A wave of H7N9 bird flu in . China that has spread into people may have the potential to . emerge as a pandemic strain in humans , scientists have warned . The H7N9 virus , one of several strains of bird flu known to . be able to infect humans , has persisted , diversified and spread . in chickens across China , the researchers said . This has fulled a resurgence of infections in people , posing a wider threat . In a study published in the journal Nature , they said : 'The expansion of genetic diversity and geographical spread . indicates that , unless effective control measures are in place , . H7N9 could be expected to persist and spread beyond the region . ' The H7N9 bird flu virus emerged in humans in March 2013 . A wave of H7N9 bird flu in China that has spread into people may have the potential toemerge as a pandemic strain in humans . It has since then infected at least 571 people in China , Taipei , . Hong Kong , Malaysia and Canada , killing 212 of them , according . to February data from the World Health Organization ( WHO ) . After an initial flare up of human cases at the start of . 2013 , the H7N9 appeared to die down - aided in large part by . Chinese authorities deciding to close live poultry markets and . issue health warnings about direct contact with chickens . But infections in people increased again last year and in . early 2015 . This promoted researchers to try to understand more . about how the virus re-emerged , how it might develop , and how it . might threaten public health . In this study , an international team of scientists led by Yi . Guan of Hong Kong university monitored the evolution and spread . of H7N9 over 15 cities across five provinces in China . By collecting and sequencing a large number of samples , they . found that the H7N9 virus is mutating frequently , acquiring . genetic changes that might increase its pandemic potential . A large number of new genetic variants of the virus have . become established in chickens and have spread across the . country , probably because of poultry trade movement , they said . Flu experts not directly involved in the research said its . findings were interesting but did not necessarily show the H7N9 . was changing in ways that made it more likely to develop into a. pandemic flu strain . An employee wearing a protection suit sprays disinfectant on chickens at a poultry market in Hefei , Anhui , China . The H7N9 bird flu virus emerged in humans in March 2013 . It has since then infected at least 571 people in China , Taipei , Hong Kong , Malaysia and Canada , killing 212 of them . 'What we do n't know from this paper is the significance of . all these mutations that are accumulating as the virus persists . and spreads , ' said Wendy Barclay , an expert in flu virology at . Imperial College , London . 'This is especially relevant . for human health - does any of this change the pandemic . potential of the virus ? , ' she told Reuters Health . In its latest update on the flu strain , the Geneva-based WHO . said it 'continues to closely monitor the H7N9 situation ' and . conduct risk assessments . 'So far , the overall risk associated with the H7N9 virus has . not changed , ' it said . Yi Guan 's team , however , said their analysis pointed to a. need for heightened vigilance of H7N9 and for curbing direct . human contact with live poultry at markets . 'Permanent closure of live poultry markets , central . slaughtering and preventing inter-regional poultry . transportation during disease outbreaks are needed to reduce the . threat of H7N9 to public health , ' they wrote .
The H7N9 virus , one of several strains of bird flu known to be able to infect humans , has persisted , diversified and spread in chickens across China . This has fulled a resurgence of infections in people , posing a wider threat . Unless control measures are put in place , the virus will spread , they warn .