The very first cross-species jump of the Influenza A virus took place in Hong Kong in 1997, when a poultry outbreak of the virus led to the infection of humans who had directly interacted with sickened birds. To prevent further spread to humans, Hong Kong killed off nearly all of its poultry inventories.
Unfortunately, the virus, known as H5N1 at the time, came back in December of 2003 and by the end of the month there were reported human cases, with the disease spreading to Japan, Thailand, Cambodia, Laos, Indonesia and China. Out of the 35 human cases throughout the region, 24 died – a 68% fatality rate.
Scientists discovered that the H5N1 had mutated from its original form in 1997, with each mutation becoming more pathogenic and able to survive longer than the previous strains. (1) However, in stark contrast to the H5N1 bird flu virus, the H7N9 virus is well adapted to jump from birds to humans.
The Spread of H7N9
The new bird flu known as H7N9 first appeared in China in February of 2013. 132 people were infected and 39 of them died. Scientists report that H7N9 is much more transmissible between humans than the H5N1 virus was. (2)
They determined this by placing ferrets that were infected with the H7N9 virus into separate cages in the same room with uninfected ferrets. One strain of the H7N9 virus spread so well through the air that it infected 100% of the ferrets exposed to the same air.
Despite the transmissibility results with ferrets, so far the virus has only infected 132 people in China, and 43 of those people have died. Scientists involved in the ferret study explained that using ferrets may not be a perfect model for human transmission, because it doesn’t take into account pre-existing immunity within the human population. (3)
So far, there have been no reports of “sustained human-to-human transmission” of H7N9. The issue scientists are most concerned about is the fact that the more the new bird flu virus comes into contact with humans, the more opportunities it will have to mutate into an even worse form.
What is most troubling is the fact that one China study found that the general public does not appear to have immunity to H7N9, meaning everyone is at risk for infection.
China health officials shut down all poultry markets in Shanghai to dramatically reduce human interaction with poultry, and many believe this action had a significant impact in the fact that no new cases of H7N9 infection have occurred since the end of May.
However, the CDC (Center for Disease Control) states on its website that this may only be a short term relief based on season and that human cases of H7N9 infection is likely to pick up again in the fall.
The major concern, according to the CDC, is the fact that if the H7N9 virus mutates further, it could represent a significant pandemic threat.
“Most concerning is the pandemic potential of this virus. Influenza viruses constantly change and it’s possible that this virus could become able to easily and sustainably spread among people, triggering a global outbreak of disease (pandemic). CDC is following this situation closely and coordinating with domestic and international partners. CDC takes routine preparedness actions whenever a new virus with pandemic potential is identified, including developing a candidate vaccine virus to make a vaccine if it were to be needed.”
Some good news is that H7N9 appears to be sensitive to typical anti-influenza drugs offered at treatment centers around the world, such as oseltamivir and zanamivir. However, there is one strain that appears to resist neuraminidase inhibitors.
In the case where an uncontrolled outbreak occurs, it can take authorities up to six months to develop a viable vaccine for H and N type viruses (4). However, WHO reports it is already collaborating with partner organizations to “identify the best candidate viruses” to manufacture a vaccine.