Nature: Urgent search for flu source

Researchers suspect H7N9 virus is in bird markets as human cases rise rapidly.

• Declan Butler

09 April 2013

 

Excerpt:

 

Each time the virus encounters new human hosts, it has fresh opportunities to mutate and to acquire the ability to spread between people. That does not seem to have occurred yet. But experts say that it will be crucial to identify and track new cases of suspicious severe pneumonia and their close contacts, and to isolate people if necessary. Researchers working on the molecular biology of the virus say that it seems to derive from a reassortment of genetic material from at least three known bird-flu groups (see Nature http://doi.org/k4j; 2013). A key component — the haemagglutinin (H) protein on the surface of the virus — already contains mutations known to shift its binding preference from bird cells to those of mammals. Scientists are watching for telltale changes that could signal a shift towards a form that is more transmissible between humans.

Because flu viruses evolve rapidly, comparing viral sequences from each of the human cases might reveal whether person-to-person transmission is occurring, says Andrew Rambaut, an expert in the evolution of human viral pathogens at the University of Edinburgh, UK. If many patients have very similar viral sequences, then that would imply human spread; if viral sequences are more diverse, it would imply that each person had separately picked up infections from birds. Only four sequences from four human cases are so far available, but virologists are sequencing more and posting them on the GISAID flu database.
If human-to-human transmission does start to occur, “further spread may be inevitable”, warns Tashiro. Humanity has never been widely exposed to H7 or N9 flu viruses, and so lacks resistance to these subtypes. If a pandemic were to occur, it would probably have a severe toll. But it is too early to predict how events will unfold; experts in emerging infectious disease are only just becoming acquainted with the latest villain in their roster.

Nature

496,

145–146

(11 April 2013)

doi:10.1038/496145a

 

http://www.nature.com/news/urgent-search-for-flu-source-1.12762