The recent weeks of seemingly continuous news of additional farms being confirmed as infected with highly pathogenic H5N2 avian influenza has made the poultry industry very nervous about its future ability to eliminate this virus. Why is this outbreak so different, and why does it appear to be so hard to control? Can we apply lessons learned from past outbreaks to control this outbreak?
Wildfowl spread H5N2 and live on
There are several factors which contribute to the unique presentation of this avian influenza outbreak. First is the relationship of this virus with wild waterfowl. The virus is highly pathogenic for chickens and turkeys but not pathogenic for waterfowl. Since the virus in our current outbreak is not pathogenic for waterfowl, the vast flocks of healthy virus-infected migratory geese and ducks travel thousands of miles, entering into our commercial poultry-producing regions while shedding tremendous quantities of infectious avian influenza virus in their feces.
Avian flu virus spread by multiple routes
The second unusual feature of this outbreak is the multiple introductions of the virus into poultry flocks. In the current outbreak, it appears the virus has been introduced into many farms by direct contamination from the surrounding environment. This can only be understood by recognizing the overwhelming amount of virus contaminating the environment by migrating waterfowl. Undoubtedly, when the outbreak investigation is completed, we will find that the virus was spread by a number of routes, including farm-to-farm and wind, as well as direct contamination from the surrounding environment.
Strict biosecurity and avian flu eradication
Past outbreaks taught us that stopping the spread of highly pathogenic avian influenza virus is dependent on the control of the movement of contaminated people, vehicles, equipment and products. Strict and thorough biosecurity is the most fundamental feature of successful eradication programs. This principle will again be the key to controlling and eradicating this virus.
How to eradicate H5N2 avian influenza
Because of the fear that the returning migratory waterfowl this fall will again be shedding the virus, the poultry industry is trying to understand how vaccination might be used to control the spread of the disease. Avian influenza vaccines do not prevent flocks from becoming infected with avian influenza virus, but they do diminish the severity of the disease in infected flocks.
Vaccinated flocks that become infected also shed the virus but typically less than unvaccinated flocks. Since vaccination cannot be relied upon to prevent infection or shed, vaccination must be used only as a tool in the eradication effort.
A system must be in place to quickly detect infection in vaccinated flocks, as those flocks are a dangerous source of virus for other flocks. Procedures must be in place to quickly quarantine and depopulate vaccinated-infected flocks. Although vaccination might be helpful in the overall eradication effort, it certainly does not substitute for sound biosecurity.
We will learn new things from this outbreak, but primarily this outbreak will likely reinforce the importance of following the principles we learned years ago.