Written By Pragati Ekamalli B.Pharm
Reviewed and Fact Checked by Vikas Londhe M.Pharm (Pharmacology)
Introduction
Bird flu, also known as avian influenza, is a sickness caused by Type A viruses. The first known case of a serious form of bird flu was reported in 1959, and in 1996, a specific strain called H5N1 was found in China. These viruses can infect farm animals like chickens and turkeys and can spread among wild aquatic birds like ducks and geese around the world. Some bird flu viruses can also affect other animals. Normally, humans do not get bird flu, but there have been rare cases where people became infected. This can happen when someone has close contact with sick birds or animals, especially if they touch their face after touching an infected animal or object. The virus can be found in the body fluids of infected animals.
History of avian influenza
In 1878, a vet in northern Italy saw many chickens dying. People didn’t understand viruses well then, so they named the sickness “fowl plague.” At first, it was mixed up with “fowl cholera,” which is caused by bacteria.
By 1901, scientists found out that “fowl plague” were caused by a virus. They figured this out because it could go through a filter, showing it was much smaller than bacteria. Later, technology showed that the virus was a type of H1N1 that affects birds.
In April 1981, at a meeting in First International Symposium on Avian Influenza at Maryland, researchers decided to stop using the name fowl plague and called it highly pathogenic avian influenza (HPAI) instead.
Types of Avian Influenza
Low Pathogenic Avian Influenza (LPAI): Low pathogenic avian influenza (LPAI) viruses typically cause mild or no symptoms in poultry and wild birds. However, in poultry, some LPAI strains can mutate into highly pathogenic forms.
Highly pathogenic avian influenza (HPAI): Highly harmful bird flu viruses, especially types A (H5) and A (H7), can make chickens very sick, often killing them within 48 hours. Most bird flu strains are less harmful, but some wild birds and ducks can carry the dangerous virus without showing signs of illness and spread it when they migrate. Some types can also kill wild birds, helping the virus spread around the world and putting both animals and people at risk.
Situation of Avian Influenza in USA
The first big outbreak of bird flu in the U.S. happened in Pennsylvania from 1983 to 1984, caused by the H5N2 strain, leading to the killing of over 17 million birds. In 2002-2003, a less severe H7N2 outbreak in Virginia led to more safety measures. The worst outbreak was in 2014-2015, when H5N2 and H5N8 strains affected the Midwest, resulting in the loss of over 50 million birds, especially in Iowa and Minnesota. Smaller outbreaks happened from 2016 to 2020, mostly affecting small farms and wild birds, highlighting the need for careful monitoring.
Currently, the U.S. is seeing cases of bird flu linked to the H5N1 strain, which has been spreading worldwide since 2021. This virus reached North America that same year, infecting many wild birds and farmed poultry in several states. Since 2022, many wild birds have tested positive for H5N1, and millions of farmed birds have been killed to stop the virus from spreading. Human cases have been rare, but there is still concern about possible transmission to people. A human case was confirmed in 2022 in Colorado involving a poultry worker who had mild symptoms and fully recovered.
In March 2024, H5N1 was found in U.S. dairy cows for the first time. The first infected herds were in Texas and Kansas, with more cases reported in over ten states. The virus was also found in raw milk and nasal swabs, leading to further investigations. This was the first time H5N1 affected large mammals in the U.S. In April 2024, a human case linked to dairy cattle was confirmed in Texas. The person, a dairy worker, had conjunctivitis and fully recovered.
While the overall risk to human health remains low, the continued spread of H5N1 among birds and now mammals represents a serious threat to the agricultural sector. The potential for viral mutations that could make human transmission more efficient is a key concern for health officials.
Current Human Avian Influenza Cases
As of April 2025, there have been several notable developments in human cases of avian influenza (bird flu), particularly involving the H5N1 subtype.
Mexico’s First Human Fatality: A 3-year-old girl from Coahuila, Mexico, tragically died from H5N1 infection, marking the country’s first confirmed human case. Investigations are ongoing to determine the source of infection, with tests on 38 close contacts returning negative results, indicating no immediate human-to-human transmission.
