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CDC: Intense surveillance needed on H7N9 in humans and animals
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Intensified surveillance in both humans and animals will answer important questions about the H7N9 virus that is currently affecting humans in China, according to Timothy M. Uyeki, MD, and Nancy J Cox, PhD, both of the Influenza Division of the CDC’s National Center for Immunization and Respiratory Diseases.
“We cannot rest our guard,” they wrote in an editorial published in The New England Journal of Medicine. “The coming weeks will reveal whether the epidemiology reflects only a widespread zoonosis, whether an H7N9 pandemic is beginning, or something in between.”
So far, there have been 82 patients with laboratory-confirmed H7N9 and 17 deaths. There has been no evidence of human-to-human transmission, but more than 1,000 close contacts of those with the virus are being monitored.
Researchers from the Chinese CDC isolated a novel reassortment avian-origin influenza A(H7N9) virus from three patients who died in the outbreak in China, according to a coinciding report in NEJM. Six internal genes were from avian influenza A(H9N2) viruses.
The first patient was an 87-year-old man with chronic obstructive pulmonary disease and hypertension who presented with cough and then high fever and dyspnea. The second patient was a 27-year-old man with a history of hepatitis B virus who presented with high fever and cough. He worked as a butcher in a market that included live birds. Both patients were from Shanghai. The third patient was a 35-year-old woman from Anhui with a history of hepatitis B virus who presented with high fever and cough. She had visited a chicken market 1 week before symptoms developed.
The researchers found substitution Q226L (H3 numbering) at the 210-loop in the hemagglutinin gene in the A/Anhui/1/2013 and the A/Shanghai/2/2013 virus, but not in the A/Shanghai/1/2013 virus. In all three, they identified a T160A mutation at the 150-loop in the hemagglutinin gene and a deletion of five amino acids in the neuraminidase stalk region.
“Severe avian influenza A(H7N9) infections, characterized by high fever and severe respiratory symptoms, may pose a serious human health risk,” the researchers wrote. “We are concerned by the sudden emergence of these infections and the potential threat to the human population.”
Uyeki and Cox said severe disease in humans caused by novel influenza A viruses “is a seminal event,” and the discovery of this virus “is of major public health significance.”
For more information:
Gao R. N Engl J Med. 2013;doi:10.1056/NEJMoa1304459.
Uyeki T. N Engl J Med. 2013;doi:10.1056/NEJMp1304661.
Perspective
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Gregory A. Poland, MD
In the United States, this outbreak is a point of concern, but not a cause for panic. There are three criteria for a pandemic. The first is a novel virus and the second is a lack of population immunity, both of which we have. The third is evidence of human-to-human transmission, which is the only part missing from this outbreak. Health officials are actively looking at close contacts of the cases, and they have not identified any evidence of human-to-human transmission. But the question remains: How are these individuals becoming infected, especially those that have not had contact with poultry? It is unclear what the source of the infection actually is.
On the plus side, the virus has been susceptible to antiviral medications. One concern that we have is that H7 strains are not very immunogenic in humans. When other types of H7 vaccines have been made, it has required larger doses and multiple doses to induce a response. If a vaccine is necessary, it will be a different kind of vaccine that isn’t currently licensed in the United States, and could require an adjuvant. CDC has received the virus from China and is making preparations to develop a vaccine if it becomes necessary.
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