Air inlets at two recently infected poultry farms, one broiler and one layer, were fitted with netting collection bags over ventilation caps and harvested every five days for 25 days, with video monitoring of wild bird visits alongside. A considerable number of mosquitoes and small quantities of particulate matter entered the inlets, mostly cobweb and plant material. No wild bird feathers were collected. Particulate samples tested negative for avian influenza virus and Salmonella, though several samples from both farms were Campylobacter positive, and the insects were negative for everything tested.
The negative influenza result should be reported honestly: this study did not catch avian influenza coming through an inlet. What it did establish is the material flow and the variables that govern it. Substantial variation existed between individual inlets on the same building, and during stormy periods significantly larger quantities entered the inlets facing into the wind. That is a siting and orientation finding rather than a filtration finding, and it applies to a building whether or not anything is fitted to the openings.
Two practical points follow. Insects enter inlets in numbers, which makes an air opening a vector route as well as a particulate route, the same conclusion the Serbian outbreak work reached from the swine side with flies as mechanical carriers of African swine fever virus. And Campylobacter positive particulate shows that inlets do convey organism-associated material even in a study where the target virus was absent. The authors recommend measures limiting this introduction route, which is a conclusion about the opening rather than about any particular technology fitted to it.