Viral tropism and detection of clade 2.3.4.4b H5N8 highly pathogenic avian influenza viruses in feathers of ducks and geese.

Highly Pathogenic Avian Influenza viruses (HPAIVs) display a tissue pantropism, which implies a possible spread in feathers. HPAIV detection from feathers had been evaluated for H5N1 or H7N1 HPAIVs. It was suggested that viral RNA loads could be equivalent or higher in samples of immature feather compared to tracheal (TS) or cloacal swabs (CS). We investigated the suitability of feathers for the detection of clade 2.3.4.4b H5N8 HPAIV in ducks and geese field samples. In the six H5N8 positive flocks that were included in this study, TS, CS and immature wing feathers were taken from at least 10 birds. Molecular loads were then estimated using real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) targetting H5 and M genes. In all flocks, viral loads were at least equivalent between feather and swab samples and in most cases up to 103 higher in feathers. Bayesian modelling confirmed that, in infected poultry, RT-qPCR was much more likely to be positive when applied on a feather sample only (estimated sensitivity between 0.89 and 0.96 depending on the positivity threshold) than on a combination of a tracheal and a cloacal swab (estimated sensitivity between 0.45 and 0.68 depending on the positivity threshold). Viral tropism and lesions in feathers were evaluated by histopathology and immunohistochemistry. Epithelial necrosis of immature feathers and follicles was observed concurrently with positive viral antigen detection and leukocytic infiltration of pulp. Accurate detection of clade 2.3.4.4b HPAIVs in feather samples were finally confirmed with experimental H5N8 infection on 10-week-old mule ducks, as viral loads at 3, 5 and 7 days post-infection were higher in feathers than in tracheal or cloacal swabs. However, feather samples were associated with lower viral loads than tracheal swabs at day 1, suggesting better detectability of the virus in feathers in the later course of infection. These results, based on both field cases and experimental infections, suggest that feather samples should be included in the toolbox of samples for detection of clade 2.3.4.4b HPAI viruses, at least in ducks and geese.

Role of Backyard Flocks in Transmission Dynamics of Highly Pathogenic Avian Influenza A(H5N8) Clade 2.3.4.4, France, 2016-2017.

Highly pathogenic avian influenza A(H5N8) clade 2.3.4.4 spread in France during 2016-2017. We assessed the biosecurity and avian influenza virus infection status of 70 backyard flocks near H5N8-infected commercial farms. One flock was seropositive for clade 2.3.4.4. Backyard flocks linked to commercial farms had elevated risk for H5 infection.

Biosecurity practices on foie gras duck farms, Southwest France.

On-farm biosecurity can be assessed by analyzing patterns of practices to better tailor technical advice to producers. Given their close contact with environmental and wildlife disease reservoirs, free-range duck farms are exposed to multiple risk factors of pathogen exposure that are rare or absent in indoor production. The recurrent emergence of Highly Pathogenic Avian Influenza (HPAI) viruses in Southeast Asia and Europe has emphasized the importance of farm-level biosecurity on free-range duck farms. This study was conducted on 46 French duck farms. The farms were visited and an 80-question survey was administered to assess biosecurity practices. Patterns of practices were explored with multiple correspondence analysis and hierarchical cluster analysis. Farms were assigned to one of three clusters in which specific farm types were overrepresented: farms specialized in rearing to grow-out phases and open-circuit full cycle (i.e., all production phases on the farm) farms in cluster 1, closed-circuit full cycle farms in cluster 2, and farms specialized in gavage in cluster 3. Differences in practices might be linked with differences in production constraints. This study provides a baseline assessment of biosecurity practices on foie gras duck farms in Southwest France and will help efforts to adapt biosecurity programs to farm types.