Reassortment of H3N2v - Credit CDC
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In 2011 a new strain of swine influenza - originally dubbed trH3N2 but renamed H3N2v (swine variant influenza) in late 2011 – was discovered to have evolved in American pigs. What made this virus different from the earlier trH3N2 novel strains was that it was a reassortant swine H3N2 which had acquired the matrix (M) gene from the 2009 H1N1 pandemic virus.
We first heard about this new strain on Sept. 2nd, 2011, via an early release from the CDC’s MMWR, which described two young children – one in Indiana and another in Pennsylvania - who were infected by a new swine-origin H3N2 virus (see Swine-Origin Influenza A (H3N2) Virus Infection in Two Children --- Indiana and Pennsylvania, July--August 2011).
While these first two cases first appeared to be one-off, dead end transmissions, it was only a few days later that Pennsylvania Reported 2 More Novel Flu Cases. On September 9th, 2011 the CDC updated their SOIV (Swine Origin Influenza Virus) page (see CDC Update On Recent Novel Swine Flu Cases), acknowledging the possibility that limited human-to-human transmission of this trH3N2 virus might be occurring.
By the end of 2011, 12 cases had been reported across 5 states. While most human infections with this virus have only produced mild to moderate illness - as a precaution - in December of 2011 the CDC announced their intention of Developing A trH3N2 Seed Vaccine.
In 2012 more than 300 swine `variant’ infections were confirmed (see A Variant Swine Flu Review) in the United States, mostly linked to attendance of state and county fairs. Based on recently published studies, this was likely a substantial undercount (see CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012).
This year has seen far fewer reported infections, with just 19 cases reported thus far. Exactly why we’ve seen this drop off isn’t clear, although better biosecurity at swine exhibits and improved hygiene by those in direct contact with pigs may be partially responsible.
Recently, scientists in Korea revealed they had found an H3N2v virus genetically closely related to the strains seen in the United States (see Study: Novel & Variant Swine Influenzas In Korean Pigs). Other regions – particularly in Europe and Hong Kong - have increased surveillance of their swine herds, looking for any signs this variant virus has shown up in their livestock as well.
All of which serves as prelude to a report from the ECDC today on a recent joint scientific assessment of the risks of H3N2v showing up in European swine. While they consider the risks to be low, they also acknowledge that:
It is not possible to predict which changes within H3N2v virus might enable it to develop pandemic properties. Hence, it is not possible at present to set up a specific system to monitor such a risk. Nevertheless, it is recommended to reinforce the monitoring of influenza strains circulating in pigs in EU.
Follow the link below to access the full report.
Joint scientific opinion assesses the likelihood of swine-origin influenza A(H3N2) in the EU as low
21 Oct 2013
The likelihood of the swine-origin influenza A(H3N2)v appearing in the EU is low. Nevertheless, it is important to reinforce the monitoring of influenza strains circulating in pigs and link this to surveillance of influenza viruses in humans concludes the joint scientific opinion of three EU agencies, European Food Safety Authority, European Medicines Agency and European Centre for Disease Prevention and Control. The opinion assesses and advises on the possible risks posed by influenza A(H3N2)v virus for animal health and the potential implications for animal and human health.
Pigs are an important host in influenza virus ecology since they are susceptible to infections with both avian and human influenza A viruses and can play a role in interspecies transmission. This can lead to co-infection and genetic reassortment of viruses of swine, human or avian origin.
In 2011, the United States of America reported a cluster of cases of human infection with a swine-origin influenza A(H3N2) variant virus H3N2v. In 2012, 309 influenza H3N2v virus infections in humans were identified in the US and 12 cases so far in 2013.
The joint scientific opinion assesses the following:
- risk of introduction of H3N2v in EU
- diagnostic capabilities to early detect H3N2v incursion in EU
- implications and consequences of the possible evolution of H3N2v virus on pig health
- the use of vaccines in relation to the possible evolution of variants of influenza viruses posing a risk to public and animal health
- factors to be monitored that would suggest a risk for the emergence of a new pandemic influenza strain from the influenza A(H3N2v) virus
The joint opinion concludes that it is recommended to reinforce the monitoring of influenza strains circulating in pigs in EU because it is not possible to predict nor monitor changes to the H3N2v virus that might enable it to develop pandemic properties.
