Differential interferon responses to influenza A and B viruses in primary ferret respiratory epithelial cells

Influenza B viruses (IBV) cocirculate with influenza A viruses (IAV) and cause periodic epidemics of disease, yet antibody and cellular responses following IBV infection are less well understood. Using the ferret model for antisera generation for influenza surveillance purposes, IAV resulted in robust antibody responses following infection, whereas IBV required an additional booster dose, over 85% of the time, to generate equivalent antibody titers. In this study, we utilized primary differentiated ferret nasal epithelial cells (FNECs) which were inoculated with IAV and IBV to study differences in innate immune responses which may result in differences in adaptive immune responses in the host. FNECs were inoculated with IAV (H1N1pdm09 and H3N2 subtypes) or IBV (B/Victoria and B/Yamagata lineages) and assessed for 72 h. Cells were analyzed for gene expression by quantitative real-time PCR, and apical and basolateral supernatants were assessed for virus kinetics and interferon (IFN), respectively. Similar virus kinetics were observed with IAV and IBV in FNECs. A comparison of gene expression and protein secretion profiles demonstrated that IBV-inoculated FNEC expressed delayed type-I/II IFN responses and reduced type-III IFN secretion compared to IAV-inoculated cells. Concurrently, gene expression of Thymic Stromal Lymphopoietin (TSLP), a type-III IFN-induced gene that enhances adaptive immune responses, was significantly downregulated in IBV-inoculated FNECs. Significant differences in other proinflammatory and adaptive genes were suppressed and delayed following IBV inoculation. Following IBV infection, ex vivo cell cultures derived from the ferret upper respiratory tract exhibited reduced and delayed innate responses which may contribute to reduced antibody responses in vivo.IMPORTANCEInfluenza B viruses (IBV) represent nearly one-quarter of all human influenza cases and are responsible for significant clinical and socioeconomic impacts but do not pose the same pandemic risks as influenza A viruses (IAV) and have thus received much less attention. IBV accounts for greater severity and deaths in children, and vaccine efficacy remains low. The ferret can be readily infected with human clinical isolates and demonstrates a similar course of disease and immune responses. IBV, however, generates lower antibodies in ferrets than IAV following the challenge. To determine whether differences in initial innate responses following infection may affect the development of robust adaptive immune responses, ferret respiratory tract cells were isolated, infected with IAV/IBV, and compared. Understanding the differences in the initial innate immune responses to IAV and IBV may be important in the development of more effective vaccines and interventions to generate more robust protective immune responses.

Mutations that adapt SARS-CoV-2 to mink or ferret do not increase fitness in the human airway

SARS-CoV-2 has a broad mammalian species tropism infecting humans, cats, dogs, and farmed mink. Since the start of the 2019 pandemic, several reverse zoonotic outbreaks of SARS-CoV-2 have occurred in mink, one of which reinfected humans and caused a cluster of infections in Denmark. Here we investigate the molecular basis of mink and ferret adaptation and demonstrate the spike mutations Y453F, F486L, and N501T all specifically adapt SARS-CoV-2 to use mustelid ACE2. Furthermore, we risk assess these mutations and conclude mink-adapted viruses are unlikely to pose an increased threat to humans, as Y453F attenuates the virus replication in human cells and all three mink adaptations have minimal antigenic impact. Finally, we show that certain SARS-CoV-2 variants emerging from circulation in humans may naturally have a greater propensity to infect mustelid hosts and therefore these species should continue to be surveyed for reverse zoonotic infections.

Serological Detection of SARS-CoV-2 Antibodies in Naturally-Infected Mink and Other Experimentally-Infected Animals

The recent emergence of SARS-CoV-2 in humans from a yet unidentified animal reservoir and the capacity of the virus to naturally infect pets, farmed animals and potentially wild animals has highlighted the need for serological surveillance tools. In this study, the luciferase immunoprecipitation systems (LIPS), employing the spike (S) and nucleocapsid proteins (N) of SARS-CoV-2, was used to examine the suitability of the assay for antibody detection in different animal species. Sera from SARS-CoV-2 naturally-infected mink (n = 77), SARS-CoV-2 experimentally-infected ferrets, fruit bats and hamsters and a rabbit vaccinated with a purified spike protein were examined for antibodies using the SARS-CoV-2 N and/or S proteins. From comparison with the known neutralization status of the serum samples, statistical analyses including calculation of the Spearman rank-order-correlation coefficient and Cohen's kappa agreement were used to interpret the antibody results and diagnostic performance. The LIPS immunoassay robustly detected the presence of viral antibodies in naturally infected SARS-CoV-2 mink, experimentally infected ferrets, fruit bats and hamsters as well as in an immunized rabbit. For the SARS-CoV-2-LIPS-S assay, there was a good level of discrimination between the positive and negative samples for each of the five species tested with 100% agreement with the virus neutralization results. In contrast, the SARS-CoV-2-LIPS-N assay did not consistently differentiate between SARS-CoV-2 positive and negative sera. This study demonstrates the suitability of the SARS-CoV-2-LIPS-S assay for the sero-surveillance of SARS-CoV-2 infection in a range of animal species.

Glycosylation generates an efficacious and immunogenic vaccine against H7N9 influenza virus

Zoonotic avian influenza viruses pose severe health threats to humans. Of several viral subtypes reported, the low pathogenic avian influenza H7N9 virus has since February 2013 caused more than 1,500 cases of human infection with an almost 40% case-fatality rate. Vaccination of poultry appears to reduce human infections. However, the emergence of highly pathogenic strains has increased concerns about H7N9 pandemics. To develop an efficacious H7N9 human vaccine, we designed vaccine viruses by changing the patterns of N-linked glycosylation (NLG) on the viral hemagglutinin (HA) protein based on evolutionary patterns of H7 HA NLG changes. Notably, a virus in which 2 NLG modifications were added to HA showed higher growth rates in cell culture and elicited more cross-reactive antibodies than did other vaccine viruses with no change in the viral antigenicity. Developed into an inactivated vaccine formulation, the vaccine virus with 2 HA NLG additions exhibited much better protective efficacy against lethal viral challenge in mice than did a vaccine candidate with wild-type (WT) HA by reducing viral replication in the lungs. In a ferret model, the 2 NLG-added vaccine viruses also induced hemagglutination-inhibiting antibodies and significantly suppressed viral replication in the upper and lower respiratory tracts compared with the WT HA vaccines. In a mode of action study, the HA NLG modification appeared to increase HA protein contents incorporated into viral particles, which would be successfully translated to improve vaccine efficacy. These results suggest the strong potential of HA NLG modifications in designing avian influenza vaccines.

This study shows that changing the pattern of N-glycosylation of the pathogenic avian influenza H7N9 virus hemagglutinin protein increases the amount of hemagglutinin incorporated into the viral membrane; the candidate vaccine virus induces neutralizing antibodies and protects animal models from lethal viral challenge.

Sequencing B cell receptors from ferrets (Mustela putorius furo)

The domestic ferret (Mustela putorius furo) provides a critical animal model to study human respiratory diseases. However immunological insights are restricted due to a lack of ferret-specific reagents and limited genetic information about ferret B and T cell receptors. Here, variable, diversity and joining genes within the ferret kappa, lambda and heavy chain immunoglobulin loci were annotated using available genomic information. A multiplex PCR approach was derived that facilitated the recovery of paired heavy and light chain immunoglobulin sequences from single sorted ferret B cells, allowing validation of predicted germline gene sequences and the identification of putative novel germlines. Eukaryotic expression vectors were developed that enabled the generation of recombinant ferret monoclonal antibodies. This work advances the ferret as an informative immunological model for viral diseases by allowing the in-depth interrogation of antibody-based immunity.

