Study: H3N2 viruses evolve quickly, move around the globe more
Compared with H3N2 influenza—which dominated the flu landscape this past season in the Northern Hemisphere and is often associated with more severe disease—H1N1 and B viruses do not show the same degree of global movement but persist for longer periods locally, according to a mapping study today in Nature.
An international team analyzed 9,604 hemagglutinin sequences in seasonal flu viruses from 2000 to 2012 and found that H3N2 viruses move between regions more frequently than the other two strains. One reason for this variation may be the rates at which the viruses evolve, the authors said. H3N2 viruses evolve relatively quickly and routinely infect people of all ages, but H1N1 (including 2009 H1N1, the pandemic strain) and B viruses evolve more slowly and mainly infect children.
Because children travel long distances much less than adults, this factor may account for differences in the global circulation of viruses, the researchers say. The slower rates of evolution of H1N1 and B viruses compared with H3N2 viruses may also explain why H1N1 and B viruses cause fewer major epidemics.
The results suggest a "complex interaction between virus evolution, epidemiology, and human behaviour," the authors conclude.
Jun 8 Nature report
Cases of chikungunya in the Americas top 1.5 million
A spike in reported chikungunya cases pushed the outbreak total in the Americas past the 1.5-million-case mark, the Pan American Health Organization (PAHO) said on Jun 5 in its weekly update. The region had 37,358 new chikungunya cases, bringing the outbreak total to 1,501,273
The numbers again include a big jump in Colombia, which has been the outbreak hot spot for weeks, although many nations have not reported for a month or more. The new cases also include a slightly larger increase in Honduras, but that country reported 6 weeks' worth of data compared with just 1 week's worth for Colombia.
Honduras had 10,999 new chikungunya cases in the most recent 6 weeks, for a total of 28,549, compared with Colombia's 10,719 new cases, for a total of 244,677. Guatemala reported 2,024 new cases over 4 weeks, for 7,236 total. El Salvador had 1,244 new cases in 1 week, for a total of 10,743.
PAHO had reported increases of 14,551and 17,165 cases in the previous 2 weeks. The total so far this year is 364,326 cases.
The epidemic began in December 2013 with the first locally acquired chikungunya case ever reported in the Americas, on St. Martin in the Caribbean.
Jun 5 PAHO update
