AASV Influenza Working Group Offers Recommendations

November 8, 2017 — Marie Culhane

To protect both human health and the swine herd, the AASV Influenza Working Group strongly advises that all personnel working in the pork-production industry be vaccinated against seasonal influenza annually (with their human health professional's approval) and against any novel human influenza A viruses as they emerge (1-4). Vaccination enhances protection for personnel while minimizing the likelihood of viral transmission from personnel to pigs.

Vaccination of people working in pork production and harvest is critically important because of the risk of human-to-swine transmission of influenza virus is quite high. The two dominant influenza A hemagglutinin (HA) types circulating in the North American swine population today are essentially of human origin. The ancestral Sw/H1 virus (A/Sw/Iowa/1930/H1N1) likely originated from the 1918 human H1N1 virus (5). The original H3 HA gene segment (A/Sw/Texas/1998/H3N2) originated from the 1976 H3 human virus and appears to have been introduced to the North American swine population in the late 1990's (6). There have been several cases of swine-to-human transmission, but subsequent human-to-human transmission of these viruses has been limited (7,8). The 2009 pandemic H1N1 had more extensive person-to-person spread due to further host adaptation in humans.

The best means to minimize the risk of swine-to-human transmission of influenza A virus (IAV) is to lower the risk of introducing novel viruses into the swine population thereby reducing the risk of viral reassortment with passage back to humans. The pork industry has taken numerous steps over the last three decades to minimize the risk of novel influenza introductions. They include:

• Preventing bird and pig interactions through the adoption of bird proof, indoor housing
• Strict protocols to limit human transmission of disease into swine herds that include showering and changing clothes prior to entering swine rearing facilities, limiting visitors to swine production facilities, and strictly enforcing time away from other livestock for all people entering the production facility
• Promotion of seasonal influenza vaccination of all animal caregivers through facilitation and financial support of vaccination for pork industry employees and families.
• Encouraging animal caretakers with influenza-like illnesses to seek medical attention and take time away from work as appropriate.

While the pork industry has been very proactive in the implementation of prevention strategies for their herds, there is a need for additional strategies designed to protect workers from influenza. Pork production workers should be considered a high priority for receiving novel influenza A strain vaccination and anti-viral therapies when they arise.

The AASV recognizes the importance that swine can play in promoting the transmission of a novel influenza virus. In the spirit of the "One Health" initiative, the AASV strongly encourages everyone involved in human and animal health to promote and facilitate vaccination of personnel involved in pork production. To that end, we recommend that people working with swine take all available precautions, including vaccination (with their human health professional's approval), to work towards prevention of bidirectional influenza transmission.

During its fall meeting, the AASV Board of Directors adopted a revised position statement on influenza promoted by the Influenza Working Group. The statement is available online.

1. Olsen CW, Brammer L, Easterday BC, Arden N, Belay E, Baker I, Cox NJ. Serologic evidence of H1 swine influenza virus infection in swine farm residents and employees. Emerg Infect Dis. 2002;8:814-819. 2. Gray GC, McCarthy T, Capuano AW, Setterquist SF, Olsen CW, Alavanja MC. Swine workers and swine influenza virus infections. Emerg Infect Dis. 2007;13:1871-1878. 3. Myers KP, Olsen CW, Setterquist SF, Capuano AW, Donham KJ, Thacker EL, Merchant JA, Gray GC. Are swine workers in the United States at increased risk of infection with zoonotic influenza virus? Clin Infect Dis. 2006;42:14-20.

4. Olsen CW, Carey S, Hinshaw L, Karasin AI. Virologic and serologic surveillance for human, swine and avian influenza virus infections among pigs in the north-central United States. Arch Virol. 2000;145:1399-1419.

5. Nelson, M.I., Vincent, A.L. Reverse zoonosis of influenza to swine: New perspectives on the human-animal interface (2015) Trends in Microbiology, 23 (3), pp. 142-153.doi: 10.1016/j.tim.2014.12.002

6. Webby RJ, Swenson SL, Krauss SL, et al. Evolution of swine H3N2 influenza viruses in the United States. J Virol. 2000;74:8243-8251.

7 Bowman, A. S., Nelson, S. W., Page, S. L., Nolting, J. M., Killian, M. L., Sreevatsan, S....Slemons, R. D. (2014). Swine-to-Human Transmission of Influenza A(H3N2) Virus at Agricultural Fairs, Ohio, USA, 2012. Emerging Infectious Diseases, 20(9), 1472-1480. https://dx.doi.org/10.3201/eid2009.131082.

8. Bowman, A. S., Walia, R. R., Nolting, J. M., Vincent, A. L., Killian, M., Zentkovich, M. M....Forshey, T. (2017). Influenza A(H3N2) Virus in Swine at Agricultural Fairs and Transmission to Humans, Michigan and Ohio, USA, 2016. Emerging Infectious Diseases, 23(9), 1551-1555. https://dx.doi.org/10.3201/eid2309.170847.

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Marie Culhane, AASV Influenza Working Group Chair