Novel H3N2 flu virus infects child in Maine

A 8 year old boy in Cumberland County Maine has been infected with the same H3N2 influenza virus that has previously infected three people in Pennsylvania and one in Indiana. This virus is apparently circulating in pigs in the US.

The people in Indiana and Pennsylvania were infected in late July and August 2011. The 8 year old boy in Maine became ill in early October 2011. He is reported to have been in close proximity to pigs at an agricultural fair. There is disagreement regarding the severity of her symptoms. Although most reports suggest that she was not hospitalised, one media source says that she was.

From Kennebec Journal, October 21, 2011

The Maine Center for Disease Control and Prevention is investigating a new type of swine flu that sickened a child in Cumberland County.

The agency has not provided any more details about who was affected or where, but said it is an isolated event in Maine and has not been detected in people who had contact with the child. The child was hospitalized and is recovering, it said.

The Maine CDC is recommending the following precautions for health care providers:

  • Maintain a heightened awareness for influenza-like illness (ILI) defined as fever greater than 100° with cough or sore throat, in the absence of another known cause.
  • Consider influenza testing by PCR for:
    1. patients with ILI with recent exposure to pigs.
    2. patients with ILI who are hospitalized,
    3. patients with ILI who have died,
    4. patients where a diagnosis of influenza would affect clinical care, infection control, or management of contacts.
  • Consider use of antivirals to quickly limit potential human transmission
  • Vaccinate patients and healthcare workers as a primary strategy to prevent influenza

The virus that infected the boy in Maine, the three people in Pennsylvania and the child in Indiana has a complex ancestry. The HA and NA genomic segments are originally derived from humans, but are different from those currently circulating in H3N2 human flu viruses. The PB1 genomic segment originated in humans. The PB2 and PA genomic segments originated in birds. The NP and NS genomic segments originated in pigs. The Matrix or M segment, came from the human 2009 pandemic H1N1 virus, apparently as a result of reassortment between a virus that has been circultating in pigs and the pandemic 2009 H1N1 virus.

Five individuals have now been reported to be infected with this virus within a relatively short time. Pig to human transmission is likely, although it is not know if this was due to direct contact or respiratory spread. Although sustained human to human spread of the new virus has not been reported, this could happen at any time. The virus could change further as result of reassortment, recombination or mutation.

Swine-Origin Influenza A (H3N2) Virus Infection in Two Children — Indiana and Pennsylvania, July–August 2011
Morbidity and Mortality Weekly Report (MMWR), September 9, 2011/60(35);1213-1215

[corrected age and gender of child based on new information, October 24, 2011. Hat-tip, Dr. Niman]


5 thoughts on “Novel H3N2 flu virus infects child in Maine

  1. The Indiana case was infected in july, as indicated in sequneces released at GISAID and Genbank and descibed in detail in the case report in the early release MMWR linked above, the sequences of the Indiana case (A/Indiana/08/2011) and the two latter Pennsylvania cases (A/Pennsylvania10/2011 and A/Pennsylvania11/2011) are virtually IDENTICAL (and all five 2011 trH3N2 cases have the same constellation of genes (including M gene from H1N1pdm09 and identical linearages for all 8 gene segments).

    Thus, the same novel trH3N2 is in all 5 human cases from 3 states collected over of 2 month time frame, and this constellation has never been reported in swine (there are 11 public US swine sets of trH3N2 sequences from 2011, including one from July, and another 2 dozen from late 2010 made public by the USDA and academic institutions.

  2. The sample for A/Indiana/08/2011 does appear to have been collected July 27, 2011.

    I don’t doubt that this it is possible that this strain may be circulating in humans. However, it is also possible that it is widespread in pigs and is only spread by close contact among humans. It would be easy to distinguish between these two possibilities by more sequencing.

    1. The constellation of flu genes in the human cases is certainly not widespread in swine. The USDA and academic institutions have increased swine surveillance since the 2009 pandemic. This increased testing has identified 11 trH3N2 cases in US swine in 2011 (as recently as July), as well as 35 more in 2010, including 21 collected after October 24, 2010. None of these swine (or any swine anywhere in the world) have been reported with the constellation of flu genes found in all five US cases (7 trH3N2 gene segments with the M gene from H1N1pdm09).

      The phylogenetic clustering of the US human trH3N2 cases was also seen in 2010, but that clustering involved most of the gene segements in most of the human cases. However, in 2011 this clustering, which involved genes from prior human cases, has evolved into identities, where all of the genes in all of the human cases match each other, with 5 genes from the dominant human series including H3 (PB2, PA, HA, NP, NS), an NA closely related to the outlier in Pennsylvania, A/Pennsylvania/14/2010, and the PB1 more closely related to the Huron County fair outbreak in 2007 (A/Ohio/01/2007 and A/Ohio/02/2007), as well as the MP gene segment from pandemic H1N1,

      Thus, this human contagion has been adapting to humans (the first human trH3N2 reported in the US was in Kansas in August, 2009, A/Kansas/13/2009, and the human adaptation in 2010 followed by identities in 2011 has been quite clear,

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