Ferret models of viral pathogenesis

Characterization of Reston virus infection in ferrets

Among the five currently recognized type viruses within the genus Ebolavirus, Reston virus (RESTV) is not known to cause disease in humans, although asymptomatic infections have been confirmed in the past. Intriguingly, despite the absence of pathogenicity in humans, RESTV is highly lethal to nonhuman primates and has been isolated from domestic pigs co-infected with other viruses in the Philippines and China. Whether infection in these animals can support the eventual emergence of a human-pathogenic RESTV remains unclear and requires further investigation. Unfortunately, there is currently no lethal small animal model available to investigate RESTV pathogenicity or pan-ebolavirus therapeutics. Here we show that wild type RESTV is uniformly lethal in ferrets. In this study, ferrets were challenged with 1260 TCID₅₀ of wild type RESTV either intramuscularly or intranasally and monitored for clinical signs, survival, virus replication, alteration in serum biochemistry and blood cell counts. Irrespective of the route of challenge, viremia occurred in all ferrets on day 5 post-infection, and all animals succumbed to infection between days 9 and 11. Additionally, several similarities were observed between this model and the other ferret models of filovirus infection, including substantial decreases in lymphocyte and platelet counts and abnormalities in serum biochemistry indicating hepatic injury. The ferret model represents the first uniformly lethal model for RESTV infection, and it will undoubtedly prove useful for evaluating virus pathogenicity as well as pan-ebolavirus countermeasures.

The effect of Zika virus infection in the ferret

Although initial observations of infections with the Zika virus describe a mild illness, more recent reports show that infections by Zika result in neurotropism. In 2015, substantial congenital malformations were observed, with numerous infants born with microcephaly in Brazil. To study the underlying mechanism and effects of the disease, it is critical to find suitable animal models. Rodents lack an immune system parallel to humans and also have lissencephalic brains, which are likely to react differently to infections. As the smallest gyrencephalic mammal, ferrets may provide an important animal model to study the Zika virus, as their brains share many characteristics with humans. To evaluate the prospect of using ferrets to study Zika virus infection, we injected seven pregnant jills with the PR strain subcutaneously on gestational day 21, corresponding to the initiation of corticogenesis. These injections resulted in mixed effects. Two animals died of apparent infection, and all kits were resorbed in another animal that did not die. The other four animals remained pregnant until gestational day 40, when the kits were delivered by caesarian section. We evaluated the animals using CT, MRI, diffusion tensor imaging, and immunohistochemistry. The kits displayed a number of features compatible with an infection that impacted both the brain and skull. The outcomes, however, were variable and differed within and across litters, which ranged from the absence of observable abnormalities to prominent changes, suggesting differential vulnerability of kits to infection by the Zika virus or to subsequent mechanisms of neurodevelopmental disruption.

Highly Efficient Transgenesis in Ferrets Using CRISPR/Cas9-Mediated Homology-Independent Insertion at the ROSA26 Locus

The domestic ferret (Mustela putorius furo) has proven to be a useful species for modeling human genetic and infectious diseases of the lung and brain. However, biomedical research in ferrets has been hindered by the lack of rapid and cost-effective methods for genome engineering. Here, we utilized CRISPR/Cas9-mediated, homology-independent insertion at the ROSA26 "safe harbor" locus in ferret zygotes and created transgenic animals expressing a dual-fluorescent Cre-reporter system flanked by PhiC31 and Bxb1 integrase attP sites. Out of 151 zygotes injected with circular transgene-containing plasmid and Cas9 protein loaded with the ROSA26 intron-1 sgRNA, there were 23 births of which 5 had targeted integration events (22% efficiency). The encoded tdTomato transgene was highly expressed in all tissues evaluated. Targeted integration was verified by PCR analyses, Southern blot, and germ-line transmission. Function of the ROSA26-CAG-LoxPtdTomatoStopLoxPEGFP (ROSA-TG) Cre-reporter was confirmed in primary cells following Cre expression. The Phi31 and Bxb1 integrase attP sites flanking the transgene will also enable rapid directional insertion of any transgene without a size limitation at the ROSA26 locus. These methods and the model generated will greatly enhance biomedical research involving lineage tracing, the evaluation of stem cell therapy, and transgenesis in ferret models of human disease.

