Abstract
Influenza is a major cause of mortality and morbidity worldwide. Despite numerous studies of the pathogenesis of influenza in humans and animal models the dynamics of infection and transmission in individual hosts remain poorly characterized. In this study, we experimentally modelled transmission using the H1N1pdm09 influenza A virus in pigs, which are considered a good model for influenza infection in humans. Using an experimental design that allowed us to observe individual transmission events occurring within an 18-hr period, we quantified the relationships between infectiousness, shed virus titre and antibody titre. Transmission event was observed on 60% of occasions when virus was detected in donor pig nasal swabs and transmission was more likely when donor pigs shed more virus. This led to the true infectious period (mean 3.9 days) being slightly shorter than that predicted by detection of virus (mean 4.5 days). The generation time of infection (which determines the rate of epidemic spread) was estimated for the first time in pigs at a mean of 4.6 days. We also found that the latent period of the contact pig was longer when they had been exposed to smaller amount of shed virus. Our study provides quantitative information on the time lines of infection and the dynamics of transmission that are key parts of the evidence base needed to understand the spread of influenza viruses though animal populations and, potentially, in humans.
Highlights
The 2009 H1N1 pandemic demonstrated the potential of swine origin influenza viruses to cause significant human morbidity and mortality globally [1,2,3]
Pigs are a natural host for influenza infection with shedding patterns similar to humans
Swine influenza viruses (SwIV) are of great economic importance for the pig industry as they contribute to the respiratory disease complex and can cause severe pulmonary distress, growth retardation and sub-optimal reproductive performance [4,5,6]
Summary
The 2009 H1N1 pandemic demonstrated the potential of swine origin influenza viruses to cause significant human morbidity and mortality globally [1,2,3]. Swine influenza viruses (SwIV) are of great economic importance for the pig industry as they contribute to the respiratory disease complex and can cause severe pulmonary distress, growth retardation and sub-optimal reproductive performance [4,5,6]. It has been previously assumed that infectiousness (which is the ability of an infected individual to transmit a pathogen) is proportional to viral titre. This hypothesis has never been tested to our knowledge. It is crucial to provide estimates of natural history parameters and to investigate the link between shed virus titre and the probability of transmission
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