Based on the ubiquitous presence of domestic pigeons (Columba livia)  in feed storage, mixing and transport facilities and on poultry farms, a series of studies was performed to investigate the susceptibility of the species to H5N1 avian influenza clade 2.3.4.4b.  Variable doses of virus were administered to pigeons confirming resistance to other than high levels of virus.  Pigeons did not demonstrate clinical signs after infection and did not transmit virus to either contact pigeons or chickens.  Low levels of viral RNA were identified in tissues from directly inoculated pigeons but absent any obvious histologic lesions.

Based on the laboratory and contact studies, pigeons are regarded as an unlikely source of avian influenza and do not pose a significant threat of zoonosis. 

DiGenova, C. et al, Pigeons Exhibit Low Susceptibility and Poor Transmission Capacity for H5N1 Clade 2.3.4.4b High Pathogenicity Avian Influenza Virus.  bioRxiv doi.org/10.1101/2025.05.02.651910

This special edition of EGG-NEWS is intended to update subscribers with recent events relating to HPAI with commentary. The past week was dominated  by the as yet single case of HPAI in a commercial farm in Brazil and the implications arising from the event. A case  of HPAI in a large egg-production complex in Arizona in late May suggests that infection may be introduced onto farms from sources other than seasonally migrating waterfowl that are currently in their breeding areas. 

The messages to be conveyed in this edition are:-

•   HPAI should be recognized as a panornitic. This dictates radical changes to traditional restraints on international trade in poultry and products. Import regulations should be amended to conform to WOAH principles and standards including regionalization, compartmentalisation, vaccination and surveillance
•   HPAI is endemic in the U.S. especially impacting  regions corresponding to the four migratory flyways.
•   Biosecurity, however stringent does not provide absolute protection
•   Vaccination against H5 avian influenza is required as an adjunct to biosecurity for U.S.egg-producing and turkey flocks in high-risk areas, subject to surveillance and certification of freedom from infection at the time of harvest or shipment of eggs

A recent publication* evaluated transmission of H5N1 influenza among dairy cattle in the U.S.  The stochastic model based on 36,000 dairy herds in the continental U.S. attempted to quantify the extent of infection.  As of January 2025, when the article was submitted for peer review, the authors concluded that the infection is under-reported and that outbreaks will increase in Arizona and in Wisconsin.  The model suggests continuing cases associated with movement of dairy cattle coupled with inadequate programs of surveillance and restriction of transport.

Persistence of bovine influenza H5N1 in dairy cattle represents a danger to the poultry industry as confirmed by the 2024 outbreak of highly pathogenic avia influenza (HPAI) in western Michigan and the possibility of cases in Colorado and more recently in Arizona.  Failure to control and suppress bovine influenza will represent an ongoing risk to egg producers given movement of personnel between dairy herds and poultry flocks.  Common feed mills with non-dedicated delivery vehicles represents a risk of cross-industry infection. Proximity of large dairy and poultry farms could result in transmission of HPAI given the possibility of aerogenous spread of virus from large dairy installations to power-ventilated egg-production complexes.

*Rawson, T. et al A mathematical model of H5N1 influenza transmission in U.S. dairy cattle. Nature Communications doi.org10.1038/s41467-025-59554-z April 2025.

A recent article in the peer-reviewed journal Vaccines evaluated immunogenicity and efficacy of commercially available vaccines against highly pathogenic avian influenza virus, strain H5N1 in commercial geese raised for slaughter.  In general, an immune response was elicited by all vaccines evaluated, but durability of immunity was dependent on the type of the initial vaccination and the sequence of subsequent booster doses. Challenge under controlled conditions showed protection from clinical disease. Vaccination did not establish sterile immunity, although viral shedding was significantly lower compared to unvaccinated controls.

• Subunit vaccines containing H5 hemagglutinin antigen elicited seroconversion after a single dose and provided clinical protection. 
• A viral vector vaccine delivering genes encoding for H5 antigen resulted in a protective level of antibodies but required a booster for complete protection, and with some viral shedding following challenge.
• An RNA vaccine delivering nucleic acid sequences to stimulate antibody offered full clinical protection following initial vaccination with a booster.
• An inactivated oil emulsion vaccine containing native viral proteins stimulated seroconversion after a single dose but a booster enhanced antibody titer and protection.

