Avian Influenza and One Health

Whenever an outbreak occurs among livestock, agriculture often gets a bad rap. The recent outbreak on dairy farms has led to a great deal of fear, despite the pasteurization of milk products³ which heats the milk to a high temperature and kills microbes.⁴ Briefly, some of the One Health factors driving this outbreak include the following: A widespread desire for affordable food has led to a decrease in small farms and an increase in larger scale farms that can weather changing market prices,⁵ and the fact that wild birds are ubiquitous and are difficult to keep out of barns where they may come in contact with (and potentially infect) livestock.⁶ As consumers of any food product, we are all complicit in the increase of aggregated large-scale agriculture. By buying into the benefits of this system – namely, affordable food – we buy into the reality that this type of agriculture bears an increased risk of disease, as one might see with larger gatherings of people.

Further, we know that contact with wildlife always carries the risk of spillovers of zoonotic diseases. This is why pets are vaccinated for diseases that pose a human threat, such as rabies. Unfortunately, farmers currently lack reliable options for keeping birds out of barns and preventing outbreaks of diseases like avian flu – for which we do not vaccinate. They do, however, have the opportunity to collaborate with researchers.

Texas dairy workers collect a nasal swab from a sick cow

UTMB’s Dr. Gregory Gray pointed out in his recent interview with Science that “if we don’t work together with agriculture, we won’t know what’s circulating”. When outbreaks do occur, farms are usually required to euthanize their livestock on a massive scale; this has occurred recently on multiple US poultry farms,⁷ resulting in a massive loss of life intended to protect our food supply.

Professor Gray draws blood from a cattle worker

While a majority of the news about the recent avian flu outbreak has discussed the repercussions on agriculture and questioned public safety, it’s important to note why humans rarely get avian flu. The reason for this has to do with the location of receptors in our respiratory system.

Human flu viruses have been found to bind to a molecule called SAα 2,6 in order to infect epithelial cells that line our upper airway.^8,11 In contrast, avian viruses bind mainly to alveolar cells, located deeper in the human lungs via SAα-2,3 Gal receptors. Although, as a precaution, people should generally avoid exposure to animals infected with avian influenza, this binding preference means humans rarely get infected unless they are in extremely close and repetitive contact. Otherwise, the viruses rarely penetrate deeply into our lungs where their targeted receptors are abundant. Once infected, avian flu viruses only replicate efficiently in the lower respiratory tract and are unlikely to be passed to other humans

According to the WHO, 889 cases of avian influenza have been reported in humans globally since 2003.⁹ Considering that the CDC estimates that 9.3 to 41 million Americans become ill with the flu each year,¹⁰ 889 avian flu cases over a 21 year period is an incredibly small fraction of the overall flu caseload. When humans do contract avian influenza, however, the resultant infection can be deadly. The WHO reports that fifty-two percent of avian influenza infections in humans result in death. Because of the extensive food safety measures, the placement of receptors in our lungs, and the fact that few Americans work in the agriculture industry, the overall risk to the public of contracting avian influenza is quite low. UTMB’s One Health laboratory team has recovered 15 highly-pathogenic avian H5N1 viruses on cattle farms this spring and is busying drafting scientific reports that will help increase our understanding regarding how the now-multistate epizootic is spreading.

Citations:

1. CDC. “Types of Influenza Viruses.” Centers for Disease Control and Prevention, 30 Mar. 2023, https://www.cdc.gov/flu/about/viruses/types.htm.
2. CDC. “Avian Influenza Current Situation Summary.” Centers for Disease Control and Prevention, 10 Apr. 2024, https://www.cdc.gov/flu/avianflu/avian-flu-summary.htm.
3. Highly Pathogenic Avian Influenza A(H5N1) Virus in Animals: Interim Recommendations for Prevention, Monitoring, and Public Health Investigations | Avian Influenza (Flu). 12 Apr. 2024, https://www.cdc.gov/flu/avianflu/hpai/hpai-interim-recommendations.html.
4. Cohen, Jon. “Bird Flu Discovered in U.S. Dairy Cows Is ‘Disturbing’ Scientist Who Tracks Infections on Cattle Farms Discusses Implications of Recently Announced Virus Detections.” Science, https://www.science.org/content/article/bird-flu-discovered-u-s-dairy-cows-disturbing.
5. The High Cost of Producing Cheap Food. https://www.ft.com/content/f04e9e61-4a12-409a-a457-fbda710e9418. Accessed 15 Apr. 2024.
6. What Can I Do about the Birds in My Barn? https://hoards.com/article-30781-what-can-i-do-about-the-birds-in-my-barn.html. Accessed 15 Apr. 2024.
7. Jacobs, Andrew. “A Cruel Way to Control Bird Flu? Poultry Giants Cull and Cash In.” The New York Times, 2 Apr. 2024. NYTimes.com, https://www.nytimes.com/2024/04/02/science/bird-flu-aid-animal-welfare.html.
8. Shinya, Kyoko, et al. “Influenza Virus Receptors in the Human Airway.” Nature, vol. 440, no. 7083, Mar. 2006, pp. 435–36. www.nature.com, https://doi.org/10.1038/440435a.
9. Avian Influenza A(H5N1) – United States of America. https://www.who.int/emergencies/disease-outbreak-news/item/2024-DON512. Accessed 15 Apr. 2024.
10. CDC. “Burden of Influenza.” Centers for Disease Control and Prevention, 28 Feb. 2024, https://www.cdc.gov/flu/about/burden/index.html.
11. Chauhan, Ravendra P., and Michelle L. Gordon. “An Overview of Influenza A Virus Genes, Protein Functions, and Replication Cycle Highlighting Important Updates.” Virus Genes, vol. 58, no. 4, Aug. 2022, pp. 255–69. Springer Link, https://doi.org/10.1007/s11262-022-01904-w.