Host responses that correlate with respiratory droplet transmission of swine-origin influenza viruses in ferrets.

The determinants of influenza transmission remain poorly understood. Swine influenza viruses preferentially attach to receptors found in the upper airways; however, most swine influenza viruses fail to transmit efficiently from swine to humans, and from human-to-human. The pandemic 2009 H1N1 (H1N1pdm) virus was a rare exception of a swine virus that acquired efficient transmissibility from human-to-human, and is reflected in efficient respiratory droplet transmission in ferrets. We hypothesize that virus-induced host responses in the upper airways correlate with airborne transmission in ferrets. To address this question, we used the H1N1pdm virus and swine influenza A/swine/Hong Kong/201/2010 (HK201) virus that has comparable titre in the ferret nasopharynx, but it exhibits differential transmissibility in ferrets via respiratory droplet route. We performed a transcriptomic analysis of tissues from the upper and lower respiratory tract from ferrets infected with either H1N1pdm or HK201 viruses using ferret-specific Agilent oligonucleotide arrays. We found differences in the kinetics of the innate immune response elicited by these two viruses that varied across tissues. Ferrets were mock inoculated with 0.5mL media or inoculated with 105 TCID50 of the A/CA/04/09 (H1N1) or A/Sw/HK/ 210/10 (H1N1) influenza viruses intra-nasally. There are a total of 9 ferrets per virus group and six ferrets for the mock group. Ferrets were euthanized at day 1 (n = 4 per virus group) and day 2 (n = 5 per virus group) post-inoculation (p.i.). Three mock inoculated ferrets were euthanized at days 1 and 2 p.i. Tissues from nasal turbinate, soft palate, pharynx, trachea, bronchus, and lungs were collected at necropsy, placed in RNAlater overnight at 4°C and conserved at -80°C. RNA was extracted and gene expression was analyzed by custom 4x180K ferret-specific oligonucleotide arrays (Agilent Cat# G4862A, design ID 48472)