31 October 2022

3 minute read

By: Chris Wright

Two presentations during the 2022 annual conference of the American Association of Avian Pathologists highlighted the importance of on-farm surveillance methods for detecting avian influenza.

Erica Spackman, from the USDA ARS Southeast Poultry Research Laboratory, compared five different devices/procedures for detecting viruses in the environment. Samples were collected from a variety of surfaces (wood, metal, plastic, etc.) in different housing types occupied by chickens experimentally exposed to avian paramyxovirus type 1, infectious bronchitis virus, or low pathogenic avian influenza virus.

Five devices/procedures were evaluated: Cotton gauze pre-moistened with brain-heart infusion buffer (moistened, not saturated), dry cotton gauze, factory pre-moistened cellulose sponges, foam swabs, and spun polyester swabs (same swabs that are used to collect oro-pharyngeal and cloacal samples from birds), Spackman said.

Across all surfaces and with all viruses, pre-moistened gauze recovered significantly more virus than any of the other devices based on titer equivalents determined by quantitative RT-PCR. The only other significant difference was that dry gauze recovered more virus than polyester swabs. The proportion of positive samples was significantly higher with pre-moistened gauze and dry gauze versus all other devices, she noted.

The device that was consistently the poorest performer (lower proportion positive, lowest titers recovered, and a limit of detection about 10X higher than pre-moistened or dry gauze) was the polyester swab. Although more manipulation is needed with premoistened gauze, the increased sensitivity is a great advantage. Cotton gauze is also inexpensive and easy to find, Spackman said.

However, she pointed out, swabs that work well for collecting samples from birds should not be used for collecting environmental samples.

Dust transmits AI

Jean-Luc Guerin of the University of Toulouse, France, investigated dust as a vehicle and surveillance sample for H5N8 highly pathogenic avian influenza (HPAI) virus in poultry farms. During the winter of 2020-2021, 492 avian influenza H5N8 HPAI outbreaks were reported primarily in southwest France.

Even though wild aquatic birds are considered the main source of initial viral introduction in commercial poultry, both inter- and intra- animal houses transmission routes are still poorly understood and ultimately poorly handled. Environmental sampling on H5N8 HPAI suspected or confirmed outbreaks were realized to assess the virus dispersion and potentially develop new surveillance sampling strategies, Guerin said.

From December 2020 to April 2021, 63 poultry houses (either ducks or chickens) were surveyed. Dust was sampled using wipes and aerosol sampling was performed with two different devices. In parallel, tracheal swabbing was performed in the framework of official surveillance. All samples were analyzed using official molecular methods and the results were analyzed using a latent class model, to assess the sensitivity and specificity of these sampling methods, he said.

Environmental sampling (either dust or aerosols) resulted in consistent PCR HPAI detection and showed an even higher sensitivity than tracheal swabs, especially in early stages of infection, when no clinical signs were observed in birds, Guerin said.

Beyond the potential application for surveillance, the data confirms that dust may play a significant role as vehicle of HPAI, both within and between farms, he concluded.