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A recent study by Chinese scientists from the Harbin Veterinary Research Institute and the Gansu Agricultural University, called H7N9 Influenza Viruses Are Transmissible in Ferrets by Respiratory Droplet, suggests that the H7N9 virus may be better equipped to spread among humans than previously believed.
We looked at its findings last week In Science: H7N9 Transmissibility Study In Ferrets.
Researchers found the virus not only binds well to human (a2,6) receptor cells, it replicates efficiently in ferrets, and at least one isolate transmitted efficiently via respiratory droplets.
In an interview last week with CIDRAP NEWS, senior author Hualan Chen, PhD said, "The transmission of AH/1 to all three ferrets suggests that the H7N9 virus has great pandemic potential."
We’ve seen a number of other studies over the past few months expressing similar concerns over H7N9’s pandemic potential, including:
Chinese Science Bulletin: Early H7N9 Risk Analysis
Nature: H7N9 Pathogenesis and Transmissibility In Ferrets & Mice
Branswell: Studies Show Transmissibility Of H7N9 In Ferrets
Despite these worrisome studies, we’ve seen a huge drop off of reported H7N9 cases over the past couple of months. Closure of live markets and warm summer temperatures have been largely credited, but the near total absence of new cases remains a bit of a mystery.
Which brings us to comments yesterday by Zeng Guang - Chief Epidemiologist at China’s CDC – who doesn’t fully agree with the conclusions of Dr. Chen.
Findings on virus 'not strong enough' to affect strategy
Updated: 2013-07-22 08:17
By Shan Juan (China Daily)
A recent study that suggests the H7N9 avian influenza virus may be highly transmissible among humans is not strong enough to lead to any changes in the current H7N9 epidemic intervention strategy, said a senior Chinese scientist.
A study published on the website of the US journal Science on July 18 said the new strain of bird flu virus is highly transmissible among ferrets, a widely used animal model for studying how flu might spread in humans.
Consequently, it is possible the virus could efficiently spread among humans eventually, posing a pandemic risk, according to the study led by Chen Hualan, director of China's National Avian Influenza Reference Laboratory at Harbin Veterinary Research Institute.
Zeng Guang, chief epidemiologist at the Chinese Center for Disease Control and Prevention, disagrees with that conclusion.
"The findings are mainly based on animal tests in the lab that have not been witnessed or substantiated among the H7N9 human cases reported. So it shouldn't affect current intervention efforts or strategy at all," he said.
"So far, no substantial evidence of H7N9 spreading among humans has been detected," he said.
The study showed one virus isolated from humans was able to transmit efficiently among ferrets through respiratory droplets, raising the possibility of eventual airborne transmission among humans.
The study also warned that the nonpathogenic nature of the H7N9 virus in poultry enables it to "replicate silently" in avian species and be transmitted to humans, providing further opportunities for the virus to acquire more mutations and become more virulent and transmissible in the human population.
While he may not be convinced that these lab findings currently translate into the field, Zeng did go on to say:
"We have to carefully watch the epidemic situation in the coming autumn, when the virus mobility tends to increase.”
A sign that no one is taking this summer’s welcomed lull in new cases as any kind of guarantee of what we’ll see this fall and winter.
