Ocular infectivity and replication of a clade 2.3.4.4b A(H5N1) influenza virus associated with human conjunctivitis in a dairy farm worker in the USA: an in-vitro and ferret study.

Summary

Human nasal and corneal models supported replication of multiple IAVs; H5N1 did not show uniquely enhanced ocular tropism relative to H7N7 or H1N1. In serologically naive ferrets, ocular-only exposure to the H5N1 Texas/37 strain resulted in systemic, often fatal infection and transmission to cage-mates, whereas pre-existing H1N1 immunity mitigated disease and prevented onward transmission.

Key Findings

• Human corneal and nasal tissue constructs supported replication of H5N1, H7N7, and H1N1; H5N1 did not exhibit uniquely enhanced ocular tropism.
• Ocular-only exposure to H5N1 Texas/37 in naive ferrets caused systemic, often fatal infection and transmission to cage mates.
• Pre-existing H1N1pdm09 immunity reduced disease severity after ocular exposure and prevented transmission to naive contacts.

Clinical Implications

Reinforce strict eye protection for exposed workers (e.g., dairy farms, laboratories) and clinicians. Consider ocular exposure pathways in risk assessments and infection control guidance, and recognize that heterosubtypic immunity may mitigate severity but not necessarily prevent infection without comprehensive PPE.

Limitations

• Exact ferret sample sizes and detailed statistical power are not provided in the abstract.
• Preclinical models may not fully capture human ocular exposure dynamics and clinical outcomes.

Future Directions

Quantify human ocular exposure risks across settings; evaluate vaccine/antiviral protection against ocular inoculation; refine PPE guidance and implement occupational surveillance in affected industries.