A conjunctivitis with hemorrhage in both eyeswithout visual impairment. It is the symptom presented by the first human case linked to the highly pathogenic H5N1 avian influenza virus epidemic circulating among dairy cattle in the United States. This is the worker of a Texan dairy company whose infection made headlines a month ago, bouncing around the international media. The description of the case is the subject of a letter to the editor published in the ‘New England Journal of Medicine’, signed by experts from the Centers for Disease Control and Prevention (Cdc) in Atlanta, the Texas Department of State Health Services and Texas Tech University Bioterrorism Response Laboratory in Lubbock, of the Texas Department of State Health Services in Austin. An image to accompany the correspondence: a photo of the patient’s eyes.
“Sporadic human infections with highly pathogenic avian influenza (Hpai) A(H5N1) viruses, with a broad spectrum of clinical severity and a cumulative mortality rate greater than 50% – recall the authors of the letter – have been reported in 23 Countries in more than 20 years. Hpai A(H5N1) viruses belonging to clade 2.3.4.4b have spread extensively among wild birds worldwide since 2020-2021, causing epidemics in poultry and other animals recently.” the same viruses “have been identified in dairy cows and in samples of unpasteurized milk in several US states”. In humans, “a case of Hpai A(H5N1) virus infection has been reported in a worker of a dairy company in Texas”, the signatories continue, going into the details concerning him.
The patient “showed redness and discomfort in the right eye at the end of March 2024”. Upon initial medical examination, “subconjunctival hemorrhage and serous drainage were noted in the eye.” Normal breathing, saturation 97%, clean lungs, no fever or respiratory symptoms, no changes in vision or anything else, the experts specify. “The worker did not report any contact with wild birds, poultry or other sick or dead animals”, but spoke of “direct and close exposure with dairy cows that appeared to be well and with others that instead showed the same signs of disease of cows from other herds in the same area of North Texas with confirmed Hpai A(H5N1) virus infection.” Again according to the man’s story, “when he worked with the animals he wore gloves, but no respiratory or eye protection”.
The patient underwent a swab, with conjunctival and nasopharyngeal samples taken. The results of both were “presumptive for influenza A and A(H5) viruses”, therefore he “was recommended home isolation and was administered” the antiviral drug “oral oseltamivir (75mg 2 times a day for 5 days)” both to the man and to his direct contacts. “The next day – continues the case description – the patient reported no symptoms, except discomfort in both eyes”. Upon re-evaluation, therefore, the doctors detected “subconjunctival hemorrhage in both eyes, without impaired vision. In the following days the worker reported resolution of the conjunctivitis, without respiratory symptoms, and family contacts remained in good health”.
From the analysis of the swabs, “the CDC confirmed the infection with the Hpai A(H5N1) virus”, the experts explain; analysis of the viral RNA obtained from the conjunctival sample “confirmed that the virus belonged to clade 2.3.4.4 b (genotype B3.13)”, and “isolation of the virus from the conjunctival and nasopharyngeal samples produced an identical virus. All genetic segments examined were closely related to viruses detected in Texas dairy cattle and other B3.13 genotype viruses detected in wild birds in Texas in March 2024. Specific genetic data relating to the virus allegedly circulating on the farm where the man worked was “not available for analysis”.
The viral sequences coming from cattle and from the patient “maintained mainly avian genetic characteristics”, point out the authors of the letter, without “changes that would have influenced the specificity of binding” being highlighted in the hemagglutinin gene (a receptor present on the viral surface). ” to receptors “localized mainly in the human upper respiratory tract” and consequently “the risk of transmission to humans”. The virus identified in the patient instead had a mutation, “PB2 E627K, which has been associated with viral adaptation to mammalian hosts and previously identified in humans and other mammals infected with Hpai A(H5N1) viruses or other viral subtypes of avian influenza, including A(H7N9) and A(H9N2)”. For now “no genetic markers associated with reduced susceptibility to antiviral influenza drugs approved by the Food and Drug Administration”.
Finally, the hemagglutinin of the patient’s virus was found to be “closely related” to that of viruses from two A(H5N1) vaccine candidates, clade 2.3.4.4b. And “since influenza A(H5N1) viruses have pandemic potential – the experts conclude – these viruses are available to companies and could be used to produce vaccines, if necessary”.