Contemporary Anti-Ebola Drug Discovery Approaches and Platforms

The Ebola virus has a grave potential to destabilize civil society as we know it. The past few deadly Ebola outbreaks were unprecedented in size: The 2014-15 Ebola West Africa outbreak saw the virus spread from the epicenter through to Guinea, Sierra Leone, Nigeria, Congo, and Liberia. The 2014-15 Ebola West Africa outbreak was associated with almost 30,000 suspected or confirmed cases and over 11,000 documented deaths. The more recent 2018 outbreak in the Democratic Republic of Congo has so far resulted in 216 suspected or confirmed cases and 139 deaths. There is a general acceptance within the World Health Organization (WHO) and the Ebola outbreak response community that future outbreaks will become increasingly more frequent and more likely to involve intercontinental transmission. The magnitude of the recent outbreaks demonstrated in dramatic fashion the shortcomings of our mass casualty disease response capabilities and lack of therapeutic modalities for supporting Ebola outbreak prevention and control. Currently, there are no approved drugs although vaccines for human Ebola virus infection are in the trial phases and some potential treatments have been field tested most recently in the Congo Ebola outbreak. Treatment is limited to pain management and supportive care to counter dehydration and lack of oxygen. This underscores the critical need for effective antiviral drugs that specifically target this deadly disease. This review examines the current approaches for the discovery of anti-Ebola small molecule or biological therapeutics, their viral targets, mode of action, and contemporary platforms, which collectively form the backbone of the anti-Ebola drug discovery pipeline.

Comparative Transcriptomics in Ebola Makona-Infected Ferrets, Nonhuman Primates, and Humans

The domestic ferret is a uniformly lethal model of infection for 3 species of Ebolavirus known to be pathogenic in humans. Reagents to systematically analyze the ferret host response to infection are lacking; however, the recent publication of a draft ferret genome has opened the potential for transcriptional analysis of ferret models of disease. In this work, we present comparative analysis of longitudinally sampled blood taken from ferrets and nonhuman primates infected with lethal doses of the Makona variant of Zaire ebolavirus. Strong induction of proinflammatory and prothrombotic signaling programs were present in both ferrets and nonhuman primates, and both transcriptomes were similar to previously published datasets of fatal cases of human Ebola virus infection.

Cellular immune response to human influenza viruses differs between H1N1 and H3N2 subtypes in the ferret lung

Seasonal influenza virus infections cause yearly epidemics which are the source of a significant public health burden worldwide. The ferret model for human influenza A virus (IAV) is widely used and has several advantages over other animal models such as comparable symptomology, similar receptor distribution in the respiratory tract to humans and the ability to be infected with human isolates without the need for adaptation. However, a major disadvantage of the model has been a paucity of reagents for the evaluation of the cellular immune response. Investigation of T-cell mediated immunity in ferrets is crucial to vaccine development and efficacy studies. In this study we have used commercially produced antibodies to ferret interferon gamma (IFN-γ) allowing us to reliably measure influenza-specific IFN-γ as a marker of the cellular immune response using both enzyme-linked immunospot (ELISpot) and enzyme-linked immunosorbent (ELISA) techniques. Here we demonstrate the application of these tools to evaluate cellular immunity in ferrets infected with clinically relevant seasonal H1N1 and H3N2 IAV subtypes at equivalent doses. Using small heparinised blood samples we were able to observe the longitudinal influenza-specific IFN-γ responses of ferrets infected with both seasonal subtypes of IAV and found a notable increase in influenza-specific IFN-γ responses in circulating peripheral blood within 8 days post-infection. Both seasonal strains caused a well-defined pattern of influenza-specific IFN-γ responses in infected ferrets when compared to naïve animals. Additionally, we found that while the influenza specific IFN-γ responses found in peripheral circulating blood were comparable between subtypes, the influenza specific IFN-γ responses found in lung lymphocytes significantly differed. Our results suggest that there is a distinct difference between the ability of the two seasonal influenza strains to establish an infection in the lung of ferrets associated with distinct signatures of acquired immunity.