Characterising antibody kinetics from multiple influenza infection and vaccination events in ferrets

The strength and breadth of an individual's antibody repertoire is an important predictor of their response to influenza infection or vaccination. Although progress has been made in understanding qualitatively how repeated exposures shape the antibody mediated immune response, quantitative understanding remains limited. We developed a set of mathematical models describing short-term antibody kinetics following influenza infection or vaccination and fit them to haemagglutination inhibition (HI) titres from 5 groups of ferrets which were exposed to different combinations of trivalent inactivated influenza vaccine (TIV with or without adjuvant), A/H3N2 priming inoculation and post-vaccination A/H1N1 inoculation. We fit models with various immunological mechanisms that have been empirically observed but have not previously been included in mathematical models of antibody landscapes, including: titre ceiling effects, antigenic seniority and exposure-type specific cross reactivity. Based on the parameter estimates of the best supported models, we describe a number of key immunological features. We found quantifiable differences in the degree of homologous and cross-reactive antibody boosting elicited by different exposure types. Infection and adjuvanted vaccination generally resulted in strong, broadly reactive responses whereas unadjuvanted vaccination resulted in a weak, narrow response. We found that the order of exposure mattered: priming with A/H3N2 improved subsequent vaccine response, and the second dose of adjuvanted vaccination resulted in substantially greater antibody boosting than the first. Either antigenic seniority or a titre ceiling effect were included in the two best fitting models, suggesting a role for a mechanism describing diminishing antibody boosting with repeated exposures. Although there was considerable uncertainty in our estimates of antibody waning parameters, our results suggest that both short and long term waning were present and would be identifiable with a larger set of experiments. These results highlight the potential use of repeat exposure animal models in revealing short-term, strain-specific immune dynamics of influenza.

Amino Acid Residue 217 in the Hemagglutinin Glycoprotein Is a Key Mediator of Avian Influenza H7N9 Virus Antigenicity

Avian influenza viruses continue to evolve and acquire mutations that facilitate antigenic drift and virulence change. In 2017, low-pathogenicity H7N9 avian influenza viruses evolved to a high-pathogenicity phenotype in China. Comparative antigenic analysis of the low- and high-pathogenicity virus strains showed marked variability. In order to identify residues that may be linked to the antigenic change among the H7N9 viruses, we serially passaged the viruses in the presence of homologous ferret antiserum. Progeny viruses able to overcome the neutralizing capacity of the antiserum were sequenced. The analysis showed that the emergent immune escape viruses contained mutations A125T, A151T, and L217Q in the hemagglutinin (HA) glycoprotein as early as passage 5 and that these mutations persisted until passage 10. The results revealed that a single mutation, L217Q, in the HA of H7N9 virus led to 23- and 8-fold reductions in hemagglutination inhibition (HI) titer with ferret and chicken antisera, respectively. Further analysis showed that this change also contributed to antigenic differences between the low- and high-pathogenicity H7N9 viruses, thus playing a major role in their antigenic diversification. Therefore, evolutionary changes at amino acid position 217 in the H7N9 viruses can serve as a genetic marker for virus antigenic diversity during vaccine seed matching and selection. The in vitro immune escape mutant selection method used in this study could also aid in the prediction of emerging antigenic variants in naturally infected or immunized animals.IMPORTANCE Avian influenza H7N9 viruses circulating in poultry and wild birds continue to evolve and acquire important phenotypic changes. Mutations to the virus hemagglutinin (HA) glycoprotein can modulate virus antigenicity and facilitate virus escape from natural or vaccine-induced immunity. The focus of this study was to identify evolutionary markers in the HA of H7N9 that drive escape from antibody-based immunity. To achieve this, we propagated low-pathogenicity H7N9 virus in the presence of polyclonal antiserum derived from ferrets infected with the same strain of virus (homologous antiserum). This selection process was repeated 10 times. The HA gene sequences of viruses recovered after the fifth passage showed that the viruses readily acquired mutations at three different amino acid positions (A125T, A151T, and L217Q). Further functional analysis of these mutations confirmed that the mutation at residue 217 in the HA was responsible for mediating changes to the immunological properties of the H7N9 virus.

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.

Impact of Sylvatic Plague Vaccine on Non-target Small Rodents in Grassland Ecosystems

Oral vaccination is an emerging management strategy to reduce the prevalence of high impact infectious diseases within wild animal populations. Plague is a flea-borne zoonosis of rodents that often decimates prairie dog (Cynomys spp.) colonies in the western USA. Recently, an oral sylvatic plague vaccine (SPV) was developed to protect prairie dogs from plague and aid recovery of the endangered black-footed ferret (Mustela nigripes). Although oral vaccination programs are targeted toward specific species, field distribution of vaccine-laden baits can result in vaccine uptake by non-target animals and unintended indirect effects. We assessed the impact of SPV on non-target rodents at paired vaccine and placebo-treated prairie dog colonies in four US states from 2013 to 2015. Bait consumption by non-target rodents was high (70.8%, n = 3113), but anti-plague antibody development on vaccine plots was low (23.7%, n = 266). In addition, no significant differences were noted in combined deer mice (Peromyscus maniculatus) and western harvest mouse (Reithrodontomys megalotis) abundance or community evenness and richness of non-target rodents between vaccine-treated and placebo plots. In our 3-year field study, we could not detect a significant positive or negative effect of SPV application on non-target rodents.

H5N2 vaccine viruses on Russian and US live attenuated influenza virus backbones demonstrate similar infectivity, immunogenicity and protection in ferrets

The continued detection of zoonotic influenza infections, most notably due to the avian influenza A H5N1 and H7N9 subtypes, underscores the need for pandemic preparedness. Decades of experience with live attenuated influenza vaccines (LAIVs) for the control of seasonal influenza support the safety and effectiveness of this vaccine platform. All LAIV candidates are derived from one of two licensed master donor viruses (MDVs), cold-adapted (ca) A/Ann Arbor/6/60 or ca A/Leningrad/134/17/57. A number of LAIV candidates targeting avian H5 influenza viruses derived with each MDV have been evaluated in humans, but have differed in their infectivity and immunogenicity. To understand these differences, we generated four H5N2 candidate pandemic LAIVs (pLAIVs) derived from either MDV and compared their biological characteristics in vitro and in vivo. We demonstrate that all candidate pLAIVs, regardless of gene constellation and derivation, were comparable with respect to infectivity, immunogenicity, and protection from challenge in the ferret model of influenza. These observations suggest that differences in clinical performance of H5 pLAIVs may be due to factors other than inherent biological properties of the two MDVs.

Safety, efficacy and immunogenicity evaluation of the SAG2 oral rabies vaccine in Formosan ferret badgers

Since 2013, rabies cases have been reported among Formosan ferret badgers in Taiwan, and they have been shown to be the major reservoirs for Taiwanese enzootics. To control and eradicate rabies, the authorities plan to implement a vaccination programme. Before distributing live vaccines in the field, this study assessed the safety, efficacy, and immunogenicity of SAG2 vaccine on ferret badgers by direct oral instillation. After application of 109 TCID50/dose, no virus was excreted into the oral cavity 1-7 days post-application, and safety was also satisfactorily verified over a 266-day period. Moreover, despite the low level of rabies virus neutralising antibodies induced after vaccination of a 108 TCID50/dose, the efficacy assessment revealed a 100% survival rate (15/15) of vaccinees and an 87.5% fatality rate (7/8) in control animals after a challenge on the 198th day post-vaccination. The immunisation and protection rates obtained more than 6 months after a single vaccination dose demonstrated that SAG2 is an ideal vaccine candidate to protect Formosan ferret badgers against rabies in Taiwan.

Vaccines for Conservation: Plague, Prairie Dogs & Black-Footed Ferrets as a Case Study

The endangered black-footed ferret (Mustela nigripes) is affected by plague, caused by Yersinia pestis, both directly, as a cause of mortality, and indirectly, because of the impacts of plague on its prairie dog (Cynomys spp.) prey base. Recent developments in vaccines and vaccine delivery have raised the possibility of plague control in prairie dog populations, thereby protecting ferret populations. A large-scale experimental investigation across the western US shows that sylvatic plague vaccine delivered in oral baits can increase prairie dog survival. In northern Colorado, an examination of the efficacy of insecticides to control fleas and plague vaccine shows that timing and method of plague control is important, with different implications for long-term and large-scale management of Y. pestis delivery. In both cases, the studies show that ambitious field-work and cross-sectoral collaboration can provide potential solutions to difficult issues of wildlife management, conservation and disease ecology.

