Abstract
Person-to-person transmission of influenza viruses occurs by contact (direct and fomites) and non-contact (droplet and small particle aerosol) routes, but the quantitative dynamics and relative contributions of these routes are incompletely understood. The transmissibility of influenza strains estimated from secondary attack rates in closed human populations is confounded by large variations in population susceptibilities. An experimental method to phenotype strains for transmissibility in an animal model could provide relative efficiencies of transmission. We developed an experimental method to detect exhaled viral aerosol transmission between unanesthetized infected and susceptible ferrets, measured aerosol particle size and number, and quantified the viral genomic RNA in the exhaled aerosol. During brief 3-hour exposures to exhaled viral aerosols in airflow-controlled chambers, three strains of pandemic 2009 H1N1 strains were frequently transmitted to susceptible ferrets. In contrast one seasonal H1N1 strain was not transmitted in spite of higher levels of viral RNA in the exhaled aerosol. Among three pandemic strains, the two strains causing weight loss and illness in the intranasally infected ‘donor’ ferrets were transmitted less efficiently from the donor than the strain causing no detectable illness, suggesting that the mucosal inflammatory response may attenuate viable exhaled virus. Although exhaled viral RNA remained constant, transmission efficiency diminished from day 1 to day 5 after donor infection. Thus, aerosol transmission between ferrets may be dependent on at least four characteristics of virus-host relationships including the level of exhaled virus, infectious particle size, mucosal inflammation, and viral replication efficiency in susceptible mucosa.
Highlights
Seasonal influenza virus is a highly contagious respiratory pathogen that causes over one million infections and is associated with approximately 3000 up to 49,000 deaths each year in the United States [1]
Infections due to the 2009 H1N1 pandemic influenza virus were primarily self-limited with the highest attack rates among children and young adults [2]
Reviews of influenza transmission among human populations have concluded that transmission is by contact and droplet spray [9,10] while others conclude that aerosol transmission contributes significantly to spread of infection [11,12]
Summary
Seasonal influenza virus is a highly contagious respiratory pathogen that causes over one million infections and is associated with approximately 3000 up to 49,000 deaths each year in the United States [1]. Infections due to the 2009 H1N1 pandemic influenza virus were primarily self-limited with the highest attack rates among children and young adults [2]. Reviews of influenza transmission among human populations have concluded that transmission is by contact and droplet spray [9,10] while others conclude that aerosol transmission contributes significantly to spread of infection [11,12]. Transmissibility is currently estimated from the spread of influenza in relatively closed populations and is expressed as the number of secondary infections derived from one contagious person (basic reproductive number R0). The R0 for the 2009 H1N1 pandemic strain has been estimated to range from 1.4 to 1.8 [13,14,15,16], values that overlap with the R0 of seasonal strains of 1.7–2.1 [17] and
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
