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Commentary
Novel
H3N2
Cases In United States Raise Pandemic Concerns
Recombinomics
Commentary 22:50
November 10, 2010
If the two cases in the WHO alert are current and have no contact with each other, then they likely signal the start of another pandemic. H3N2 triple reassortants are commonly found in swine and are widespread in the United States. They have much in common with pandemic H1N1, except the H1 and N1 are replaced by human H3 and human H2. These viruses occasionally jump to humans, but transmission is limited in the human population.
However, reports of two independent cases in the US would be much like the first two cases of pandemic H1N1 in southern California in 2009. The two children were over 100 miles apart and had no known contact with each other or swine. The novel H3N2 cases are over 500 miles apart and swine contact by a 7 month old child seems unlikely.
Since swine H3N2 triple reassortants have human H3 and N2, detection of these novel reassortants requires sequencing. Novel H3N2 would be positive on an influenza A test as well as a seasonal H3 sub-typing test. However, sequencing would readily detect a triple reassortant because the other six genes would be similar to pH1N1 (avian PB2 and PA, human PB1, and swine NP, MP, NS).
Generation of novel H3N2 viruses would be elevated at this time because pH1N1 readily jumps to humans, as well as from humans to swine. Thus, pH1N1 is now widespread in humans and swine, and human H3N2 in swine or in new seasonal flu cases would increase the frequency of such novel triple reassortants, which would generate a new pandemic if transmission was sustained.
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