Novel hemagglutinin nanoparticle influenza vaccine with Matrix-M™ adjuvant induces hemagglutination inhibition, neutralizing, and protective responses in ferrets against homologous and drifted A(H3N2) subtypes

Influenza viruses frequently acquire mutations undergoing antigenic drift necessitating annual evaluation of vaccine strains. Highly conserved epitopes have been identified in the hemagglutinin (HA) head and stem regions, however, current influenza vaccines induce only limited responses to these conserved sites. Here, we describe a novel seasonal recombinant HA nanoparticle influenza vaccine (NIV) formulated with a saponin-based adjuvant, Matrix-M™. NIV induced hemagglutination inhibition (HAI) and microneutralizing (MN) antibodies against a broad range of influenza A(H3N2) subtypes. In a comparison of NIV against standard-dose and high-dose inactivated influenza vaccines (IIV and IIV-HD, respectively) in ferrets NIV elicited HAI and MN responses exceeding those induced by IIV-HD against homologous A(H3N2) by 7 fold, A(H1N1) by 26 fold, and B strain viruses by 2 fold. NIV also induced MN responses against all historic A/H3N2 strains tested, spanning more than a decade of viral evolution from the 2000-2017 influenza seasons whereas IIV and IIV-HD induced HAI and MN responses were largely directed against the homologous A(H3N2), A(H1N1), and B virus strains. NIV induced superior protection compared to IIV and IIV-HD in ferrets challenged with a homologous or 10-year drifted influenza A(H3N2) strain. HAI positive and HAI negative neutralizing monoclonal antibodies derived from mice immunized with NIV were active against homologous and drifted influenza A(H3N2) strains. Taken together these observations suggest that NIV can induce responses to one or more highly conserved HA head and stem epitopes and result in highly neutralizing antibodies against both homologous and drift strains.

Development of an anti-ferret CD4 monoclonal antibody for the characterisation of ferret T lymphocytes

The ferret is an established animal model for a number of human respiratory viral infections, such as influenza virus and more recently, Ebola virus. However, a paucity of immunological reagents has hampered the study of cellular immune responses. Here we describe the development and characterisation of a novel monoclonal antibody (mAb) against the ferret CD4 antigen and the characterisation of ferret CD4 T lymphocytes. Recombinant production and purification of the ferret CD4 ectodomain soluble protein allowed hybridoma generation and the generation of a mAb (FeCD4) showing strong binding to ferret CD4 protein and lymphoid cells by flow cytometry. FeCD4 bound to its cognate antigen post-fixation with paraformaldehyde (PFA) which is routinely used to inactivate highly pathogenic viruses. We have also used FeCD4 in conjunction with other immune cell markers to characterise ferret T cells in both primary and secondary lymphoid organs. In summary, we have developed an important reagent for the study of cellular immunological responses in the ferret model of infectious disease.

Eyedrop Vaccination Induced Systemic and Mucosal Immunity against Influenza Virus in Ferrets

We investigated eyedrop vaccination (EDV) in pre-clinical development for immunological protection against influenza and for potential side effects involving ocular inflammation and the central nervous system (CNS). Live attenuated influenza EDV, CA07 (H1N1), PZ-4 (H1N2) and Uruguay (H3N2), induced both systemic and mucosal virus-specific antibody responses in ferrets. In addition, EDV resulted in a clinically significant protection against viral challenge, and suppression of viral replication in nasal secretion and lung tissue. Regarding safety, we found that administered EDV flow through the tear duct to reach the base of nasal cavity, and thus do not contact the olfactory bulb. All analyses for potential adverse effects due to EDV, including histological and functional examinations, did not reveal significant side effects. On the basis of these findings, we propose that EDV as effective, while being a safe administration route with minimum local side effects, CNS invasion, or visual function disturbance.

Selection of antigenically advanced variants of seasonal influenza viruses

Influenza viruses mutate frequently, necessitating constant updates of vaccine viruses. To establish experimental approaches that may complement the current vaccine strain selection process, we selected antigenic variants from human H1N1 and H3N2 influenza virus libraries possessing random mutations in the globular head of the haemagglutinin protein (which includes the antigenic sites) by incubating them with human and/or ferret convalescent sera to human H1N1 and H3N2 viruses. We also selected antigenic escape variants from human viruses treated with convalescent sera and from mice that had been previously immunized against human influenza viruses. Our pilot studies with past influenza viruses identified escape mutants that were antigenically similar to variants that emerged in nature, establishing the feasibility of our approach. Our studies with contemporary human influenza viruses identified escape mutants before they caused an epidemic in 2014-2015. This approach may aid in the prediction of potential antigenic escape variants and the selection of future vaccine candidates before they become widespread in nature.

Coronavirus Infection in Ferrets: Antigen Distribution and Inflammatory Response

Multisystemic granulomatous lesions are the most common finding in ferrets infected by ferret systemic coronavirus (FRSCV). To characterize the inflammatory response developed against this virus, lesions from 4 naturally infected ferrets were examined. Lesions were classified into the 4 known types of granulomas (granulomas without necrosis [G], granulomas with necrosis [G-N], granulomas with neutrophils [G-NL], and diffuse granulomatous inflammation [DG]). The cellular composition of the lesions was characterized on the basis of cellular morphology and immunohistochemistry using markers for T and B-lymphocytes, plasma cells, macrophages, and neutrophils. The extent and distribution of viral antigen expression was also assessed. In G lesions, macrophages were mainly located in the center of the granuloma, with a moderate number of T-lymphocytes scattered among the macrophages, plasma cells, and B-lymphocytes. G-N lesions exhibited a necrotic center surrounded by abundant macrophages, some T-lymphocytes, plasma cells, and a few B-lymphocytes. In G-NL lesions, there was a central area dominated by neutrophils with low numbers of macrophages, plasma cells, and lymphocytes. DG presented similar cell proportions, but distributed evenly throughout the lesions. FRSCV was expressed in G, G-NL, G-N, and DG, with decreasing numbers of immunoreactive cells. This study reveals the important role of macrophages in the inflammatory response of ferrets against the virus and the variable proportions of leukocytes among different types of lesions, indicating their variable age. The results also confirm the similarities of the disease in ferrets to feline infectious peritonitis.

Structural and functional characterisation of ferret interleukin-2

While the ferret is a valuable animal model for a number of human viral infections, such as influenza, Hendra and Nipah, evaluating the cellular immune response following infection has been hampered by the lack of a number of species-specific immunological reagents. Interleukin 2 (IL-2) is one such key cytokine. Ferret recombinant IL-2 incorporating a C-terminal histidine tag was expressed and purified and the three-dimensional structure solved and refined at 1.89 Å by X-ray crystallography, which represents the highest resolution and first non-human IL-2 structure. While ferret IL-2 displays the classic cytokine fold of the four-helix bundle structure, conformational flexibility was observed at the second helix and its neighbouring region in the bundle, which may result in the disruption of the spatial arrangement of residues involved in receptor binding interactions, implicating subtle differences between ferret and human IL-2 when initiating biological functions. Ferret recombinant IL-2 stimulated the proliferation of ferret lymph node cells and induced the expression of mRNA for IFN-γ and Granzyme A.

