A recombinant chimeric influenza virus vaccine expressing the consensus H3 hemagglutinin elicits broad hemagglutination inhibition antibodies against divergent swine H3N2 influenza viruses.

The global distribution and ongoing evolution of type A swine influenza virus (IAV-S) continue to pose significant challenges against developing broadly protective vaccines to control swine influenza. This study focuses on the hemagglutinin (HA) consensus-based approach towards developing a more broadly protective swine influenza vaccine against various H3 strains circulating in domestic pig populations. By computationally analyzing >1000 swine H3 full-length HA sequences, we generated a consensus H3 and expressed it in the context of influenza A WSN/33 reverse genetics system. The derived recombinant chimeric swine influenza virus with the consensus H3 was inactivated and further evaluated as a potential universal vaccine in pigs. The consensus H3 vaccine elicited broadly active hemagglutination inhibition (HI) antibodies against divergent swine H3N2 influenza viruses including human H3N2 variant of concern, and strains belong to genetic clusters IV, IV-A, IV-B, IV-C, IV-D and IV-F. Importantly, vaccinated pigs were completely protected against challenge with a clinical swine H3N2 isolate in that neither viral shedding nor replication in lungs of vaccinated pigs were observed. These findings warrant further study of the consensus H3 vaccine platform for broad protection against diverse swine influenza viruses.

A fully human monoclonal antibody possesses antibody-dependent cellular cytotoxicity (ADCC) activity against the H1 subtype of influenza A virus by targeting a conserved epitope at the HA1 protomer interface.

The DiversitabTM system produces target specific high titer fully human polyclonal IgG immunoglobulins from transchromosomic (Tc) bovines shown to be safe and effective against multiple virulent pathogens in animal studies and Phase 1, 2 and 3 human clinical trials. We describe the functional properties of a human monoclonal antibody (mAb), 38C2, identified from this platform, which recognizes recombinant H1 hemagglutinins (HAs) and induces appreciable antibody-dependent cellular cytotoxicity (ADCC) activity in vitro. Interestingly, 38C2 monoclonal antibody demonstrated no detectable neutralizing activity against H1N1 virus in both hemagglutination inhibition and virus neutralization assays. Nevertheless, this human monoclonal antibody induced appreciable ADCC against cells infected with multiple H1N1 strains. The HA-binding activity of 38C2 was also demonstrated in flow cytometry using Madin-Darby canine kidney cells infected with multiple influenza A H1N1 viruses. Through further investigation with the enzyme-linked immunosorbent assay involving the HA peptide array and 3-dimensional structural modeling, we demonstrated that 38C2 appears to target a conserved epitope located at the HA1 protomer interface of H1N1 influenza viruses. A novel mode of HA-binding and in vitro ADCC activity pave the way for further evaluation of 38C2 as a potential therapeutic agent to treat influenza virus infections in humans.

Influenza C and D Viruses Demonstrated a Differential Respiratory Tissue Tropism in a Comparative Pathogenesis Study in Guinea Pigs.