Neuraminidase-Inhibiting Antibody Titers Correlate with Protection from Heterologous Influenza Virus Strains of the Same Neuraminidase Subtype

Immune responses induced by currently licensed inactivated influenza vaccines are mainly directed against the hemagglutinin (HA) glycoprotein, the immunodominant antigen of influenza viruses. The resulting antigenic drift of HA requires frequent updating of the vaccine composition and annual revaccination. On the other hand, the levels of antibodies directed against the neuraminidase (NA) glycoprotein, the second major influenza virus antigen, vary greatly. To investigate the potential of the more conserved NA protein for the induction of subtype-specific protection, vesicular stomatitis virus-based replicons expressing a panel of N1 proteins from prototypic seasonal and pandemic H1N1 strains and human H5N1 and H7N9 isolates were generated. Immunization of mice and ferrets with the replicon carrying the matched N1 protein resulted in robust humoral and cellular immune responses and protected against challenge with the homologous influenza virus with an efficacy similar to that of the matched HA protein, illustrating the potential of the NA protein as a vaccine antigen. The extent of protection after immunization with mismatched N1 proteins correlated with the level of cross-reactive neuraminidase-inhibiting antibody titers. Passive serum transfer experiments in mice confirmed that these functional antibodies determine subtype-specific cross-protection. Our findings illustrate the potential of NA-specific immunity for achieving broader protection against antigenic drift variants or newly emerging viruses carrying the same NA but a different HA subtype.IMPORTANCE Despite the availability of vaccines, annual influenza virus epidemics cause 250,000 to 500,000 deaths worldwide. Currently licensed inactivated vaccines, which are standardized for the amount of the hemagglutinin (HA) antigen, primarily induce strain-specific antibodies, whereas the immune response to the neuraminidase (NA) antigen, which is also present on the viral surface, is usually low. Using NA-expressing single-cycle vesicular stomatitis virus replicons, we show that the NA antigen conferred protection of mice and ferrets against not only the matched influenza virus strains but also viruses carrying NA proteins from other strains of the same subtype. The extent of protection correlated with the level of cross-reactive NA-inhibiting antibodies. This highlights the potential of the NA antigen for the development of more broadly protective influenza vaccines. Such vaccines may also provide partial protection against newly emerging strains with the same NA but a different HA subtype.

The tree shrew as a model for infectious diseases research

Despite major advances in medicine, infectious diseases still pose a significant threat to humanity. Mammalian models of disease have proved extremely useful in adding to the understanding of infectious diseases and the development of prophylactic and/or therapeutic interventions. Arguably the most important considerations of any animal model are (I) the similarity of the model to humans with respect to anatomy, physiology, immunology and disease progression, and (II) the expense of conducting experiments using the model organism. Often the choice of a model represents a compromise between these factors. Here we review the Northern Tree shrew (Tupaia belangeri), or tupaia, as a useful model for the study of infectious diseases. Tupaias are non-human primates similar in size to squirrels that are indigenous to Asia. Their genome has been sequenced and, overall, shows relatively high similarity to humans. There is also a close homology of many aspects of tupaia biology with human biology. Importantly, from an infectious diseases viewpoint, tupaias are susceptible to infection with unadapted human pathogens and manifest clinical signs akin to human infections. Overall, the relatively small size of the tupaia, their homology to humans and their susceptibility to human pathogens make them a useful model for the study of infectious diseases.

