Diversity of circulating H5N1 Clades – Credit WHO
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While we tend to talk about H5N1 (aka `bird flu’) as if it were a single entity, in reality, the virus has continually evolved and mutated since its emergence was first noted in 1996. At least 20 distinct clades of the virus have been identified thus far, with numerous variants among each clade.
`Clades’ are essentially branches on the virus’s family tree. Each new branch has a clearly identifiable lineage from its parental strain, but has mutated far enough away to become a new strain. And different clades can possess different characteristics .
Different areas of the world have seen different clades set up hen-house keeping, with clade 2.3.2 very common in South East Asia, clades 2.2.1 and 2.2 endemic in Egypt and clades 2.1.1, 2.1.2. and 2.1.3 circulating throughout Indonesia.
While not every new clade has what it takes to thrive and persist, one of the more successful `newer’ clades making inroads over the past few years has been clade 2.3.2.
I wrote of the spread of this emerging clade back in 2011 in What Goes Around, Comes Around and EID Journal: H5N1 Branching Out. In the spring of 2010 we began to see reports of poultry vaccine failures in Vietnam due to the spread of a mutated version this clade (further classified as clade 2.3.2.1), which led to this statement FAO Warns On Bird Flu.
In December of 2012, after several months of reports of large poultry die offs in Indonesia, we first heard that his emerging 2.3.2.1 clade had been detected on the Island of Java (see VOA Report On The Indonesian Duck Die Off & Report: Clade 2.3.2 H5N1 Detected In Indonesia). A month later, we saw reports that Indonesia: H5N1 Clade 2.3.2 Reaches Bali.
While we’ve heard relatively little out of Indonesia on the bird flu front over the past year, today we have a detailed look at this new H5N1 clade that arrive in Java in 2012, via a dispatch in the CDC’s EID Journal.
Genetic Characterization of Clade 2.3.2.1 Avian Influenza A(H5N1) Viruses, Indonesia, 2012
Ni Luh Putu Indi Dharmayanti
, Risza Hartawan, Hendra Wibawa, Amanda Balish, Ruben Donis, C. Todd Davis, Gina Samaan, and Pudjiatmoko Hardiman
Abstract
After reports of unusually high mortality rates among ducks on farms in Java Island, Indonesia, in September 2012, influenza A(H5N1) viruses were detected and characterized. Sequence analyses revealed all genes clustered with contemporary clade 2.3.2.1 viruses, rather than enzootic clade 2.1.3 viruses, indicating the introduction of an exotic H5N1 clade into Indonesia.
<SNIP>
Conclusions
Detection of a novel clade of A(H5N1) virus in Indonesia marks a potential turning point in the molecular epidemiology of this virus. Indonesia has the highest number of human A(H5N1) infections because of ongoing outbreaks in poultry (14,15).
Whether this new virus will become entrenched, as did clade 2.1.3 viruses over the past decade, remains to be seen, as do its effects on the incidence of human infection. Potential cocirculation of subtypes of 2 different clades warrants review of diagnostic methods and vaccination strategy to maximize effectiveness of disease control interventions.
The lack of antigenic relatedness between the clade 2.3.2.1 and 2.1.3.2 viruses must be considered when evaluating A(H5N1) serologic diagnostic reagents used in Indonesia. This change also may have implications in selecting prepandemic candidate vaccine virus for the region. Furthermore, poultry vaccines may need to be matched antigenically to circulating virus if clade 2.3.2.1 virus continues to circulate in Indonesia.
Introduction of this virus is a stark reminder of the value of control measures to reduce the spread of subtype H5N1 and the need for enhanced surveillance of humans and poultry to monitor changes in its genetic and immunologic features.
Last November, in EID Journal: The Expanding Variants Of H5N1 we looked at three new variations of the H5N1 virus (this time clade 2.3.4) detected in Vietnam between 2009 and 2012. And last month, in Moving Viral Targets, we saw a recommendation – based on a virus isolated in Hubei - that a new clade 7.2 candidate vaccine virus be developed.
And there is no reason to believe we won’t see new genetic permutations like these continue to come down the pike in the months and years to come.
A reminder that influenza viruses (of all types) are moving targets, and that we dare not become complacent simply because the novel viruses in circulation right now aren’t particularly good at transmitting from one human to the next.
For more influenza clades and variants than we can possibly keep track of, tomorrow is always another day.
