By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University
SYNOPSIS: The spread of influenza H5N1 in dairy cows with documentation of a human infection raises pandemic concern.
SOURCE: Uyeki TM, Milton S, Abdul Hamid C, et al. Highly pathogenic avian influenza A(H5N1) virus infection in a dairy farm worker. N Engl J Med 2024; May 3. doi: 10.1056/NEJMc24 al05371. [Online ahead of print].
On March 27, 2024, a dairy worker in Texas developed conjunctivitis and a subconjunctival hemorrhage. He had no respiratory or systemic symptoms. Among the cows with which he had had occupational contact were some with symptoms similar to those seen in other dairy cows nearby in northern Texas that had been infected with avian influenza A(H5N1). These symptoms included decreased milk production, reduced appetite, lethargy, fever, and dehydration.
Reverse transcription polymerase chain reaction (RT-PCR) testing of conjunctival and nasopharyngeal swab specimens from the patient initially were deemed presumptively positive for H5N1. The patient was isolated at home and was treated with oseltamivir, which also was made available to his contacts for prophylactic purposes. His conjunctivitis rapidly resolved. The Centers for Disease Control and Prevention confirmed the detected virus as H5N1, and sequencing demonstrated that it belonged to clade 2.3.4.4b and was closely related to isolates from cattle and peridomestic wild birds in Texas during the same month. The virus also was found to have a polymorphism (PB2 E627K) known to be associated with adaptation to mammalian hosts and that previously had been detected in virus infecting humans.
Separately, H5N1 also was detected in milk and tissue samples from cattle in Kansas. Additional reports indicate that the virus had affected cows in at least nine states by May 1. The virus also was found in tissue samples from two deceased cats from an affected dairy farm in Texas.1 Domestic cats have been known to be susceptible to H5N1 infection, most often from consuming infected wild birds or poultry.
COMMENTARY
The first report of H5N1 infection of humans occurred in the context of a 1997 outbreak in Hong Kong live bird markets.2 Eighteen infections were identified. The illness was severe, with a 61% incidence of pneumonia and with 51% requiring intensive care; 33% died. No new cases were reported after slaughter of poultry.
The virus is detected in cow milk in a very high concentration, and, on April 25, the U.S. Department of Agriculture reported H5N1 ribonucleic acid was detected in 20% of retail cow milk samples tested. It also has been reported that viral cultures of PCR-positive milk samples were negative, consistent with effective pasteurization.
The Food and Drug Administration requires discarding milk from infected cows before they can be moved across state lines. As always, people must avoid unpasteurized dairy products. Aggressive public health activities are critical.
The hemagglutinin of the epidemic clade is closely related to that of two available clades that provide the opportunity for rapid development of a vaccine. The virus is reported to be susceptible to oseltamivir, which should be used to treat human cases and as prophylaxis of contacts. However, one concern is the possibility of further viral changes due to segment reassortment, as large numbers of infected cows may serve as viral “mixing vessels” with emergence of a novel virus.
REFERENCES
- Burrough ER, Magstadt DR, Petersen B, et al. Highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b virus infection in domestic dairy cattle and cats, United States, 2024. Emerg Infect Dis 2024;30. doi: 10.3201/eid3007.240508. [Online ahead of print].
- Al-Tawfiq JA, Tirupathi R, Temsah MH. Feathered fears: Could avian H5N1 influenza be the next pandemic threat of disease X? New Microbes New Infect 2024;59:101416.
