The Centers for Disease Control and Prevention (CDC) has issued an alert after a human infection with highly pathogenic avian influenza (HPAI) A(H5N1) virus in the United States following exposure to presumed infected dairy cattle. “A farm worker on a commercial dairy farm in Texas developed conjunctivitis on approximately March 27, 2024, and subsequently tested positive for HPAI A(H5N1) virus infection,” the CDC reported.1 “HPAI A(H5N1) viruses have been reported in the area’s dairy cattle and wild birds. The patient reported conjunctivitis with no other symptoms, was not hospitalized, and is recovering. The patient was recommended to isolate and received antiviral treatment with oseltamivir.” The patient’s household members received the antiviral as well for post-exposure prophylaxis. No human-to-human transmission of HPAI A(H5N1) virus has been identified.
The avian “bird flu” was considered the next possible pandemic after some cases in the late 1990s and the beginning of this century. The problem — to our great fortune — is that H5N1 has not been able to effectively transmit between humans.
There is a published report in 2000 of two healthcare workers being infected while treating patients with H5N1 avian flu.2 The concern has long been that the bird flu could mutate with an influenza strain infectious to humans — possibly using a pig as the “mixing vessel” — and then spread to a susceptible population. Of course, with every human infection, there is the opportunity for mutation.
“CDC has sequenced the influenza virus genome identified in a specimen collected from the patient and compared it with HPAI A(H5N1) sequences from cattle, wild birds, and poultry,” the agency reported. “While minor changes were identified in the virus sequence from the patient specimen compared to the viral sequences from cattle, both cattle and human sequences lack changes that would make them better adapted to infect mammals.”
This patient is the second person to test positive for HPAI A(H5N1) virus in the United States, with the first reported in 2022 in Colorado after exposure to poultry. Avian flu viruses typically circulate among wild birds, sometimes causing infections in poultry and sporadic cases in mammals. Thus, the risk is low, but it is somewhat higher for those who work with these animals.
REFERENCES
- Centers for Disease Control and Prevention. Highly pathogenic avian influenza A(H5N1) virus: Identification of human infection and recommendations for investigations and response. CDC Health Alert Network. Published April 5, 2024. https://emergency.cdc.gov/han/2024/han00506.asp
- Bridges CB, Katz JM, Seto WH, et al. Risk of influenza A (H5N1) infection among health care workers exposed to patients with influenza A (H5N1), Hong Kong. J Infect Dis 2000;181:344-388.
The Centers for Disease Control and Prevention has issued an alert after a human infection with highly pathogenic avian influenza (HPAI) A(H5N1) virus in the United States following exposure to presumed infected dairy cattle. No human-to-human transmission of HPAI A(H5N1) virus has been identified.
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