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Commentary
Vietnam H3N2v
Swine Flu
Case Raises Pandemic Concerns
Recombinomics Commentary 11:00
February 15, 2012
Yang said, this is the first case reported in Vietnam A/H3N2 flu originated from pigs. This slight movement of cases and no evidence of transmission from person to person.
The above translation is from an AP report that is being carried widely in Vietnam. In contrast to last week’s report, which was a rewrite of a December report describing Vietnam’s efforts to detect H3N2v cases, today’s report cites confirmation with the CDC PCR test and gives the age, gender (2F) and location (Long An) of the current case, which is the first human case reported in Asia.
However, the report does not cite sequence data, so the relationship with this case to 2011 cases in the United States is unclear. Vietnam has released sequences from swine trH3N2, and Hong Kong has recently released sequences from swine cases which have Asian H3 and N2 on isolates with H1N1pdm09 internal genes. The H3 sequences in Hong Kong and China (Guangxi) are similar to those reported in Vietnam, and are easily distinguished from US cases, since the US sequences link back to season H3n2 circulating in humans in the mid-1990’s, which had D225G. In contrast, the 2010/2011 sequences have an H3 from seasonal H3N2 co-culating in 2003/2004, which are easily distinguished from the sequences from the 1990’s, and are wide type at position 225 (have a D).
In the US, all H3N2v cases were identified after the start of the 2009 pandemic. The first case, A/Kansas/13/2009, had a PB1 gene with E618D, which was also present in all six confirmed cases in 2010. E618D is in virtually all H1N1pdm09 sequences, and was not in swine isolates collected prior to the pandemic. In 2011 the human H3N2v cases in the US were reassortants which had acquired PB1, N2, and MP from H1N2v or H3N2v swine sequences, which no longer had E618D, but did have an H1N1pdm09 M gene. This was also true to the H1N1v and H1N2v human cases in 2011, so all 20 human cases in 2010 and 2011 either had an H1N1pdm09 E618D or an H1N1pdm09 M gene.
Although all 12 human H3N2v cases in the US had an H1N1pdm09 M gene, only two matching sequences have been found in swine, and both swine isolates were identified from September, 2011 collections.
Moreover, the most recent US cases were from clusters (in Iowa and West Virginia) which had no reported swine exposure, including the 23 cases with ILI who were contacts of the index case at the Mineral County day care center.
All five of the most recent confirmed cases were between the ages of 1-3, as was the confirmed case in Vietnam. However, the epidemiological information of the case in Vietnam has not been disclosed, which is also true for the sequences from this case.
Therefore, it is not clear if this case in Vietnam is similar to the 2010 US cases (with PB1 E618D) or 2011 (with H1N1pdm09 M gene) or if the H3 is from the linear that trances back to the mid-90’s (and had D225G), or is a match for the swine sequences in Vietnam, China, or Hong Kong.
The US has not reported H3N2v cases since the December cluster in West Virginia, although detection requires cross reactivity with seasonal H3 and H1N1pdm09 NP genes, which may limit detection. In contrast, the H3 in H3N2v cases in Vietnam may be more easily detected because a 2003/2004 H3 geen would be more closely related to the H3 sequence used in the CDC PCR test.
Of course a match of the H3N2v in Vietnam with the US cases would support widespread human transmission and provide more evidence for an emerging pandemic. A match of Asian H3 would signal more lineages / constellations of swine H3N2v cases which can jump to humans.
Release of sequence data from this case would be useful.
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