What condition may be seen in patients infected with avian flu from cows?

Conjunctivitis is the Primary Condition Seen in Patients Infected with Avian Flu from Cows

The most common clinical manifestation in patients infected with avian influenza (H5N1) from dairy cattle is conjunctivitis (eye inflammation), with most infected individuals experiencing primarily eye symptoms. 1

Clinical Presentation of Avian Influenza from Cattle

The highly pathogenic avian influenza A(H5N1) virus, specifically clade 2.3.4.4b, has recently been identified in dairy cattle in the United States, representing an expansion of the virus's host range to include ruminants. Human cases linked to these infected cattle have shown distinct clinical patterns:

• Primary manifestation: Conjunctivitis (eye inflammation) 1
• Severity: Generally mild symptoms in humans 2
• Other possible symptoms: Influenza-like illness (ILI) 1

Recent Cases in the United States

In 2024, several human cases of H5N1 infection have been documented in dairy farm workers who had direct contact with infected cows:

• In March 2024, an individual working on a dairy farm in Texas tested positive for HPAI A(H5N1) 1
• Additional cases were identified in dairy farm workers in Michigan 1
• A fourth case was identified in a dairy farm worker in Colorado in July 2024 1

Importantly, all infected individuals primarily experienced eye symptoms or conjunctivitis, and all recovered from their infections 1. This pattern of predominantly ocular symptoms differs from the more severe respiratory and systemic manifestations seen with other avian influenza infections in humans.

Transmission Patterns

The recent cases represent a significant development in avian influenza epidemiology:

• These are believed to be the first documented cases of mammalian-to-human transmission of HPAI H5N1 2
• The virus appears to replicate primarily in the mammary tissue of infected cows 2
• High viral loads have been detected in unpasteurized milk from infected cattle 3, 2
• There has been no evidence of person-to-person spread of these H5N1 viruses 1

Comparison to Other Avian Influenza Presentations

The clinical presentation of cattle-associated H5N1 infections (primarily conjunctivitis) differs from other avian influenza infections:

• H5N1 infections acquired directly from birds typically cause severe respiratory illness with high mortality (approximately 60%) 1
• Other avian influenza subtypes like H7N7 and H7N3 have also been associated with conjunctivitis in humans 1
• H7N2 infections have been linked to both lower respiratory tract disease and conjunctivitis 1

Risk Factors and Prevention

Individuals at highest risk for acquiring avian influenza from cattle include:

• Dairy farm workers with direct contact with infected animals 1, 2
• Persons handling unpasteurized milk or colostrum from infected cows 3

Preventive measures recommended by public health authorities include:

• Seasonal influenza vaccination for persons working with potentially infected animals 1
• This won't prevent avian influenza infection but may reduce the theoretical risk of viral reassortment 1
• Following biosecurity protocols when working with potentially infected animals 4

Clinical Implications

For clinicians evaluating patients with potential avian influenza from cattle exposure:

• Consider H5N1 infection in patients with conjunctivitis who have had recent contact with dairy cattle
• Recognize that the presentation may be milder than avian influenza acquired directly from birds
• Be aware that while human infections have been mild so far, the virus has caused fatal systemic infections in cats fed raw milk from infected cows 3
• Report suspected cases to public health authorities for appropriate testing and surveillance

The emergence of H5N1 in dairy cattle represents an important evolution in the epidemiology of avian influenza, with conjunctivitis being the hallmark clinical manifestation in humans infected through this route.