Virus Infection In Ferrets Research Articles

Concurrent 2009 Pandemic Influenza A (H1N1) Virus Infection in Ferrets and in a Community in Pennsylvania

We report a fall 2010 cluster of pandemic influenza A/H1N1 (pH1N1) infections in pet ferrets in Lehigh Valley region of Pennsylvania. The ferrets were associated with one pet shop. The influenza cluster occurred during a period when the existing human surveillance systems had identified little to no pH1N1 in humans in the Lehigh Valley, and there were no routine influenza surveillance systems for exotic pets. The index case was a 2.5-month-old neutered male ferret that was presented to a veterinary clinic with severe influenza-like illness (ILI). In response to laboratory notification of a positive influenza test result, and upon request from the Pennsylvania Department of Health (PADOH), the Pennsylvania Department of Agriculture (PDA) conducted an investigation to identify other ill ferrets and to identify the source and extent of infection. PDA notified the PADOH of the pH1N1 infection in the ferrets, leading to enhanced human surveillance and the detection of pH1N1 human infections in the surrounding community. Five additional ferrets with ILI linked to the pet shop were identified. This simultaneous outbreak of ferret and human pH1N1 demonstrates the important link between animal health and public health and highlights the potential use of veterinary clinics for sentinel surveillance of diseases shared between animals and humans.

Seasonal Trivalent Inactivated Influenza Vaccine Protects against 1918 Spanish Influenza Virus Infection in Ferrets

The influenza virus H1N1 pandemic of 1918 was one of the worst medical catastrophes in human history. Recent studies have demonstrated that the hemagglutinin (HA) protein of the 1918 virus and 2009 H1N1 pandemic virus [A(H1N1)pdm09], the latter now a component of the seasonal trivalent inactivated influenza vaccine (TIV), share cross-reactive antigenic determinants. In this study, we demonstrate that immunization with the 2010-2011 seasonal TIV induces neutralizing antibodies that cross-react with the reconstructed 1918 pandemic virus in ferrets. TIV-immunized ferrets subsequently challenged with the 1918 virus displayed significant reductions in fever, weight loss, and virus shedding compared to these parameters in nonimmune control ferrets. Seasonal TIV was also effective in protecting against the lung infection and severe lung pathology associated with 1918 virus infection. Our data demonstrate that prior immunization with contemporary TIV provides cross-protection against the 1918 virus in ferrets. These findings suggest that exposure to A(H1N1)pdm09 through immunization may provide protection against the reconstructed 1918 virus which, as a select agent, is considered to pose both biosafety and biosecurity threats.

Neuropathology of H5N1 virus infection in ferrets

Highly pathogenic H5N1 virus remains a potential threat to humans. Over 289 fatalities have been reported in WHO confirmed human cases since 2003, and lack of effective vaccines and early treatments contribute to increasing numbers of cases and fatalities. H5N1 encephalitis is a recognized cause of death in Vietnamese cases, and brain pathology is described in other human cases and naturally infected animals. However, neither pathogenesis of H5N1 viral infection in human brain nor post-infection effects in survivors have been fully investigated. We report the brain pathology in a ferret model for active infection and 18-day survival stages. This model closely resembles the infection pattern and progression in human cases of influenza A, and our report is the first description of brain pathology for longer term (18-day) survival in ferrets. We analyzed viral replication, type and severity of meningoencephalitis, infected cell types, and cellular responses to infection. We found viral replication to very high titers in ferret brain, closely correlating with severity of meningoencephalitis. Viral antigens were detected predominantly in neurons, correlating with inflammatory lesions, and less frequently in astrocytes and ependymal cells during active infection. Mononuclear cell infiltrates were observed in early stages predominantly in cerebral cortex, brainstem, and leptomeninges, and less commonly in cerebellum and other areas. Astrogliosis was mild at day 4 post-infection, but robust by day 18. Early and continuous treatment with an antiviral agent (peramivir) inhibited virus production to non-detectable levels, reduced severity of brain injury, and promoted higher survival rates.

