The Farm Reservoir

Sources of influenza A virus infection on the farm

Influenza A virus in swine (IAV-S) can circulate continuously within a herd. IAV-S often appears on a farm with the introduction of new but infected animals. Once this occurs, the virus can transmit to susceptible animals like newborn piglets or new groups of replacement animals, allowing it to persist. This can lead to the virus becoming endemic in the herd.¹

Weaning —

Young piglets are a source of IAV-S for other pigs if they are infected at the time of weaning.^2,3

Growing —

As pigs grow, they can be infected early in the nursery by virus shedding from weaned pigs as well as laterally from neighbor animals.

Gilt development unit (GDU) —

Replacement gilts can be sources of new viruses and reservoirs for endemic viruses in the breeding herd. Replacement gilts newly moved to a farm have a higher likelihood of testing positive for IAV-S than gilts who have been present on the farm for more than 4 weeks.⁴

Sow —

One study found a positive correlation between sow level serostatus and finishing pigs testing positive.⁵