The authors concluded that vaccination of geese, irrespective of the type of vaccine administered provided clinical protection and reduced viral excretion.  The results confirmed that vaccines could be incorporated into a program of HPAI prevention for geese that are highly susceptible and represent a significant industry in eastern Europe. 

The need for surveillance of vaccinated flocks was stressed to confirm attainment of protective levels of circulating antibody. Sequencing viral isolates is necessary to detect possible mutations associated with application of vaccination, recommOended as an adjunct to biosecurity measure to protect growing geese and presumably other commercial poultry species.

Despite the fact that migratory waterfowl are now established in their summer breeding grounds, outbreaks of highly pathogenic avian influenza (HPAI) persist.  The latest case in Maricopa County, AZ, involving a complex of 2.3 million hens indicates the persistence of infection.  Sequencing of the implicated virus will determine whether it is an avian-related D1.1 or a cattle B3.13 strain that will provide evidence of the source and route of infection.  The outbreak in Arizona was preceded by an April 30^th case involving 0.6 million hens in Aurora, SD. 

The severe losses that have occurred in 2025 to date include 33.2 million egg-producing hens on 60 farms or complexes. The incidence rate has obviously declined over the past three months but diagnosed outbreaks persist.  Growing turkeys are affected along with individual and obviously under-reported cases in backyard flocks.  Isolation of H5N1 avian influenza virus from live bird markets confirms the presence of undiagnosed supply flocks. Based on the absence of reports there is no certainty that USDA-APHIS is conducting traceback investigations to identify the source farms supplying live markets along the Atlantic seaboard.  The APHIS dashboard relating to detection of highly pathogenic avian influenza in wild birds updated on May 13, indicates isolation of H5N1 virus with a Eurasian genome from diverse states involving both waterfowl, black vultures  during Q1 and swallows during January.

Outbreaks among commercial and backyard flocks since February are indicated below:

This table confirms a declining incidence rate of cases among commercial flocks but unlike previous epornitics, outbreaks have persisted during late spring.

For 2025 to date, and based on an egg -producing population of 285 million hens, losses have attained:

Losses among caged hens are disproportionately high due to the effect of individual large complexes being affected.  Among the cage-free losses most were in large aviary complexes.  Organic and other cage-free hens in barns and in small commercial flocks were relatively unaffected despite regular feed delivery, egg collection and relatively lower levels of biosecurity as compared to in-line complexes.

Despite the USDA whack-a-mole approach to eradication and for the past three years as a program of control, highly pathogenic avian influenza has become endemic in the U.S. High risk areas include wetlands where migratory waterfowl congregate and along the four major flyways.  Although rapid flock depopulation has apparently reduced inter-flock transmission, it is obvious that virus is introduced into large complexes with power ventilation, whether caged or aviary housed, by the aerogenous route. Additional mechanisms include infected rodents, defects in biosecurity, transport and vaccination crews.

For the past three years, the industry has suffered from a lack of epidemiologic information relating to risk factors and specific routes of introduction of virus. It is known that APHIS in conjunction with federal and state wildlife agencies has conducted surveys on free-living mammals and birds in the vicinity of outbreaks on large complexes.  Results have yet to be published. These deficiencies have impeded the design and implementation of innovative methods of protection including vaccination.

Responding to high egg prices and escalating costs for control, the USDA announced a ‘five-pronged’ approach to address HPAI that effectively offered nothing new especially in the immediate and short-term. The program studiously avoided adoption of vaccination as an adjunct to biosecurity alone that clearly fails to offer absolute protection from infection.

On May 16^th, the Brazil, Ministry of Agriculture reported a confirmed outbreak of highly pathogenic avian influenza (HPAI) in a broiler breeder farm with 17,000 birds located in the Municipality of Montenegro in the state of Rio Grande do Sul.  The farm concerned  Is contracted to Vibera Foods that has an association with Tyson Foods. The farm was rapidly depopulated and eggs were retrieved from hatcheries in the state in addition to facilities in Minas Gerais and Parana states.

The outbreak occurred concurrently with a diagnosis in a bird sanctuary in Sapucaia do Sul, approximately 30 miles from the index case. It is presumed that this facility with a lake and the index farm were infected  concurerently by migratory birds rather than by direct or indirect contact. Brazil has reported numerous diagnoses of avian influenza H5N1 in migratory birds along the Atlantic littoral but prior to the present report the infection has not occurred in commercial flocks. 

