SARS-Cov-2 infection at the animal-human interface: longevity and re-infection dynamics with virus evolution

SARS-CoV-2 infection causes asymptomatic through severe clinical presentations in humans. Parameters around infection and transmission dynamics have been studied in animal models. However, there are growing reports of 'reactivation' and re-infection with variant SARS-CoV-2 viruses, months after 'recovery'. The frequency, timing, clinical and virological consequence, in terms of infectious virus shedding and onward transmission following secondary intra- and inter-species infections, remain unknown. The underlying immunological mechanisms behind these infections also remain unexplored. Additionally, SARS-CoV-2 infection in mink has generated novel virus variants, capable of infecting and partially evading existing immunity in humans, increasing the threats of re-infection. Here, we propose to use our established ferret model of SARS-CoV-2 (human and animal adapted viruses), to study longitudinal outcomes of respiratory droplet infection for two genetically different viruses over a six-month period. We will monitor virological and immunological progression of longitudinal SARS-CoV-2 infection; investigate the consequences of SARS-CoV-2 re-infection with homologous and heterologous strains; and investigate the effect of adaptation and immunity on the evolution of SARS-CoV-2 during these infections. We hypothesise that productive re-infection with SARS-CoV-2 variants can result in both infected and infectious stages, the latter being able to transmit disease irrespective of prior exposure and immune status. These investigations will provide detailed robust novel information relevant to mitigation strategies such as droplet avoidance, herd immunity, vaccination and virus evolution. It will also address questions regarding the emergence and maintenance of SARS-CoV-2 in animal reservoirs which may threaten eradication and long-term management of COVID