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.
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】.
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】.
Among the 46 infected individuals, 93% developed conjunctivitis (eye redness and inflammation), while 49% had fever and 36% experienced respiratory symptoms【5】.
Most symptoms resolved within 4 days, and no hospitalizations were reported【5】.
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】.
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】.
✅ 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
✅ 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
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】.
【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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