2 December 2024

4 minute read

By: Chris Wright

North America

Editors note: Due to the ongoing highly pathogenic avian influenza outbreak in the US that has caused infections in poultry and dairy farm workers, this study from the pork industry seems very relevant across species. The following is from a presentation by Joaquin Alvarez-Norambuena and colleagues, University of Minnesota, during the 2024 Leman Swine Conference. 

Influenza A virus (IAV) transmission between pigs and swine farm workers is a risk to public health. Farm workers can get exposed to IAV by direct contact with infected animals and indirectly by touching contaminated surfaces and breathing infectious aerosols containing virus-laden particles.

Personal protective equipment consisting of face masks can be used to decrease the risk of exposure to aerosols. Some of the face masks that farm workers can use to protect themselves include N95 respirators, dust masks, and surgical masks. However, the convenience and level of protection these face masks offer vary greatly among them.

A study evaluated and quantified the reduction of IAV exposure by the various face masks in farm workers. Ultimately, this study aimed to validate intervention strategies to decrease influenza transmission at the interface of pigs and people.

Twenty-four swine workers from three Midwestern farms were enrolled in the study. The selected farms had confirmed infection of IAV in the pigs. Participation of workers in the study was voluntary and participants could drop from the study at any time.

Workers were asked to wear one of three masks on a given day which included an N95 mask, dust mask, or surgical mask. Workers were also asked not to wear a mask as part of one of the treatments. Each worker wore each mask type for a total of 5 days. Each participant was asked to self-collect a nasal swab sample before wearing the face mask at the beginning of the workday. Then, workers wore the assigned face mask for at least 2 hours each day. After that, workers removed their face mask and self-collected another nasal swab.

A total of 79 out of 832 (9.50%) samples tested RT-PCR positive for IAV. Twenty-eight out of 416 (6.73%) samples collected before using the face mask tested positive while 51 out of 416 (12.26%) tested positive after wearing masks. 

The current study provides evidence that using face masks decreases the level of exposure to IAV in swine farm workers. The results add to the evidence that IAV exposure in swine farms is common, and usage of facemasks should be considered as one of the strategies to decrease the risk of infection at the human/animal interface.

This work was funded by the National Pork Board.

Airborne influenza A

The following is from a presentation by Juan Mena-Vásquez and colleagues, University of Minnesota, during the 2024 Leman Swine Conference.

Workers in swine facilities are at risk of exposure to IAV. Swine IAV has been detected in air samples under both experimental and field conditions. However, the concentration, size, and infectivity of airborne IAV-containing particles in swine facilities are poorly understood. Airborne transmission represents a critical gap in biosecurity measures, playing a key role in both animal disease containment and zoonotic disease transmission.

A study assessed airborne concentration, size, and infectivity of IAV-laden particles in swine facilities. Four grow-to-finish swine farms (F1 to F4) in the Midwestern U.S. were selected based on their history of IAV infection. Two visits per farm were conducted in the winter and spring of 2024. Pig nasal wipes and air samples were collected from one barn at each farm. Nasal wipes from pigs in ten pens (five pigs per pen) were sampled to confirm IAV status during each visit.

The non-viable Andersen cascade impactor (ACI) was used to measure IAV airborne concentration and the size of associated airborne particles. The ACI sampler separates particles into nine aerodynamic size intervals simulating the human respiratory tract and degree of penetration by these particles. Three samples were collected for 30 minutes per sample, at a flow rate of 28.3 L/min during each visit.

During the first visit, pigs in all 4 farms tested positive for IAV, with nasal wipe samples having high Ct values ranging from 34.4 to 37.5. During the second visit, only pigs in F1 and F4 tested positive for IAV and had lower Ct values (28.8 and 28.7, respectively), indicative of a more acute infection compared to visit 1.

Sizing of virus laden particles in F1 resulted in positive results in particles larger than 2.1µm with concentrations ranging from 6.3x105 to 8.9x106 RNA copies/m³, while in F4, positive samples were obtained in particles larger than 3.3µm with ranges between 4.7 x105 and 2.0x106 RNA copies/m³.