Why Cambodia’s Novel H5N1 Reassortant Virus Requires Vigilant Monitoring: Key Insights and Implications

Sub: Sci

Sec: Health

Why in News

Cambodia has seen a resurgence of H5N1 bird flu cases after over a decade, with a notable rise in cases linked to a novel reassortant strain of the virus, reported between February 2023 and August 2024. This new strain, a result of genetic mixing between two H5N1 clades, poses potential zoonotic risks, highlighting the urgent need for heightened surveillance and control measures to prevent human infection.

Background:

After more than ten years without reported H5N1 cases, Cambodia recorded 16 human infections from February 2023 to August 2024.
The novel reassortant virus combines gene segments from clade 2.3.2.1c (circulating in Southeast Asia) and clade 2.3.4.4b (detected worldwide).
This reassortment appears to have emerged due to factors such as high-density poultry farming, migratory birds, and cross-border poultry trade in Southeast Asia.
The novel reassortant virus has caused deaths but, as of now, there is no evidence of human-to-human transmission.
A collaborative One Health approach was used, employing rapid whole-genome sequencing to trace human infections back to poultry.
Key Genetic Mutations: Researchers detected the PB2 627K mutation in the reassortant virus, a mutation associated with enhanced mammalian adaptation and airborne transmission, particularly concerning for zoonotic potential.
Other mutations in clade 2.3.4.4b suggest an increased capability for mammalian infection, prompting calls for further risk assessment through in silico, ex vivo, in vivo, and in vitro studies.

What is the PB2 627K Mutation?

The PB2 gene in influenza virus codes for a protein critical for the replication and transcription of viral RNA.
The mutation refers to a change at position 627 in the PB2 protein, where lysine (K) replaces glutamic acid (E). This is represented as E627K (glutamic acid to lysine).
The PB2 627K mutation has been associated with increased efficiency of viral replication in mammalian hosts, including humans.
It allows avian influenza viruses, which primarily circulate among birds, to infect and spread more easily in mammals. This adaptation is particularly concerning in terms of zoonotic transmission—the ability of the virus to jump from animals to humans.
In the recent novel reassortant H5N1 strain detected in Cambodia, the PB2 627K mutation was found. This presence raises concerns as it suggests the virus might be more adaptable to humans and potentially transmissible in mammalian populations.

What is the H5N1 virus?

Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus, which causes influenza (flu), predominantly in birds.
It is enzootic (maintained in the population) in many bird populations, and also panzootic (affecting animals of many species over a wide area).
A/H5N1 virus can also infect mammals (including humans) that have been exposed to infected birds; in these cases, symptoms are frequently severe or fatal.
Ever since it emerged in 1996, H5N1 has resulted in the mass killing of billions of wild birds as well as fowls.
According to scientists, the virus lacks changes that would make it better adapted to transmit between people and therefore, the risk to human health remains low.
The potential for influenza viruses to rapidly evolve and the wide geographic spread of H5N1 signals that more human infections should be expected.
New Clade Emergence: The Avian Influenza H5N1 (clade 2.3.4.4b) emerged in late 2020, leading to a global outbreak primarily spread by migratory birds.