A pleiotropic recurrent dominant ITPR3 variant causes a complex multisystemic disease.

Inositol 1,4,5-trisphosphate (IP3) receptor type 1 (ITPR1), 2 (ITPR2), and 3 (ITPR3) encode the IP3 receptor (IP3R), a key player in intracellular calcium release. In four unrelated patients, we report that an identical ITPR3 de novo variant-NM_002224.3:c.7570C>T, p.Arg2524Cys-causes, through a dominant-negative effect, a complex multisystemic disorder with immunodeficiency. This leads to defective calcium homeostasis, mitochondrial malfunction, CD4+ lymphopenia, a quasi-absence of naïve CD4+ and CD8+ cells, an increase in memory cells, and a distinct TCR repertoire. The calcium defect was recapitulated in Jurkat knock-in. Site-directed mutagenesis displayed the exquisite sensitivity of Arg2524 to any amino acid change. Despite the fact that all patients had severe immunodeficiency, they also displayed variable multisystemic involvements, including ectodermal dysplasia, Charcot-Marie-Tooth disease, short stature, and bone marrow failure. In conclusion, unlike previously reported ITPR1-3 deficiencies leading to narrow, mainly neurological phenotypes, a recurrent dominant ITPR3 variant leads to a multisystemic disease, defining a unique role for IP3R3 in the tetrameric IP3R complex.

Characterization of the antispike IgG immune response to COVID-19 vaccines in people with a wide variety of immunodeficiencies.

Research on coronavirus disease 2019 vaccination in immune-deficient/disordered people (IDP) has focused on cancer and organ transplantation populations. In a prospective cohort of 195 IDP and 35 healthy volunteers (HV), antispike immunoglobulin G (IgG) was detected in 88% of IDP after dose 2, increasing to 93% by 6 months after dose 3. Despite high seroconversion, median IgG levels for IDP never surpassed one-third that of HV. IgG binding to Omicron BA.1 was lowest among variants. Angiotensin-converting enzyme 2 pseudo-neutralization only modestly correlated with antispike IgG concentration. IgG levels were not significantly altered by receipt of different messenger RNA-based vaccines, immunomodulating treatments, and prior severe acute respiratory syndrome coronavirus 2 infections. While our data show that three doses of coronavirus disease 2019 vaccinations induce antispike IgG in most IDP, additional doses are needed to increase protection. Because of the notably reduced IgG response to Omicron BA.1, the efficacy of additional vaccinations, including bivalent vaccines, should be studied in this population.

Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.

Paired box 1 (PAX1) deficiency has been reported in a small number of patients diagnosed with otofaciocervical syndrome type 2 (OFCS2). We described six new patients who demonstrated variable clinical penetrance. Reduced transcriptional activity of pathogenic variants confirmed partial or complete PAX1 deficiency. Thymic aplasia and hypoplasia were associated with impaired T cell immunity. Corrective treatment was required in 4/6 patients. Hematopoietic stem cell transplantation resulted in poor immune reconstitution with absent naïve T cells, contrasting with the superior recovery of T cell immunity after thymus transplantation. Normal ex vivo differentiation of PAX1-deficient CD34+ cells into mature T cells demonstrated the absence of a hematopoietic cell-intrinsic defect. New overlapping features with DiGeorge syndrome included primary hypoparathyroidism (n = 5) and congenital heart defects (n = 2), in line with PAX1 expression during early embryogenesis. Our results highlight new features of PAX1 deficiency, which are relevant to improving early diagnosis and identifying patients requiring corrective treatment.

Multicenter analysis of neutrophil extracellular trap dysregulation in adult and pediatric COVID-19.

Dysregulation in neutrophil extracellular trap (NET) formation and degradation may play a role in the pathogenesis and severity of COVID-19; however, its role in the pediatric manifestations of this disease, including multisystem inflammatory syndrome in children (MIS-C) and chilblain-like lesions (CLLs), otherwise known as "COVID toes," remains unclear. Studying multinational cohorts, we found that, in CLLs, NETs were significantly increased in serum and skin. There was geographic variability in the prevalence of increased NETs in MIS-C, in association with disease severity. MIS-C and CLL serum samples displayed decreased NET degradation ability, in association with C1q and G-actin or anti-NET antibodies, respectively, but not with genetic variants of DNases. In adult COVID-19, persistent elevations in NETs after disease diagnosis were detected but did not occur in asymptomatic infection. COVID-19-affected adults displayed significant prevalence of impaired NET degradation, in association with anti-DNase1L3, G-actin, and specific disease manifestations, but not with genetic variants of DNases. NETs were detected in many organs of adult patients who died from COVID-19 complications. Infection with the Omicron variant was associated with decreased NET levels when compared with other SARS-CoV-2 strains. These data support a role for NETs in the pathogenesis and severity of COVID-19 in pediatric and adult patients.

