.

The G1-like clade of H9N2 influenza viruses can undergo genetic reassortment with other influenza virus subtypes to produce novel zoonotic viruses, such as the Gs/GD lineage H5N1, H7N9, H10N8, and H5N8 viruses. Since 1998, the G1-like subclade of H9N2 influenza virus has been widely circulating in birds in Central Asia and the Middle East and a number of human cases have been reported. However, little is known about the biological properties of H9N2 viruses in this epicentre of infection. Our data showed that, during about two decades of evolution in nature, G1-like subclade strains evolved to produce strains with appreciably higher replication phenotypes in Central Asia and the Middle East, which led to their expanded host range, including to humans. Therefore, G1-like subclade strains in these areas may accumulate mutations to produce novel viruses and the large gene pool in these areas would enable reassortment with other influenza viruses. This study indicated the need for studies of H9N2 viruses in such areas to monitor their evolutionary dynamics and possible genetic changes.

What factors explain the geographical range of mammalian parasites?

Free-living species vary substantially in the extent of their spatial distributions. However, distributions of parasitic species have not been comprehensively compared in this context. We investigated which factors most influence the geographical extent of mammal parasites. Using the Global Mammal Parasite Database we analysed 17 818 individual geospatial records on 1806 parasite species (encompassing viruses, bacteria, protozoa, arthropods and helminths) that infect 396 carnivore, ungulate and primate host species. As a measure of the geographical extent of each parasite species we quantified the number and area of world ecoregions occupied by each. To evaluate the importance of variables influencing the summed area of ecoregions occupied by a parasite species, we used Bayesian network analysis of a subset ( n = 866) of the parasites in our database that had at least two host species and complete information on parasite traits. We found that parasites that covered more geographical area had a greater number of host species, higher average phylogenetic relatedness between host species and more sampling effort. Host and parasite taxonomic groups had weak and indirect effects on parasite ecoregion area; parasite transmission mode had virtually no effect. Mechanistically, a greater number of host species probably increases both the collective abundance and habitat breadth of hosts, providing more opportunities for a parasite to have an expansive range. Furthermore, even though mammals are one of the best-studied animal classes, the ecoregion area occupied by their parasites is strongly sensitive to sampling effort, implying mammal parasites are undersampled. Overall, our results support that parasite geographical extent is largely controlled by host characteristics, many of which are subsumed within host taxonomic identity.

Slicing and dicing viruses: antiviral RNA interference in mammals

To protect against the harmful consequences of viral infections, organisms are equipped with sophisticated antiviral mechanisms, including cell-intrinsic means to restrict viral replication and propagation. Plant and invertebrate cells utilise mostly RNA interference (RNAi), an RNA-based mechanism, for cell-intrinsic immunity to viruses while vertebrates rely on the protein-based interferon (IFN)-driven innate immune system for the same purpose. The RNAi machinery is conserved in vertebrate cells, yet whether antiviral RNAi is still active in mammals and functionally relevant to mammalian antiviral defence is intensely debated. Here, we discuss cellular and viral factors that impact on antiviral RNAi and the contexts in which this system might be at play in mammalian resistance to viral infection.

A viral metagenomic survey identifies known and novel mammalian viruses in bats from Saudi Arabia

Bats are implicated as natural reservoirs for a wide range of zoonotic viruses including SARS and MERS coronaviruses, Ebola, Marburg, Nipah, Hendra, Rabies and other lyssaviruses. Accordingly, many One Health surveillance and viral discovery programs have focused on bats. In this report we present viral metagenomic data from bats collected in the Kingdom of Saudi Arabia [KSA]. Unbiased high throughput sequencing of fecal samples from 72 bat individuals comprising four species; lesser mouse-tailed bat (Rhinopoma hardwickii), Egyptian tomb bat (Taphozous perforatus), straw-colored fruit bat (Eidolon helvum), and Egyptian fruit bat (Rousettus aegyptiacus) revealed molecular evidence of a diverse set of viral families: Picornaviridae (hepatovirus, teschovirus, parechovirus), Reoviridae (rotavirus), Polyomaviridae (polyomavirus), Papillomaviridae (papillomavirus), Astroviridae (astrovirus), Caliciviridae (sapovirus), Coronaviridae (coronavirus), Adenoviridae (adenovirus), Paramyxoviridae (paramyxovirus), and unassigned mononegavirales (chuvirus). Additionally, we discovered a bastro-like virus (Middle East Hepe-Astrovirus), with a genomic organization similar to Hepeviridae. However, since it shared homology with Hepeviridae and Astroviridae at ORF1 and in ORF2, respectively, the newly discovered Hepe-Astrovirus may represent a phylogenetic bridge between Hepeviridae and Astroviridae.