Efficacy of Single Intravenous Injection of Peramivir against Influenza B Virus Infection in Ferrets and Cynomolgus Macaques

We evaluated the efficacy of a single intravenous dose peramivir for treatment of influenza B virus infection in ferrets and cynomolgus macaques in the present study. A single dose of peramivir (60 mg/kg of body weight) given to ferrets on 1 day postinfection with influenza B virus significantly reduced median area under the curve (AUC) virus titers (peramivir, 8.3 log(10) 50% tissue culture infective doses [TCID(50)s] · day/ml; control, 10.7 log(10) TCID(50)s · day/ml; P < 0.0001). Furthermore, nasal virus titers on day 2 postinfection in ferrets receiving a single injection of peramivir (30 mg/kg) and AUCs of the body temperature increase in ferrets receiving a single injection of peramivir (30 and 60 mg/kg) were lower than those in ferrets administered oral oseltamivir phosphate (30 and 60 mg/kg/day twice daily for 3 days). In macaques infected with influenza B virus, viral titers in the nasal swab fluid on days 2 and 3 postinfection and body temperature after a single injection of peramivir (30 mg/kg) were lower than those after oral administration of oseltamivir phosphate (30 mg/kg/day for 5 days). The two animal models used in the present study demonstrated that inhibition of viral replication at the early time point after infection was critical in reduction of AUCs of virus titers and interleukin-6 production, resulting in amelioration of symptoms. Our results shown in animal models suggest that the early treatment with a single intravenous injection of peramivir is clinically recommended to reduce symptoms effectively in influenza B virus infection.

Pathogenesis of Influenza A/H5N1 Virus Infection in Ferrets Differs between Intranasal and Intratracheal Routes of Inoculation

Most patients infected with highly pathogenic avian influenza A/H5N1 virus develop severe pneumonia resulting in acute respiratory distress syndrome, with extrarespiratory disease as an uncommon complication. Intranasal inoculation of ferrets with influenza A/H5N1 virus causes lesions in both the respiratory tract and extrarespiratory organs (primarily brain). However, the route of spread to extrarespiratory organs and the relative contribution of extrarespiratory disease to pathogenicity are largely unknown. In the present study, we characterized lesions in the respiratory tract and central nervous system (CNS) of ferrets (n = 8) inoculated intranasally with influenza virus A/Indonesia/5/2005 (H5N1). By 7 days after inoculation, only 3 of 8 ferrets had a mild or moderate bronchointerstitial pneumonia. In contrast, all 8 ferrets had moderate or severe CNS lesions, characterized by meningoencephalitis, choroiditis, and ependymitis, and centered on tissues adjoining the cerebrospinal fluid. These findings indicate that influenza A/H5N1 virus spread directly from nasal cavity to brain, and that CNS lesions contributed more than pulmonary lesions to the pathogenicity of influenza A/H5N1 virus infection in ferrets. In comparison, intratracheal inoculation of ferrets with the same virus reproducibly caused severe bronchointerstitial pneumonia. The method of virus inoculation requires careful consideration in the design of ferret experiments as a model for influenza A/H5N1 in humans.

A new intranasal influenza vaccine based on a novel polycationic lipid-ceramide carbamoyl-spermine (CCS). II. Studies in mice and ferrets and mechanism of adjuvanticity