Influenza vaccination accelerates recovery of ferrets from lymphopenia

Ferrets are a useful animal model for human influenza virus infections, since they closely mimic the pathogenesis of influenza viruses observed in humans. However, a lack of reagents, especially for flow cytometry of immune cell subsets, has limited research in this model. Here we use a panel of primarily species cross-reactive antibodies to identify ferret T cells, cytotoxic T lymphocytes (CTL), B cells, and granulocytes in peripheral blood. Following infection with seasonal H3N2 or H1N1pdm09 influenza viruses, these cell types showed rapid and dramatic changes in frequency, even though clinically the infections were mild. The loss of B cells and CD4 and CD8 T cells, and the increase in neutrophils, were especially marked 1–2 days after infection, when about 90% of CD8+ T cells disappeared from the peripheral blood. The different virus strains led to different kinetics of leukocyte subset alterations. Vaccination with homologous vaccine reduced clinical symptoms slightly, but led to a much more rapid return to normal leukocyte parameters. Assessment of clinical symptoms may underestimate the effectiveness of influenza vaccine in restoring homeostasis.

GLA-AF, an emulsion-free vaccine adjuvant for pandemic influenza

The ongoing threat from Influenza necessitates the development of new vaccine and adjuvant technologies that can maximize vaccine immunogenicity, shorten production cycles, and increase global vaccine supply. Currently, the most successful adjuvants for Influenza vaccines are squalene-based oil-in-water emulsions. These adjuvants enhance seroprotective antibody titers to homologous and heterologous strains of virus, and augment a significant dose sparing activity that could improve vaccine manufacturing capacity. As an alternative to an emulsion, we tested a simple lipid-based aqueous formulation containing a synthetic TLR4 ligand (GLA-AF) for its ability to enhance protection against H5N1 infection. GLA-AF was very effective in adjuvanting recombinant H5 hemagglutinin antigen (rH5) in mice and was as potent as the stable emulsion, SE. Both adjuvants induced similar antibody titers using a sub-microgram dose of rH5, and both conferred complete protection against a highly pathogenic H5N1 challenge. However, GLA-AF was the superior adjuvant in ferrets. GLA-AF stimulated a broader antibody response than SE after both the prime and boost immunization with rH5, and ferrets were better protected against homologous and heterologous strains of H5N1 virus. Thus, GLA-AF is a potent emulsion-free adjuvant that warrants consideration for pandemic influenza vaccine development.

Enhanced neutralizing antibody titers and Th1 polarization from a novel Escherichia coli derived pandemic influenza vaccine

Influenza pandemics can spread quickly and cost millions of lives; the 2009 H1N1 pandemic highlighted the shortfall in the current vaccine strategy and the need for an improved global response in terms of shortening the time required to manufacture the vaccine and increasing production capacity. Here we describe the pre-clinical assessment of a novel 2009 H1N1 pandemic influenza vaccine based on the E. coli-produced HA globular head domain covalently linked to virus-like particles derived from the bacteriophage Qβ. When formulated with alum adjuvant and used to immunize mice, dose finding studies found that a 10 µg dose of this vaccine (3.7 µg globular HA content) induced antibody titers comparable to a 1.5 µg dose (0.7 µg globular HA content) of the licensed 2009 H1N1 pandemic vaccine Panvax, and significantly reduced viral titers in the lung following challenge with 2009 H1N1 pandemic influenza A/California/07/2009 virus. While Panvax failed to induce marked T cell responses, the novel vaccine stimulated substantial antigen-specific interferon-γ production in splenocytes from immunized mice, alongside enhanced IgG2a antibody production. In ferrets the vaccine elicited neutralizing antibodies, and following challenge with influenza A/California/07/2009 virus reduced morbidity and lowered viral titers in nasal lavages.

Replication and immunogenicity of swine, equine, and avian h3 subtype influenza viruses in mice and ferrets

Since it is difficult to predict which influenza virus subtype will cause an influenza pandemic, it is important to prepare influenza virus vaccines against different subtypes and evaluate the safety and immunogenicity of candidate vaccines in preclinical and clinical studies prior to a pandemic. In addition to infecting humans, H3 influenza viruses commonly infect pigs, horses, and avian species. We selected 11 swine, equine, and avian H3 influenza viruses and evaluated their kinetics of replication and ability to induce a broadly cross-reactive antibody response in mice and ferrets. The swine and equine viruses replicated well in the upper respiratory tract of mice. With the exception of one avian virus that replicated poorly in the lower respiratory tract, all of the viruses replicated in mouse lungs. In ferrets, all of the viruses replicated well in the upper respiratory tract, but the equine viruses replicated poorly in the lungs. Extrapulmonary spread was not observed in either mice or ferrets. No single virus elicited antibodies that cross-reacted with viruses from all three animal sources. Avian and equine H3 viruses elicited broadly cross-reactive antibodies against heterologous viruses isolated from the same or other species, but the swine viruses did not. We selected an equine and an avian H3 influenza virus for further development as vaccines.

Validation of the modified hemagglutination inhibition assay (mHAI), a robust and sensitive serological test for analysis of influenza virus-specific immune response

BACKGROUND

The hemagglutination inhibition assay (HAI) is universally regarded as the gold standard in influenza virus serology. Nevertheless, difficulties in titre readouts are common and interlaboratory variations are frequently reported.

OBJECTIVE

We developed and validated the modified HAI to facilitate reliable, accurate and reproducible analysis of sera derived from influenza vaccination studies.

STUDY DESIGN

Clinical and preclinical serum samples, NIBSC reference sera and seasonal influenza virus type A (H1N1 and H3N2) and type B antigens were employed to validate the mHAI. Moreover, pandemic virus strains (H5N1 and H1N1pdm09) were used to prove assay robustness.

RESULTS

Utilisation of a 0.08% solution of stabilised human erythrocytes, assay buffer containing bovine serum albumin and microscopical plate readout are the major differences between the modified and standard HAI assay protocols. Validation experiments revealed that the mHAI is linear, specific and up to eightfold more sensitive than the standard HAI. In 95.6% of all measurements mHAI titres were precisely measured irrespective of the assay day, run or operator. Moreover, 96.4% (H1N1) or 95.2% (H3N2 and B), respectively, of all serum samples were determined within one dilution step of the nominal values for spiked samples. Finally, the mHAI results remained unaffected by variations in virus antigens, erythrocytes, reagents, laboratory location, sample storage conditions or matrix components.

CONCLUSION

The modified HAI is easy to analyse, requires only a single source of erythrocytes and allows utilisation of numerous influenza virus antigens, also including virus strains which are difficult to handle by the standard HAI (e.g. H3N2, H5N1 and H1N1pdm09).

Comparison of the protection of ferrets against pandemic 2009 influenza A virus (H1N1) by 244 DI influenza virus and oseltamivir

The main antivirals employed to combat seasonal and pandemic influenza are oseltamivir and zanamivir which act by inhibiting the virus-encoded neuraminidase. These have to be deployed close to the time of infection and antiviral resistance to the more widely used oseltamivir has arisen relatively rapidly. Defective interfering (DI) influenza virus is a natural antiviral that works in a different way to oseltamivir and zanamivir, and a cloned version (segment 1 244 DI RNA in a cloned A/PR/8/34 virus; 244/PR8) has proved effective in preclinical studies in mice. The active principle is the DI RNA, and this is thought to interact with all influenza A viruses by inhibiting RNA virus synthesis and packaging of the cognate virion RNA into nascent DI virus particles. We have compared the ability of DI virus and oseltamivir to protect ferrets from intranasal 2009 pandemic influenza virus A/California/04/09 (A/Cal, H1N1). Ferrets were treated with a single 2 μg intranasal dose of 244 DI RNA delivered as 244/PR8 virus, or a total of 25mg/kg body weight of oseltamivir given as 10 oral doses over 5 days. Both DI virus and oseltamivir reduced day 2 infectivity and the influx of cells into nasal fluids, and permitted the development of adaptive immunity. However DI virus, but not oseltamivir, significantly reduced weight loss, facilitated better weight gain, reduced respiratory disease, and reduced infectivity on days 4 and 6. 244 DI RNA was amplified by A/Cal by >25,000-fold, consistent with the amelioration of clinical disease. Treatment with DI virus did not delay clearance or cause persistence of infectious virus or DI RNA. Thus in this system DI virus was overall more effective than oseltamivir in combatting pandemic A/California/04/09.