Antigenicity and Immunogenicity of Differentially Glycosylated Hepatitis C Virus E2 Envelope Proteins Expressed in Mammalian and Insect Cells

The development of a prophylactic vaccine for hepatitis C virus (HCV) remains a global health challenge. Cumulative evidence supports the importance of antibodies targeting the HCV E2 envelope glycoprotein to facilitate viral clearance. However, a significant challenge for a B cell-based vaccine is focusing the immune response on conserved E2 epitopes capable of eliciting neutralizing antibodies not associated with viral escape. We hypothesized that glycosylation might influence the antigenicity and immunogenicity of E2. Accordingly, we performed head-to-head molecular, antigenic, and immunogenic comparisons of soluble E2 (sE2) produced in (i) mammalian (HEK293) cells, which confer mostly complex- and high-mannose-type glycans; and (ii) insect (Sf9) cells, which impart mainly paucimannose-type glycans. Mass spectrometry demonstrated that all 11 predicted N-glycosylation sites were utilized in both HEK293- and Sf9-derived sE2, but that N-glycans in insect sE2 were on average smaller and less complex. Both proteins bound CD81 and were recognized by conformation-dependent antibodies. Mouse immunogenicity studies revealed that similar polyclonal antibody responses were generated against antigenic domains A to E of E2. Although neutralizing antibody titers showed that Sf9-derived sE2 induced moderately stronger responses than did HEK293-derived sE2 against the homologous HCV H77c isolate, the two proteins elicited comparable neutralization titers against heterologous isolates. Given that global alteration of HCV E2 glycosylation by expression in different hosts did not appreciably affect antigenicity or overall immunogenicity, a more productive approach to increasing the antibody response to neutralizing epitopes may be complete deletion, rather than just modification, of specific N-glycans proximal to these epitopes.IMPORTANCE The development of a vaccine for hepatitis C virus (HCV) remains a global health challenge. A major challenge for vaccine development is focusing the immune response on conserved regions of the HCV envelope protein, E2, capable of eliciting neutralizing antibodies. Modification of E2 by glycosylation might influence the immunogenicity of E2. Accordingly, we performed molecular and immunogenic comparisons of E2 produced in mammalian and insect cells. Mass spectrometry demonstrated that the predicted glycosylation sites were utilized in both mammalian and insect cell E2, although the glycan types in insect cell E2 were smaller and less complex. Mouse immunogenicity studies revealed similar polyclonal antibody responses. However, insect cell E2 induced stronger neutralizing antibody responses against the homologous isolate used in the vaccine, albeit the two proteins elicited comparable neutralization titers against heterologous isolates. A more productive approach for vaccine development may be complete deletion of specific glycans in the E2 protein.

Immune genes are hotspots of shared positive selection across birds and mammals

Consistent patterns of positive selection in functionally similar genes can suggest a common selective pressure across a group of species. We use alignments of orthologous protein-coding genes from 39 species of birds to estimate parameters related to positive selection for 11,000 genes conserved across birds. We show that functional pathways related to the immune system, recombination, lipid metabolism, and phototransduction are enriched for positively selected genes. By comparing our results with mammalian data, we find a significant enrichment for positively selected genes shared between taxa, and that these shared selected genes are enriched for viral immune pathways. Using pathogen-challenge transcriptome data, we show that genes up-regulated in response to pathogens are also enriched for positively selected genes. Together, our results suggest that pathogens, particularly viruses, consistently target the same genes across divergent clades, and that these genes are hotspots of host-pathogen conflict over deep evolutionary time.

Antiviral RNA interference in mammals

Infection of plants and insects with RNA and DNA viruses triggers Dicer-dependent production of virus-derived small interfering RNAs (vsiRNAs), which subsequently guide specific virus clearance by RNA interference (RNAi). Consistent with a major antiviral function of RNAi, productive virus infection in these eukaryotic hosts depends on the expression of virus-encoded suppressors of RNAi (VSRs). The eukaryotic RNAi pathway is highly conserved, particularly between insects and mammals. This review will discuss key recent findings that indicate a natural antiviral function of the RNAi pathway in mammalian cells. We will summarize the properties of the characterized mammalian vsiRNAs and VSRs and highlight important questions remaining to be addressed on the function and mechanism of mammalian antiviral RNAi.

