Evidence of influenza A infection and risk of transmission between pigs and farmworkers

Abstract

Interspecies transmission of influenza A virus (IAV) between pigs and people represents a threat to both animal and public health. To better understand the risks of influenza transmission at the human–animal interface, we evaluated 1) the rate of IAV detection in swine farmworkers before and after work during two human influenza seasons, 2) assessed risk factors associated with IAV detection in farmworkers and 3) characterized the genetic sequences of IAV detected in both workers and pigs. Of 58 workers providing nasal passage samples during 8‐week periods during the 2017/18 and 2018/19 influenza seasons, 33 (57%) tested positive by rRT‐PCR at least once. Sixteen (27%) workers tested positive before work and 24 (41%) after work. At the sample level, 58 of 1,785 nasal swabs (3.2%) tested rRT‐PCR positive, of which 20 of 898 (2.2%) were collected prior to work and 38 of 887 (4.3%) after work. Although farmworkers were more likely to test positive at the end of the working day (OR = 1.98, 95% CI 1.14–3.41), there were no influenza‐like illness (ILI) symptoms, or other risk indicators, associated with IAV detection before or after reporting to work. Direct whole‐genome sequencing from samples obtained from worker nasal passages indicated evidence of infection of a worker with pandemic 2009 H1N1 of human‐origin IAV (H1‐pdm 1A 3.3.2) when reporting to work, and exposure of several workers to a swine‐origin IAV (H1‐alpha 1A 1.1) circulating in the pigs on the farm where they were employed. Our study provides evidence of 1) risk of IAV transmission between pigs and people, 2) pandemic H1N1 IAV infected workers reporting to work and 3) workers exposed to swine harbouring swine‐origin IAV in their nasal passages temporarily. Overall, our results emphasize the need to implement surveillance and transmission preventive protocols at the pig/human interface.

A New Sampling Approach for the Detection of Swine Influenza a Virus on European Sow Farms

“…In accordance with the aforementioned studies, we observed a significantly higher chance of detecting influenza by rRT-PCR in weaners compared to suckling piglets or nursery pigs, which most likely results from the mixing of piglets after weaning, either for transport or within the pens. Furthermore, the additional subsequent spread of the virus in the nursery units, due to airflow or even farm stuff [ 11 ], plays a role. The speed of infection depends on the subtypes involved [ 38 ], the extent of mixing, and the group sizes within the nursery units [ 34 ].…”

“…Our data clearly show that in farms either suspecting an endemic circulation of swIAV or an acute outbreak, the percentage of healthy swIAV-positive suckling piglets (7.2% of all samples) was higher than the percentage of diseased swIAV-positive suckling piglets (4.2% of all samples). As suckling piglets can serve as a reservoir for swIAV, the main aspects that have to be considered to reduce swIAV circulation during the suckling period include the vaccination management of sows and gilts [ 30 , 45 ] and the management of suckling piglets, to minimize transmission [ 11 ].…”

“…These previously infected sows can transfer maternally derived antibodies (MDA) to their piglets [ 10 ]. MDA can prevent clinical signs in suckling piglets that either get infected by virus-shedding sows, by airborne transmission, by farm workers [ 11 ], or from other sources. However, clinically protected suckling piglets will shed the same amount of virus particles after infection as do piglets that did not receive MDA [ 12 , 13 ]; therefore, these clinically unsuspicious suckling piglets can transfer the virus into the nursery.…”

A stochastic compartmental model to simulate intra- and inter-species influenza transmission in an indoor swine farm

“…Another study using whole genome sequencing found that IAV samples from five workers had identical clade classification to swine-origin IAV samples from pigs on the same farm (27).…”

“…In a separate seroprevalence study evaluating farmers, meat processing workers (from pork production facilities), veterinarians with swine exposure and controls with no known contact with swine, it was found that farmers had the highest odds of swine influenza exposure (Odds Ratio [OR], 35.3; 95% CI, 7.7 – 161.8) (26). Another study using whole genome sequencing found that IAV samples from five workers had identical clade classification to swine-origin IAV samples from pigs on the same farm (27).…”