Vaccine breakthrough hypoxemic COVID-19 pneumonia in patients with auto-Abs neutralizing type I IFNs.

Life-threatening 'breakthrough' cases of critical COVID-19 are attributed to poor or waning antibody response to the SARS-CoV-2 vaccine in individuals already at risk. Pre-existing autoantibodies (auto-Abs) neutralizing type I IFNs underlie at least 15% of critical COVID-19 pneumonia cases in unvaccinated individuals; however, their contribution to hypoxemic breakthrough cases in vaccinated people remains unknown. Here, we studied a cohort of 48 individuals (age 20-86 years) who received 2 doses of an mRNA vaccine and developed a breakthrough infection with hypoxemic COVID-19 pneumonia 2 weeks to 4 months later. Antibody levels to the vaccine, neutralization of the virus, and auto-Abs to type I IFNs were measured in the plasma. Forty-two individuals had no known deficiency of B cell immunity and a normal antibody response to the vaccine. Among them, ten (24%) had auto-Abs neutralizing type I IFNs (aged 43-86 years). Eight of these ten patients had auto-Abs neutralizing both IFN-α2 and IFN-ω, while two neutralized IFN-ω only. No patient neutralized IFN-ß. Seven neutralized 10 ng/mL of type I IFNs, and three 100 pg/mL only. Seven patients neutralized SARS-CoV-2 D614G and the Delta variant (B.1.617.2) efficiently, while one patient neutralized Delta slightly less efficiently. Two of the three patients neutralizing only 100 pg/mL of type I IFNs neutralized both D61G and Delta less efficiently. Despite two mRNA vaccine inoculations and the presence of circulating antibodies capable of neutralizing SARS-CoV-2, auto-Abs neutralizing type I IFNs may underlie a significant proportion of hypoxemic COVID-19 pneumonia cases, highlighting the importance of this particularly vulnerable population.

Multicenter analysis of neutrophil extracellular trap dysregulation in adult and pediatric COVID-19.

Dysregulation in neutrophil extracellular trap (NET) formation and degradation may play a role in the pathogenesis and severity of COVID-19; however, its role in the pediatric manifestations of this disease including MIS-C and chilblain-like lesions (CLL), otherwise known as "COVID toes", remains unclear. Studying multinational cohorts, we found that, in CLL, NETs were significantly increased in serum and skin. There was geographic variability in the prevalence of increased NETs in MIS-C, in association with disease severity. MIS-C and CLL serum samples displayed decreased NET degradation ability, in association with C1q and G-actin or anti-NET antibodies, respectively, but not with genetic variants of DNases. In adult COVID-19, persistent elevations in NETs post-disease diagnosis were detected but did not occur in asymptomatic infection. COVID-19-affected adults displayed significant prevalence of impaired NET degradation, in association with anti-DNase1L3, G-actin, and specific disease manifestations, but not with genetic variants of DNases. NETs were detected in many organs of adult patients who died from COVID-19 complications. Infection with the Omicron variant was associated with decreased levels of NETs when compared to other SARS-CoV-2 strains. These data support a role for NETs in the pathogenesis and severity of COVID-19 in pediatric and adult patients. Summary: NET formation and degradation are dysregulated in pediatric and symptomatic adult patients with various complications of COVID-19, in association with disease severity. NET degradation impairments are multifactorial and associated with natural inhibitors of DNase 1, G-actin and anti-DNase1L3 and anti-NET antibodies. Infection with the Omicron variant is associated with decreased levels of NETs when compared to other SARS-CoV-2 strains.

Epididymal epithelium propels early sexual transmission of Zika virus in the absence of interferon signaling.

