Understanding influenza A virus: linking transmission, evolutionary dynamics, pathogenesis and immunity in pigs

Swine influenza attracts considerable attention because of the threat of zoonotic infections causing human pandemics. During the pandemic, a fear that viruses emerging from pigs may infect people resulted in the widespread destruction of animals in some countries and trade bans. Consequently, the insidious effects of this highly prevalent virus on the health and welfare of pig populations, estimated to increase the cost of production by £7 per finished pig, have not been given due regard. The primary disease caused by influenza virus in usually mild, but results in greater susceptibility to secondary infections. Vaccination will be a key control measure for influenza in pigs to improve general herd health. Through our studies we will develop a more detailed understanding of the dynamics of virus transmission and the consequences of transmission and vaccination in driving viral evolution. During these studies we will also define a range of parameters, for example local and systemic immune responses and sites of virus replication, which are associated with the onset and cessation of transmission. We need to know if current and proposed novel vaccines not only prevent clinical signs but also stop viruses being transmitted unnoticed. Furthermore, if viruses can be transmitted unnoticed are they changing because of the immune response in the population? To answer these questions we need to understand virus transmission in detail and how the viruses change when they pass between animals. We can then apply this new knowledge to population wide models of disease spread to predict the efficiency of any proposed control measures. This knowledge will also inform the design of novel vaccines. Vaccination against influenza in pigs is not routinely performed in Europe mainly for two reasons: the cost benefit of vaccination has not been clearly demonstrated and it is not clear that the available vaccines will protect against the strains currently circulating in the pig population. The most striking example of the latter is that current vaccines do not include pandemic H1N1 influenza virus antigen. These studies will provide essential evidence to design control programmes for influenza in pigs, most notably: i) finding out how efficient are the current prophylactic methods at controlling the spread of infection; ii) what level of immunity is required in a population to prevent the spread of infection and the evolution of new strains of virus and iii) determine whether new, broadly cross protective vaccines are more effective at controlling influenza infections in swine to enhance animal health and livestock production. Importantly, this type of information is not available for any natural mammalian hosts of influenza viruses, including humans and horses. Therefore, the results of our studies will have a broad impact on influenza control measures.