Influenza C virus (ICV) is increasingly associated with community-acquired pneumonia (CAP) in children and its disease severity is worse than the influenza B virus, but similar to influenza A virus associated CAP. Despite the ubiquitous infection landscape of ICV in humans, little is known about its replication and pathobiology in animals. The goal of this study was to understand the replication kinetics, tissue tropism, and pathogenesis of human ICV (huICV) in comparison to the swine influenza D virus (swIDV) in guinea pigs. Intranasal inoculation of both viruses did not cause clinical signs, however, the infected animals shed virus in nasal washes. The huICV replicated in the nasal turbinates, soft palate, and trachea but not in the lungs while swIDV replicated in all four tissues. A comparative analysis of tropism and pathogenesis of these two related seven-segmented influenza viruses revealed that swIDV-infected animals exhibited broad tissue tropism with an increased rate of shedding on 3, 5, and 7 dpi and high viral loads in the lungs compared to huICV. Seroconversion occurred late in the huICV group at 14 dpi, while swIDV-infected animals seroconverted at 7 dpi. Guinea pigs infected with huICV exhibited mild to moderate inflammatory changes in the epithelium of the soft palate and trachea, along with mucosal damage and multifocal alveolitis in the lungs. In summary, the replication kinetics and pathobiological characteristics of ICV in guinea pigs agree with the clinical manifestation of ICV infection in humans, and hence guinea pigs could be used to study these distantly related influenza viruses. IMPORTANCE Similar to influenza A and B, ICV infections are seen associated with bacterial and viral co-infections which complicates the assessment of its real clinical significance. Further, the antivirals against influenza A and B viruses are ineffective against ICV which mandates the need to study the pathobiological aspects of this virus. Here we demonstrated that the respiratory tract of guinea pigs possesses specific viral receptors for ICV. We also compared the replication kinetics and pathogenesis of huICV and swIDV, as these viruses share 50% sequence identity. The tissue tropism and pathology associated with huICV in guinea pigs are analogous to the mild respiratory disease caused by ICV in humans, thereby demonstrating the suitability of guinea pigs to study ICV. Our comparative analysis revealed that huICV and swIDV replicated differentially in the guinea pigs suggesting that the type-specific genetic differences can result in the disparity of the viral shedding and tissue tropism.

Novel hepatoviruses in synanthropic bats in the upper Midwestern United States.

A nearly complete genome sequence of hepatovirus G was isolated from an Eptesicus fuscus bat submitted for rabies virus testing due to human exposure in South Dakota. The predicted polyprotein sequence was 78.2% and 74.4% identical to genotypes G1 and G2, respectively, recovered from bats in Ghana. Quantitative PCR on 90 E. fuscus bats showed that eight (8.9%) were positive for hepatovirus G. Targeted sequencing of the VP2 region of the genome for five positive samples showed >99% identity to hepatovirus G strain Ef15893, demonstrating that hepatovirus G commonly circulates in E. fuscus bats in the upper Midwest.

Identification of Pulmonary Infections With Porcine Rotavirus A in Pigs With Respiratory Disease.

While rotavirus (RV) is primarily known to cause gastroenteritis in many animals, several epidemiological studies have shown concurrent respiratory symptoms with fecal and nasal virus shedding. However, respiratory RV infections have rarely been investigated. By screening clinical samples submitted for diagnostic testing, porcine rotavirus A (RVA) was detected by quantitative reverse transcription PCR (qRT-PCR) in 28 out of 91 (30.8%) lungs obtained from conventionally reared pigs with respiratory signs. Among the positive cases, intensive RVA signals were mainly localized in alveolar macrophages (n = 3) and bronchiolar epithelial cells (n = 1) by RNAscope® in situ hybridization (ISH). The signals of RVA in bronchiolar epithelial cells were verified by ISH with different probes, immunohistochemistry, and transmission electron microscopy. Furthermore, additional cases with RVA ISH-positive signals in alveolar macrophages (n = 9) and bronchial epithelial cells (n = 1) were identified by screening 120 archived formalin-fixed and paraffin-embedded lung samples using tissue microarrays. Overall, our study showed a high frequency of RVA detection in lungs from conventional pigs with respiratory disease. Further research is needed to determine if RVA infection in the respiratory epithelium correlates with nasal shedding of rotavirus and its contribution to respiratory disease.

Experimental Infection of Horses with Influenza D Virus.

