Comparison of traditional intranasal and aerosol inhalation inoculation of mice with influenza A viruses

AbstractIntranasal instillation of virus in a liquid suspension (IN) is the most frequently employed method to inoculate small mammalian models with influenza virus, but does not reflect a natural route of exposure. In contrast, inoculation via aerosol inhalation (AR) more closely resembles human exposure to influenza virus. Studies in mice have yielded conflicting results regarding virulence induced by virus inoculated by these routes, and have not controlled for potential strain-specific differences, or examined contemporary influenza viruses and avian viruses with pandemic potential. We used a whole-body AR inoculation method to compare infectivity and disease progression of a highly pathogenic H5N1, a low pathogenic H7N9, and a 2009 H1N1 virus with traditional IN inoculation in the mouse model. Generally comparable levels of morbidity and mortality were observed with all viruses examined using either inoculation route, indicating that both IN and AR delivery are appropriate for murine studies investigating influenza virus pathogenicity

Pathogenesis and transmission of swine origin A(H3N2)v influenza viruses in ferrets

Recent isolation of a novel swine-origin influenza A H3N2 variant virus [A(H3N2)v] from humans in the United States has raised concern over the pandemic potential of these viruses. Here, we analyzed the virulence, transmissibility, and receptor-binding preference of four A(H3N2)v influenza viruses isolated from humans in 2009, 2010, and 2011. High titers of infectious virus were detected in nasal turbinates and nasal wash samples of A(H3N2)v-inoculated ferrets. All four A(H3N2)v viruses possessed the capacity to spread efficiently between cohoused ferrets, and the 2010 and 2011 A(H3N2)v isolates transmitted efficiently to naïve ferrets by respiratory droplets. A dose-dependent glycan array analysis of A(H3N2)v showed a predominant binding to α2-6–sialylated glycans, similar to human-adapted influenza A viruses. We further tested the viral replication efficiency of A(H3N2)v viruses in a relevant cell line, Calu-3, derived from human bronchial epithelium. The A(H3N2)v viruses replicated in Calu-3 cells to significantly higher titers compared with five common seasonal H3N2 influenza viruses. These findings suggest that A(H3N2)v viruses have the capacity for efficient replication and transmission in mammals and underscore the need for continued public health surveillance.National Institutes of Health (U.S.) (GM 57073)Singapore-MIT Alliance for Research and Technolog

Transmission and Pathogenesis of Swine-Origin 2009 A(H1N1) Influenza Viruses in Ferrets and Mice

available in PMC 2010 October 12Recent reports of mild to severe influenza-like illness in humans caused by a novel swine-origin 2009 A(H1N1) influenza virus underscore the need to better understand the pathogenesis and transmission of these viruses in mammals. In this study, selected 2009 A(H1N1) influenza isolates were assessed for their ability to cause disease in mice and ferrets and compared with a contemporary seasonal H1N1 virus for their ability to transmit to naïve ferrets through respiratory droplets. In contrast to seasonal influenza H1N1 virus, 2009 A(H1N1) influenza viruses caused increased morbidity, replicated to higher titers in lung tissue, and were recovered from the intestinal tract of intranasally inoculated ferrets. The 2009 A(H1N1) influenza viruses exhibited less efficient respiratory droplet transmission in ferrets in comparison with the highly transmissible phenotype of a seasonal H1N1 virus. Transmission of the 2009 A(H1N1) influenza viruses was further corroborated by characterizing the binding specificity of the viral hemagglutinin to the sialylated glycan receptors (in the human host) by use of dose-dependent direct receptor-binding and human lung tissue–binding assays

Influenza Virus Respiratory Infection and Transmission Following Ocular Inoculation in Ferrets

While influenza viruses are a common respiratory pathogen, sporadic reports of conjunctivitis following human infection demonstrates the ability of this virus to cause disease outside of the respiratory tract. The ocular surface represents both a potential site of virus replication and a portal of entry for establishment of a respiratory infection. However, the properties which govern ocular tropism of influenza viruses, the mechanisms of virus spread from ocular to respiratory tissue, and the potential differences in respiratory disease initiated from different exposure routes are poorly understood. Here, we established a ferret model of ocular inoculation to explore the development of virus pathogenicity and transmissibility following influenza virus exposure by the ocular route. We found that multiple subtypes of human and avian influenza viruses mounted a productive virus infection in the upper respiratory tract of ferrets following ocular inoculation, and were additionally detected in ocular tissue during the acute phase of infection. H5N1 viruses maintained their ability for systemic spread and lethal infection following inoculation by the ocular route. Replication-independent deposition of virus inoculum from ocular to respiratory tissue was limited to the nares and upper trachea, unlike traditional intranasal inoculation which results in virus deposition in both upper and lower respiratory tract tissues. Despite high titers of replicating transmissible seasonal viruses in the upper respiratory tract of ferrets inoculated by the ocular route, virus transmissibility to naïve contacts by respiratory droplets was reduced following ocular inoculation. These data improve our understanding of the mechanisms of virus spread following ocular exposure and highlight differences in the establishment of respiratory disease and virus transmissibility following use of different inoculation volumes and routes

Environmental Conditions Affect Exhalation of H3N2 Seasonal and Variant Influenza Viruses and Respiratory Droplet Transmission in Ferrets.

