Role of farmworkers and management practices in influenza A virus transmission within breeding herds

Abstract

Influenza is considered an endemic disease in swine caused by the influenza A virus (IAV) that inflicts economic losses to swine producers and negatively impacts pig’s health, productivity, and well-being. Influenza is also a shared disease between pigs and humans: therefore, controlling of IAV in pigs has public health relevance. The objective of this thesis was to elucidate the relevance of farmworkers and farm management practices in IAV transmission within breeding herds in order to help guide swine producers towards control strategies to reduce the burden of influenza in pigs. Understanding the risk of bidirectional transmission of IAV between pigs and farmworkers, and whether there are risk factors indicative of infection, is needed in order to take preventive measures in swine farms. We found that farmworkers can report to work testing IAV positive without any indication of infection and that some of the workers carry IAV strains with potential of transmission to pigs. We also found evidence of multiple farmworkers’ exposure to the IAV circulating in pigs but we did not find evidence of infection in the farmworkers as a result of exposure to the swine-origin IAV strains. Our results support the general understanding that swine farms can be a setting on which bidirectional IAV transmission can occur, and where biosecurity programs are warranted. Indirect transmission of IAV via fomites has been documented. However, it is not known which farm activities result in higher risk of farmworkers contamination that then could facilitate the spread of IAV within breeding herds. We found that activities that involve extensive piglet handling near weaning age, like vaccination and weaning, represent a high risk of IAV contamination of the worker’s hands and clothing. Protocols that limit piglet and sow movements within farrowing rooms have been used before to limit pathogen spread. However, there are limited reports regarding their implementation for IAV control. When management practices were altered to limit pathogen exposure to newborn piglets, IAV dissemination within the farrowing house was delayed. However, IAV prevalence at weaning was not altered which led us to investigate a whole-herd approach where the protocol was implemented in all farrowing rooms at once in combination with IAV mass-vaccination of all mature animals with the aim of weaning IAV negative piglets. We found that the combination of sow vaccination and strict management practices can result in a reduction on IAV prevalence and weaning of IAV negative piglets from breeding herds. In conclusion, results from this thesis emphasize the relevance that farmworkers have as biological and mechanical carriers of IAV in breeding herds. It also highlights how altering certain management practices can reduce the risk of IAV transmission within breeding herds and result in the weaning of IAV negative pigs.