Antibodies to influenza D virus (IDV) have been detected in horses, but no evidence of disease in the field has been reported. To determine whether IDV is infectious, immunogenic, and pathogenic in horses, four 2-year-old horses seronegative for both influenza A (H3N8) and D viruses were intranasally inoculated with 6.25 × 107 TCID50/animal of D/bovine/California/0363/2019 (D/CA2019) virus, using a portable equine nebulizer system. Horses were observed daily for clinical signs including rectal temperature, nasal discharge, coughing, lung sounds, tachycardia, and tachypnea. No horses exhibited clinical signs of disease. Nasopharyngeal swabs collected from 1-8 days post-infection demonstrated virus shedding by qRT-PCR. The horses showed evidence of seroconversion as early as 13 days post-infection (dpi) and the geometric mean of the antibody titers (GMT) of all four horses ranged from 16.82-160 as demonstrated by the microneutralization assay. Further, deep RNA sequencing of the virus isolated in embryonated chicken eggs revealed no adaptive mutations indicating that IDV can replicate in horses, suggesting the possibility of interspecies transmission of IDV with bovine reservoir into equids in nature.

Bovine rhinitis B virus is highly prevalent in acute bovine respiratory disease and causes upper respiratory tract infection in calves.

Bovine respiratory disease (BRD) is the most significant cause of cattle morbidity and mortality worldwide. This multifactorial disease has a complex aetiology. Dogma posits a primary viral infection followed by secondary bacterial pneumonia. Bovine rhinitis B virus (BRBV) is an established aetiological agent of BRD, but little is known regarding its pathogenesis. Here, a BRD PCR panel identified 18/153 (11.8 %) lung samples and 20/49 (40.8 %) nasal swabs collected from cattle with respiratory signs as positive for BRBV, which was the most prevalent virus in nasal swabs. Primary bovine tracheal epithelial cells were used to isolate BRBV that was phylogenetically related to contemporary sequences from the USA and Mexico and genetically divergent from the previous sole BRBV isolate. To investigate virus pathogenesis, 1-week-old colostrum-deprived dairy calves were inoculated intranasally with 7.0 log10 TCID50 BRBV. Virus was isolated from nasal swabs, nasal turbinates, trachea and the brain of the challenged animals. Neutralizing antibodies were detected beginning 7 days post-inoculation and peaked at day 14. In situ hybridization (ISH) localized BRBV infection in the upper respiratory ciliated epithelial and goblet cells, occasionally associated with small defects of the superficial cilia lining. Sporadically, pinpoint ISH signals were also detected in cells resembling glial cells in the cerebrum in one calf. Together, these results demonstrate the BRBV infection is highly prevalent in acute BRD samples and while the pathogenicity of BRBV is minimal with infection largely limited to the upper respiratory tract, further research is needed to elucidate a possible initiatory role in BRD.

Alphacoronaviruses Are Common in Bats in the Upper Midwestern United States.

Bats are a reservoir for coronaviruses (CoVs) that periodically spill over to humans, as evidenced by severe acute respiratory syndrome coronavirus (SARS-CoV) and SARS-CoV-2. A collection of 174 bat samples originating from South Dakota, Minnesota, Iowa, and Nebraska submitted for rabies virus testing due to human exposure were analyzed using a pan-coronavirus PCR. A previously partially characterized CoV, Eptesicus bat CoV, was identified in 12 (6.9%) samples by nested RT-PCR. Six near-complete genomes were determined. Genetic analysis found a high similarity between all CoV-positive samples, Rocky Mountain bat CoV 65 and alphacoronavirus HCQD-2020 recently identified in South Korea. Phylogenetic analysis of genome sequences showed EbCoV is closely related to bat CoV HKU2 and swine acute diarrhea syndrome CoV; however, topological incongruences were noted for the spike gene that was more closely related to porcine epidemic diarrhea virus. Similar to some alphaCoVs, a novel gene, ORF7, was discovered downstream of the nucleocapsid, whose protein lacked similarity to known proteins. The widespread circulation of EbCoV with similarities to bat viruses that have spilled over to swine warrants further surveillance.

Spillover of Canine Parvovirus Type 2 to Pigs, South Dakota, USA, 2020.