United States Occupational Exposures: In 2024, the U.S. reported 46 human H5N1 cases across six states, primarily among poultry and dairy workers. Most cases were mild, with no critical illnesses or fatalities. Notably, personal protective equipment (PPE) usage among these workers was found to be suboptimal.
Retrospective Worldwide fatality of H5N1
Indonesia: Indonesia has reported the highest number of human fatalities from avian influenza (H5N1) globally, with over 160 deaths since 2003. Most cases resulted from close contact with infected poultry.
Egypt: Egypt has had the highest number of H5N1 cases in the Middle East and Africa, with over 120 confirmed cases and more than 35 fatalities, primarily affecting rural areas with backyard poultry.
Vietnam: Vietnam has experienced 63 deaths from H5N1 since 2003. Despite aggressive control measures, sporadic outbreaks and fatalities have continued due to poultry exposure.
Cambodia: Cambodia has reported over 30 human cases of H5N1, with a high fatality rate, most of the infected individuals died, often due to delayed treatment in rural areas.
China: China has reported fewer human deaths compared to other countries, but still significant, with over 50 fatalities from H5N1 and other avian influenza strains like H7N9, which emerged in 2013.
Cumulative Global Cases: Since 2003, over 950 human H5N1 infections have been reported across 24 countries, with a case fatality rate of approximately 49%.
Public Health Response
Vaccine Development: In response to the growing threat, the U.S. Department of Health and Human Services has allocated $590 million to Moderna for the development of mRNA-based vaccines targeting multiple bird flu subtypes.
Arcturus Therapeutics Holdings Inc. has received FDA clearance to initiate clinical trials for its H5N1 pandemic influenza vaccine candidate, ARCT-2304, also known as LUNAR-H5N1. This self-amplifying mRNA (sa-mRNA) vaccine utilizes Arcturus’ proprietary STARR® platform and LUNAR® delivery technology.
Surveillance Efforts: The Centers for Disease Control and Prevention (CDC) is actively monitoring the situation, utilizing flu surveillance systems to detect H5 bird flu activity in humans and working with states to monitor individuals with animal exposures, subsequently, in April 2025, the FDA granted Fast Track designation to ARCT-2304, aiming to expedite its development and review process.
Conclusion
Bird flu, especially the H5N1 type, has changed from a small problem in birds to a serious worry for both animals and people. More cases are being seen in wild birds, farm animals, and even cows. The virus is showing it can jump from one species to another. While there are not many human cases, the chance that it could change and spread more widely is a big concern. This shows we need to keep a close watch, respond quickly, and speed up vaccine development. As the situation develops, countries need to work together to reduce the risk of a future outbreak and keep people healthy and food supplies safe.
Introduction
Bird flu, also known as avian influenza, is a sickness caused by Type A viruses. The first known case of a serious form of bird flu was reported in 1959, and in 1996, a specific strain called H5N1 was found in China. These viruses can infect farm animals like chickens and turkeys and can spread among wild aquatic birds like ducks and geese around the world. Some bird flu viruses can also affect other animals. Normally, humans do not get bird flu, but there have been rare cases where people became infected. This can happen when someone has close contact with sick birds or animals, especially if they touch their face after touching an infected animal or object. The virus can be found in the body fluids of infected animals.
History of avian influenza
In 1878, a vet in northern Italy saw many chickens dying. People didn’t understand viruses well then, so they named the sickness “fowl plague.” At first, it was mixed up with “fowl cholera,” which is caused by bacteria.
By 1901, scientists found out that “fowl plague” were caused by a virus. They figured this out because it could go through a filter, showing it was much smaller than bacteria. Later, technology showed that the virus was a type of H1N1 that affects birds.
In April 1981, at a meeting in First International Symposium on Avian Influenza at Maryland, researchers decided to stop using the name fowl plague and called it highly pathogenic avian influenza (HPAI) instead.
Types of Avian Influenza
Low Pathogenic Avian Influenza (LPAI): Low pathogenic avian influenza (LPAI) viruses typically cause mild or no symptoms in poultry and wild birds. However, in poultry, some LPAI strains can mutate into highly pathogenic forms.
