In ovo model predicts virulence of bird flu virus

May 2, 2024

The virulence of HPAI viruses differs significantly. Viruses causing only mild symptoms could remain undetected, and as a result the risk of virus spread may not be controlled optimally. PhD-researcher Luca Bordes together with colleagues from Wageningen Bioveterinary Research (WBVR, part of Wageningen University & Research) developed an in ovo model to assess the virulence of bird flu viruses. “Our model can be used to quickly assess the virulence of these viruses, allowing for a more targeted approach for HPAI surveillance”, according to Bordes.

Highly pathogenic avian influenza (HPAI) H5-viruses are circulating in wild birds and are repeatedly introduced to poultry causing outbreaks in the Netherlands. The largest epizootic ever recorded in Europe was caused by HPAI H5N1 clade viruses in the period 2021–2022. The recent H5-clade viruses were found to differ in their virulence for chickens and ducks. Viruses causing only mild disease may remain undetected for a longer period and in the meantime spread to other farms, wild birds and mammals. With financial support of the Dutch ministry of Agriculture (LNV) a team from Wageningen Bioveterinary Research (WBVR) developed an in ovo (in egg) model to determine the virulence of HPAI viruses. “Ex vivo models such as our in ovo model can be rapidly implemented during emergence of novel HPAI viruses to accurately discriminate viruses”, explains PhD-researcher Luca Bordes of WBVR.


To determine the setup and reliability of the in ovo model, five contemporary H5-viruses with known virulence characteristics, were compared studying replication rate, average time to death and virus spread in the embryo (in ovo). Remarkable differences in virulence were observed between H5-viruses and between poultry species (duck versus chicken). “The H5N1-2021 virus was found to have a fast replication rate in both the chicken and duck in ovo models. However, the H5N1-2021 virus had a slower systemic virus dissemination compared to three other H5-clade viruses.”

Rapid detection

The results of the research show the potential of in ovo models. “The in ovo models will not be suitable to directly replace the animal research which is currently used to determine virulence of HPAI viruses. However, our model can be used to quickly determine the virulence of novel HPAI viruses. The model also supports research into potential virulence factors which can help to better guide the surveillance in poultry”, concludes Bordes.

Additional tool

“Since our model can distinguish the small differences in HPAI virulence in both chickens and ducks, we expect that differences in virulence between LPAI and HPAI viruses can also be detected using the in ovo model presented in this study.” The ex vivo models developed in this study have lower costs, do not make use of adult animals, and are less time consuming than the currently applied models based on animal research. According to the research team, the results of this study show that ex vivo models are highly valuable tools for risk assessment of HPAI viruses, allowing for a more targeted approach for HPAI surveillance benefiting both public health and animal health.