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New avian influenza virus kills 7 humans in China
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Chinese health officials have reported a total of 24 cases of human infection with the novel avian influenza virus A(H7N9) as of April 8. The death toll is seven, according to Michael Shaw, PhD, associate director of laboratory science for the CDC’s Influenza Division.
Michael Shaw
There has been no evidence of human-to-human transmission so far, Shaw said, but the virus has been found in pigeons, chickens and quail. Birds have been slaughtered in markets where birds have tested positive, but there is no noticeable pathogenicity related to the virus among birds.
“The problem is that if you don’t know the bird is sick, then you don’t know that you are being exposed to the virus,” Shaw told Infectious Disease News. “With the H5N1 outbreak in 1997, it was an advantage for human health that the birds were dying because it was obvious that something was happening. In the case of H7N9, we don’t have that warning.”
In a telebriefing Friday, CDC Director Thomas Frieden, MD, MPH, said that there have been no cases reported in the United States. He said that many contacts of those infected have been assessed and monitored by Chinese health authorities and none have developed illness.
Thomas Frieden
“In contrast, in influenza, we would expect at least 20% to 30% of family members to develop illness,” Frieden said. “So the fact that there are that many contacts, and no illness has been identified, is encouraging.”
Most of the cases being investigated have had direct contact with poultry, but Frieden said the disease could spread to neighboring countries, especially where there are live markets.
According to the CDC, drug manufacturers are working in concert with the US government to develop a candidate virus that could be used to develop a vaccine if one is needed.
“This would be produced if there were evidence of widespread transmission from person to person,” Frieden said. “That’s not something we’re seeing at this time.”
The Chinese government is investigating and emphasized stronger infection prevention and control in health care settings. The government has advised stronger communication between animal health and human health sectors.
Joseph Bresee, MD, chief of the epidemiology and prevention branch of the CDC’s influenza division, said Chinese health authorities have improved their surveillance since the introduction of H5N1 in 2003.
“If you think about China’s ability to detect clusters of illness, to detect new illnesses, and to see how this potential outbreak may or may not spread, I think they’re really well positioned to do that,” Bresee said.
According to Frieden, Chinese health authorities are working closely with the United States and other global health agencies to monitor A(H7N9).
WHO and the CDC have not recommended any travel or trade restrictions.
Perspective
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Arnold S. Monto, MD
This is a very strange situation, in that it is a totally novel virus. There are receptors on mammalian cells, which is something we have to watch, especially since no one has any immunity. You have to ask yourself what in the world is going on here. There are so many more unanswered questions, especially since there is only one childhood case and more in adults older than 27 years.
Perspective
Back to TopKathryn M. Edwards, MD
It is hard to know what will happen, but this is certainly a cause of concern. The most immediate need is to characterize the strain and begin work on a potential vaccine candidate, determine its origin and what other animals that might be infected. Then determine whether the strain has the potential to spread from person to person.
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Pedro A. Piedra, MD
This is a very dynamic and evolving situation that is being monitored closely by the CDC, WHO and China CDC. The concerning issues are 1) H7N9 has not previously been detected in humans, 2) at least 14 cases have been identified from 4 different provinces in China, 3) approximately a third of the cases detected to date have resulted in death, 4) the reservoir for the virus has not been identified, although a pigeon in a live market in Shanghai was found to have the H7N9 virus, and 5) the genetic analysis of three of the H7N9 viruses isolated from humans suggest that the virus is adapting to be able to replicate in mammals. Evidence for efficient human-to-human transmission has not been detected. In the next few weeks we will learn whether this outbreak will remain confined or spread. If it remains confined, a lot of work will go into identifying the reservoir, removing the threat (for example culling exposed or infected birds), and enhancing surveillance in animals and humans, infection control measures and treatment protocols. If it spreads efficiently within humans there is a potential for the next pandemic. The lessons we learned from the nH1N1 pandemic will allow us to be better prepared to respond to the next pandemic.
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