Recognition of Zika virus (ZIKV) sexual transmission (ST) among humans challenges our understanding of the maintenance of mosquito-borne viruses in nature. Here we dissected the relative contributions of the components of male reproductive system (MRS) during early male-to-female ZIKV transmission by utilizing mice with altered antiviral responses, in which ZIKV is provided an equal opportunity to be seeded in the MRS tissues. Using microRNA-targeted ZIKV clones engineered to abolish viral infectivity to different parts of the MRS or a library of ZIKV genomes with unique molecular identifiers, we pinpoint epithelial cells of the epididymis (rather than cells of the testis, vas deferens, prostate, or seminal vesicles) as a most likely source of the sexually transmitted ZIKV genomes during the early (most productive) phase of ZIKV shedding into the semen. Incorporation of this mechanistic knowledge into the development of a live-attenuated ZIKV vaccine restricts its ST potential.

Zika virus tropism during early infection of the testicular interstitium and its role in viral pathogenesis in the testes.

Sexual transmission and persistence of Zika virus (ZIKV) in the testes pose new challenges for controlling virus outbreaks and developing live-attenuated vaccines. It has been shown that testicular infection of ZIKV is initiated in the testicular interstitium, followed by spread of the virus in the seminiferous tubules. This leads to testicular damage and/or viral dissemination into the epididymis and eventually into semen. However, it remains unknown which cell types are targeted by ZIKV in the testicular interstitium, and what is the specific order of infectious events leading to ZIKV invasion of the seminiferous tubules. Here, we demonstrate that interstitial leukocytes expressing mir-511-3p microRNA are the initial targets of ZIKV in the testes, and infection of mir-511-3p-expressing cells in the testicular interstitium is necessary for downstream infection of the seminiferous tubules. Mir-511-3p is expressed concurrently with CD206, a marker of lineage 2 (M2) macrophages and monocyte derived dendritic cells (moDCs). Selective restriction of ZIKV infection of CD206-expressing M2 macrophages/moDCs results in the attenuation of macrophage-associated inflammatory responses in vivo and prevents the disruption of the Sertoli cell barrier in vitro. Finally, we show that targeting of viral genome for mir-511-3p significantly attenuates early ZIKV replication not only in the testes, but also in many peripheral organs, including spleen, epididymis, and pancreas. This incriminates M2 macrophages/moDCs as important targets for visceral ZIKV replication following hematogenous dissemination of the virus from the site of infection.

Stable and Highly Immunogenic MicroRNA-Targeted Single-Dose Live Attenuated Vaccine Candidate against Tick-Borne Encephalitis Constructed Using Genetic Backbone of Langat Virus.

Tick-borne encephalitis virus (TBEV), a member of the genus Flavivirus, is one of the most medically important tick-borne pathogens of the Old World. Despite decades of active research, attempts to develop of a live attenuated virus (LAV) vaccine against TBEV with acceptable safety and immunogenicity characteristics have not been successful. To overcome this impasse, we generated a chimeric TBEV that was highly immunogenic in nonhuman primates (NHPs). The chimeric virus contains the prM/E genes of TBEV, which are expressed in the genetic background of an antigenically closely related, but less pathogenic member of the TBEV complex-Langat virus (LGTV), strain T-1674. The neurovirulence of this chimeric virus was subsequently controlled by robust targeting of the viral genome with multiple copies of central nervous system-enriched microRNAs (miRNAs). This miRNA-targeted T/1674-mirV2 virus was highly stable in Vero cells and was not pathogenic in various mouse models of infection or in NHPs. Importantly, in NHPs, a single dose of the T/1674-mirV2 virus induced TBEV-specific neutralizing antibody (NA) levels comparable to those seen with a three-dose regimen of an inactivated TBEV vaccine, currently available in Europe. Moreover, our vaccine candidate provided complete protection against a stringent wild-type TBEV challenge in mice and against challenge with a parental (not miRNA-targeted) chimeric TBEV/LGTV in NHPs. Thus, this highly attenuated and immunogenic T/1674-mirV2 virus is a promising LAV vaccine candidate against TBEV and warrants further preclinical evaluation of its neurovirulence in NHPs prior to entering clinical trials in humans.IMPORTANCE Tick-borne encephalitis virus (TBEV) is one of the most medically important tick-borne pathogens of the Old World. Despite decades of active research, efforts to develop of TBEV live attenuated virus (LAV) vaccines with acceptable safety and immunogenicity characteristics have not been successful. Here we report the development and evaluation of a highly attenuated and immunogenic microRNA-targeted TBEV LAV.