We recently showed that lipid assemblies comprised of a novel polycationic sphingolipid (ceramide carbamoyl-spermine, CCS) are an effective adjuvant/carrier when complexed with cholesterol (CCS/C) for influenza and other vaccines administered parenterally and intranasally (i.n.) in mice. Here we expand these studies to ferrets, an established model of influenza infection. We also address the question of why the CCS/C-based liposomal vaccine (also known as VaxiSome™) in mice is superior to vaccines based on liposomes of other lipid compositions (neutral, anionic or cationic). Ferrets immunized i.n. with CCS/C-influenza vaccine produced significantly higher hemagglutination inhibition (HI) antibody titers compared to ferrets immunized intramuscularly with the unadjuvanted influenza vaccine, indicating that the CCS/C-based vaccine is very immunogenic. Furthermore, the i.n. adjuvanted vaccine was shown to significantly reduce the severity of influenza virus infection in ferrets following homologous viral challenge as determined by weight loss, temperature rise and viral titer. No adverse reactions were observed. Pharmacokinetic and biodistribution studies following i.n. administration in mice of CCS/C-based vaccine showed that both the lipids and antigens are retained in the nose and lung for at least 24 h, and it appears that this retention correlates with the superior immunogenicity elicited by the adjuvanted vaccine formulation. The CCS lipid also increases production of cytokines (mainly IFN gamma, IL-2 and IL-12) and co-stimulatory molecules’ expression, which might further explain the robust adjuvantation of this liposome-based vaccine.

Vaccination against Seasonal Influenza A/H3N2 Virus Reduces the Induction of Heterosubtypic Immunity against Influenza A/H5N1 Virus Infection in Ferrets

Infection with seasonal influenza viruses induces a certain extent of protective immunity against potentially pandemic viruses of novel subtypes, also known as heterosubtypic immunity. Here we demonstrate that infection with a recent influenza A/H3N2 virus strain induces robust protection in ferrets against infection with a highly pathogenic avian influenza virus of the H5N1 subtype. Prior H3N2 virus infection reduced H5N1 virus replication in the upper respiratory tract, as well as clinical signs, mortality, and histopathological changes associated with virus replication in the brain. This protective immunity correlated with the induction of T cells that cross-reacted with H5N1 viral antigen. We also demonstrated that prior vaccination against influenza A/H3N2 virus reduced the induction of heterosubtypic immunity otherwise induced by infection with the influenza A/H3N2 virus. The implications of these findings are discussed in the context of vaccination strategies and vaccine development aiming at the induction of immunity to pandemic influenza.

Efficacy of vaccination with different combinations of MF59-adjuvanted and nonadjuvanted seasonal and pandemic influenza vaccines against pandemic H1N1 (2009) influenza virus infection in ferrets.

Serum antibodies induced by seasonal influenza or seasonal influenza vaccination exhibit limited or no cross-reactivity against the 2009 pandemic swine-origin influenza virus of the H1N1 subtype (pH1N1). Ferrets immunized once or twice with MF59-adjuvanted seasonal influenza vaccine exhibited significantly reduced lung virus titers but no substantial clinical protection against pH1N1-associated disease. However, priming with MF59-adjuvanted seasonal influenza vaccine significantly increased the efficacy of a pandemic MF59-adjuvanted influenza vaccine against pH1N1 challenge. Elucidating the mechanism involved in this priming principle will contribute to our understanding of vaccine- and infection-induced correlates of protection. Furthermore, a practical consequence of these findings is that during an emerging pandemic, the implementation of a priming strategy with an available adjuvanted seasonal vaccine to precede the eventual pandemic vaccination campaign may be useful and life-saving.

Recombinant Soluble, Multimeric HA and NA Exhibit Distinctive Types of Protection against Pandemic Swine-Origin 2009 A(H1N1) Influenza Virus Infection in Ferrets