Host gene expression signatures discriminate between ferrets infected with genetically similar H1N1 strains

Different respiratory viruses induce virus-specific gene expression in the host. Recent evidence, including those presented here, suggests that genetically related isolates of influenza virus induce strain-specific host gene regulation in several animal models. Here, we identified systemic strain-specific gene expression signatures in ferrets infected with pandemic influenza A/California/07/2009, A/Mexico/4482/2009 or seasonal influenza A/Brisbane/59/2007. Using uncorrelated shrunken centroid classification, we were able to accurately identify the infecting influenza strain with a combined gene expression profile of 10 selected genes, independent of the severity of disease. Another gene signature, consisting of 7 genes, could classify samples based on lung pathology. Furthermore, we identified a gene expression profile consisting of 31 probes that could classify samples based on both strain and severity of disease. Thus, we show that expression-based analysis of non-infected tissue enables distinction between genetically related influenza viruses as well as lung pathology. These results open for development of alternative tools for influenza diagnostics.

Evaluation of synthetic infection-enhancing lipopeptides as adjuvants for a live-attenuated canine distemper virus vaccine administered intra-nasally to ferrets

BACKGROUND

Inactivated paramyxovirus vaccines have been associated with hypersensitivity responses upon challenge infection. For measles and canine distemper virus (CDV) safe and effective live-attenuated virus vaccines are available, but for human respiratory syncytial virus and human metapneumovirus development of such vaccines has proven difficult. We recently identified three synthetic bacterial lipopeptides that enhance paramyxovirus infections in vitro, and hypothesized these could be used as adjuvants to promote immune responses induced by live-attenuated paramyxovirus vaccines.

METHODS

Here, we tested this hypothesis using a CDV vaccination and challenge model in ferrets. Three groups of six animals were intra-nasally vaccinated with recombinant (r) CDV(5804P)L(CCEGFPC) in the presence or absence of the infection-enhancing lipopeptides Pam3CSK4 or PHCSK4. The recombinant CDV vaccine virus had previously been described to be over-attenuated in ferrets. A group of six animals was mock-vaccinated as control. Six weeks after vaccination all animals were challenged with a lethal dose of rCDV strain Snyder-Hill expressing the red fluorescent protein dTomato.

RESULTS

Unexpectedly, intra-nasal vaccination of ferrets with rCDV(5804P)L(CCEGFPC) in the absence of lipopeptides resulted in good immune responses and protection against lethal challenge infection. However, in animals vaccinated with lipopeptide-adjuvanted virus significantly higher vaccine virus loads were detected in nasopharyngeal lavages and peripheral blood mononuclear cells. In addition, these animals developed significantly higher CDV neutralizing antibody titers compared to animals vaccinated with non-adjuvanted vaccine.

CONCLUSIONS

This study demonstrates that the synthetic cationic lipopeptides Pam3CSK4 and PHCSK4 not only enhance paramyxovirus infection in vitro, but also in vivo. Given the observed enhancement of immunogenicity their potential as adjuvants for other live-attenuated paramyxovirus vaccines should be considered.

Mycobacterial infection in the ferret

Mycobacteriosis is an important disease in the feral ferret (Mustela putorius furo) of New Zealand; elsewhere, reports of tuberculosis in the ferret are sporadic. Genus Mycobacterium consists of aerobic, non-spore-forming, gram-positive, nonmotile bacteria that characteristically feature a cell wall rich in mycolic acids and esters. The epidemiology of mycobacteriosis in the ferrets of New Zealand involves complex interactions between ferrets, possums, and livestock. Investigators have shown that the ferret is highly susceptible only to Mycobacterium bovis infection and is more resistant to infection by other Mycobacterium spp. The principal site of all mycobacterial infection in the ferret is the gastrointestinal tract.

Influenza H5 hemagglutinin DNA primes the antibody response elicited by the live attenuated influenza A/Vietnam/1203/2004 vaccine in ferrets

Priming immunization plays a key role in protecting individuals or populations to influenza viruses that are novel to humans. To identify the most promising vaccine priming strategy, we have evaluated different prime-boost regimens using inactivated, DNA and live attenuated vaccines in ferrets. Live attenuated influenza A/Vietnam/1203/2004 (H5N1) candidate vaccine (LAIV, VN04 ca) primed ferrets efficiently while inactivated H5N1 vaccine could not prime the immune response in seronegative ferrets unless an adjuvant was used. However, the H5 HA DNA vaccine alone was as successful as an adjuvanted inactivated VN04 vaccine in priming the immune response to VN04 ca virus. The serum antibody titers of ferrets primed with H5 HA DNA followed by intranasal vaccination of VN04 ca virus were comparable to that induced by two doses of VN04 ca virus. Both LAIV-LAIV and DNA-LAIV vaccine regimens could induce antibody responses that cross-neutralized antigenically distinct H5N1 virus isolates including A/HongKong/213/2003 (HK03) and prevented nasal infection of HK03 vaccine virus. Thus, H5 HA DNA vaccination may offer an alternative option for pandemic preparedness.

Improvement of H5N1 influenza vaccine viruses: influence of internal gene segments of avian and human origin on production and hemagglutinin content

The H5N1-clade 1 influenza vaccine strain NIBRG-14 produces exceptionally low amounts of antigen, a problem recently encountered also for initial pandemic H1N1-2009 vaccine seeds. Here, we report on a strategy that may contribute to overcome this obstacle. Influenza vaccine viruses usually consist of two segments coding for the antigenic HA and NA proteins of a wild-type strain and the six residual internal gene segments of the vaccine donor strain A/PR/8/34 (PR8). To enhance the antigen yield from H5N1 vaccine virus we generated by reverse genetics a set of PR8-based reassortant viruses expressing the HA and NA segments of the prototypic strain A/Vietnam/1203/2004 and additional replacements of the internal M or PB1 genes of PR8. The reassortants were compared to the parental PR8 and H5N1 viruses in terms of growth in embryonated chicken eggs and the amount of incorporated antigenic HA protein. Compared to NIBRG-14, three out of six viruses displayed an increased replication in embryonated chicken eggs and higher HA content that was also maintained after ether/detergent extraction of virions. Electron microscopic analysis showed that the reassortment hardly affected particle shape and size. Two selected H5N1 reassortant viruses were investigated concerning their pathogenicity in ferrets and found to behave as low pathogenic as the PR8 donor strain. In conclusion, this study shows that replication and antigen content of PR8-derived H5N1 influenza vaccine viruses can be improved by incorporation of heterologous internal gene segments without compromising their attenuated character.

Properly folded bacterially expressed H1N1 hemagglutinin globular head and ectodomain vaccines protect ferrets against H1N1 pandemic influenza virus

BACKGROUND

In the face of impending influenza pandemic, a rapid vaccine production and mass vaccination is the most effective approach to prevent the large scale mortality and morbidity that was associated with the 1918 "Spanish Flu". The traditional process of influenza vaccine production in eggs is time consuming and may not meet the demands of rapid global vaccination required to curtail influenza pandemic.

METHODOLOGY/PRINCIPAL FINDINGS

Recombinant technology can be used to express the hemagglutinin (HA) of the emerging new influenza strain in a variety of systems including mammalian, insect, and bacterial cells. In this study, two forms of HA proteins derived from the currently circulating novel H1N1 A/California/07/2009 virus, HA1 (1-330) and HA (1-480), were expressed and purified from E. coli under controlled redox refolding conditions that favoured proper protein folding. However, only the recombinant HA1 (1-330) protein formed oligomers, including functional trimers that bound receptor and caused agglutination of human red blood cells. These proteins were used to vaccinate ferrets prior to challenge with the A/California/07/2009 virus. Both proteins induced neutralizing antibodies, and reduced viral loads in nasal washes. However, the HA1 (1-330) protein that had higher content of multimeric forms provided better protection from fever and weight loss at a lower vaccine dose compared with HA (1-480). Protein yield for the HA1 (1-330) ranged around 40 mg/Liter, while the HA (1-480) yield was 0.4-0.8 mg/Liter.