Predictably the report resulted in importing nations imposing embargos that will impact exports over the short term but may have longer term implications for both Brazil and world broiler trade if additional cases emerge or are disclosed especially if in multiple states. At the outset, the U.S. broiler industry should refrain from Schadenfreude, that unique Teutonic characteristic of deriving pleasure in someone else’s misfortune.  Brazil expects to resume exports in the near future since many customer nations are imposing only limited localized embargos and will follow the World Organization of Animal Health (WOAH) limitation of 28 days following completion of decontamination. Despite an optimistic statement from the USA Poultry and Egg Export Council concerning acquisition of new markets, U.S. integrators are currently unable to supply the whole birds and other products exported by Brazil.

Investigations subsequent to the Rio Grande do Sul outbreak failed to confirm HPAI in commercial farms located in Ipumirim in Santa Catarina and in Aguiarnopolis in Tocantins state. In addition a number of backyard flocks have yielded negative results.

To place the importance of Brazil in perspective, production in Brazil during 2025 will attain 15,250 million metric tons representing 14.4 percent of world output of 105.8 million metric tons, excluding feet. Production in Brazil is approximately 70 percent of projected U.S. output of 21.7 million metric tons.

Domestic consumption in Brazil will attain10.17 million metric tons in 2025, equivalent to a per capita value of 47.9 kg. assuming a population of 212 million.  According to USDA estimates, Brazil will export 5.3 million metric tons comprising a diverse range of RTC products in 2025 representing 37 percent of world trade and 1.7 times the volume of U.S. exports of 3.3 million metric tons, with 97 percent as leg quarters.  In 2024 Brazil exported 5.3 million metric tons valued at $9.94 billion at a unit price of $1,878 per ton.  In comparison the U.S. exported 3.3 million metric tons valued at $4.8 billion equivalent to a unit price of $1,459 per metric ton, reflecting a preponderance of relatively low-value leg quarters.

Exports of poultry products from Brazil including fertile eggs, breeding stock and RTC could be severely impacted given initial nationwide embargos by China, the E.U. and South Korea. Some nations recognizing their respective needs for chicken from Brazil have imposed state or regional embargos including Japan, Saudi Arabia and the United Arab Emirates among 17 nations.

The potential for disruption in trade from Brazil can be judged by 2024 exports:

During the first quarter of 2023 neighbors of Brazil including Argentina, Bolivia, Uruguay, Peru and Ecuador reported HPAI, strain H5N1 in wild birds, backyard flocks and some commercial farms.  In addition, Peru reported the death of over 1,000 sea lions and more than 65,000 migratory marine birds.  At this time, Brazil announced that suspect cases of HPAI in Rio Grande do Sul and Amazonas states were negative for the pathogen.  Producers in Brazil implemented extreme biosecurity measures to prevent infection, given the probability of introduction of the disease into commercial flocks by migratory birds following the pattern in north and central America and also in Asia and Africa.  By May 15^th 2023, Brazil had diagnosed 139 cases of HPAI in wild birds and subsistence poultry but inexplicably not on commercial farms as defined by the World Organization of Animal Health.

Carlos Favaro, the Minister of Agriculture for Brazil announced an emergency program to combat HPAI in August 2023 as a result of the extensive infection among migratory birds.  This was in recognition that any outbreak of HPAI in a commercial flock would trigger national, regional or state bans on shipments by importers including China and middle-East nations.

Brazil has remained free of reported avian influenza until the recently disclosed outbreak.

In mid-July 2024, Brazil suspended exports of all poultry products following mortality on a single table-egg production farm that was eventually diagnosed as velogenic, viscerotropic Newcastle disease (END) acquired following contact with wild birds.  After prompt depopulation and appropriate quarantine measures with surveillance, exports resumed with corresponding assurances to importers.  At the time it was questioned whether the specific case was in fact END since response to this infection would have been the same as an isolated case of HPAI. 

