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Highly Pathogenic Avian Influenza A(H5N1): Recent Human Infection Cases and Prevention Strategies

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Summary

Recently, cases of Highly Pathogenic Avian Influenza A(H5N1) virus transmission from dairy cows and poultry to humans have been reported in the United States. Between March and October 2024, 46 human infections were identified, mostly presenting with mild symptoms such as conjunctivitis, fever, and mild respiratory issues. Contact with infected animals was the primary source of infection, and inadequate use of personal protective equipment (PPE) increased the risk of exposure. While no evidence of human-to-human transmission has been observed so far, continued monitoring of the virus’s evolution and enhanced protection measures for farm workers are necessary.

1. What is A(H5N1) Virus?

A(H5N1) is a highly pathogenic avian influenza (HPAI) virus that can infect poultry, mammals, and humans. First reported in Hong Kong in 1997, it has since caused over 900 human infections globally with a fatality rate of approximately 50%【5】. In 2024, the virus has been increasingly detected in dairy cows and poultry in the United States, leading to human infections【5】.

2. Analysis of 2024 U.S. Human Infections

(1) Infection Pathways

According to the U.S. Centers for Disease Control and Prevention (CDC), 46 human infections were reported between March and October 2024. The primary exposure routes were direct contact with infected animals【5】.

  • Dairy cow exposure (25 cases): Handling infected cows and raw milk
  • Poultry exposure (20 cases): Contact with infected birds during depopulation and processing
  • Unknown source (1 case): The individual was diagnosed through routine surveillance with no clear exposure history

(2) Common Symptoms

Among the 46 infected individuals, 93% developed conjunctivitis (eye redness and inflammation), while 49% had fever and 36% experienced respiratory symptoms【5】.

  • Conjunctivitis: 42 cases (93%)
  • Fever: 22 cases (49%)
  • Cough & sore throat: 16 cases (36%)
  • Muscle aches & fatigue: 10 cases (22%)
  • Diarrhea & vomiting: 2 cases (4%)

Most symptoms resolved within 4 days, and no hospitalizations were reported【5】.

(3) Treatment & Prevention Measures

  • 87% of infected individuals received antiviral treatment (Oseltamivir/Tamiflu), with an average treatment duration of 5 days【5】.
  • A total of 97 household contacts were monitored, but no secondary infections were identified【5】.

3. Case Studies & Key Takeaways

Case 1: Outbreak at a Dairy Farm

In September 2024, an outbreak of A(H5N1) infections at a dairy farm in California led to four workers contracting the virus. All experienced conjunctivitis and fever, and the primary cause was inadequate PPE use. Following the outbreak, the farm implemented mandatory use of face masks and goggles【5】.

Case 2: Poultry Processing Workers Infected

In Colorado, nine poultry workers contracted A(H5N1) while handling infected birds. These individuals did not use adequate eye protection or face masks while participating in depopulation activities. The incident highlights the importance of PPE and hand hygiene in preventing transmission【5】.

4. Practical Prevention Tips

(1) For Farm Workers

✅ Minimize direct contact with infected animals
✅ Wear PPE: masks, goggles, gloves, waterproof clothing
✅ Maintain proper hand hygiene
✅ Boil milk and cook poultry properly before consumption

(2) For the General Public

✅ Avoid consuming raw milk, raw eggs, or undercooked poultry
✅ Wash hands after visiting poultry farms or live markets
✅ Seek medical attention immediately if experiencing fever, cough, or conjunctivitis

5. Conclusion: How Should We Prepare for A(H5N1)?

Although human-to-human transmission has not been observed, farm workers and individuals exposed to infected animals face a higher risk of infection. Proper hygiene, PPE use, and cooking practices are essential in reducing the risk. Continued surveillance of A(H5N1) mutations and rapid public health response will be necessary to prevent further outbreaks【5】.

References

【5】 New England Journal of Medicine (NEJM), February 27, 2025, “Highly Pathogenic Avian Influenza A(H5N1) Virus Infections in Humans,” DOI: 10.1056/NEJMoa2414610.

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H5N9 Avian Influenza: Risks and Prevention Tips

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H5N9 avian influenza has recently emerged as a concern after being detected at a duck farm in California, USA. This subtype of the avian flu virus has drawn attention for its potential to affect both birds and humans. In this post, we’ll explore the risks associated with H5N9, its potential for human transmission, and practical tips for preventing an outbreak.

What Is H5N9 Avian Influenza?

H5N9 is a subtype of the avian influenza virus that primarily affects birds. Historically, it has been considered a low-pathogenic virus, but recent cases have shown it evolving into a high-pathogenic strain. This has heightened concerns about its potential impact on poultry, humans, and even the global economy.

Can H5N9 Infect Humans?

Currently, H5N9 is primarily confined to birds, with no confirmed cases of human transmission. However, the virus contains the N9 gene, which could potentially facilitate infection in humans if genetic mutations occur. Individuals who have close contact with infected birds, such as poultry workers, are considered to be at the highest risk.

Risk of an Outbreak

While the likelihood of a large-scale outbreak remains low at this time, the high pathogenicity of H5N9 in birds is a cause for vigilance. Experts emphasize the need for continuous monitoring, robust biosecurity measures, and vaccine development to minimize the chances of the virus spreading to humans or causing widespread damage to poultry populations.

H5N9 Avian Influenza Prevention Tips

  1. Avoid Contact with Infected Birds: If you work in close proximity to birds, always wear personal protective equipment such as masks and gloves.
  2. Practice Hand Hygiene: Wash your hands frequently, especially after handling poultry or eggs.
  3. Cook Food Thoroughly: Ensure poultry and eggs are fully cooked before consumption to eliminate any potential pathogens.
  4. Follow Public Health Guidelines: Stay informed about local health advisories and report any unusual bird deaths to authorities.
  5. Stay Updated on Vaccinations: Keep track of vaccination options for avian influenza and consider them if recommended in your area.

Conclusion

H5N9 avian influenza serves as a reminder of the ongoing risks posed by emerging viruses. While the current risk to humans is minimal, it’s crucial to take preventive steps and stay informed about potential developments. Protecting yourself and your community begins with education and vigilance.

Stay safe and proactive in maintaining your health and well-being!

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