In 1978, canine parvovirus type 2 originated from spillover of a feline panleukopenia-like virus, causing a worldwide pandemic of enteritis and myocarditis among canids. In 2020, the virus was identified in pigs in South Dakota, USA, by PCR, sequencing, in situ hybridization, and serology. Genetic analysis suggests spillover from wildlife.

Eptesicus fuscus Orthorubulavirus, a Close Relative of Human Parainfluenza Virus 4, Discovered in a Bat in South Dakota.

Bats are a reservoir for many zoonotic viruses and host large numbers of genetically diverse species in the families Rhabdoviridae, Coronaviridae, and Paramyxoviridae. Viruses from these families have repeatedly spilled over to humans in recent decades, causing significant clinical disease and deaths. Here, metagenomic sequencing of a big brown bat (Eptesicus fuscus) submitted for rabies testing due to human exposure identified a novel paramyxovirus, Eptesicus fuscus orthorubulavirus (EfORV), in South Dakota, United States. The nearly complete 15,814-nucleotide genome shared 72% identity with that of human parainfluenza virus 4 (HPIV4), a virus that causes significant clinical disease, typically bronchiolitis and pneumonia, in children less than 2 years of age. Phylogenetic analysis confirmed a close evolutionary history between EfORV and HPIV4, reminiscent of other orthorubulaviruses with highly similar bat and mammalian species, including conspecific human and bat mumps virus, mammalian parainfluenza virus 5 and bat Alston virus, and porcine La Piedad Michoacán virus and bat Mapuera virus. These results support the idea that bats are a reservoir for diverse paramyxoviruses with closely shared evolutionary histories, compared with a number of significant human pathogens, and expand the range of bat paramyxoviruses to North America. Given the propensity of paramyxoviruses to overcome species barriers, additional surveillance and characterization of EfORV are warranted. IMPORTANCE Bats are a reservoir of large numbers of viruses. Among bat-borne zoonotic viruses, members of Coronaviridae and Paramyxoviridae have had the largest impact on human health. The repeated spillover of bat viruses to humans, often with devastating results, has led to increased surveillance and virus discovery efforts in hot spots for virus emergence, largely Asia and Africa. Apart from rabies virus, little surveillance of viruses in bats is performed in North America. Here, viral metagenomic sequencing identified a close relative to HPIV4 in a big brown bat found in a motel room in South Dakota. The virus, EfORV, was 72% identical to HPIV4, which causes clinically significant respiratory disease, mainly in children; it represents the first bat paramyxovirus identified in North America. Close genetic relationships between bat and mammalian orthorubulaviruses underscore the importance of bats as a reservoir for zoonotic viruses.

Porcine Parvovirus 2 Is Predominantly Associated With Macrophages in Porcine Respiratory Disease Complex.

Porcine respiratory disease complex (PRDC) is a significant source of morbidity and mortality, manifested by pneumonia of multiple etiologies, where a variety of pathogens and environment and management practices play a role in the disease. Porcine reproductive and respiratory syndrome virus (PRRSV), influenza A virus (IAV), and porcine circovirus 2 (PCV2) are well-established pathogens in PRDC. Porcine parvovirus 2 (PPV2) has been identified in both healthy and clinically diseased pigs at a high prevalence worldwide. Despite widespread circulation, the significance of PPV2 infection in PRDC and its association with other co-infections are unclear. Here, PPV2 was detected in the lung tissue in 39 of 100 (39%) PRDC-affected pigs by quantitative polymerase chain reaction (qPCR). Using in situ hybridization (ISH) in conjunction with tissue microarrays (TMA), PPV2 infection was localized in alveolar macrophages and other cells in the lungs with interstitial pneumonia in 28 of 99 (28.2%) samples. Viral load tended to correlate with the number of macrophages in the lungs. Assessment of the frequency, viral titers, and tissue distributions showed no association between infection of PPV2 and other major viral respiratory pathogens. In one-third of the PPV2-positive samples by qPCR, no other known viruses were identified by metagenomic sequencing. The genome sequences of PPV2 were 99.7% identical to the reference genomes. Although intensive intranuclear and intracytoplasmic signals of PPV2 were mainly detected in alveolar macrophages by ISH, no obvious virus replication was noted in in vitro cell culture. Together, these results suggest that PPV2 is associated, but may not be the sole causative agent, with PRDC, warranting the control and prevention of this underdiagnosed virus.