Routes of Zika virus dissemination in the testis and epididymis of immunodeficient mice.

Sexual transmission and persistence of Zika virus (ZIKV) in the male reproductive tract (MRT) poses new challenges for controlling virus outbreaks and developing live-attenuated vaccines. To elucidate routes of ZIKV dissemination in the MRT, we here generate microRNA-targeted ZIKV clones that lose the infectivity for (1) the cells inside seminiferous tubules of the testis, or (2) epithelial cells of the epididymis. We trace ZIKV dissemination in the MRT using an established mouse model of ZIKV pathogenesis. Our results support a model in which ZIKV infects the testis via a hematogenous route, while infection of the epididymis can occur via two routes: (1) hematogenous/lymphogenous and (2) excurrent testicular. Co-targeting of the ZIKV genome with brain-, testis-, and epididymis-specific microRNAs restricts virus infection of these organs, but does not affect virus-induced protective immunity in mice and monkeys. These defined alterations of ZIKV tropism represent a rational design of a safe live-attenuated ZIKV vaccine.

Strand-Specific Dual RNA Sequencing of Bronchial Epithelial Cells Infected with Influenza A/H3N2 Viruses Reveals Splicing of Gene Segment 6 and Novel Host-Virus Interactions.

Host-influenza virus interplay at the transcript level has been extensively characterized in epithelial cells. Yet, there are no studies that simultaneously characterize human host and influenza A virus (IAV) genomes. We infected human bronchial epithelial BEAS-2B cells with two seasonal IAV/H3N2 strains, Brisbane/10/07 and Perth/16/09 (reference strains for past vaccine seasons) and the well-characterized laboratory strain Udorn/307/72. Strand-specific RNA sequencing (RNA-seq) of the infected BEAS-2B cells allowed for simultaneous analysis of host and viral transcriptomes, in addition to pathogen genomes, to reveal changes in mRNA expression and alternative splicing (AS). In general, patterns of global and immune gene expression induced by the three IAVs were mostly shared. However, AS of host transcripts and small nuclear RNAs differed between the seasonal and laboratory strains. Analysis of viral transcriptomes showed deletions of the polymerase components (defective interfering-like RNAs) within the genome. Surprisingly, we found that the neuraminidase gene undergoes AS and that the splicing event differs between seasonal and laboratory strains. Our findings reveal novel elements of the host-virus interaction and highlight the importance of RNA-seq in identifying molecular changes at the genome level that may contribute to shaping RNA-based innate immunity.IMPORTANCE The use of massively parallel RNA sequencing (RNA-seq) has revealed insights into human and pathogen genomes and their evolution. Dual RNA-seq allows simultaneous dissection of host and pathogen genomes and strand-specific RNA-seq provides information about the polarity of the RNA. This is important in the case of negative-strand RNA viruses like influenza virus, which generate positive (complementary and mRNA) and negative-strand RNAs (genome) that differ in their potential to trigger innate immunity. Here, we characterize interactions between human bronchial epithelial cells and three influenza A/H3N2 strains using strand-specific dual RNA-seq. We focused on this subtype because of its epidemiological importance in causing significant morbidity and mortality during influenza epidemics. We report novel elements that differ between seasonal and laboratory strains highlighting the complexity of the host-virus interplay at the RNA level.

A Live Attenuated Chimeric West Nile Virus Vaccine, rWN/DEN4Δ30, Is Well Tolerated and Immunogenic in Flavivirus-Naive Older Adult Volunteers.

West Nile virus (WNV) is a major cause of mosquito-borne illness in the United States. Human disease ranges from mild febrile illness to severe fatal neurologic infection. Adults aged >60 years are more susceptible to neuroinvasive disease accompanied by a high mortality rate or long-lasting neurologic sequelae. A chimeric live attenuated West Nile virus vaccine, rWN/DEN4Δ30, was shown to be safe and immunogenic in healthy adults aged 18-50 years. This study evaluated rWN/DEN4Δ30 in flavivirus-naive adults aged 50-65 years and found it to be safe and immunogenic. Outbreaks of WNV infection tend to be unpredictable, and a safe and effective vaccine will be an important public health tool.

Concurrent micro-RNA mediated silencing of tick-borne flavivirus replication in tick vector and in the brain of vertebrate host.