Small Animal Models for Evaluating Filovirus Countermeasures

The development of novel therapeutics and vaccines to treat or prevent disease caused by filoviruses, such as Ebola and Marburg viruses, depends on the availability of animal models that faithfully recapitulate clinical hallmarks of disease as it is observed in humans. In particular, small animal models (such as mice and guinea pigs) are historically and frequently used for the primary evaluation of antiviral countermeasures, prior to testing in nonhuman primates, which represent the gold-standard filovirus animal model. In the past several years, however, the filovirus field has witnessed the continued refinement of the mouse and guinea pig models of disease, as well as the introduction of the hamster and ferret models. We now have small animal models for most human-pathogenic filoviruses, many of which are susceptible to wild type virus and demonstrate key features of disease, including robust virus replication, coagulopathy, and immune system dysfunction. Although none of these small animal model systems perfectly recapitulates Ebola virus disease or Marburg virus disease on its own, collectively they offer a nearly complete set of tools in which to carry out the preclinical development of novel antiviral drugs.

Type I interferon receptor knockout mice as models for infection of highly pathogenic viruses with outbreak potential

Due to their inability to generate a complete immune response, mice knockout for type I interferon (IFN) receptors (Ifnar^–/–) are more susceptible to viral infections, and are thus commonly used for pathogenesis studies. This mouse model has been used to study many diseases caused by highly pathogenic viruses from many families, including the Flaviviridae, Filoviridae, Arenaviridae, Bunyaviridae, Henipaviridae, and Togaviridae. In this review, we summarize the findings from these animal studies, and discuss the pros and cons of using this model versus other known methods for studying pathogenesis in animals.

Pathogenesis, Humoral Immune Responses, and Transmission between Cohoused Animals in a Ferret Model of Human Respiratory Syncytial Virus Infection

Small-animal models have been used to obtain many insights regarding the pathogenesis and immune responses induced following infection with human respiratory syncytial virus (hRSV). Among those described to date, infections in cotton rats, mice, guinea pigs, chinchillas, and Syrian hamsters with hRSV strains Long and/or A2 have been well characterized, although clinical isolates have also been examined. Ferrets are also susceptible to hRSV infection, but the pathogenesis and immune responses elicited following infection have not been well characterized. Here, we describe the infection of adult ferrets with hRSV Long or A2 via the intranasal route and characterized virus replication, as well as cytokine induction, in the upper and lower airways. Virus replication and cytokine induction during the acute phase of infection (days 0 to 15 postinfection) were similar between the two strains, and both elicited high levels of F glycoprotein-specific binding and neutralizing antibodies following virus clearance (days 16 to 22 postinfection). Importantly, we demonstrate transmission from experimentally infected donor ferrets to cohoused naive recipients and have characterized virus replication and cytokine induction in the upper airways of infected contact animals. Together, these studies provide a direct comparison of the pathogenesis of hRSV Long and A2 in ferrets and highlight the potential of this animal model to study serological responses and examine interventions that limit transmission of hRSV.IMPORTANCE Ferrets have been widely used to study pathogenesis, immunity, and transmission following human influenza virus infections; however, far less is known regarding the utility of the ferret model to study hRSV infections. Following intranasal infection of adult ferrets with the well-characterized Long or A2 strain of hRSV, we report virus replication and cytokine induction in the upper and lower airways, as well as the development of virus-specific humoral responses. Importantly, we demonstrate transmission of hRSV from experimentally infected donor ferrets to cohoused naive recipients. Together, these findings significantly enhance our understanding of the utility of the ferret as a small-animal model to investigate aspects of hRSV pathogenesis and immunity.

Pathogenicity testing of influenza candidate vaccine viruses in the ferret model

The development of influenza candidate vaccine viruses (CVVs) for pre-pandemic vaccine production represents a critical step in pandemic preparedness. The multiple subtypes and clades of avian or swine origin influenza viruses circulating world-wide at any one time necessitates the continuous generation of CVVs to provide an advanced starting point should a novel zoonotic virus cross the species barrier and cause a pandemic. Furthermore, the evolution and diversity of novel influenza viruses that cause zoonotic infections requires ongoing monitoring and surveillance, and, when a lack of antigenic match between circulating viruses and available CVVs is identified, the production of new CVVs. Pandemic guidelines developed by the WHO Global Influenza Program govern the design and preparation of reverse genetics-derived CVVs, which must undergo numerous safety and quality tests prior to human use. Confirmation of reassortant CVV attenuation of virulence in ferrets relative to wild-type virus represents one of these critical steps, yet there is a paucity of information available regarding the relative degree of attenuation achieved by WHO-recommended CVVs developed against novel viruses with pandemic potential. To better understand the degree of CVV attenuation in the ferret model, we examined the relative virulence of six A/Puerto Rico/8/1934-based CVVs encompassing five different influenza A subtypes (H2N3, H5N1, H5N2, H5N8, and H7N9) compared with the respective wild-type virus in ferrets. Despite varied virulence of wild-type viruses in the ferret, all CVVs examined showed reductions in morbidity and viral shedding in upper respiratory tract tissues. Furthermore, unlike the wild-type counterparts, none of the CVVs spread to extrapulmonary tissues during the acute phase of infection. While the magnitude of virus attenuation varied between virus subtypes, collectively we show the reliable and reproducible attenuation of CVVs that have the A/Puerto Rico/9/1934 backbone in a mammalian model.

Infection of Ferrets with Influenza Virus Elicits a Light Chain-Biased Antibody Response against Hemagglutinin

The domestic ferret (Mustela putorius furo) is a commonly used animal model for the study of influenza virus infection and vaccination. Recently, our group has developed murine mAbs with specificity for the κ (Igκ) and λ (Igλ) L chains of ferret Ig. These mAbs were used to quantify the abundance of Igκ and Igλ in serum and to evaluate L chain usage of the Ab response against the hemagglutinin (HA) protein elicited by influenza infection. After influenza A infection of immunologically naive ferrets with various H1N1 or H3N2 strains, the acute Ab response against HA exhibited an inherent bias toward λ L chain usage. In contrast, secondary infection of H1N1 preimmune ferrets with an antigenically distinct H1N1 virus elicited a recall response against the original HA that was no longer biased toward Igλ and possessed differential specificity. Moreover, sequential infection of ferrets with H1N1 influenza viruses elicited an Igκ-biased Ab response directed against the HA globular head and stem regions. Furthermore, sequential infection of ferrets with viral vectors expressing chimeric HA, aimed at boosting Ab reactivity against the HA stem region, also elicited an Igκ-biased response. Collectively, these findings suggest that ferret B cells expressing an Igκ or Igλ BCR possess differential specificities, and highlight the utility of our recently developed mAbs for studying the immune response to influenza virus infection and vaccination in the ferret model.

Generation of Monoclonal Antibodies against Immunoglobulin Proteins of the Domestic Ferret (Mustela putorius furo)

The domestic ferret (Mustela putorius furo) serves as an animal model for the study of several viruses that cause human disease, most notably influenza. Despite the importance of this animal model, characterization of the immune response by flow cytometry (FCM) is severely hampered due to the limited number of commercially available reagents. To begin to address this unmet need and to facilitate more in-depth study of ferret B cells including the identification of antibody-secreting cells, eight unique murine monoclonal antibodies (mAb) with specificity for ferret immunoglobulin (Ig) were generated using conventional B cell hybridoma technology. These mAb were screened for reactivity against ferret peripheral blood mononuclear cells by FCM and demonstrate specificity for CD79β⁺ B cells. Several of these mAb are specific for the light chain of surface B cell receptor (BCR) and enable segregation of kappa and lambda B cells. Additionally, a mAb that yielded surface staining of nearly all surface BCR positive cells (i.e., pan ferret Ig) was generated. Collectively, these MαF-Ig mAb offer advancement compared to the existing portfolio of polyclonal anti-ferret Ig detection reagents and should be applicable to a wide array of immunologic assays including the identification of antibody-secreting cells by FCM.

