# In Ovo Models to Predict Virulence of Highly Pathogenic Avian Influenza H5-Viruses for Chickens and Ducks

## TL;DR

Researchers developed fast and low-cost in ovo models to assess the virulence of H5 avian influenza viruses in chickens and ducks, helping improve poultry surveillance.

## Contribution

The study introduces in ovo models as a novel, efficient method to evaluate HPAI virus virulence in poultry species.

## Key findings

- In ovo models revealed significant differences in virulence among H5-viruses and between chickens and ducks.
- The H5N1-2021 virus replicated quickly but spread more slowly compared to other H5-clade 2.3.4.4b viruses.
- The models can help identify virulence factors and support surveillance strategies in poultry.

## Abstract

Highly pathogenic avian influenza (HPAI) H5-viruses are circulating in wild birds and are repeatedly introduced to poultry causing outbreaks in the Netherlands since 2014. The largest epizootic ever recorded in Europe was caused by HPAI H5N1 clade 2.3.4.4b viruses in the period 2021–2022. The recent H5-clade 2.3.4.4 viruses were found to differ in their virulence for chickens and ducks. Viruses causing only mild disease may remain undetected, increasing the risk of virus spread to other farms, wild birds and mammals. We developed in ovo models to determine the virulence of HPAI viruses for chickens and ducks, which are fast and have low costs. The virulence of five contemporary H5-viruses was compared studying replication rate, average time to death and virus spread in the embryo. Remarkable differences in virulence were observed between H5-viruses and between poultry species. The H5N1-2021 virus was found to have a fast replication rate in both the chicken and duck in ovo models, but a slower systemic virus dissemination compared to three other H5-clade 2.3.4.4b viruses. The results show the potential of in ovo models to quickly determine the virulence of novel HPAI viruses, and study potential virulence factors which can help to better guide the surveillance in poultry.