Highly pathogenic avian influenza (HPAI): Highly harmful bird flu viruses, especially types A (H5) and A (H7), can make chickens very sick, often killing them within 48 hours. Most bird flu strains are less harmful, but some wild birds and ducks can carry the dangerous virus without showing signs of illness and spread it when they migrate. Some types can also kill wild birds, helping the virus spread around the world and putting both animals and people at risk.
Situation of Avian Influenza in USA
The first big outbreak of bird flu in the U.S. happened in Pennsylvania from 1983 to 1984, caused by the H5N2 strain, leading to the killing of over 17 million birds. In 2002-2003, a less severe H7N2 outbreak in Virginia led to more safety measures. The worst outbreak was in 2014-2015, when H5N2 and H5N8 strains affected the Midwest, resulting in the loss of over 50 million birds, especially in Iowa and Minnesota. Smaller outbreaks happened from 2016 to 2020, mostly affecting small farms and wild birds, highlighting the need for careful monitoring.
Currently, the U.S. is seeing cases of bird flu linked to the H5N1 strain, which has been spreading worldwide since 2021. This virus reached North America that same year, infecting many wild birds and farmed poultry in several states. Since 2022, many wild birds have tested positive for H5N1, and millions of farmed birds have been killed to stop the virus from spreading. Human cases have been rare, but there is still concern about possible transmission to people. A human case was confirmed in 2022 in Colorado involving a poultry worker who had mild symptoms and fully recovered.
In March 2024, H5N1 was found in U.S. dairy cows for the first time. The first infected herds were in Texas and Kansas, with more cases reported in over ten states. The virus was also found in raw milk and nasal swabs, leading to further investigations. This was the first time H5N1 affected large mammals in the U.S. In April 2024, a human case linked to dairy cattle was confirmed in Texas. The person, a dairy worker, had conjunctivitis and fully recovered.
While the overall risk to human health remains low, the continued spread of H5N1 among birds and now mammals represents a serious threat to the agricultural sector. The potential for viral mutations that could make human transmission more efficient is a key concern for health officials.
Current Human Avian Influenza Cases
As of April 2025, there have been several notable developments in human cases of avian influenza (bird flu), particularly involving the H5N1 subtype.
Mexico’s First Human Fatality: A 3-year-old girl from Coahuila, Mexico, tragically died from H5N1 infection, marking the country’s first confirmed human case. Investigations are ongoing to determine the source of infection, with tests on 38 close contacts returning negative results, indicating no immediate human-to-human transmission.
United States Occupational Exposures: In 2024, the U.S. reported 46 human H5N1 cases across six states, primarily among poultry and dairy workers. Most cases were mild, with no critical illnesses or fatalities. Notably, personal protective equipment (PPE) usage among these workers was found to be suboptimal.
Retrospective Worldwide fatality of H5N1
Indonesia: Indonesia has reported the highest number of human fatalities from avian influenza (H5N1) globally, with over 160 deaths since 2003. Most cases resulted from close contact with infected poultry.
Egypt: Egypt has had the highest number of H5N1 cases in the Middle East and Africa, with over 120 confirmed cases and more than 35 fatalities, primarily affecting rural areas with backyard poultry.
Vietnam: Vietnam has experienced 63 deaths from H5N1 since 2003. Despite aggressive control measures, sporadic outbreaks and fatalities have continued due to poultry exposure.
Cambodia: Cambodia has reported over 30 human cases of H5N1, with a high fatality rate, most of the infected individuals died, often due to delayed treatment in rural areas.
China: China has reported fewer human deaths compared to other countries, but still significant, with over 50 fatalities from H5N1 and other avian influenza strains like H7N9, which emerged in 2013.
Cumulative Global Cases: Since 2003, over 950 human H5N1 infections have been reported across 24 countries, with a case fatality rate of approximately 49%.
Public Health Response
Vaccine Development: In response to the growing threat, the U.S. Department of Health and Human Services has allocated $590 million to Moderna for the development of mRNA-based vaccines targeting multiple bird flu subtypes.
