Influenza strains are categorized by the protein spikes on the surface of the virus and scientists are aware of 17 subtypes of the hemagglutinin protein (the “H”) and ten of the neuraminidase protein (the “N”). The new strain is from the H7 family, which has popped up before in both animals and humans.
But in the past, H7 strains have mostly caused mild sickness in people; the one notable exception is from 2003, when a veterinarian developed respiratory illness and died after an H7N7 outbreak in the Netherlands.
Generally, however, infected people come down with eye infections or mild flu symptoms, as was the case in 2004, when an H7N3 outbreak in British Columbia infected two people and prompted the culling of 19 million poultry.
On Sunday, however, Chinese health officials announced that two Shanghai men have died in the first known cases of human infection with H7N9: an 87-year-old and a 27-year-old. The older man had two sons who also contracted pneumonia, one of whom died, but neither has yet to test positive for H7N9, according to a World Health Organization spokesperson.
The third person, a 35-year-old woman, was apparently infected in the city of Chuzhou in Anhui province, hundreds of kilometres northwest of Shanghai. She remains in critical condition.
All three people fell ill between Feb. 19 and March 15, according to the World Health Organization.
“To me, I think the most interesting aspect of the cases that were described were the geographical separation of the cases,” said flu expert Dr. Richard Webby, a virologist with St. Jude Children’s Research Hospital in Memphis, Tenn.
This has two possible implications, he suggested; the virus is “either widespread in some poultry population — or the other more sinister explanation, which is it’s spreading amongst people.”