CONCLUSIONS/SIGNIFICANCE

This is the first study that describes production in bacterial system of properly folded functional globular HA1 domain trimers, lacking the HA2 transmembrane protein, that elicit potent neutralizing antibody responses following vaccination and protect ferrets from in vivo challenge. The combination of bacterial expression system with established quality control methods could provide a mechanism for rapid large scale production of influenza vaccines in the face of influenza pandemic threat.

Expression of biologically active recombinant ferret (Mustela putorius furo) interleukin-8 from Escherichia coli

The authors expressed recombinant ferret interleukin-8 protein (rfrIL-8) in Escherichia coli as a glutathione-S-transferase fusion protein. Western blot analyses revealed that anti-ovine IL-8 antibody reacted with rfrIL-8 at 10 kDa. To confirm that the rfrIL-8 was biologically active, the authors examined chemotaxis and respiratory burst activity of ferret polymorphonuclear blood cells (PMNs) exposed to rfrIL-8. The rfrIL-8 strongly induced chemotactic and respiratory burst activities in a statistically significant manner as compared with a negative control. Thus, the authors were able to successfully express biologically active rfrIL-8.

A trivalent virus-like particle vaccine elicits protective immune responses against seasonal influenza strains in mice and ferrets

There is need for improved human influenza vaccines, particularly for older adults who are at greatest risk for severe disease, as well as to address the continuous antigenic drift within circulating human subtypes of influenza virus. We have engineered an influenza virus-like particle (VLP) as a new generation vaccine candidate purified from the supernatants of Sf9 insect cells following infection by recombinant baculoviruses to express three influenza virus proteins, hemagglutinin (HA), neuraminidase (NA), and matrix 1 (M1). In this study, a seasonal trivalent VLP vaccine (TVV) formulation, composed of influenza A H1N1 and H3N2 and influenza B VLPs, was evaluated in mice and ferrets for the ability to elicit antigen-specific immune responses. Animals vaccinated with the TVV formulation had hemagglutination-inhibition (HAI) antibody titers against all three homologous influenza virus strains, as well as HAI antibodies against a panel of heterologous influenza viruses. HAI titers elicited by the TVV were statistically similar to HAI titers elicited in animals vaccinated with the corresponding monovalent VLP. Mice vaccinated with the TVV had higher level of influenza specific CD8+ T cell responses than a commercial trivalent inactivated vaccine (TIV). Ferrets vaccinated with the highest dose of the VLP vaccine and then challenged with the homologous H3N2 virus had the lowest titers of replicating virus in nasal washes and showed no signs of disease. Overall, a trivalent VLP vaccine elicits a broad array of immunity and can protect against influenza virus challenge.

Cloning, expression and immunoassay detection of ferret IFN-gamma

Ferrets (Mustela putorius furo) develop symptoms upon influenza infection that resemble those of humans, including sneezing, body temperature variation and weight loss. Highly pathogenic strains of influenza A, such as H5N1, have the capacity to cause severe illness or death in ferrets. The use of ferrets as a model of influenza infection is currently limited by a lack of species-specific immunological reagents. Interferon gamma (IFN-gamma) plays a key role in the development of innate and adaptive immunity and the regulation of Th1-type immune responses. Here we describe the cloning of the full-length cDNA for ferret IFN-gamma. Multiple sequence alignment of the predicted amino acid sequence with those of other species indicates that the predicted ferret protein shares the highest identity with Eurasian badger IFN-gamma. We raised two hybridoma clones expressing monoclonal antibodies against recombinant ferret IFN-gamma capable of detecting IFN-gamma protein derived from mitogen-stimulated ferret PBMCs by immunoblotting, ELISA and ELISPOT assay. Finally, an ELISA utilizing the ferret-specific antibodies detected elevated levels of IFN-gamma in serum samples from H3N2 influenza A-infected ferrets.

Evaluation of replication and pathogenicity of avian influenza a H7 subtype viruses in a mouse model

Avian influenza A H7 subtype viruses pose a significant threat to human health because of their ability to transmit directly from domestic poultry to humans and to cause disease and, sometimes, death. Although it is important to develop vaccines against viruses of this subtype, very limited information is available on the immune response and pathogenesis of H7 viruses in animal models such as mice and ferrets. Ten H7 viruses were selected for possible vaccine development on the basis of their phylogenetic relationships and geographical locations. The virulence of the 10 viruses for mice and the immunogenicity of the viruses in mice and ferrets were evaluated to study the extent of antigenic relatedness and the level of cross-reactivity of antibodies. Most of the viruses showed similar patterns of cross-reactivity with mouse and ferret antisera. The Eurasian viruses elicited broadly cross-reactive antibodies that neutralized viruses from both Eurasian and North American lineages, but the converse was not true. A subset of the viruses was also evaluated for the ability to replicate and cause disease in BALB/c mice following intranasal administration. H7 subtype viruses were able to infect mice without adaptation and manifested different levels of lethality and kinetics of replication. On the basis of phylogenetic data, induction of broadly cross-neutralizing antibodies in mouse and ferret antisera, and their ability to replicate in mice, we have selected A/Netherlands/219/03 (subtype H7N7) and A/chicken/BC/CN-7/04 (subtype H7N3) viruses for vaccine development. The mouse model can be used for the preclinical evaluation of these vaccines against H7 subtype viruses.

Inefficient transmission of H5N1 influenza viruses in a ferret contact model

The abilities to infect and transmit efficiently among humans are essential for a novel influenza A virus to cause a pandemic. To evaluate the pandemic potential of widely disseminated H5N1 influenza viruses, a ferret contact model using experimental groups comprised of one inoculated ferret and two contact ferrets was used to study the transmissibility of four human H5N1 viruses isolated from 2003 to 2006. The effects of viral pathogenicity and receptor binding specificity (affinity to synthetic sialosaccharides with alpha2,3 or alpha2,6 linkages) on transmissibility were assessed. A/Vietnam/1203/04 and A/Vietnam/JP36-2/05 viruses, which possess "avian-like" alpha2,3-linked sialic acid (SA) receptor specificity, caused neurological symptoms and death in ferrets inoculated with 10(3) 50% tissue culture infectious doses. A/Hong Kong/213/03 and A/Turkey/65-596/06 viruses, which show binding affinity for "human-like" alpha2,6-linked SA receptors in addition to their affinity for alpha2,3-linked SA receptors, caused mild clinical symptoms and were not lethal to the ferrets. No transmission of A/Vietnam/1203/04 or A/Turkey/65-596/06 virus was detected. One contact ferret developed neutralizing antibodies to A/Hong Kong/213/03 but did not exhibit any clinical signs or detectable virus shedding. In two groups, one of two naïve contact ferrets had detectable virus after 6 to 8 days when housed together with the A/Vietnam/JP36-2/05 virus-inoculated ferrets. Infected contact ferrets showed severe clinical signs, although little or no virus was detected in nasal washes. This limited virus shedding explained the absence of secondary transmission from the infected contact ferret to the other naïve ferret that were housed together. Our results suggest that despite their receptor binding affinity, circulating H5N1 viruses retain molecular determinants that restrict their spread among mammalian species.

Immunization with reverse-genetics-produced H5N1 influenza vaccine protects ferrets against homologous and heterologous challenge

BACKGROUND

Multiple cases of transmission of avian H5N1 influenza viruses to humans illustrate the urgent need for an efficacious, cross-protective vaccine.

METHODS

Ferrets were immunized with inactivated whole-virus vaccine produced by reverse genetics with the hemagglutinin (HA) and neuraminidase genes of A/HK/213/03 virus. Ferrets received a single dose of vaccine (7 or 15 microg of HA) with aluminum hydroxide adjuvant or 2 doses (7 microg of HA each) without adjuvant and were challenged with 10(6) 50% egg infectious doses of A/HK/213/03, A/HK/156/97, or A/Vietnam/1203/04 virus.

