The epidemic spread of avian influenza among dairy cattle – in more than 700 farms, more than 71% of the total – has forced Californian governor to declare a state of emergency, on December 18, 2024. (1)
The situation continues to worsen, even in other US states, (2) and fears are beginning to be raised of the virus mutating, with species jumping (spillover) to humans. Serious damage to production chains, and some concerns.
1) Avian influenza, premise.
The first outbreak of highly pathogenic avian influenza (HPAI) virus H5N1 A/goose/Guangdong/1/1996 emerged in 1996. Since then, avian H5 subtype viruses have spread widely in Europe, Africa, North America and Asia via migratory birds, giving rise to several phylogenetic clades and subclades.
The latest epidemic still ongoing H5N8 outbreak has itself spread from western Russia and northern Kazakhstan to Europe and beyond via migratory birds (3,4). And in late 2021, an H5N1 virus detected in North America has been able to infect a broad spectrum of avian and mammalian species, both marine and terrestrial.
2) California, avian influenza in more than 700 dairy cattle farms
H5N1 virus infection of clade 2.3.4.4b was first reported in dairy cattle in Texas and Kansas (USA) in March 2024. It has rapidly spread to 16 states of the federation, causing mild infections also in some farm workers. Although the virus has so far retained specificity for avian receptors.
California– the largest dairy producing state in the US – has seen the highest number of infections in dairy herds so far, with a flurry of reports in recent months. Its governor has therefore mobilized a comprehensive, across-the-board response aimed at minimizing exposure to farm workers and contamination of raw dairy products.
The State has drawn on the technical and operational expertise of local, state, and federal governments to educate the public, health care providers, employers, and workers on prevention and control measures to reduce the risk of exposure to avian influenza. In addition, it has distributed millions of pieces of personal protective equipment to high-risk workers in dairy and poultry operations. (2)
3) Risks of virus mutation
AMVA (American Veterinary Medical Association), in a report dated December 30, 2024, recalled a scientific study on the H5N1 virus, published in December in the journal Science. (5) The researchers (Lin et al., 2024) performed genetic and structural analysis of possible mutations in the 2.3.4.4b clade, finding that:
– a single mutation (from glutamine to leucine in residue 226, of the virus haemagglutinin) is sufficient to switch from avian to human specificity
– the analysis is in any case limited to the specificity of the receptors, without considering all the factors associated with the transmission of influenza viruses from human to human.
‘H5N1 infection of dairy workers provides selective pressure for human-type receptor specificity. Furthermore, in the influenza season, co-infection with seasonal influenza viruses could lead to reassortment of bovine and human viruses and the creation of a hybrid virus more adapted to human infection’. (6)
4) Human infections generally not serious
A study funded by the Centers for Disease Control and Prevention (Ison et al., 2024) analyzed the first 46 human cases of avian influenza A(H5N1) infection identified from March to October 2024 in the United States. Of these:
- 20 subjects were exposed to infected poultry, 25 were exposed to infected or suspected infected dairy cows, and one individual had no identified exposure.
- Among the 45 patients with animal exposure (mean age 34 years) the progression was mild, with a mean duration of 4 days (range 1 to 8), without hospitalizations or complications.
- Use of personal protective equipment by workers exposed to infected animals was ‘suboptimal’. Gloves (71%), eye protection (60%) and few face masks (47%)
- 42 patients (93%) had conjunctivitis, 22 (49%) fever, and 16 (36%) respiratory symptoms; 15 (33%) had conjunctivitis only. (7)
5) First cases of serious human disease
The first case of serious human disease concerns a 13-year-old Canadian girl, affected by obesity, admitted to the hospital of British Columbia on November 7, 2024 in conditions of respiratory failure, pneumonia, acute kidney injury, thrombocytopenia and leukopenia. The girl – after 30 days of dialysis and 40 of ECMO (ExtraCorporeal Membrane Oxygenation) – was discharged from the intensive care unit. (8)
The probable cause of H5N1 clade 2.3.4.4b infection has been identified in contact with wild geese, perhaps mediated by a domestic animal.
The second case was instead reported by CDC, on December 18, 2024 in Louisiana. The patient would have contracted the infection through his backyard chickens and was hospitalized for a serious ‘case of infection with avian influenza A(H5N1) virus’. CDC – without providing details on the patient’s health status – recalled that even non-professional hunters and breeders must use ‘personal protective equipment’ (PPE) whenever they may come into contact with sick birds and their feces. (9)
6) Impacts on supply chains and ongoing work on vaccines
The livestock supply chains are suffering serious damage due to avian influenza. The culling of over 50,5 million heads of poultry, in 46 US states, has also caused a significant increase in prices. (10) And the analyses continue on cow’s milk.
The universities meanwhile, continue research on potentially useful vaccines to improve the immune response to avian influenza. Following work at Wageningen University, work at Stanford University’s School of Medicine is noted (11,12).
Dario Dongo
Footnote
(1) Governor Newsom takes proactive action to strengthen robust state response to Bird Flu. Government of California, US. December 18, 2024 https://tinyurl.com/mvxsy7km
(2) Animal and Plant Health Inspection Service, USDA. HPAI Confirmed Cases in Livestock. Latest retrieved January 2, 2024 https://tinyurl.com/yr5mv66h
(3) Dario Dongo, Carmela Mele. Avian flu, alert in Europe. Update. FT (Food Times). November 18, 2020
(4) Giorgio Perrone. Avian flu, growing contagion on farms. FT (Food Times). 2.12.21
(5) R. Scott Nolen, Malinda Larkin. Novel bird flu strain continues to threaten animal, public health. AMVA News. December 30, 2024 https://tinyurl.com/4pwe5rc6
(6) Ting-Hui Lin et al. (2024). A single mutation in bovine influenza H5N1 hemagglutinin switches specificity to human receptors. Science 386, 1128-1134. Doi: 10.1126/science.adt0180
(7) Michael G. Ison, Jeanne Marrazzo (2024). The Emerging Threat of H5N1 to Human Health. New England Journal of Medicine, 0, 0, (undefined). doi/full/10.1056/NEJMe2416323
(8) Critical Illness in an Adolescent with Influenza A(H5N1) Virus Infection. Letter to the editor. New England Journal of Medicine. December 31, 2024 https://tinyurl.com/2cx2w695
(9) CDC Confirms First Severe Case of H5N1 Bird Flu in the United States. CDC. December 18, 2024 https://tinyurl.com/ywyrbfrc
(10) US poultry farms forced to eliminate 50,5 million chickens because of avian flu. MercoPress. December 29, 2024 https://tinyurl.com/yfxyprpk
(11) Dario Dongo. Highly pathogenic avian flu boom, Wageningen trials three vaccines. FT (Food Times). October 11, 2022
(12) Vamsee Mallajosyula et al. (2024). Coupling antigens from multiple subtypes of influenza can broaden antibody and T cell responses. Science 386, 1389-1395. Doi:10.1126/science.adi2396
Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