The emergence and subsequent swift and global spread of the swine-origin influenza virus A(H1N1) in 2009 once again emphasizes the strong need for effective vaccines that can be developed rapidly and applied safely. With this aim, we produced soluble, multimeric forms of the 2009 A(H1N1) HA (sHA(3)) and NA (sNA(4)) surface glycoproteins using a virus-free mammalian expression system and evaluated their efficacy as vaccines in ferrets. Immunization twice with 3.75-microg doses of these antigens elicited strong antibody responses, which were adjuvant dependent. Interestingly, coadministration of both antigens strongly enhanced the HA-specific but not the NA-specific responses. Distinct patterns of protection were observed upon challenge inoculation with the homologous H1N1 virus. Whereas vaccination with sHA(3) dramatically reduced virus replication (e.g., by lowering pulmonary titers by about 5 log(10) units), immunization with sNA(4) markedly decreased the clinical effects of infection, such as body weight loss and lung pathology. Clearly, optimal protection was achieved by the combination of the two antigens. Our observations demonstrate the great vaccine potential of multimeric HA and NA ectodomains, as these can be easily, rapidly, flexibly, and safely produced in high quantities. In particular, our study underscores the underrated importance of NA in influenza vaccination, which we found to profoundly and specifically contribute to protection by HA. Its inclusion in a vaccine is likely to reduce the HA dose required and to broaden the protective immunity.

Gene Expression Analysis of Host Innate Immune Responses during Lethal H5N1 Infection in Ferrets

How viral and host factors contribute to the severe pathogenicity of the H5N1 subtype of avian influenza virus infection in humans is poorly understood. We identified three clusters of differentially expressed innate immune response genes in lungs from H5N1 (A/Vietnam/1203/04) influenza virus-infected ferrets by oligonucleotide microarray analysis. Interferon response genes were more strongly expressed in H5N1-infected ferret lungs than in lungs from ferrets infected with the less pathogenic H3N2 subtype. In particular, robust CXCL10 gene expression in H5N1-infected ferrets led us to test the pathogenic role of signaling via CXCL10's cognate receptor, CXCR3, during H5N1 influenza virus infection. Treatment of H5N1-infected ferrets with the drug AMG487, a CXCR3 antagonist, resulted in a reduction of symptom severity and delayed mortality compared to vehicle treatment. We contend that unregulated host interferon responses are at least partially responsible for the severity of H5N1 infection and provide evidence that attenuating the CXCR3 signaling pathway improves the clinical course of H5N1 infection in ferrets.

An unusual presentation of canine distemper virus infection in a domestic ferret (Mustela putorius furo)

A 4.5-year-old, male castrated ferret was examined with a 27-day history of severe pruritus, generalized erythema and scaling. Skin scrapings and a trichogram were negative for mites and dermatophyte organisms. A fungal culture of hair samples was negative. The ferret was treated presumptively for scabies and secondary bacterial and yeast infection with selamectin, enrofloxacin, fluconazole, diphenhydramine and a miconazole-chlorhexidine shampoo. The ferret showed mild improvement in clinical signs over the subsequent 3 weeks, but was inappetent and required supportive feeding and subcutaneous fluids by the owner. The ferret was then examined on an emergency basis at the end of 3 weeks (53 days following initial signs of illness) for severe blood loss from a haematoma over the interscapular region, hypotension and shock. The owners elected euthanasia due to a poor prognosis and deteriorating condition. On post-mortem examination intraepithelial canine distemper viral inclusions were identified systemically, and abundant canine distemper virus antigen was identified with immunohistochemical staining. It is important to note the prolonged course of disease along with the absence of respiratory and neurological signs because this differs from the classic presentation of canine distemper virus infection in ferrets. Canine distemper virus should remain a clinical suspicion for ferrets with skin lesions that do not respond to appropriate therapy, even in animals that were previously vaccinated.

Screening monoclonal antibodies for cross-reactivity in the ferret model of influenza infection

Influenza virus infections carry a high public health cost, and pandemics are potentially catastrophic. Though the ferret is generally regarded as the best model for human influenza, few reagents are available for the analysis of cellular immunity. We thus screened monoclonal antibodies (mAbs) made for identifying immune cells in other species to see if any were cross-reactive. Flow cytometric analysis of lymphocytes isolated from blood, spleen, and lung of normal and virus-infected ferrets indicated that several mouse mAbs bound to the corresponding antigens in ferrets. Typing bronchoalveolar lavage populations from pneumonic ferrets with mAb to human CD8 showed the massive CD8+ T cell enrichment characteristic of this infection in mice. The availability of this, and several other mAbs that showed cross-reactivity, should allow us to begin the dissection of cell-mediated immunity in the ferret, which, at least from these early results, looks similar to the situation in mice.