Arcturus Therapeutics Holdings Inc. has received FDA clearance to initiate clinical trials for its H5N1 pandemic influenza vaccine candidate, ARCT-2304, also known as LUNAR-H5N1. This self-amplifying mRNA (sa-mRNA) vaccine utilizes Arcturus’ proprietary STARR® platform and LUNAR® delivery technology.
Surveillance Efforts: The Centers for Disease Control and Prevention (CDC) is actively monitoring the situation, utilizing flu surveillance systems to detect H5 bird flu activity in humans and working with states to monitor individuals with animal exposures, subsequently, in April 2025, the FDA granted Fast Track designation to ARCT-2304, aiming to expedite its development and review process.
Conclusion
Bird flu, especially the H5N1 type, has changed from a small problem in birds to a serious worry for both animals and people. More cases are being seen in wild birds, farm animals, and even cows. The virus is showing it can jump from one species to another. While there are not many human cases, the chance that it could change and spread more widely is a big concern. This shows we need to keep a close watch, respond quickly, and speed up vaccine development. As the situation develops, countries need to work together to reduce the risk of a future outbreak and keep people healthy and food supplies safe.
References
1.Tripathi AK, Sendor AB, Sapra A. Avian Influenza. [Updated 2025 Feb 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan. Available from:https://www.ncbi.nlm.nih.gov/books/NBK553072/
2. Avian Influenza, World Organization for Animal Health, available from https://www.woah.org/en/disease/avian-influenza/
3. H5 Bird Flu: Current Situation, US centres for disease control and prevention, 11 April 2025, available from https://www.cdc.gov/bird-flu/situation-summary/index.html
4. Confirmations of Highly Pathogenic Avian Influenza in Commercial and Backyard Flocks, Animal and Plant Health Inspection Service, U.S. Department Of Agriculture
5. Lycett SJ, Duchatel F, Digard P. A Brief History of Bird Flu. Philos Trans R Soc Lond B Biol Sci. 2019 Jun 24; 374(1775):20180257. Doi: 10.1098/rstb.2018.0257. PMID: 31056053; PMCID: PMC6553608.
6. 2020-2024 Highlights in the History of Avian Influenza (Bird Flu) Timeline, US centres for disease control and prevention, 30 April 2024, available from https://www.cdc.gov/bird-flu/avian-timeline/2020s.html
7. What Are the Earliest Known Origins of Bird Flu? Available from https://www.history.com/articles/bird-flu-origins-humans-pandemic
8. Past Reported Global Human Cases with Highly Pathogenic Avian Influenza A (H5N1) (HPAI H5N1) by Country, 1997-2025, avian Influenza (Bird Flu), available from https://www.cdc.gov/bird-flu/php/avian-flu-summary/chart-epi-curve-ah5n1.html
9. Avian Influenza Weekly Update # 993: 11 April 2025, World Health Organization, available from https://www.who.int/westernpacific/publications/m/item/avian-influenza-weekly-update—993–11-april-2025
10. Global Avian Influenza Viruses with Zoonotic Potential situation update, Animal Health, Food and Agriculture organization of United Nations, available from https://www.fao.org/animal-health/situation-updates/global-aiv-with-zoonotic-potential/en
11. Avian Influenza (H5N1) Vaccines: What’s the Status? American Society of Microbiology, 04 March 2025, available from https://asm.org/articles/2025/march/avian-influenza-h5n1-vaccines-what-status
12. US awards Moderna $590 million for bird flu vaccine development, Reuters, January 18 2025, available from https://www.reuters.com/business/healthcare-pharmaceuticals/us-awards-moderna-590-million-bird-flu-vaccine-development-2025-01-17/
13. Arcturus Therapeutics Receives U.S. FDA Fast Track Designation for the STARR® mRNA Vaccine Candidate ARCT-2304 for Pandemic Influenza A Virus H5N1, Arcturus Therapeutics, 10 April 2025, available from https://ir.arcturusrx.com/node/13116/pdf
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