Performance of highly pathogenic avian influenza virus surveillance in vaccinated farms

A study published in the international journal Emerging Infectious Diseases (EID) by Toulouse-based scientists from UMR IHAP (INRAE/ENVT) demonstrates that enhanced event-based surveillance, based on weekly sampling of ducks found dead, is the most effective strategy for rapidly detecting the presence of highly pathogenic avian influenza (HPAI) virus in duck farms vaccinated against HPAI. This approach proves to be more sensitive and earlier in detecting the virus than taking samples from live ducks. It is therefore more effective in limiting the risk of silent virus circulation.

Researchers from Toulouse’s UMR IHAP (INRAE/ENVT - Host-Pathogen Interactions) have studied the effectiveness of different surveillance strategies for detecting the presence of highly pathogenic avian influenza (HPAI) virus in duck farms vaccinated against HPAI. Using a mathematical model, they compared different surveillance strategies for the early detection of the virus, which represents a persistent threat to the poultry industry in Europe and particularly in France. They studied event-based surveillance (based on increased mortality), enhanced event-based surveillance (based on diagnostic tests on ducks found dead) and programmed surveillance (based on diagnostic tests on a sample of live ducks). To do this, they simulated the spread of the virus in a farm of vaccinated ducks, and estimated the probability of virus detection and the time to detection for each.

The study shows that enhanced event-based surveillance, based on weekly sampling of dead ducks, offers the best sensitivity (up to 90% of infected farms are detected) and the earliest detection, of all the surveillance strategies studied. This method therefore appears to be more effective than monthly sampling of a random sample of live ducks (programmed surveillance).

Identifying the silent circulation of the virus is a major challenge in vaccinated farms, as vaccination considerably reduces mortality and clinical symptoms, which are traditionally used to detect the presence of the virus. Monitoring vaccinated farms to control the spread of the virus is therefore a real challenge. The researchers therefore insist on the need to focus surveillance efforts on regular testing of dead ducks, while reducing less effective and more costly programmed surveillance strategies.

This work, carried out as part of the French HPAI vaccination campaign, offers practical recommendations for optimizing surveillance protocols and limiting the risk of epizootics. The results also underline the importance of a judicious combination of vaccination and surveillance measures to safeguard animal health and support the poultry sector in the face of current health challenges.

https://wwwnc.cdc.gov/eid/­article/31/1/­24-1140_article

Sophie Planchand¹, Timothée Vergne¹, Jean-Luc Guérin¹, Séverine Rautureau², Guillaume Gerbier², Sébastien Lambert¹.

¹IHAP, University of Toulouse, INRAE, ENVT, Toulouse, France

²Ministère de l’Agriculture et de la Souveraineté Alimentaire, France

Reference

Planchard S., Vergne T., Guerin J. et al. (2025). Surveillance Strategy in Duck Flocks Vaccinated against Highly Pathogenic Avian Influenza Virus. Emerging Infectious Diseases, DOI : https://doi.org/10.3201/eid3101.241140