Dual microRNA Screens Reveal That the Immune-Responsive miR-181 Promotes Henipavirus Entry and Cell-Cell Fusion

Hendra and Nipah viruses (family Paramyxoviridae, genus Henipavirus) are bat-borne viruses that cause fatal disease in humans and a range of other mammalian species. Gaining a deeper understanding of host pathways exploited by henipaviruses for infection may identify targets for new anti-viral therapies. Here we have performed genome-wide high-throughput agonist and antagonist screens at biosafety level 4 to identify host-encoded microRNAs (miRNAs) impacting henipavirus infection in human cells. Members of the miR-181 and miR-17~93 families strongly promoted Hendra virus infection. miR-181 also promoted Nipah virus infection, but did not affect infection by paramyxoviruses from other genera, indicating specificity in the virus-host interaction. Infection promotion was primarily mediated via the ability of miR-181 to significantly enhance henipavirus-induced membrane fusion. Cell signalling receptors of ephrins, namely EphA5 and EphA7, were identified as novel negative regulators of henipavirus fusion. The expression of these receptors, as well as EphB4, were suppressed by miR-181 overexpression, suggesting that simultaneous inhibition of several Ephs by the miRNA contributes to enhanced infection and fusion. Immune-responsive miR-181 levels was also up-regulated in the biofluids of ferrets and horses infected with Hendra virus, suggesting that the host innate immune response may promote henipavirus spread and exacerbate disease severity. This study is the first genome-wide screen of miRNAs influencing infection by a clinically significant mononegavirus and nominates select miRNAs as targets for future anti-viral therapy development.

Ferrets Infected with Bundibugyo Virus or Ebola Virus Recapitulate Important Aspects of Human Filovirus Disease

Bundibugyo virus (BDBV) is the etiological agent of a severe hemorrhagic fever in humans with a case-fatality rate ranging from 25 to 36%. Despite having been known to the scientific and medical communities for almost 1 decade, there is a dearth of studies on this pathogen due to the lack of a small animal model. Domestic ferrets are commonly used to study other RNA viruses, including members of the order Mononegavirales To investigate whether ferrets were susceptible to filovirus infections, ferrets were challenged with a clinical isolate of BDBV. Animals became viremic within 4 days and succumbed to infection between 8 and 9 days, and a petechial rash was observed with moribund ferrets. Furthermore, several hallmarks of human filoviral disease were recapitulated in the ferret model, including substantial decreases in lymphocyte and platelet counts and dysregulation of key biochemical markers related to hepatic/renal function, as well as coagulation abnormalities. Virological, histopathological, and immunohistochemical analyses confirmed uncontrolled BDBV replication in the major organs. Ferrets were also infected with Ebola virus (EBOV) to confirm their susceptibility to another filovirus species and to potentially establish a virus transmission model. Similar to what was seen with BDBV, important hallmarks of human filoviral disease were observed in EBOV-infected ferrets. This study demonstrates the potential of this small animal model for studying BDBV and EBOV using wild-type isolates and will accelerate efforts to understand filovirus pathogenesis and transmission as well as the development of specific vaccines and antivirals.

IMPORTANCE

The 2013-2016 outbreak of Ebola virus in West Africa has highlighted the threat posed by filoviruses to global public health. Bundibugyo virus (BDBV) is a member of the genus Ebolavirus and has caused outbreaks in the past but is relatively understudied, likely due to the lack of a suitable small animal model. Such a model for BDBV is crucial to evaluating vaccines and therapies and potentially understanding transmission. To address this, we demonstrated that ferrets are susceptible models to BDBV infection as well as to Ebola virus infection and that no virus adaptation is required. Moreover, these animals develop a disease that is similar to that seen in humans and nonhuman primates. We believe that this will improve the ability to study BDBV and provide a platform to test vaccines and therapeutics.