The adaptation of codon usage of +ssRNA viruses to their hosts

Viruses depend on their host's cellular structure to survive. Most of them do not have tRNAs, their translation relies on hosts' tRNA pools. Over the course of evolution, viruses needed to optimally exploit cellular processes of their host. Thus, codon usage of a virus should coevolve with its host to efficiently and rapidly replicate. Some viruses can invade a broad spectrum of hosts (BSTVs), while others can invade a narrow spectrum only (NSTVs). Consequently, we test the hypothesis that similarity of codon usage preference and the degree of matching between BSTVs and their hosts will be lower than that of NSTVs, which only need to coevolve with few hosts. We compare the patterns of codon usage in 255 virus genomes to test this hypothesis. Our results show that NSTVs have a higher degree of matching to their hosts' tRNA pools than BSTVs. Further, analysis of the effective number of codons (ENC) infers that codon usage bias of NSTVs is relatively stronger than that of BSTVs. Thus, codon usage of NSTVs tends to better match their host than that of BSTVs. This supports the hypothesis that viruses adapt to the expression system of their host(s).

Silent Orthohantavirus Circulation Among Humans and Small Mammals from Central Minas Gerais, Brazil

New World orthohantaviruses are emerging RNA viruses that cause hantavirus cardiopulmonary syndrome (HCPS). These viruses are a burden to public health around the world with a lethality rate of around 60%. In South America, rodents of Sigmodontinae subfamily are the main reservoirs of orthohantaviruses. We described a serosurvey for orthohantaviruses circulation in an apparently healthy human population and small mammals from rural areas in Central Minas Gerais State, Brazil. A total of 240 individuals and 50 small mammals (26 rodents belonging to 10 different species and 24 marsupials from 4 different species) were sampled during 2012-2013. The seroprevalence rates of IgG/IgM antibodies in humans were 7.1 and 1.6%, respectively. Only one rodent, an Oligoryzomys nigripes captured in peridomestic area, tested positive for IgG antibodies and viral RNA. Our findings suggest a silent circulation of orthohantaviruses in a region of intensive agriculture production. The detection of seropositive humans in an area with a lack of previous HCPS reports highlights potential oligosymptomatic cases and the need for surveillance strategies that could reduce the risk of future outbreaks.

Using Bloodmeal Analysis to Assess Disease Risk to Wildlife at the New Northern Limit of a Mosquito Species

The historically southeastern mosquito species Culex erraticus has over the last 30 years undergone a marked expansion north. We evaluated this species' potential to participate in local disease cycles in the northeastern USA by identifying the vertebrate sources of blood in Cx. erraticus specimens from New Jersey. We found that the majority of bloodmeals (92.6%) were derived from birds, followed by 6.8% from mammals (of which half were human), and a single amphibian bloodmeal from a spring peeper (0.56%). Medium- and large-sized water birds from the order Pelecaniformes made up 60.4% of the bird species and 55.9% of all identified hosts. This group of birds is known enzootic hosts of arboviruses such as eastern equine encephalitis virus, for which Cx. erraticus is a competent vector. Additionally, we screened blooded mosquitoes for avian malaria parasites and identified three different lineages of Plasmodium, including what may represent a new Plasmodium species (likely a wetland bird specialist) in bloodmeals from Green Herons, a Great Egret, and a Double-Crested Cormorant. Our results support the utility of mosquito bloodmeals as sources of information about circulating wildlife pathogens and reveal the potential of range-expanding species to intensify local zoonoses and bridge enzootic pathogens to humans.

Powassan Virus and Other Arthropod-Borne Viruses in Wildlife and Ticks in Ontario, Canada

Powassan virus (POWV) is a tick-borne zoonosis maintained in natural enzootic cycles between ixodid ticks and wild mammals. Reported human cases have increased in recent years; these infections can be fatal or lead to long-term neurologic sequelae. However, both the geographic distribution and the role of common, potential mammalian hosts in POWV transmission are poorly understood, creating challenges to public health surveillance. We looked for evidence of POWV infection among candidate wildlife host species and ticks collected from mammals and birds in southern Ontario. Tissues (including blood) and ticks from trapped wild mammals were collected in the summers of 2015 and 2016. Ticks removed from dogs in 2015-2016 and wildlife diagnostic cases from 2011 to 2013 were also included. Tissue and tick (Ixodes spp.) homogenates were tested for POWV by reverse transcriptase-polymerase chain reaction (RT-PCR). In addition, sera from wild mammals were tested for antibodies to POWV, West Nile virus (WNV), and heartland virus (HRTV) by plaque reduction neutralization test. All 724 tissue samples were negative for POWV by RT-PCR. One of 53 pools of Ixodes cookei (among 98 total tick pools) was RT-PCR positive for deer tick virus (POWV) lineage. Antibodies to POWV and WNV were detected in 0.4% of 265 and 6.1% of 264 samples, respectively, and all of 219 serum samples tested negative for anti-HRTV antibodies. These results reveal low POWV detection rates in southern Ontario, while highlighting the challenges and need for continued efforts into understanding POWV epidemiology and targeted surveillance strategies.