AVIAN INFLUENZA VIRUSES

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Context: The recent study published in Nature sheds light on the changing dynamics of highly pathogenic avian H5 influenza viruses, indicating a significant shift in their global distribution and evolutionary patterns.

Key Findings of the Study

Global Spread Intensification	●Since 2021, highly pathogenic avian H5N1 virus activity has intensified globally, infecting and killing increasing numbers of wild birds and poultry, as well as posing a risk to mammals, including humans.
Escalation Beyond Asia	●While H5 outbreaks in wild birds escalated beyond Asia since 2014, the origins of these resurgences were unclear. The study identifies key resurgent events in 2016/17, with genome analysis tracing these viral lineages back to Asia, specifically China.
Shift in Epicenter	●The significant finding of the study is the shift in the epicentre of these viruses. ●Two new H5 viruses, identified between 2020 and 2022, emerged from African and European bird populations, indicating a notable shift away from Asia.
Driving Factors	●The increasing persistence of avian influenza in wild bird populations is identified as a driving factor behind the evolution and spread of new strains. ●The study suggests that this persistence is facilitating geographic and host range expansion, accelerating dispersion velocity, and increasing the potential for genetic reassortment.
Implications	●The findings underscore the importance of continued elimination strategies to limit viral spread and control the prevalence of highly pathogenic avian influenza within global bird populations. Additionally, understanding viral evolution is crucial to mitigating and reacting to new strains effectively.

Avian Influenza Viruses (AIVs)

• Avian influenza viruses (AIVs), commonly known as bird flu, are a type of influenza virus that primarily infects birds, including domestic poultry and wild birds.
• AIVs occur naturally in birds, especially waterfowl such as ducks, geese, and shorebirds. Wild birds are the natural reservoir of influenza A viruses and can carry the virus without showing symptoms.

Transmission to Humans

• While AIVs typically do not infect humans, certain strains have caused infections in humans. Most cases of human infection have resulted from direct or close contact with infected poultry or contaminated environments. Human infections with AIVs can range from mild to severe, and in some cases, they can be fatal.

Types of Avian Influenza in Birds

• Low Pathogenic Avian Influenza (LPAI): Most AIV strains are low pathogenic, meaning they cause mild or no symptoms in birds.
• Highly Pathogenic Avian Influenza (HPAI): Some AIV strains can mutate into highly pathogenic forms, leading to severe illness and high mortality rates in poultry. HPAI strains can cause significant economic losses in the poultry industry.

Mutation and Antigenic Drift

• AIVs, like other influenza viruses, can undergo genetic changes through mutation and reassortment. Mutation and antigenic drift contribute to the continuous evolution of AIVs, making it challenging to develop effective vaccines for both birds and, potentially, humans.

Global Concerns

• AIVs are of global concern due to their potential to cause pandemics if they acquire the ability to spread easily among humans. Monitoring and surveillance of AIVs in both birds and humans are essential to early detection and management of potential outbreaks.

Prevention and Control

• Control measures for AIVs in poultry include biosecurity practices, culling infected birds, and vaccination (for low pathogenic strains). Surveillance in both wild and domestic birds is crucial for early detection. In humans, early antiviral treatment and vaccines (in development) are the primary methods of prevention and control.

Conclusion

• The study highlights the evolving nature of avian influenza viruses, emphasizing the need for ongoing surveillance, research, and global cooperation to monitor and respond to these changing threats effectively.

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