Influenza virus aerosol exposure and analytical system for ferrets

Understanding the transmission ability of newly emerging influenza viruses is central to the development of public health preparedness and prevention strategies. Animals are used to model influenza virus infection and transmission, but the routinely used intranasal inoculation of a liquid virus suspension does not reflect natural infection. We report the development of an inoculation method that delivers an influenza virus aerosol inoculum to ferrets and the characterization of size distribution and viable virus present in aerosols shed from infected ferrets during normal breathing and sneezing. By comparing virus deposition, infectivity, virulence, and transmissibility among animals inoculated intranasally or by aerosols with a human (H3N2) or avian (H5N1) influenza virus, we demonstrate that aerosol inoculations more closely resemble a natural, airborne influenza virus infection and that viable virus is measurable in droplets and droplet nuclei exhaled by infected ferrets. These methods will provide improved risk assessment of emerging influenza viruses that pose a threat to public health.