Tick-borne viruses include medically important zoonotic pathogens that can cause life-threatening diseases. Unlike mosquito-borne viruses, whose impact can be restrained via mosquito population control programs, for tick-borne viruses only vaccination remains the reliable means of disease prevention. For live vaccine viruses a concern exists, that spillovers from viremic vaccinees could result in introduction of genetically modified viruses into sustainable tick-vertebrate host transmission cycle in nature. To restrict tick-borne flavivirus (Langat virus, LGTV) vector tropism, we inserted target sequences for tick-specific microRNAs (mir-1, mir-275 and mir-279) individually or in combination into several distant regions of LGTV genome. This caused selective attenuation of viral replication in tick-derived cells. LGTV expressing combinations of target sequences for tick- and vertebrate CNS-specific miRNAs were developed. The resulting viruses replicated efficiently and remained stable in simian Vero cells, which do not express these miRNAs, however were severely restricted to replicate in tick-derived cells. In addition, simultaneous dual miRNA targeting led to silencing of virus replication in live Ixodes ricinus ticks and abolished virus neurotropism in highly permissive newborn mice. The concurrent restriction of adverse replication events in vertebrate and invertebrate hosts will, therefore, ensure the environmental safety of live tick-borne virus vaccine candidates.

A Full-Length Infectious cDNA Clone of Zika Virus from the 2015 Epidemic in Brazil as a Genetic Platform for Studies of Virus-Host Interactions and Vaccine Development.

UNLABELLED: An arthropod-borne virus, Zika virus (ZIKV), has recently emerged as a major human pathogen. Associated with complications during perinatal development and Guillain-Barré syndrome in adults, ZIKV raises new challenges for understanding the molecular determinants of flavivirus pathogenesis. This underscores the necessity for the development of a reverse genetic system based on an epidemic ZIKV strain. Here, we describe the generation and characterization in cell cultures of an infectious cDNA clone of ZIKV isolated from the 2015 epidemic in Brazil. The cDNA-derived ZIKV replicated efficiently in a variety of cell lines, including those of both neuronal and placental origin. We observed that the growth of cDNA-derived virus was attenuated compared to the growth of the parental isolate in most cell lines, which correlates with substantial differences in sequence heterogeneity between these viruses that were determined by deep-sequencing analysis. Our findings support the role of genetic diversity in maintaining the replicative fitness of viral populations under changing conditions. Moreover, these results indicate that caution should be exercised when interpreting the results of reverse-genetics experiments in attempts to accurately predict the biology of natural viruses. Finally, a Vero cell-adapted cDNA clone of ZIKV was generated that can be used as a convenient platform for studies aimed at the development of ZIKV vaccines and therapeutics. IMPORTANCE: The availability of genetic tools and laboratory models determines the progress in understanding mechanisms of virus emergence and pathogenesis. Recent large-scale outbreaks of Zika virus (ZIKV) that were linked to complications during perinatal development and Guillain-Barré syndrome in adults emphasize the urgency for the development of a reverse-genetics system based on an epidemic ZIKV strain. Here, we report a stable infectious cDNA clone for ZIKV isolated during the 2015 epidemic in Brazil, as well as a Vero cell-adapted version of it, which will be used for virus-host interaction studies and vaccine development.

MicroRNA-based control of tick-borne flavivirus neuropathogenesis: Challenges and perspectives.

In recent years, microRNA-targeting has become an effective strategy for selective control of tissue-tropism and pathogenicity of both DNA and RNA viruses. Previously, we reported the successful application of this strategy to control the neurovirulent phenotype of a model chimeric tick-borne encephalitis/dengue type 4 virus (TBEV/DEN4), containing the structural protein genes of a highly virulent TBEV in the genetic backbone of non-neuroinvasive DEN4 virus. In the present study, we investigated the suitability of this approach for the attenuation of the more neurovirulent chimeric virus (TBEV/LGTV), which is based on the genetic backbone of the naturally attenuated member of the TBEV serocomplex, a Langat virus (LGTV). Unlike the TBEV/DEN4, the TBEV/LGTV virus retained the ability of its parental viruses to spread from the peripheral site of inoculation to the CNS. We evaluated ten potential sites in the 3'NCR of the TBEV/LGTV genome for placement of microRNA (miRNA) targets and found that the TBEV/LGTV genome is more restrictive for such genetic manipulations compared to TBEV/DEN4. In addition, unlike TBEV/DEN4 virus, the introduction of multiple miRNA targets into either the 3'NCR or ORF of the TBEV/LGTV genome had only a modest effect on virus attenuation in the developing CNS of highly permissive newborn mice. However, simultaneous miRNA-targeting in the ORF and 3'NCR had synergistic effect on control and silencing of virus replication in the brain and completely abolished the virus neurotropism. Furthermore, neuroinvasiveness of miRNA-targeted TBEV/LGTV viruses in very sensitive immunodeficient SCID mice was significantly limited. Immunocompetent animals immunized with such viruses were completely protected against challenge with the neurovirulent LGTV parent. These findings support the rationale of the miRNA-targeting approach to develop live attenuated virus vaccines against various neurotropic viruses.

