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Review
. 2025 Mar 1;33(1):76-89.
doi: 10.53854/liim-3301-7. eCollection 2025.

H5N1 influenza A virus: lessons from past outbreaks and emerging threats

Massimo Galli  1 , Andrea Giacomelli  1   2 , Alessia Lai  1   3 , Gianguglielmo Zehender  1
Affiliations
Review

H5N1 influenza A virus: lessons from past outbreaks and emerging threats

Massimo Galli et al. Infez Med. .

Abstract

The first highly pathogenic H5N1 emerged in 1959 on a chicken farm in Scotland. The ancestor of the strains presently circulating was isolated in 1996 from a domestic goose in China. Since 1997, more than 900 severe human infections have been reported. However, in nearly thirty years, H5N1 has failed to adapt to human-to-human transmission. At present the abundant circulation in various animal species, including mammals, increases the possibility of reassortments of new pandemic strains. Particularly alarming was the recent report of H5N1 infection among U.S. dairy cattle. A strong international effort from a global health perspective addressed to limit the avian strains circulation and to improve the preparedness for a new pandemic is urgently needed.

Keywords: H5N1; Influenza A virus; avian influenza; global health; prepandemic vaccines.

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Conflict of interest statement

Conflict of interest: None to declare

Figures

Figure 1
Figure 1
Numbers of human cases (blue bars) and deaths from H5N1 infection (orange bars) from 2003 to 2014.
Figure 2
Figure 2
Timeline of the evolution and spread of H5 strains.
Figure 3
Figure 3
Numbers of human cases (blue bars) and deaths from H5N1 infection (orange bars) from 2015 to December 2024 (the reports of 2024 might be incomplete).
Figure 4
Figure 4
Diagnostic workup of avian flu. Epidemiological criteria: Exposure to HPAI A(H5N1) virus-infected birds or other animals, OR exposure to an infected person, OR laboratory exposure. Clinical criteria: Persons with signs and symptoms consistent with acute upper or lower respiratory tract infections, conjunctivitis, or complications of acute respiratory illness of unknown origin. Additionally, gastrointestinal symptoms, such as diarrhea, are often reported with HPAI A(H5N1) virus infection. Public health response: Asymptomatic individuals should be monitored and tested in accordance with public health measure.
See this image and copyright information in PMC

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