Identification of boosepivirus B in U.S. calves.

Bovine enteric disease has a complex etiology that can include viral, bacterial, and parasitic pathogens and is a significant source of losses due to morbidity and mortality. Boosepivirus was identified in calves with enteric disease with unclear etiology in Japan in 2009 and has not been reported elsewhere. Metagenomic sequencing and PCR here identified boosepivirus in bovine enteric disease diagnostic submissions from six states in the USA with 98% sequence identity to members of the species Boosepivirus B. In all cases, boosepivirus was identified as a coinfection with the established pathogens bovine coronavirus, bovine rotavirus, and cryptosporidia. Further research is needed to determine the clinical significance of boosepivirus infection.

Identification of a novel statovirus in a faecal sample from a calf with enteric disease.

A novel clade of RNA viruses was identified in the mammalian gastrointestinal tract by next-generation sequencing. Phylogenetically, these viruses are related to the genera Tombusviridae (plant viruses) and Flaviviridae, which includes mammalian, avian and insect hosts. Named in line with their characterization as stool-associated Tombus-like viruses, it is unclear if statoviruses infect mammals or are dietary in origin. Here, metagenomic sequencing of faecal material collected from a 10-week-old calf with enteric disease found that 20 % of the reads mapped to a de novo-assembled 4 kb contig with homology to statoviruses. Phylogenetic analysis of the statovirus genome found a clear evolutionary relationship with statovirus A, but, with only 47 % similarity, we propose that the statovirus sequence presents a novel species, statovirus F. A TaqMan PCR targeting statovirus F performed on faecal material found a cycle threshold of 11, suggesting a high titre of virus shed from the calf with enteric disease. A collection of 48 samples from bovine enteric disease diagnostic submissions were assayed by PCR to investigate statovirus F prevalence and 6 of 48 (12.5 %) were positive. An ELISA to detect antibodies to the coat protein found that antibodies to statovirus F were almost ubiquitous in bovine serum. Combined, the PCR and ELISA results suggest that statovirus F commonly infects cattle. Further research is needed to elucidate the aetiological significance of statovirus infection.

Identification of a Ruminant Origin Group B Rotavirus Associated with Diarrhea Outbreaks in Foals.

Equine rotavirus group A (ERVA) is one of the most common causes of foal diarrhea. Starting in February 2021, there was an increase in the frequency of severe watery to hemorrhagic diarrhea cases in neonatal foals in Central Kentucky. Diagnostic investigation of fecal samples failed to detect evidence of diarrhea-causing pathogens including ERVA. Based on Illumina-based metagenomic sequencing, we identified a novel equine rotavirus group B (ERVB) in fecal specimens from the affected foals in the absence of any other known enteric pathogens. Interestingly, the protein sequence of all 11 segments had greater than 96% identity with group B rotaviruses previously found in ruminants. Furthermore, phylogenetic analysis demonstrated clustering of the ERVB with group B rotaviruses of caprine and bovine strains from the USA. Subsequent analysis of 33 foal diarrheic samples by RT-qPCR identified 23 rotavirus B-positive cases (69.69%). These observations suggest that the ERVB originated from ruminants and was associated with outbreaks of neonatal foal diarrhea in the 2021 foaling season in Kentucky. Emergence of the ruminant-like group B rotavirus in foals clearly warrants further investigation due to the significant impact of the disease in neonatal foals and its economic impact on the equine industry.

Functional study of a role of N-terminal HA stem region of swine influenza A virus in virus replication.