RESULTS

One or 2 doses of vaccine induced a protective antibody response to the vaccine strain. All immunization regimens completely protected ferrets from challenge with homologous wild-type A/HK/213/03 virus: no clinical signs of infection were observed, virus replication was significantly reduced (P<.05) and was restricted to the upper respiratory tract, and spread of virus to the brain was prevented. Importantly, all vaccinated ferrets were protected against lethal challenge with the highly pathogenic strain A/Vietnam/1203/04. The 2-dose schedule induced higher levels of antibodies that were cross-reactive to antigenically distinct H5N1 viruses.

CONCLUSIONS

H5N1 vaccines may stimulate an immune response that is more cross-protective than what might be predicted by in vitro assays and, thus, hold potential for being stockpiled as "initial" pandemic vaccines.

Cross reactive antigenicity in orally vaccinated foxes and raccoon dogs against European Bat Lyssavirus type 1 and 2

For the first time, the effectiveness of oral rabies vaccines against European Bat Lyssaviruses Type 1 (EBLV-1) and Type 2 (EBLV-2) by means of cross-neutralization assays was investigated. Sera from orally vaccinated red foxes (Vulpes vulpes) and raccoon dogs (Nyctereutes procyonoides) with the Street Alabama Dufferin (SAD) B19 and SAD P5/88 live-modified vaccine viruses were used to study the cross reactive antigenicity against CVS-11 (genotype 1), EBLV-1 (genotype 5) and EBLV-2 (genotype 6). For comparison, similar crossneutralization assays with sera from EBLV-1 and EBLV-2 infected ferrets (Mustela putorius furo) and/or foxes were conducted. Sera from animals vaccinated with the two oral rabies vaccines were reactive against CVS-11 (homologous virus), EBLV-1 and EBLV-2 (heterologous virus). There was a positive relationship among the virus neutralising antibody titres (VNA); high VNA titres against CVS-11 also resulted in high VNA titres against each EBLV, whereas in general, the VNA-titres obtained with homologous virus were statistically higher than those with the heterologous virus except for SAD P5/88 vaccinated raccoon dogs. No significant difference was found between EBLV-1 and EBLV-2 VNA titres. A similar trend was observed when the results of the cross-neutralization data of the foxes and ferrets inoculated i.m. with EBLV-1 and/or EBLV-2 was analysed. Based on the similarity of the EBLV-VNA titres obtained in our study questions were raised on whether the genetic distance of genotype 5 & 6 within phylogroup 1 really does reflect their antigenetic characteristics or whether this is a feature of attenuated live vaccine viruses. This broad cross protection, however, demonstrated that the representatives of attenuated SAD strains of oral rabies vaccines currently used in Germany are most likely able to protect the reservoir species, red fox and raccoon dog, against EBLV-1 and EBLV-2 infection.

Survey of zona pellucida antigens for immunocontraception of cats

The purpose of this study was to screen a panel of native zona pellucida (ZP) antigens isolated from five mammalian species for immunocontraceptive activity in the cat (Felis catus). Native soluble-isolated ZP (SIZP) was prepared from the ovaries of cows (bZP), cats (fZP), ferrets (feZP), dogs (cZP), and mink (mZP). Vaccines were constructed using SIZP from each of the above species encapsulated in liposomes suspended in saline and emulsified with Freund's complete adjuvant (SpayVac). Female cats were immunized once (n = 3 cats per group). Serum was collected for determination of antibody titers against SIZP and for binding of antibodies to feline ovaries. All cats responded to immunization by producing anti-SIZP antibodies. The most immunogenic SIZP in cats was from mink, followed by feZP, cZP, and fZP in descending order. Antibodies had low reactivity for fZP, and no reactivity against feline ovaries was detected by immunohistochemistry. A breeding trial was commenced 20 weeks after immunization. All cats became pregnant, averaging 4.1 +/- 0.7 viable kittens per litter. We have previously shown that porcine SIZP is not an effective antigen for immunocontraception of cats. In this study, SIZP from five other mammalian species were immunogenic in the cat, but ZP antibodies failed to bind to fZP in situ, and fertility was not impeded.

Strong local and systemic protective immunity induced in the ferret model by an intranasal virosome-formulated influenza subunit vaccine

The proliferation of influenza viruses causes costly, recurrent, annual epidemics. Current vaccines, mainly administered parenterally, have been shown to be suboptimal in terms of efficacy, particularly where local IgA responses are concerned. Recent investigations of virosomes as delivery systems for viral HA and NA antigens have demonstrated an improved immune response. This paper investigates the efficacy of a novel virosome-based intranasal influenza vaccine by its ability to reduce disease symptoms and its effect on viral shedding in nasal secretions of immunised ferrets. The use of ferrets in the study of influenza vaccines is based on the good comparability between ferret and human response to the disease. Intranasal, as opposed to parenteral, administration of a trivalent virosome-based subunit vaccine adjuvanted with HLT provides an almost total prevention of virus shedding combined with a high level of immunological protection against homologous virus challenge. The ease of application of an intranasal vaccine may have positive repercussions in the adoption of influenza vaccinations, particularly in 'at-risk' groups.

Generation and characterization of a cold-adapted influenza A H9N2 reassortant as a live pandemic influenza virus vaccine candidate

H9N2 subtype influenza A viruses have been identified in avian species worldwide and were isolated from humans in 1999, raising concerns about their pandemic potential and prompting the development of candidate vaccines to protect humans against this subtype of influenza A virus. Reassortant H1N1 and H3N2 human influenza A viruses with the internal genes of the influenza A/Ann Arbor/6/60 (H2N2) (AA) cold-adapted (ca) virus have proven to be attenuated and safe as live virus vaccines in humans. Using classical genetic reassortment, we generated a reassortant virus (G9/AA ca) that contains the hemagglutinin and neuraminidase genes from influenza A/chicken/Hong Kong/G9/97 (H9N2) (G9) and six internal gene segments from the AA ca virus. When administered intranasally, the reassortant virus was immunogenic and protected mice from subsequent challenge with wild-type H9N2 viruses, although it was restricted in replication in the respiratory tract of mice. The G9/AA ca virus bears properties that are desirable in a vaccine for humans and is available for clinical evaluation and use, should the need arise.

Genetic and antigenic analysis of the first A/New Caledonia/20/99-like H1N1 influenza isolates reported in the Americas

From February through May of 1999, 13 cases of Influenza A virus (FLUAV), type H1N1 were reported at a Department of Defense influenza surveillance sentinel site in Lima, Peru. Genetic and antigenic analysis by hemagglutination inhibition and direct nucleotide sequencing of the HA1 region of the hemagglutinin gene were performed on two isolates, A/Peru/1641/99 and A/Peru/1798/99. Both isolates were distinct from the Bayern/7/95-like viruses circulating in the Americas and closely related to a Beijing/262/95-like variant, A/New Caledonia/20/99. With the exception of travel-related cases, the detection of these isolates represents the first appearance of New Caledonia/20/99-like viruses in the Americas. Since the characterization of these Peru isolates, a number of New Caledonia/20/99-like viruses have been reported worldwide. For the 2000/01 and 2001/02 influenza seasons, the World Health Organization (WHO) has recommended the inclusion of A/New Caledonia/20/99 as the H1N1 vaccine component for both the southern and northern hemispheres.

Cats differ from mink and ferrets in their response to commercial vaccines: a histologic comparison of early vaccine reactions

Early histologic changes in lesions at vaccine sites were compared in cats, mink, and ferrets. Twenty-four 4-month-old cats, 20 4-month-old mink, and 20 12-month-old ferrets were vaccinated with three rabies virus vaccines, two feline leukemia virus vaccines, alum adjuvant, and saline. Injection sites were excised at selected time points up to 21 days postvaccination. Histologic examination of the tissue revealed significant differences among the cats, mink, and ferrets in the local response to the commercial vaccines. When compared with ferrets and mink, cats had more lymphocytes in response to all three rabies vaccines. Production of fibroblasts, collagen, and macrophages differed among the three killed aluminum-adjuvanted vaccines in cats but did not differ significantly in mink or ferrets. Cats produced fewer binucleate cells than did mink or ferrets in response to the two adjuvanted leukemia virus vaccines. Differences seen in early tissue response of cats to commercial vaccines may be related to the increased predisposition of cats to vaccine-associated sarcomas.