Disease Manifestations of Canine Distemper Virus Infection in Ferrets Are Modulated by Vitamin A Status ,

The measles virus (MV) causes half a million childhood deaths annually. Vitamin A supplements significantly reduce measles-associated mortality and morbidity. The mechanisms whereby vitamin A acts against MV are not understood and currently there is no satisfactory small animal model for MV infection. We report on the development of a ferret model to study antiviral activity of vitamin A against canine distemper virus (CDV). CDV is closely related to MV at the molecular level and distemper in ferrets mimics measles in humans. We infected vitamin A-replete (control) and vitamin A-depleted ferrets with CDV and assessed the ability of high-dose vitamin A supplements to influence CDV disease. In control ferrets, CDV infection caused fever, rash, conjunctivitis, cough, coryza, and diarrhea. In contrast, control ferrets that were given 30 mg of vitamin A did not develop typical distemper after infection and exhibited only a mild rash. The supplement did not negatively affect ferret health and resulted in a 100% increase in serum and liver vitamin A concentrations. We also found that profound vitamin A deficiency is inducible in ferrets and can be rapidly reversed upon high-dose vitamin A supplementation. Vitamin A deficiency caused anorexia, diarrhea, cataracts, behavioral abnormalities, and ultimately death, with or without CDV infection. All ferrets that received vitamin A supplements, however, recovered uneventfully from CDV infection. These results replicate many aspects of the observations of vitamin A therapy in humans with measles and suggest that CDV infection in ferrets is an appropriate model for the study of the antiviral mechanism of vitamin A.

Bacterial Sinusitis and Otitis Media following Influenza Virus Infection in Ferrets

Streptococcus pneumoniae is the leading cause of otitis media, sinusitis, and pneumonia. Many of these infections result from antecedent influenza virus infections. In this study we sought to determine whether the frequency and character of secondary pneumococcal infections differed depending on the strain of influenza virus that preceded bacterial challenge. In young ferrets infected with influenza virus and then challenged with pneumococcus, influenza viruses of any subtype increased bacterial colonization of the nasopharynx. Nine out of 10 ferrets infected with H3N2 subtype influenza A viruses developed either sinusitis or otitis media, while only 1 out of 11 ferrets infected with either an H1N1 influenza A virus or an influenza B virus did so. These data may partially explain why bacterial complication rates are higher during seasons when H3N2 viruses predominate. This animal model will be useful for further study of the mechanisms that underlie viral-bacterial synergism.

Nucleotide sequence and polymerase chain reaction/restriction fragment length polymorphism analyses of Aleutian disease virus in ferrets in Japan.

Two ferrets with spontaneous Aleutian disease (AD) were found in Japan. The diagnosis was verified by polymerase chain reaction (PCR) amplification of part of the capsid gene specific to AD virus (ADV). The nucleotide sequences (365 bp in length) of the amplified fragments from the 2 ferrets differed by a single nucleotide, producing an amino acid alteration. Compared with other types of ADV, these isolates had 96% sequence similarity to a published ferret ADV (FADV) in contrast to <91% homology to various types of mink ADV (MADV). The phylogenetic tree of ADVs indicates that these 2 isolates and the published FADV belong to the same genetic group and definitely are divergent from MADVs. The predicted amino acid sequence of the hypervariable segment in the capsid gene was conserved among the 3 types of FADV. These results indicated that the 2 isolates found in Japan were new DNA types of FADV and could have been derived from FADV(s). A restriction fragment length polymorphism (RFLP) method to distinguish the ferret types of ADV from the mink types of ADV was developed on the basis of differences in their nucleotide sequences. Digestion of the PCR products with Afal or ScaI provided different cleavage patterns for FADV and MADV. This PCR/RFLP analysis of the ADV capsid gene will be a valuable asset for diagnosis of this virus infection in ferrets.

