Scientists have sounded a warning over the threat of the H7N9 bird flu which has infected 130 people on the Chinese mainland, saying it could generate a severe pandemic and even has the potential to mutate and infect horses.
H7N9 avian influenza was first reported in March in China, with 130 cases so far confirmed in people. Death resulted in 37 cases. There has been no evidence of human-to-human transmission so far.
Chinese researchers, writing in the Chinese Science Bulletin, said the outbreak was already graded as a Grade III severe outbreak and was likely to evolve into a Grade IV (very severe) outbreak soon.
Qing Ye Zhuang from the China National Avian Influenza Professional Laboratory at the China Animal Health and Epidemiology Center in Qingdao, joined fellow researchers in predicting the H7N9 avian influenza virus (AIV) would probably circulate in humans, birds and pigs for years.
“Moreover, with the driving force of natural selection, the virus will probably evolve into highly pathogenic AIV in birds, and into a deadly pandemic influenza virus in humans.
“Therefore, the H7N9 outbreak has been assumed severe, and it is likely to become very or extremely severe in the future, highlighting the emergent need of forceful scientific measures to eliminate any infected animal flocks.”
Zhuang and his 10 fellow researchers described the risk posed by the outbreak as enormous.
“Beyond that the virus can infect humans and birds, we think that the virus can also infect pigs which support circulation of both AIVs and human influenza viruses. Additionally, [we] cannot exclude that the virus will not circulate in horse flocks (sic) after it has accumulated some mutations if it will circulate widely in the nature, as H7 subtype influenza virus had widely circulated in horses in the world for decades of the last century.”
They said it was difficult to identify the humans, birds or pigs infected with the H7N9 virus from clinical signs, and it was extremely tough to conduct large-scale detection or surveillance to identify the virus infections in humans, birds, or pigs for a long period.
They warned the novel H7N9 virus may mutate into highly pathogenic flu during its future probable long circulation in birds, which will prove as disastrous as the H5N1 highly pathogenic flu circulating in many countries for years.
“The probable long existence of the H7N9 virus in humans will provide the driving force to the virus to adapt to humans through mutations,” they wrote.
“The virus may thus obtain human-to-human transmission, and may spark a pandemic influenza thereafter.”
Such a pandemic may be dangerous, they wrote, given the high mortality rate so far.
“Some experts thought that the H7N9 outbreak was not that serious,” they noted.
However, the H7 subtype influenza virus had never widely circulated in humans, and thus persons of all ages were likely susceptible to infection.
“Therefore, the future possible H7N9 pandemic will be likely more severe than the pandemic H1N1 influenza in 2009.”
They predicted the outbreak could worsen and become very severe, highlighting the need for forceful scientific measures, such as building enough stockpile of H7N9 vaccine for human use.
They continued: “We do not exclude completely the possibility that the H7N9 will disappear naturally, or maintain its low pathogenicity in birds and limited transmission ability in humans for a long period, without forceful scientific control measures.
“However, such a mild scenario of the outbreak evolution is of less possibility than the very or extremely severe scenario described above. The main reason is that some random mutations leading to the improved adaption of the virus to humans will emerge naturally during its long existence in humans, as the virus usually evolves rapidly.
“These mutants will become dominant by natural selection as they are more adaptive in humans. They thus may spread in humans rapidly and can spark a deadly pandemic.
“Possibly only one natural force exists inhibiting the dangerous development of the H7N9 outbreak, namely the structural constraint of the virus. That is to say, the mutations leading to human-to-human transmission of the virus, or leading to high pathogenicity of the virus in birds are also fatal to the virus itself.”
Epidemiological and risk analysis of the H7N9 subtype influenza outbreak in China at its early stage
ZHUANG QingYe, WANG SuChun, WU MeiLi, LIU Shuo,, JIANG WenMing, HOU GuangYu, LI JinPing, WANG KaiCheng, YU JianMin, CHEN JiMing, and CHEN JiWang.
Chinese Science Bulletin