Pathogenesis of two strains of lion (Panthera leo) morbillivirus in ferrets (Mustela putorius furo)

Canine distemper virus (CDV) was previously considered to have a host range restricted to the canid family. In 1994, the virus was associated with sporadic outbreaks of distemper in captive felids. However, after severe mortality occurred in the Serengeti lions (Panthera leo), attention became focused on the pathogenesis of the virus and a concerted effort was made to identify the virus as CDV or a closely related feline morbillivirus. The present study was designed to explore the susceptibility of ferrets to challenge with two morbilliviruses isolated from lions and the protective effects of a modified-live mink distemper vaccine. Because mortality in ferrets infected with pathogenic CDV approaches 100%, the ferret was selected as a test animal. Two strains of lion morbillivirus were used as a challenge, A92-27/20 (California lion isolate) and A94-11/13 (Serengeti lion isolate). The two strains of lion morbillivirus were antigenically related to CDV (Rockborn strain), and ferrets were susceptible to both of the viruses when inoculated intraperitoneally. The inoculated ferrets were anorectic at 5-6 days postinoculation (PI), exhibited oculonasal discharge at 9-12 days PI, and became moribund at 12-22 days PI. Severe bilateral conjunctivitis was the typical clinical sign. Inclusion bodies characteristic of morbillivirus (eosinophilic, intranuclear, and intracytoplasmic) were distributed in many epithelial cells, including those of the skin, conjunctiva, gallbladder, liver, pancreas, stomach, trachea, lung, urinary bladder, and kidney. Virus was reisolated from selected lung tissues collected at necropsy and identified by CDV-specific immunofluorescence. Ferrets vaccinated with the mink distemper vaccine (Onderstepoort strain) were protected from challenge with the two lion strains, adding further support to the premise that the viruses are closely related to CDV.

In vitro control of Mycobacterium bovis by macrophages

Mycobacterium bovis is frequently seen inside macrophages in vivo. The outcome of M. bovis infection depends on T cell interactions with macrophages, however mycobacteria are thought to be relatively resistant to macrophage killing. Little is known about the immunological mechanisms which control intracellular growth of M. bovis, and in the absence of T cell help the organism is capable of intracellular survival and replication. We have investigated the role of macrophages in controlling growth of virulent M. bovis or M. bovis BCG in vitro. At a multiplicity of infection of 5:1, macrophages from a range of animal species including cattle, deer, possums, ferrets and mice restricted growth of BCG while M. bovis grew progressively. Inter-species variation in controlling growth of M. bovis by alveolar macrophages was observed. Pre-treatment of macrophages with interferon-gamma and lipopolysaccharide inhibited intracellular growth of M. bovis. Addition of freshly recruited macrophages further inhibited M. bovis, and intracellular growth was arrested by activated fresh macrophages. Our observations suggest that naïve macrophages can prevent BCG growth, while T cell activation in conjunction with freshly recruited macrophages is required for preventing growth of M. bovis.

Serologic evaluation, efficacy, and safety of a commerical modified-live canine distemper vaccine in domestic ferrets

OBJECTIVE

To determine efficacy and safety of a commercial modified-live canine distemper virus (CDV) vaccine used for prophylaxis in domestic ferrets.

ANIMALS

Sixteen 16-week-old neutered male ferrets.

PROCEDURES

Equal groups of ferrets were inoculated subcutaneously at 16 and 20 weeks of age with saline (0.9% NaCl) solution or a vaccine derived from the Onderstepoort CDV strain and attenuated in a primate cell line. Live virulent CDV was administered to all ferrets intranasally and orally 3 weeks after the second inoculation. Clinical signs and body weights were monitored regularly during the study. Blood samples for serologic examination were drawn prior to each inoculation, before challenge exposure, and 10, 15, and 21 days after exposure. Blood samples for reverse transcriptase polymerase chain reaction (RT-PCR) were obtained 5 days after the first vaccination, and 5, 10, 15, and 21 days after challenge exposure.

RESULTS

After challenge exposure, control ferrets had significantly more clinical signs and weight loss, compared with vaccinates. All vaccinated ferrets survived, whereas all control ferrets died. The RT-PCR assay was successful in detecting CDV in blood and fresh or formalin-fixed tissues from infected ferrets.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings suggest that the vaccine when given SC to domestic ferrets as directed is safe and protective against challenge exposure with virulent CDV. The RT-PCR assay may simplify detection of CDV in fresh and fixed tissues.

Oral infection of ferrets with virulent Mycobacterium bovis or Mycobacterium avium: susceptibility, pathogenesis and immune response

Ferrets are important wildlife reservoirs of tuberculosis in New Zealand, where they acquire infection primarily through scavenging infected carrion. In the present study, groups of laboratory-reared ferrets were infected orally with 5 x 10(6)colony-forming units of Mycobacterium bovis or Mycobacterium avium. Body weight and tuberculin-specific immune reactivity were monitored at intervals (pre-infection, and 4 and 20 weeks post-infection) and animals were killed at 20 weeks post-infection for post-mortem, histopathological and bacteriological examinations. Weight loss was significantly greater in M. bovis -infected than in M. avium -infected ferrets. M. bovis, unlike M. avium, sometimes produced gross necrotic lesions in the mesenteric lymph nodes. M. bovis invariably produced microscopical foci of mycobacterial infection or tissue necrosis typical of tuberculosis, whereas M. avium did so in only one of nine animals. Mycobacteria were recovered from the lymphatic tissues of all M. bovis -infected ferrets but from only five of nine M. avium -infected animals; and the mean bacterial burdens of the lymph nodes of the head and intestinal regions were > 10-fold and > 100-fold greater, respectively, for M. bovis -infected than for M. avium -infected animals. M. bovis, unlike M. avium, evoked tuberculin-specific peripheral blood lymphocyte reactivity and serum antibody responses.

Effect of field capture on the measurement of cellular immune responses in wild ferrets (Mustela furo), vectors of bovine tuberculosis in New Zealand

Ferrets are recognised as significant wildlife vectors of bovine tuberculosis (Tb) in New Zealand. Disease management strategies, such as the development of a protective wildlife vaccine, could be assisted by the ability to measure pertinent cellular immune responses among wild animals. In the present study, we investigated whether it is possible to measure in vitro lymphocyte reactivity in wild-caught ferrets, and also determined levels of physiological stress in these animals, and we compared these responses to those observed in laboratory-maintained domesticated ferrets. Over a 12-month period, 80 ferrets were live-captured from a Tb-endemic region (Otago, southern New Zealand); cardiac blood was withdrawn on-site, and mononuclear cell cultures were successfully established from 75 of these animals. Lymphocyte transformation (LT) responses to T cell and T/B cell mitogens (Concanavalin A [Con A] and pokeweed mitogen) were measured via uridine incorporation assay. The magnitude of these responses did not differ significantly between animals that had been captured in wire-framed cage traps and those captured using soft-jawed leg-hold traps. Levels of serum cortisol and glucose (as indicators of physiological and oxidative stress, respectively) were highest in animals captured using leg-hold traps. In comparison to domesticated ferrets, wild-caught ferrets had lower overall LT responses to Con A, but significantly higher levels of serum cortisol. Finally, 10/80 animals captured from the wild were severely diseased (Tb+), as evidenced by gross tuberculous lesions at autopsy. Successful mononuclear cell cultures were established from nine of these animals; LT responses to Con A were significantly lower in Tb+ ferrets than in either wild-caught/non-diseased (Tb-) or domesticated ferrets. These results demonstrate that it is possible to measure cellular immune responses from the blood of wild-caught ferrets, but that field capture and disease status may have detrimental effects on in vitro T cell function, possibly due to the influence of physiological stress.