Swine influenza A virus (SIV) is both a pathogen of economic significance to the swine industry and a potential zoonotic organism that may be transmitted to humans. We described here the detailed characterization of a role of N-terminal B-loop and CD helix of HA2 in swine influenza A virus replication. Results of our experiments demonstrated that Hemagglutinin (HA) protein of swine influenza virus could tolerate some mutations in functionally conserved B-loop and CD helix. These mutations, however, have substantially attenuated influenza virus replication in both cell lines and porcine primary tracheal epithelial cells. Significantly, we found that some B-loop or CD helix mutations generated virus mutants that replicated in MDCK and ST cell lines but failed to replicate in primary tracheal epithelial cells, thereby suggesting that swine HA protein may function as a viral virulence and pathogenesis factor. The described mutations may be further explored as attenuated vaccine candidates that can effectively prevent or eliminate the spread of influenza virus within and between swine herds.

Emergence of new phylogenetic lineage of Influenza D virus with broad antigenicity in California, United States.

Influenza D virus (IDV), with bovines as a primary host, circulates widely in cattle populations across North America and Eurasia. Here we report the identification of a novel IDV group with broad antigenicity in U.S. bovine herds, which is genetically different from previously known lineages of IDV.

Piglet immunization with a spike subunit vaccine enhances disease by porcine epidemic diarrhea virus.

Immunization with an insect cell lysate/baculovirus mixture containing recombinant porcine epidemic diarrhea virus (PEDV) spike protein induced high levels of neutralizing antibodies in both mice and piglets. However, immunization of piglets with this vaccine resulted in enhancement of disease symptoms and virus replication in vaccine recipients exposed to PEDV challenge. Thus, these observations demonstrate a previously unrecognized challenge of PEDV vaccine research, which has important implications for coronavirus vaccine development.

Persistent infection of American bison (Bison bison) with bovine viral diarrhea virus and bosavirus.

Bovine viral diarrhea viruses (BVDV) are significant pathogens of cattle, leading to losses associated with reproductive failure, respiratory disease and immune dysregulation. While cattle are the reservoir for BVDV, a wide range of domestic and wild ruminants are susceptible to infection and disease caused by BVDV. Samples from four American bison (Bison bison) from a captive herd were submitted for diagnostic testing due to their general unthriftiness. Metagenomic sequencing on pooled nasal swabs and serum identified co-infection with a BVDV and a bovine bosavirus. The BVDV genome was more similar to the vaccine strain Oregon C24 V than to other BVDV sequences in GenBank, with 92.7 % nucleotide identity in the open reading frame. The conserved 5'-untranslated region was 96.3 % identical to Oregon C24 V. Bosavirus has been previously identified in pooled fetal bovine serum but its clinical significance is unknown. Sequencing results were confirmed by virus isolation and PCR detection of both viruses in serum and nasal swab samples from two of the four bison. One animal was co-infected with both BVDV and bosavirus while separate individuals were positive solely for BVDV or bosavirus. Serum and nasal swabs from these same animals collected 51 days later remained positive for BVDV and bosavirus. These results suggest that both viruses can persistently infect bison. While the etiological significance of bosavirus infection is unknown, the ability of BVDV to persistently infect bison has implications for BVDV control and eradication programs. Possible synergy between BVDV and bosavirus persistent infection warrants further study.

Novel and Diverse Non-Rabies Rhabdoviruses Identified in Bats with Human Exposure, South Dakota, USA.

