Indirect Transmission of Influenza A Virus between Pig Populations under Two Different Biosecurity Settings

Abstract

Respiratory disease due to influenza virus is common in both human and swine populations around the world with multiple transmission routes capable of transmitting influenza virus, including indirect routes. The objective of this study was to evaluate the role of fomites in influenza A virus (IAV) transmission between pig populations separated by two different biosecurity settings. Thirty-five pigs were divided into four experimental groups: 10 pigs (1 replicate) were assigned to the infected group (I), 10 pigs (2 replicates of 5 pigs) were assigned to the low biosecurity sentinel group (LB), 10 pigs (2 replicates of 5 pigs) were assigned to the medium biosecurity sentinel group (MB), and 5 pigs (1 replicate) were assigned to the negative control group (NC). Eight of 10 pigs in the infected group were inoculated with IAV and 36 hours following inoculation, personnel movement events took place in order to move potentially infectious clothing and personal protective equipment (PPE) to sentinel pig rooms. Following contact with the infected group, personnel moved to the MB group after designated hygiene measures while personnel moved directly to the LB group. Nasal swabs and blood samples were collected from pigs to assess IAV infection status and fomites were sampled and tested via RRT-PCR. All experimentally inoculated pigs were infected with IAV and 11 of the 144 fomite samples collected following contact with infected pigs were low level positive for IAV genome. One replicate of each sentinel groups LB and MB became infected with IAV and all five pigs were infected over time. This study provides evidence that fomites can serve as an IAV transmission route from infected to sentinel pigs and highlights the need to focus on indirect routes as well as direct routes of transmission for IAV.

Figure 1. Isolation facility layout.

Figure 2. Timeline following arrival and during movement events.

*In relation to day of inoculation.

Figure 3. Influenza A Multiscreen ELISA S/N ratios (±SE) by experimental group and replicate.

The black horizontal line represents the cutoff value (≤0.673 is considered positive). *Significantly lower ELISA S/N ratios prior to euthanasia compared to -5 DPI (P<0.05).