A recent surge of bird flu infections in humans this season has alarmed scientists and public health officials. Although the risk of sustained transmission between humans remains low, the changing nature of influenza viruses requires close monitoring, the World Health Organization (WHO) said on Wednesday.
Since October, China has reported 460 confirmed human infections of the A(H7N9) avian influenza virus – more than any of the previous four seasons and constituting more than a third of total cases since it was first reported humans in 2013. H7N9 kills about a third of those diagnosed. Other symptoms of bird flu range from pink eye to flu-like symptoms to severe pneumonia.
Health officials are also concerned by recurring outbreaks of another H5 virus in poultry and wild birds in Europe, Africa and Asia, as sporadic infection of H5N1 in humans can occur with a higher mortality rate of 60 percent. More than 1,000 outbreaks having been reported to the U.N. Organization for Animal Health (OIE), and four cases of H5 infections in humans have been reported to the WHO in recent months.
“Our core message is that the risk of sustained human-to-human transmission of H7N9 remains low, as it does for other subtypes of avian influenzas,” Wenqing Zhang, head of the WHO’s global influenza program, said on a telephone media briefing. “However, constant change is the nature of all influenza viruses, and that is why we follow the developments so closely.”
Especially given the rapid spread of bird flu over its short history, Zhang’s warning rings true. Avian influenza was first recognized as a threat to human health in 1997, when a highly pathogenic – causing severe disease – H5N1 virus infected 18 people in Hong Kong.
“Since that time these viruses have continued to change their genetic makeup and have developed into many distinguishable groups that now infect domestic and wild birds in many regions of the world,” Jackie Katz, director of the Centers for Disease Control and Prevention (CDC) in Atlanta, told reporters.
Millions of birds and several hundred humans have been infected or died around the world, not to mention the significant impact of the outbreaks on livelihoods, economies and international trade.
To keep the virus at bay, one change that scientists have monitored carefully is resistance to antivirals. In this ongoing fifth wave of H7N9, about 7 percent of human cases exhibited genetic mutations for resistance to neuraminidase inhibitors – a category of antivirals that includes the often recommended and stockpiled drug, Tamiflu, or oseltamivir.
However, 7 percent is similar to previous waves, the WHO said, and all but one resistant H7N9 viruses were found in treated human patients, not the environment or birds.
“The scientific meaning for that is that because human infections are caused by exposure to poultry, that means the circulating virus is not presenting any antiviral drug resistance,” Yuelong Shu, director of the Chinese Center for Disease Control and and Prevention (CDC), told reporters.
Therefore, the WHO is not recommending major changes to the clinical management of the virus, and prevention advice remains the same: Avoid areas or contact with live poultry, wash your hands, cover your face when coughing or sneezing and cook food thoroughly.
However, the mutations have made H7N9 highly pathogenic in birds, whereas it was previously considered “low pathogenic” in birds, not causing visible outbreaks of disease. Still, there is no evidence that pathogenicity or transmissibility in humans has increased, according to Zhang.
As the number of cases in China have begun to decline, Shu said that the current wave has already peaked. However, flu experts are meeting with vaccine companies in Geneva this week to determine which viral strains should be in next winter’s shots and whether new candidate vaccine viruses are needed for avian influenza.
“This is important because we need to prepare for the possibility that avian viruses may acquire additional genetic changes that could allow them to infect people more easily or to spread from person to person,” Katz said. “If avian viruses were to acquire these changes, this could result in a pandemic.”