Brazil has a history of withholding information on diseases which may impact exports.  This is exemplified by Tom Vilsack, then USDA Secretary of Agriculture, addressing a formal letter to the Government of Brazil requiring improvement in detection and reporting of bovine spongiform encephalopathy. He stated “I urge Brazil in the strongest terms to continue its progress in streamlining timely animal disease reporting.”  The admonition by the USDA followed delays in reporting BSE with two cases of atypical infection diagnosed without prompt notification to the WOAH or importers.  Punitive import restrictions were imposed by trading partners on beef from Brazil following the revelation leading to the rejection of 140,000 metric tons of beef valued at $20 billion.  The fact that Brazil repeatedly failed to report cases of BSE raises the question of HPAI in commercial flocks.  The seven nations surrounding Brazil have reported H5N1 infection in free-living birds, backyard flocks or commercial farms but Brazil has only acknowledged extensive infection in migratory birds.

Conclusions can be derived from the most recent report of HPAI in a commercial flock in Brazil with implications for world trade:-

• HPAI is a panornitic occurring on all inhabited continents and including the Antarctic, affecting marine mammals and birds.  Accordingly, the question of “freedom” from highly pathogenic avian influenza and self-serving attempts to discriminate against exporters reporting localized or regional outbreaks is considered as factious.

• Avian influenza strain H5N1, clade 2.3.4.4b is endemic among migratory marine birds some species of which die of infection and others remain clinically unaffected carriers and disseminators of the pathogen.  Interaction among migratory marine birds and waterfowl through cohabitation on waterways and along coastal areas creates the risk of infection for susceptible commercial flocks.  Given that the pathogen can be transmitted by the aerogenous route over distances that may exceed one mile, even the most stringent biosecurity measures cannot assure absolute protection.

• The patchwork arrangement of trade agreements specifying embargos on entire nations, states or provinces or even regions are generally unjustified especially when importing nations report cases of HPAI in wild birds and free-living mammals and in their own commercial flocks.

• It is possible with PCR technology to confirm whether flocks of origin for exports are free of infection at the time of harvest allowing for certification under WOAH guidelines. 

• Given the geographic extent of both Brazil and the U.S. as the major exporting nations, imposition of countrywide bans is based either on ignorance of the epidemiology of HPAI or the misapplication of phytosanitary regulations to protect local industries.

• Despite the regularly updated recommendation of WOAH, there is an evident lack of uniformity in both adoption and recognition of diagnostic standards, certification and export regulations.  A point in question is compliance with the 28-day period following flock depopulation and decontamination following an outbreak of HPAI or END.  Some nations impose a 60-day embargo and in the case of China resumption of trade may be delayed for years. Harmonization and compliance with scientific standards is overdue.

• The overwhelming lesson from the ongoing panornitic, in progress since 2022, is that current methods of prevention are inadequate given the epidemiology of the infection.  Accordingly, the WOAH acceptance of preventive vaccination should be more extensively applied as an adjunct to biosecurity. Administration of commercially available effective vaccines should establish immune populations and would reduce inter-farm spread within a given area and will absolutely reduce expenditure on depopulation with accompanying indemnity.

Avian influenza should be regarded as the Newcastle disease of the 2020s.  During the 1970s END was in every way as catastrophic as HPAI and the infection is effectively suppressed in nations where a high level of immunity is achieved through diligent vaccination.

In an April 22^nd position statement, the American Association of Avian Pathologists (AAAP) reviewed current realities relating to vaccination of commercial poultry.  At the outset, the Association recognizes that highly pathogenic avian influenza (HPAI) is endemic in the U.S. and has affected all sectors of the poultry industry and has now emerged in dairy herds. Concurrently infection has been diagnosed in terrestrial mammals, companion animals, and domestic wild birds in addition to migratory marine species and waterfowl.  The AAAP panel responsible for the position statement points to the susceptibility of commercial poultry species and the failure to suppress the epornitic in commercial flocks since emergence of infection in 2022.

A case is made for vaccination consistent with the advocacy by EGG-NEWS over the past three years. Creating immune populations, especially in high-risk areas, will reduce the incidence rate by minimizing the susceptibility of flocks that will continue to be exposed to infection.

The position statement recognizes technical limitations relating to vaccination, the most important of which is failure to elicit sterile immunity. Vaccinated flocks if infected will shed virus although at a lower rate and extensive mortality will be suppressed.

The major restraint to deployment of commercially available vaccines of various types relates to the potential for trade embargos despite the acceptance of vaccination as an adjunct to biosecurity by the World Organization of Animal Health (WOAH).  Vaccination against avian influenza using rHVT-H5 vaccines has proven effective in the Netherlands, Italy and Belgium.  Other studies have shown the protective effect of inactivated oil emulsion H5 vaccines in numerous countries as a primary immunogenic agent or as a booster.

