This presentation gives an overview of PRRSV transmission routes with the biosecurity intervention points that correspond to each pathway. Its organising idea is that a route without an intervention attached to it is an open route, regardless of how well the other routes are managed.
The airborne route is one entry in that framework, and it is the one with the most measurement behind it. Dee and colleagues recovered infectious PRRSV at 4.7 kilometres in 2009 and Otake and colleagues at 9.1 kilometres in 2010, both in a small fraction of samples collected over long periods. Alonso and colleagues quantified what closing that route is worth in 2013, reporting an approximately 80 percent reduction in the risk of novel introduction across 20 filtered and 17 non filtered herds over seven years. Havas and colleagues in 2023 found the strongest protection where air filtration and feed mitigation were both in place.
The framing is useful precisely because it prevents a single control from being read as a solution. Approximately 80 percent risk reduction implies a residual, and the residual runs through the routes filtration does not touch: animal movement, transport, personnel, feed and fomites. For a producer, a route by route audit is the way to find out which interventions are actually in place and which are assumed to be, and the result of that audit determines what the filtration is able to deliver.