H5N1 shows atypical 'pink eye' cases
- U.S. and global H5N1 surveillance has highlighted an unusual pattern: many recent human infections, especially among dairy workers, have presented mainly as conjunctivitis. - A 2025 Nature Medicine analysis of 70 U.S. cases found 62 patients reported eye redness, while respiratory symptoms were reported less often. - New airway-organoid experiments from 10 animal species offer a faster way to map which hosts influenza may infect next. (tandfonline.com)
Bird flu is usually framed as a lung disease, but many recent U.S. H5N1 infections have shown up first as conjunctivitis, or pink eye. (cdc.gov) (nature.com) That pattern emerged after H5N1 spread into U.S. dairy cattle in March 2024 and then into exposed workers. As of March 6, 2026, the Centers for Disease Control and Prevention says the United States has recorded 71 human cases since 2024. (cdc.gov) A Nature Medicine paper published in July 2025 reviewed 70 U.S. cases detected from March 2024 to May 2025. It found 62 patients, or 89%, reported eye redness, compared with 29, or 41%, who had respiratory symptoms. (nature.com) California’s fall 2024 cluster showed the same pattern in farm investigations. A March 2025 Morbidity and Mortality Weekly Report said public health agencies should investigate either influenza-like illness or conjunctivitis in workers exposed to infected animals. (cdc.gov) Scientists have been trying to understand why the eye keeps appearing in these cases. A Lancet Microbe study reported that the current clade 2.3.4.4b H5N1 virus could infect and replicate in human eye tissue and in corneal tissue from cows. (thelancet.com) At the same time, researchers are building “mini airways,” called organoids, from stem cells and animal tissue. These are lab-grown stand-ins for real respiratory tracts, giving virologists a way to test host range without infecting live animals first. (tandfonline.com) In one 2026 study, researchers established airway organoids from 10 wildlife and livestock species and infected them with pandemic H1N1 and clade 2.3.4.4b H5N1. The infections produced species-by-species differences in susceptibility that the authors said matched field and animal data. (tandfonline.com) (forbes.com) The point of those organoids is speed. Instead of waiting for outbreaks to reveal which mammals a virus can use, labs can compare how efficiently a strain grows across species-specific airway tissue in advance. (tandfonline.com) Public health agencies have not said the current H5N1 situation has become a general-population emergency. The Centers for Disease Control and Prevention says there is still no known person-to-person spread in the United States and that the current public health risk remains low. (cdc.gov) But the clinical picture has changed from the classic image of severe bird-flu pneumonia. For doctors, farm operators and exposed workers, a red eye has become one of the clearest signals to test for H5N1 early. (nature.com) (cdc.gov)
