While avian flu is capturing all of the headlines right now, it wasn't but a few months ago we were watching a two-state outbreak of a novel swine variant H3N2 virus associated with pig exposure at county fairs (see MMWR: Investigation Into H3N2v Outbreak In Ohio & Michigan - Summer 2016).
Last year also saw scattered swine H1N2v cases in the United States.
Over the past 10 years we've seen roughly 400 human infections with swine variant viruses in the United States, with the H3N2v strain the most common, making up 94% of all reported cases (n=372) and H1N1v coming in 2nd, with 20 cases (4%). Least common, with just 9 reported cases, has been H1N2v.
Swine variant viruses continue to spread and evolve around the world, and while surveillance is non-existent in many regions, we manage to keep an eye on several different lineages. They are a concern because one could someday become well enough adapted to human physiology to transmit efficiently in the community - which is essentially what happened in 2009 when the pandemic H1N1 virus emerged.
Most of the time, people infected with these swine variant viruses experience only mild or moderate illness, but of late we've started seeing some more severely ill cases.
Last December, in Eurosurveillance: Severe acute respiratory infection caused by swine influenza virus in a child, we looked at a report on a school-aged child in the Netherlands whose condition deteriorated enough to require ECMO (Extracorporeal membrane oxygenation) life support. In this case, the patient reported no direct contact with pigs, but had visited a piggery. The virus was H1N1v.
Today we've another report in Eurosurveillance, this time from Italy, of a man with indirect pig exposure (he lived with someone who worked with pigs), who became critically ill, and required ECMO life support, during his 30 day hospitalization for an H1N1v infection.
Eurosurveillance, Volume 22, Issue 5, 02 February 2017
Swine influenza A (H1N1) virus (SIV) infection requiring extracorporeal life support in an immunocompetent adult patient with indirect exposure to pigs, Italy, October 2016(SNIP)
F Rovida 1 2 , A Piralla 1 2 , FC Marzani 3 , A Moreno 4 , G Campanini 1 , F Mojoli 3 5 , M Pozzi 3 , A Girello 1 , C Chiapponi 6 , F Vezzoli 7 , P Prati 8 , E Percivalle 1 , A Pavan 9 , M Gramegna 10 , GA Iotti 3 5 , F Baldanti 1 11
Received:17 January 2017; Accepted:02 February 2017
DiscussionExposure to swine is often considered a risk factor for human SIV infections . Here we describe a severe case of swine influenza A(H1N1) virus infection requiring ECMO in an adult immunocompetent man with a BMI > 30 as a risk factor, who had indirect exposure to pigs through a brother working as a breeder on a pig farm. Twelve pigs of the farm tested positive for influenza A, and the strain sequenced from one of them was closely related to the virus recovered from the patient. In addition, antibodies against swine influenza A strains (including the strain recovered from the patient) were detected in the serum sample of the patient’s brother. These data support the hypothesis that SIV infecting our patient was circulating on the pig farm and the patient’s brother might have operated as a bridge for transmission of the virus.
As SIV infection in humans is mild in most cases, its frequency might be underdiagnosed [9,11]. Nevertheless, in the same month of October, Fraaij et al. reported a case of severe infection caused by swine influenza A(H1N1) in a child requiring ECMO support in the Netherlands . In our phylogenetic analysis of HA and NA, this Dutch strain  and the strain A/Pavia/65/2016, circulating in the same period in Europe, clustered into distinct branches of the trees.
We have reported here a case of severe swine influenza A infection following indirect exposure to pigs. One possible path of infection could be human-to-human. However, other routes (e.g. contact with contaminated clothing, surfaces etc.) cannot be excluded. These data further highlight the need of strict surveillance of influenza in humans and in animals.
(Continue. . . )
Due to its normally mild presentation, and the limited testing for influenza subtypes, we don't really know how many people are infected with these swine variant viruses each year. The odds are, it is a lot more common than we know.
As with avian influenza, swine flu viruses are constantly evolving, which is why we watch reports like today's with particular interest. For more on swine variant viruses, both in the United States and around the world, you may wish to revisit: