Zoonotic risk of avian influenza: past and present in United States

Authors: Suarez, David

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/26/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Avian influenza is recognized as having zoonotic potential. The zoonotic risk is not thought to be different whether the virus is low pathogenic or highly pathogenic. It is well characterized in chickens, that multiple basic amino acids on inserts at the hemagglutinin cleavage site can change a virus from low pathogenic to highly pathogenic in chickens and turkeys where the virus can replicate systemically and by definition will kill 75% or more of challenged chickens in a standardized test. A HPAI virus in chickens may or may not cause systemic infection in other avian species. For example, many HPAI viruses that are deadly for chickens may infect but cause no clinical disease in ducks. For viruses that do infect humans, the symptoms are usually restricted to the respiratory tract, although severe atypical pneumonia with a high case fatality rate may occur. Rare cases may present with encephalitis, but this can also be seen in seasonal human influenza, especially in children. In the U.S. only rare cases of avian influenza have been reported to cause human infection. The most serious zoonotic concern has been the recent outbreak of H5N1 HPAI 2.3.4.4b virus that was recently reported in dairy cows. The virus can replicate to high titer in the mammary gland with large amounts of virus in milk. There has been considerable concern about the potential for live HPAI virus being found in milk, and surveys have identified live virus in bulk milk tank samples before pasteurization. Fortunately, available data supports that pasteurization effectively inactivates virus and a recent retail milk survey showed evidence of viral RNA, but no live virus. This supports that pasteurized milk is safe, but there is a potential for human exposure in consumption of raw milk and by the farm workers working with infected cows. Currently there have been three human cases. Two of the cases only had conjunctivitis and a third had mild respiratory symptoms. There is concern that the ability to replicate in cows may increase the risk of human infections, but currently that has not been observed. Analysis of other avian influenza outbreaks in people have identified amino acid changes that are related to mammalian infection. Currently one mammalian amino acid marker has been found, but not the more common ones (PB2 627) found in other human infections. Because of the zoonotic risk, outbreaks are handled with extreme care and workers should be wearing personal protective equipment, including respiratory protection and safety glasses to help prevent exposure.