What can imaging tell us about influenza virus transmission and protection?

The emergence of zoonotic influenza infections is a constant threat to public health. One of the major determinants of pandemic potential is the ability to transmit from animal to human and/or human to human via respiratory droplets. Understanding viral tropism and spread is crucial for predicting which viruses represent the most threatening to human health. Recently, a replication-competent influenza reporter virus was described that permitted in vivo imaging and visualization of infection in ferrets for the first time. This review will focus on the applications of luminescent reporter viruses toward understanding transmission of influenza viruses and development of therapeutic interventions.

The Domestic Ferret (Mustela putorius furo) as a Lethal Infection Model for 3 Species of Ebolavirus

Small-animal models have been developed for several Filoviridae species; however, serial adaptation was required to produce lethal infection. These adapted viruses have sequence changes in several genes, including those that modulate the host immune response. Nonhuman primate models do not require adaptation of filoviruses. Here, we describe lethal models of disease for Bundibugyo, Sudan, and Zaire species of Ebolavirus in the domestic ferret, using wild-type nonadapted viruses. Pathologic features were consistent with disease in primates. Of particular importance, this is the only known small-animal model developed for Bundibugyo and the only uniformly lethal animal model for Bundibugyo.

Using the Ferret as an Animal Model for Investigating Influenza Antiviral Effectiveness

The concern of the emergence of a pandemic influenza virus has sparked an increased effort toward the development and testing of novel influenza antivirals. Central to this is the animal model of influenza infection, which has played an important role in understanding treatment effectiveness and the effect of antivirals on host immune responses. Among the different animal models of influenza, ferrets can be considered the most suitable for antiviral studies as they display most of the human-like symptoms following influenza infections, they can be infected with human influenza virus without prior viral adaptation and have the ability to transmit influenza virus efficiently between one another. However, an accurate assessment of the effectiveness of an antiviral treatment in ferrets is dependent on three major experimental considerations encompassing firstly, the volume and titer of virus, and the route of viral inoculation. Secondly, the route and dose of drug administration, and lastly, the different methods used to assess clinical symptoms, viral shedding kinetics and host immune responses in the ferrets. A good understanding of these areas is necessary to achieve data that can accurately inform the human use of influenza antivirals. In this review, we discuss the current progress and the challenges faced in these three major areas when using the ferret model to measure influenza antiviral effectiveness.

Respiratory nanoparticle-based vaccines and challenges associated with animal models and translation

Vaccine development has had a huge impact on human health. However, there is a significant need to develop efficacious vaccines for several existing as well as emerging respiratory infectious diseases. Several challenges need to be overcome to develop efficacious vaccines with translational potential. This review focuses on two aspects to overcome some barriers - 1) the development of nanoparticle-based vaccines, and 2) the choice of suitable animal models for respiratory infectious diseases that will allow for translation. Nanoparticle-based vaccines, including subunit vaccines involving synthetic and/or natural polymeric adjuvants and carriers, as well as those based on virus-like particles offer several key advantages to help overcome the barriers to effective vaccine development. These include the ability to deliver combinations of antigens, target the vaccine formulation to specific immune cells, enable cross-protection against divergent strains, act as adjuvants or immunomodulators, allow for sustained release of antigen, enable single dose delivery, and potentially obviate the cold chain. While mouse models have provided several important insights into the mechanisms of infectious diseases, they are often a limiting step in translation of new vaccines to the clinic. An overview of different animal models involved in vaccine research for respiratory infections, with advantages and disadvantages of each model, is discussed. Taken together, advances in nanotechnology, combined with the right animal models for evaluating vaccine efficacy, has the potential to revolutionize vaccine development for respiratory infections.