It is possible to establish a program of surveillance over vaccinated flocks including quantifying immune response applying serology and to confirm freedom from HPAI using PCR.  Available technology and logistics can be applied to certify that export consignments derived from specified flocks are free of infection at the time of harvest.

Currently, trade in poultry products and especially broiler meat is subject to a patchwork of regulations imposed by importers. The most extreme restrictions demand nationwide bans or less onerous state or provincial embargos. The reactions of importers are based on outmoded traditional approaches to control of catastrophic infections, to protect domestic industries from competition or as an economic weapon.  The World Organization of Animal Health accepts vaccination as an adjunct to biosecurity if conducted in accordance with established surveillance.

With the advent of HPAI in Brazil, the infection can be regarded as a panornitic and accordingly, trade should be regulated in accordance with sound epidemiologic and scientific principles. It is now incumbent on exporting nations to press for adoption of uniform policies on diagnosis of avian influenza, control measures including vaccination, enforcement of regionalization and compartmentalization and harmonizing documentation.

USDA-APHIS has long labored under the misconception that HPAI can be eradicated by a program of sequential depopulation.  The Agency has not responded to the endemic status of the infection, involving seasonal reintroduction and dissemination of HPAI virus by migratory waterfowl, the potential reservoir status associated with terrestrial mammals and free-living domestic birds and the reality of aerogenous transmission. An inflexible adherence to past policy has impeded rational decisions relating to suppression of the infection. 

The justifiable concern by the broiler segment of the U.S. poultry industry relating to export embargos should not continue to restrict the deployment of avian influenza vaccination in high-risk areas for egg-production and turkey grow-out flocks.  The cost to the public sector for indemnity and logistics in addition to the burden borne by consumers far outweighs the potential benefits accruing to broiler exports.  The emergence of bovine influenza-H5N1 raises the issue albeit remote of the possibility of mutation to become a zoonotic pathogen capable of contagion. This eventuality should influence veterinary and public health agencies to implement protection of flocks by regulated and strategic vaccination, as advocated by the AAAP.

The American Association of Avian Pathologists (AAAP) issued a position statement on bovine influenza on April 22^nd.  The release urges an immediate regulatory and industry response.

The AAAP notes the “narrow focus of testing restricted to lactating dairy cows that are moved interstate”.  It was suggested that surveillance should be intensified with specific reference to control areas surrounding positive herds.

The AAAP identified the absence of a national risk-based strategy incorporating scientific and epidemiologic principles that could be applied to reduce the spread of bovine influenza-H5N1.  Control strategies should incorporate a consideration of potential reservoir hosts including avian and mammalian species.

In the opinion of the AAAP, the USDA-APHIS has failed to investigate (or publish) pathways of transmission and risk factors despite emergence of H5N1 infection in the dairy industry as early as February 2024.  This negligence parallels the situation in commercial poultry and free-living birds.

As with poultry, it is evident that an effective vaccine, or series of vaccines, will be required to suppress and control infection.  Accordingly, it will be incumbent on USDA to establish trade agreements that will allow the limited use of H5 vaccine (in cattle as well as poultry) without compromising trade conducted in accordance with World Organization of Animal Health guidelines.

The AAAP emphasized the need for upgraded laboratory capability and resources necessary to maintain a program of surveillance and management of a comprehensive national vaccination program.  The Association urges federal funding for dedicated personnel and laboratory installations and equipment to initiate and sustain a control program consistent with an economically significant infection with a potential zoonotic implication.

A diagnosis of H5N1 Highly Pathogenic Avian Influenza in a single flock in the State of Rio Grande do Sul has disrupted exports. Domestic consumers in Brazil may benefit, at least over the short term. Given a population of 212 million per capita domestic consumption is 48kg (106lb) and is equivalent to 65 percent of annual production.  

This will indirectly benefit the Government of President Luiz Lula da Silva, currently criticized for high food prices.  Over the past twelve months through April, food prices increased by 7.8 percent with poultry and eggs up by 12.3 percent.

Economists consider that the beneficial effect from increased domestic supply and hence, a decline in prices will be transitory.  If the outbreak of HPAI is contained, exports will resume.  In the event that the disease spreads, extensive depopulation may reduce availability.  The consequence will be an increase over existing prices for poultry meat, the staple animal protein for much of the population.