Bats are a host and reservoir for a large number of viruses, many of which are zoonotic. In North America, the big brown bat (Eptesicus fuscus) is widely distributed and common. Big brown bats are a known reservoir for rabies virus, which, combined with their propensity to roost in human structures, necessitates testing for rabies virus following human exposure. The current pandemic caused by severe acute respiratory syndrome coronavirus 2, likely of bat origin, illustrates the need for continued surveillance of wildlife and bats for potentially emerging zoonotic viruses. Viral metagenomic sequencing was performed on 39 big brown bats and one hoary bat submitted for rabies testing due to human exposure in South Dakota. A new genotype of American bat vesiculovirus was identified in seven of 17 (41%) heart and lung homogenates at high levels in addition to two of 23 viscera pools. A second rhabdovirus, Sodak rhabdovirus 1 (SDRV1), was identified in four of 23 (17%) viscera pools. Phylogenetic analysis placed SDRV1 in the genus Alphanemrhavirus, which includes two recognized species that were identified in nematodes. Finally, a highly divergent rhabdovirus, Sodak rhabdovirus 2 (SDRV2), was identified in two of 23 (8.7%) big brown bats. Phylogenetic analysis placed SDRV2 as ancestral to the dimarhabdovirus supergroup and Lyssavirus. Intracranial inoculation of mouse pups with rhabdovirus-positive tissue homogenates failed to elicit clinical disease. Further research is needed to determine the zoonotic potential of these non-rabies rhabdoviruses.

North American Big Brown Bats (Eptesicus fuscus) Harbor an Exogenous Deltaretrovirus.

Bats are the reservoir for a large number of zoonotic viruses, including members of Coronaviridae (severe acute respiratory syndrome coronavirus [SARS-CoV] and SARS-CoV-2), Paramyxoviridae (Hendra and Nipah viruses), Rhabdoviridae (rabies virus), and Filoviridae (Ebola virus) as exemplars. Many retroviruses, such as human immunodeficiency virus, are similarly zoonotic; however, only infectious exogenous gammaretroviruses have recently been identified in bats. Here, viral metagenomic sequencing of samples from bats submitted for rabies virus testing, largely due to human exposure, identified a novel, highly divergent exogenous Deltaretrovirus from a big brown bat (Eptesicus fuscus) in South Dakota. The virus sequence, corresponding to Eptesicus fuscus deltaretrovirus (EfDRV), comprised a nearly complete coding region comprised of canonical 5'-gag-pro-pol-env-3' genes with 37% to 51% identity to human T-lymphotropic virus (HTLV), an infectious retrovirus that causes T-cell lymphoma. A putative tax gene with 27% identity to HTLV was located downstream of the pol gene along with a gene harbored in an alternative reading frame which possessed a conserved domain for an Epstein-Barr virus nuclear antigen involved in gene transactivation, suggesting a regulatory function similar to that of the deltaretrovirus rex gene. A TaqMan reverse transcriptase PCR (RT-PCR) targeting the pol gene identified 4/60 (6.7%) bats as positive for EfDRV, which, combined with a search of the E. fuscus genome that failed to identify sequences with homology to EfDRV, suggests that EfDRV is an infectious exogenous virus. As all known members of Deltaretrovirus can cause malignancies and E. fuscus is widely distributed in the Americas, often with a colonial roosting behavior in human dwellings, further studies are needed to investigate potential zoonosis.IMPORTANCE Bats host a large numbers of viruses, many of which are zoonotic. In the United States, the big brown bat (Eptesicus fuscus) is widely distributed and lives in small colonies that roost in cavities, often in human dwellings, leading to frequent human interaction. Viral metagenomic sequencing of samples from an E. fuscus bat submitted for rabies testing identified the first exogenous bat Deltaretrovirus The E. fuscus deltaretrovirus (EfDRV) genome consists of the typical deltaretrovial 5'-gag-pro-pol-env-3' genes along with genes encoding two putative transcriptional transactivator proteins distantly related to the Tax protein of human T-cell lymphotrophic virus and nuclear antigen 3B of Epstein-Barr virus. Searches of the E. fuscus genome sequence failed to identify endogenous EfDRV. RT-PCR targeting the EfDRV pol gene identified 4/60 (6.7%) bats with positive results. Together, these results suggest that EfDRV is exogenous. As all members of Deltaretrovirus are associated with T- and B-cell malignancies or neurologic disease, further studies on possible zoonosis are warranted.