Avian Flu Diary: The Return Of H1N1v

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# 6556

Yesterday’s FluView report, in addition to updating the number of new H3N2v cases, announced the detection of a single H1N1v flu infection in a person living in Missouri. That patient has fully recovered.

H1N1v is one of the `viral contenders’ I mentioned two weeks ago in An Increasingly Complex Flu Field, and until just over a year ago, was the most commonly reported variant swine flu virus detected in humans since 2005.

This week’s announced case brings to 14 the total number of H1N1v cases reported since 2005. The last reported case of H1N1v infection came from Wisconsin in December of 2011.

Of particular interest, this week’s detection is the second time that the H1N1v virus has been found to contain the M (matrix) gene from the 2009 H1N1 pandemic virus.

Here is how this week’s FluView describes it:

Confirmatory testing at CDC identified H1N1v with the matrix (M) gene from the 2009 H1N1 influenza virus in specimens collected from this patient. Cases of H1N1v have been detected previously, and the current case marks the second report of H1N1v with the M gene from the 2009 H1N1 virus.

This M gene has been showing up regularly in swine variant viruses (H1N1v, H1N2v, H3N2v) for more than a year. The CDC has previously stated that `This M gene may confer increased transmissibility to and among humans, compared to other variant influenza viruses.’

The $64 question is, what to make of all of this?

Since the outbreak of H3N2v began in earnest in mid July, the CDC and local health departments have stepped up testing for novel or variant flu viruses.

And as one might expect, the harder you look, the more you are likely to find.

Given the limits of surveillance, testing, and reporting – we really don’t know what the normal `background rate’ of these types of infections are in humans. The smattering of reports since 2005 indicate they are fairly rare, but certainly not unheard of.

For now, the H3N2v virus – due to roughly 300 human infections across the Midwest - has captured the bulk of our attention.

But these other cases serve to remind us that nature continues to churn out and test new viral variations, and that the next public health threat could come out of left field.

The CDC’s assessment on the H3N2v virus reads:

It's possible that sporadic infections and even localized outbreaks among people with this virus will continue to occur. While there is no evidence at this time that sustained human-to-human transmission is occurring, all influenza viruses have the capacity to change and it's possible that this virus may become widespread.

So far, the severity of illnesses associated with this virus in people has been similar to the severity of illnesses associated with seasonal flu virus infections. Limited serologic studies indicate that adults may have some pre-existing immunity to this virus while children do not.

CDC is closely monitoring human infections with all novel influenza viruses, including H3N2v viruses, and will provide more information as it becomes available.

For more on all of this, Robert Roos of CIDRAP NEWS, has an excellent report from last night.