Animals as sentinels of human health hazards of environmental chemicals.

A workshop titled "Using Sentinel Species Data to Address the Potential Human Health Effects of Chemicals in the Environment," sponsored by the U.S. Army Center for Environmental Health Research, the National Center for Environmental Assessment of the EPA, and the Agency for Toxic Substances and Disease Registry, was held to consider the use of sentinel and surrogate animal species data for evaluating the potential human health effects of chemicals in the environment. The workshop took a broad view of the sentinel species concept, and included mammalian and nonmammalian species, companion animals, food animals, fish, amphibians, and other wildlife. Sentinel species data included observations of wild animals in field situations as well as experimental animal data. Workshop participants identified potential applications for sentinel species data derived from monitoring programs or serendipitous observations and explored the potential use of such information in human health hazard and risk assessments and for evaluating causes or mechanisms of effect. Although it is unlikely that sentinel species data will be used as the sole determinative factor in evaluating human health concerns, such data can be useful as for additional weight of evidence in a risk assessment, for providing early warning of situations requiring further study, or for monitoring the course of remedial activities. Attention was given to the factors impeding the application of sentinel species approaches and their acceptance in the scientific and regulatory communities. Workshop participants identified a number of critical research needs and opportunities for interagency collaboration that could help advance the use of sentinel species approaches.

In Vivo Localization of Staphylococcus aureus in Nasal Tissues of Healthy and Influenza A Virus-Infected Ferrets

An in vivo ferret model was used to study the association of Staphylococcus aureus with specific tissues of the nasal cavity in both control and influenza A virus-infected animals. Ferrets were inoculated intranasally with various doses of influenza A3/Hong Kong/1/68 virus. On Days 2, 5, 9 and 14, four or five virus-inoculated and two uninoculated controls were challenged intranasally with a 1-ml volume of radiolabeled S. aureus (3 mg dry wt), a clinical isolate of low passage history. Ferrets were allowed to clear the staphylococci in vivo for 60 to 90 min before sacrifice. The animals were anesthetized, exsanguinated, and decapitated, and the lower jaw was removed. The nasal fossae were exposed by dissection and turbinates from the left nasal fossa were used for virus isolation. The median septum and tissues from the right nasal fossa, which included vestibule and anterior and posterior turbinates, were harvested and processed for radioassay. The percentage of recoverable staphylococci from virus-infected ferrets (Days 2 and 5) was greater than or equal to 10-fold higher compared with controls and animals infected with suboptimal doses of virus; greater than or equal to 76% of the recoverable staphylococci, whether from controls or virus-infected animals, was associated with the anterior turbinates. Histologic examination of the anterior turbinates from virus-infected ferrets, particularly on Days 2 and 5 postexposure to virus, showed that the staphylococci were adhering to desquamating respiratory epithelial cells. In contrast, the anterior turbinates from control ferrets uninoculated with virus and posterior turbinates from both control and virus-infected animals showed no evidence of bacteria adhering to host cells; instead, the staphylococci were found in association with the mucus gel layer of respiratory mucosa. Examination of vestibular tissue showed staphylococci in association with cells of the stratum granulosum in both virus-infected and control animals. Results of this study suggest that the early events of S. aureus interaction with different sites of ferret nasal tissues are effected by different mechanisms, and that the interaction is significantly enhanced by virus-infection.

Bacterial adherence to the upper respiratory tract of ferrets infected with influenza A virus.

