Predator-Prey Trophic Interactions and Seasonality of Highly Pathogenic Avian Influenza Virus in Denmark, 2016-2023

Trophic interactions between populations of birds are assumed to facilitate the transmission of highly pathogenic avian influenza virus (HPAIV). However, evidence from the field is lacking to support the hypothesis of trophic AIV transmission.

We compared the timing of predatory versus prey wild bird HPAIV cases reported in Denmark (primarily via passive surveillance) between 2016 and 2023. We classified the species reported as 'predator' (case) or 'prey' (control). Spatial clusters of predator reports were identified using the scan statistic. Logistic regression models were fit.

Predator species were found more likely to be reported as HPAIV cases in winter (odds ratio (OR) 5.7, 95% confidence interval (CI) 2.4-13.8), spring (14.1, 5.8-34.5) and summer (10.2, 2.1-49.6) than in autumn. Controlling for temporal (year of report) and spatial clustering, the estimated risk of predator reports increased in winter (12.1, 3.7-39.2) and spring (OR 21.5, 5.8-79.6) compared to autumn.

Our results suggest that predator species become infected later during the transmission season than prey species, which has implications for the design of HPAIV surveillance systems. For example, in active surveillance resources could be more focused on prey species in autumn, and predator species in winter and spring. Likewise, in passive surveillance public messaging could reflect this species shift. The sensitivity of surveillance might further be increased by considering potential seasonal changes in the spatial distribution of species affected by HPAIV.