The seasonality of influenza virus infections in temperate climates and the role of environmental conditions like temperature and humidity in the transmission of influenza virus through the air are not well understood. Using ferrets housed at four different environmental conditions, we evaluated the respiratory droplet transmission of two influenza viruses (a seasonal H3N2 virus and an H3N2 variant virus, the etiologic virus of a swine to human summertime infection) and concurrently characterized the aerosol shedding profiles of infected animals. Comparisons were made among the different temperature and humidity conditions and between the two viruses to determine if the H3N2 variant virus exhibited enhanced capabilities that may have contributed to the infections occurring in the summer. We report here that although increased levels of H3N2 variant virus were found in ferret nasal wash and exhaled aerosol samples compared to the seasonal H3N2 virus, enhanced respiratory droplet transmission was not observed under any of the environmental settings. However, overall environmental conditions were shown to modulate the frequency of influenza virus transmission through the air. Transmission occurred most frequently at 23°C/30%RH, while the levels of infectious virus in aerosols exhaled by infected ferrets agree with these results. Improving our understanding of how environmental conditions affect influenza virus infectivity and transmission may reveal ways to better protect the public against influenza virus infections

Pathogenesis and Transmission of Triple-Reassortant Swine H1N1 Influenza Viruses Isolated before the 2009 H1N1 Pandemic▿

The 2009 H1N1 pandemic influenza virus represents the greatest incidence of human infection with an influenza virus of swine origin to date. Moreover, triple-reassortant swine (TRS) H1N1 viruses, which share similar host and lineage origins with 2009 H1N1 viruses, have been responsible for sporadic human cases since 2005. Similar to 2009 H1N1 viruses, TRS viruses are capable of causing severe disease in previously healthy individuals and frequently manifest with gastrointestinal symptoms; however, their ability to cause severe disease has not been extensively studied. Here, we evaluated the pathogenicity and transmissibility of two TRS viruses associated with disease in humans in the ferret model. TRS and 2009 H1N1 viruses exhibited comparable viral titers and histopathologies following virus infection and were similarly unable to transmit efficiently via respiratory droplets in the ferret model. Utilizing TRS and 2009 H1N1 viruses, we conducted extensive hematologic and blood serum analyses on infected ferrets to identify lymphohematopoietic parameters associated with mild to severe influenza virus infection. Following H1N1 or H5N1 influenza virus infection, ferrets were found to recapitulate several laboratory abnormalities previously documented with human disease, furthering the utility of the ferret model for the assessment of influenza virus pathogenicity

Comparative viral pathogenesis between intranasal and ocular inoculation day 3 p.i. in extra-ocular tissue.

a<p>All viral titers expressed per gram of tissue except NW, NT, and RS samples which are expressed per ml. Limit of detection is 1.5 log₁₀ EID₅₀. The mean viral titer of all ferrets with positive virus isolation (denoted in parentheses) is shown.</p>b<p>Route of inoculation. i.n., intranasal (10⁶ EID₅₀/ml) unless otherwise specified; i.o.; ocular inoculation (10⁶ EID₅₀/100 µl).</p>c<p>i.o. NW and RS samples are inclusive of 6 ferrets tested.</p>d<p>Viral titers represent a pooled intestinal sample consisting of the duodenum, jejuno-ileal loop, and descending colon.</p>e<p>Intranasal inoculation performed using 10⁶ EID₅₀/100 µl virus dose.</p>f<p>ND, not detected.</p

Virus deposition in ferrets following different routes of inoculation.

<p>Fluorescent-labeled A/NL/219/03 virus (NL219-FL) was administered to ferrets by the intranasal or ocular route. Each ferret was euthanized 15 min following virus administration and organs were collected for <i>ex vivo</i> imaging. Nasal turbinates are contained within the cap; left and right conjunctiva and eyes are below, respectively. An increasing fluorescence signal is indicated by brightness from red to yellow. Images are representative of triplicate independent inoculations for each route. Percentages represent the mean maximum relative efficiency for each tissue (n = 3) above levels in corresponding naïve tissue for each route of inoculation.</p

Comparison of influenza virus recovery in conjunctival wash samples following ocular inoculation of ferrets.

<p>Ferrets were inoculated by the ocular route with 10⁶ EID₅₀/ml of each virus shown. Viral titers were measured in conjunctival washes (CW) collected on indicated days following serial titration in eggs; endpoint titers are expressed as mean log₁₀ EID₅₀/ml plus standard deviation (left y-axis and bars). Relative viral RNA copy number in conjunctival washes was determined by real-time PCR using a universal M1 primer and extrapolated using a standard curve based on samples of known virus (right y-axis and lines). The limit of virus detection was 10^1.5 EID₅₀/ml. †, no ferrets survived until day 9 p.i. R-squared values are shown for those viruses where a statistically significant (p<0.05) correlation between viral titer and viral RNA copy number exists. NS, not significant.</p