Dual miRNA targeting restricts host range and attenuates neurovirulence of flaviviruses.

Mosquito-borne flaviviruses are among the most significant arboviral pathogens worldwide. Vaccinations and mosquito population control programs remain the most reliable means for flavivirus disease prevention, and live attenuated viruses remain one of the most attractive flavivirus vaccine platforms. Some live attenuated viruses are capable of infecting principle mosquito vectors, as demonstrated in the laboratory, which in combination with their intrinsic genetic instability could potentially lead to a vaccine virus reversion back to wild-type in nature, followed by introduction and dissemination of potentially dangerous viral strains into new geographic locations. To mitigate this risk we developed a microRNA-targeting approach that selectively restricts replication of flavivirus in the mosquito host. Introduction of sequences complementary to a mosquito-specific mir-184 and mir-275 miRNAs individually or in combination into the 3'NCR and/or ORF region resulted in selective restriction of dengue type 4 virus (DEN4) replication in mosquito cell lines and adult Aedes mosquitos. Moreover a combined targeting of DEN4 genome with mosquito-specific and vertebrate CNS-specific mir-124 miRNA can silence viral replication in two evolutionally distant biological systems: mosquitoes and mouse brains. Thus, this approach can reinforce the safety of newly developed or existing vaccines for use in humans and could provide an additional level of biosafety for laboratories using viruses with altered pathogenic or transmissibility characteristics.

Severity of clinical disease and pathology in ferrets experimentally infected with influenza viruses is influenced by inoculum volume.

UNLABELLED: Ferrets are a valuable model for influenza virus pathogenesis, virus transmission, and antiviral therapy studies. However, the contributions of the volume of inoculum administered and the ferret's respiratory tract anatomy to disease outcome have not been explored. We noted variations in clinical disease outcomes and the volume of inoculum administered and investigated these differences by administering two influenza viruses (A/California/07/2009 [H1N1 pandemic] and A/Minnesota/11/2010 [H3N2 variant]) to ferrets intranasally at a dose of 10(6) 50% tissue culture infective doses in a range of inoculum volumes (0.2, 0.5, or 1.0 ml) and followed viral replication, clinical disease, and pathology over 6 days. Clinical illness and respiratory tract pathology were the most severe and most consistent when the viruses were administered in a volume of 1.0 ml. Using a modified micro-computed tomography imaging method and examining gross specimens, we found that the right main-stem bronchus was consistently larger in diameter than the left main-stem bronchus, though the latter was longer and straighter. These anatomic features likely influence the distribution of the inoculum in the lower respiratory tract. A 1.0-ml volume of inoculum is optimal for delivery of virus to the lower respiratory tract of ferrets, particularly when evaluation of clinical disease is desired. Furthermore, we highlight important anatomical features of the ferret lung that influence the kinetics of viral replication, clinical disease severity, and lung pathology. IMPORTANCE: Ferrets are a valuable model for influenza virus pathogenesis, virus transmission, and antiviral therapy studies. Clinical disease in ferrets is an important parameter in evaluating the virulence of novel influenza viruses, and findings are extrapolated to virulence in humans. Therefore, it is highly desirable that the data from different laboratories be accurate and reproducible. We have found that, even when the same virus was administered at similar doses, different investigators reported a range of clinical disease outcomes, from asymptomatic infection to severe weight loss, ocular and nasal discharge, sneezing, and lethargy. We found that a wide range of inoculum volumes was used to experimentally infect ferrets, and we sought to determine whether the variations in disease outcome were the result of the volume of inoculum administered. These data highlight some less explored features of the model, methods of experimental infection, and clinical disease outcomes in a research setting.