Canadian doctors are reporting what may be the first case of a new flu virus created after a child became co-infected with two influenza strains - pandemic H1N1 and seasonal H3N2.
The 16-month-old boy from the Greater Toronto Area was admitted to an area hospital on January 24 and discharged home after about a 15-hour stay.
The child, who was suffering both respiratory and gastrointestinal symptoms, recovered from his illness without complications and none of his family members or other close contacts contracted the virus.
Doctors only discovered the toddler had been infected with an altered flu virus after testing of nasal-throat swabs turned up evidence of what's called "reassortment": Genes from the H1N1 and H3N2 flu viruses had been swapped, creating a virus with a new genetic combination.
"To the best of our knowledge, this is the first case of reassortment involving [pandemic]H1N1 and seasonal H3N2," said Jonathan Gubbay, a medical microbiologist at the Ontario Agency for Health Protection and Promotion.
"We can never definitely say it's the first ever, but we're pretty sure it is, that it hasn't been [previously]reported," he said in an interview.
Dr. Gubbay and colleagues who reported the case Thursday said the new virus is unlikely to pose a public health threat as the current seasonal flu vaccine protects against both H1N1 and H3N2, and it should provoke an antibody response against the combination virus as well.
"This was a bit of a serendipitous finding in the sense that they took two swabs and were able to see what we thought were discordant results but were in fact evidence he was infected with two influenza viruses," said Donald Low, microbiologist-in-chief at Toronto's Mount Sinai Hospital.
The lab culture of the child's saliva samples "grew up a virus which is a combination of the two," Dr. Low said. "What I guess it emphasizes is the potential for sort of a real-life experiment, how these two different viruses were able to recombine."
Dr. Low said the concern about genetic reassortment is that a new strain could be born that is far more virulent than either of its parent viruses and to which people have no natural immunity.
That's not the case with this microbe, he said.
"The thing that prevents us from this event really having much of a public health consequence is that we have vaccines that have been widely distributed for both types [of flu virus] So the H3N2 that is now in that child, in that new virus, is included in the yearly vaccine, as is the H1N1 that originally had infected the child.
"So you don't have a new virus being created that is going to be introduced into a large susceptible population."
Dr. Gubbay said testing at Ontario's Public Health Laboratory where he works and at the National Microbiology Lab in Winnipeg confirmed that the child's co-infection had produced the new flu strain, which arose from a cellular scrambling of the eight genes that make up influenza viruses.
"We can't really comment with just our one case how transmissible this virus may be; all we can say is we did not observe any transmission of this virus," Dr. Gubbay added.
"I think definitely it highlights the need for ongoing surveillance for these sort of events. … Obviously, if that child had not presented to hospital, we would not have known about it."
The Canadian Press