As we move into the midpoint of the fourth quarter, it is evident that the U.S. poultry industry is facing a recurrence of seasonal avian influenza. Outbreaks have claimed 21 million hens year to date with the fall cases amounting to five million hens over six weeks in five states. Effectively APHIS has not changed its approach to control the infection since the 1985 outbreaks in Pennsylvania and adjoining states.  Since this time, the impact of HPAI has increased exponentially with expansion of the egg and turkey industries that have been the most affected but with disease having the potential to decimate broiler production.

It is evident that diagnosis of HPAI has been facilitated by recent technological advancements including PCR and lateral flow immunodiffusion assay kits.  From bitter experience, state and federal agencies are now able to rapidly confirm HPAI and then quarantine and dispose of infected flocks.  Notwithstanding experience in depopulating large caged-hen and aviary egg production complexes, it may take more than five days to euthanize and dispose of a flock comprising one million or more hens.

It is time that APHIS recognized that HPAI is at least seasonally and regionally endemic with migratory waterfowl and marine birds serving as reservoirs and disseminators of virus each fall and spring. Given the duration of the current epornitic it is possible that domestic, resident avian and mammalian species may perpetuate infection that can be transmitted to commercial poultry.

Despite seasonal reoccurrence of the infection since 2022, APHIS has pursued a futile policy of attempting to “stamp out” the infection.  This approach would be justified if an exotic viral disease were to be imported into the U.S. and introduced onto a single farm through defective biosecurity.  Eradication would be possible with rapid diagnosis and expedient depopulation and disposal of carcasses.  The reality of HPAI is far different from the situation envisaged in the APHIS conceptual model. With respect to HPAI, “stamping out” in the classic sense is inappropriate, outdated and inconsistent with epidemiologic reality. 

APHIS has at its disposal personnel with experience in field epidemiology. Despite this resource, the Agency has not conducted thorough epidemiologic investigations relating to the mode of transmission of virus from migratory bird reservoirs to farms.  The belated and incomplete publications on outbreaks during 2022 failed to identify what is evident to poultry health professionals in North America. It appears that the infection can be transmitted over distances of up to a mile by the aerogenous route. APHIS has failed to publish on any structured evaluation of environmental variables that may influence transmission or viability of H5N1 virus including humidity, wind movement, cloud cover or temperature.  A number of scientific studies have confirmed the possibility of aerogenous transmission as reported in EGG-NEWS during the past year.  If it is accepted that avian influenza virus can be transmitted on entrained dust or soil particles then even the most rigorous structural and operational biosecurity will not provide absolute protection for power-ventilated houses as denoted by the circumstances associated with a number of outbreaks.

It is questioned whether APHIS administrators actually want to know how the virus enters farms.  To accept that the infection is seasonally and regionally endemic and is transmitted by air movement over as yet undetermined distances, presumes that stamping out will not be possible. Seasonal reintroduction of H5 and H7 influenza viruses predicates a new approach.

Attempting to eradicate avian influenza in commercial flocks by serial depopulation imposes a cost on the public sector through indemnity and logistics.  Producers lose income while replacing flocks. Welfare advocates including legislators have condemned extensive depopulation including VSD. The cost of uncontrolled infection for consumers is immense, overshadowing direct costs for control. Depopulation of over 50 million hens during the 2022-2023 epornitic resulted in a constant reduction in the national flock by at least 10 million laying hens resulting in a conservative incremental cost of $2 per dozen spread over 12 months.  With domestic sales of shell eggs and products amounting to seven billion dozen, consumers paid an incremental $15 billion as a result of the prolonged and uncontrolled infection.  A similar situation is playing out in 2024 with the total flock approximately 12 million under the pre-HPAI level of 326 million.

The adaptation of H5N1 avian virus to dairy herds has created an additional problem for the poultry industry in addition to milk producers.  To date, there have been 492 diagnosed cases of bovine influenza among dairy herds.  This figure is in all probability an undercount given the reluctance of states other than California and Colorado to impose rigorous surveillance programs based on assay of bulk milk.  California has diagnosed 278 cases within three months despite a program of rapid diagnosis with mandatory quarantines.  Bovine influenza-H5N1 is a risk to poultry as evidenced by spillovers to farms in Michigan, Utah and Colorado and possibly in the Central Valley of California.  APHIS has yet to release the results of epidemiologic studies that presumably have been conducted on the transmission of H5N1 strain B3.13 in the dairy industry.

The zoonotic aspect of H5N1 influenza virus is a growing concern.  Although a reassortment    event may result in a strain with both human and avian genes becoming infectious to humans, additional mutations will be required for contagion necessary to precipitate an epidemic.  The consequences of an H5 influenza pandemic would far exceed the economic and health effects of the SARS-CoV-19 pandemic. The quicker that the virus can be suppressed in the commercial poultry industry, the safer our population will be.

Creating immune poultry populations especially in areas with a high density of egg or turkey production and with large in-line complexes will reduce the financial impact of avian influenza and mitigate against emergence of a zoonotic strain.  The World Organization of Animal Health accepts the principle of immunization as an adjunct to biosecurity and quarantine to control the infection.  France and Mexico have successfully deployed vaccination to reduce incidence rates.   It is axiomatic that avian influenza is the Newcastle disease of the 2020s.  This infection was as catastrophic with respect to commercial production in the 1960s as avian influenza is at the present time.  Newcastle disease is effectively controlled by vaccination. Vaccination is obviously not perfect since nothing in biology is absolute. 

We are all too aware of the trade restraints associated with vaccination.  If, however, the infection emerges in high-density broiler production areas of the U.S. or if Brazil, the major world exporter of broiler products, encounters (or admits) to infection among commercial flocks, the approach of blanket national restrictions would fall away. Importing nations should be guided by the World Organization for Animal Health principles of compartmentalization and regionalization and controlled application of vaccination.  The incidence rate of avian influenza in the U.S. with the costs to both private and public sectors and the obvious futility of applying a “stamping out” program predicates immunization using available vaccines on a limited and controlled basis.  Turkeys and commercial egg production flocks, especially in areas of high risk, should receive priority consideration.  Vaccination of broiler breeder flocks or even commercial growing birds would be based on cost to benefit studies taking into account risks of infection, the financial impact of losses and also trade considerations that may have been overstated.

What is evident is that the program APHIS has following for three years is flat just not working.  Hope that migratory birds will cease shedding is not a viable strategy.  Current administrators of APHIS should step back from their present policy and restraints and reconsider the limited application of vaccination to protect flocks at the greatest risk based on the history of regional exposure.

Any representative or spokesperson for APHIS or colleagues who wishes to defend the status quo or advance the principle of limited and controlled vaccination is welcome to submit a comment to be posted.