A ferret model was used to study bacterial adherence in animals with influenza. Ferrets were inoculated intranasally with influenza A3/Hong Kong/1/68 virus. Antiviral serum antibodies were apparent by Day 5. On Days 3, 5, 7, 9, and 11, three virus-inoculated and two uninoculated controls were anesthetized, exsanguinated, and decapitated, and the lower jaw was removed. Each animal was inoculated intranasally with a 1-ml suspension containing 20 mg (dry wt) of either 3H-labeled Staphylococcus aureus or 3H-labeled group B Streptococcus type Ia and incubated for 45 min at ambient temperature. In animals challenged with staphylococci, 80% of the original inoculum remained free in suspension; of the remaining 20%, the distribution in the upper respiratory tracts of virus-infected and control animals was significantly different. Of the staphylococci remaining in the nasopharynx of control animals, 74% was present in mucinous plugs, 11% was bound to host cells present in washes of the nasal cavity, and 15% was released by protease treatment of the nasopharynx. Of the staphylococci remaining in the upper respiratory tract of virus-infected ferrets, 36% was recovered in plugs, 24% was bound to cells in nasal washes, and 40% was released by enzyme treatment. Overall, adherence-positive staphylococci represented 64% of recoverable bacteria in virus-infected ferrets versus 26% in controls. Adherence was increased twofold (Days 5 and 7) to threefold (Days 3, 9, and 11) in virus-infected ferrets compared to uninfected controls. In contrast, only 7% of the original streptococcal inoculum was recovered from virus-infected and uninfected control animals and virus infection did not enhance streptococcal adherence except for an approximately threefold increase that was seen on Day 11.

Presence of oligoclonal immunoglobulin G bands and lack of matrix protein antibodies in cerebrospinal fluids and sera of ferrets with measles virus encephalitis

Young adult ferrets were immunized with measles vaccine and 5 to 6 weeks later inoculated intracerebrally with Vero cells persistently infected with cell-associated strain D.R. of measles virus isolated from a patient with subacute sclerosing panencephalitis. Of nine ferrets which survived the infection for 3 weeks or longer, five showed neurological signs. At the time of death they had widespread inflammation in their brains, and cell-associated virus was isolated from three ferrets sacrificed from 5 weeks to 7 months after inoculation. Four ferrets did not develop clinical signs, but two of these had mild inflammation in the brain 7 months and 2 1/2 years after inoculation, respectively. Cerebrospinal fluids drawn by cisternal puncture from infected ferrets at the time of sacrifice had neutralizing titers against measles virus similar to the titers found in sera, but antibody against the measles virus matrix protein was not detectable. Cerebrospinal fluid showed increased immunoglobulin G (IgG) and had distinct measles virus-specific oligoclonal IgG bands. The intensity of the bands correlated with the neutralizing titers of the fluids. These results confirm and extend earlier findings and indicate that persistent measles virus infection in ferrets is similar to human subacute sclerosing panencephalitis and can be used to study certain aspects of persistent brain infections leading to subacute encephalitis.

Antiviral effects of single-stranded polynucleotide inhibitors of the influenza virion-associated transcriptase against influenza virus infection of hamsters and ferrets

Administration of a single-stranded polynucleotide copolymer containing 9% cytidine residues and 91% 4-thiouridine residues [poly(C,S 4U 10)], a known potent inhibitor of the virion transcriptase of influenza viruses, suppressed the amount of virus recoverable from the nasal washes of influenza virus-infected hamsters and ferrets. The incidence of sneezing and nasal discharge in infected ferrets was also reduced. In hamsters, poly(C,S 4U 10) was more effective than amantadine-HCl given at a 5-fold higher dose; in ferrets, its effect was comparable with amantadine-HCl or Virazole. Polyinosinic acid in combination with poly-5-hydroxy cytidylic acid also had anti-influenza effects. Poly(C,S 4U 10) annealed to polyadenylic acid was not effective, nor was the double-stranded polymer (polyinosinic acid) · (polycytidylic acid), even when complexed with carboxymethylcellulose and polylysine. No toxic effects of poly(C,S 4U 10) were apparent in the treated hamsters and ferrets, and high doses (≥ 2.86 g/kg) administered intraperitoneally to mice produced no adverse effects.