Twice over the past couple of weeks we saw reports of county fairs in Ohio closing their pig barns when swine H3N2 was detected in exhibition pigs (see Second Ohio County Fair Closes Hog Barn Over Swine Flu).
When swine influenza viruses jump to humans, they are dubbed swine variant viruses. The CDC describes Swine Variant viruses in their Key Facts FAQ.
What is a variant influenza virus?
When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant influenza virus.” For example, if a swine origin influenza A H3N2 virus is detected in a person, that virus will be called an “H3N2 variant” virus or “H3N2v” virus.Since the influenza subtypes that commonly circulate in swine (H1, H2 & H3) are also the same HA subtypes as have caused all of the human pandemics going back 130 years (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?), swine influenza viruses are watched carefully for signs of jumping to humans.
While only rarely reported, these infections probably happen far more often than we know. But since swine variant influenza infections look like seasonal flu, and testing for swine variant viruses is only sporadically done, we don't often hear about it.The last swine variant infection in the US was reported from Texas last May. Today the CDC has announced 11 additional H3N2v (variant) infections, all from the state of Ohio and linked to county fair attendance in the past couple of weeks. All were mild, no one was hospitalized, and all have recovered.
Eleven human infections with novel influenza A viruses were detected in Ohio during week 29. All 11 persons were infected with influenza A (H3N2) variant (H3N2v) viruses and reported exposure to swine in a fair setting during the week preceding illness onset. Ten of the 11 patients were children less than 18 years of age and one patient was an adult aged 50-64 years.
None were hospitalized and all have fully recovered from their illness. No human-to-human transmission has been identified. Swine influenza A (H3N2) viruses were identified from respiratory samples collected from pigs at the same fair. Public health and agriculture officials are investigating the extent of disease among humans and swine, but no increases in influenza-like illness in the community have been reported. These 11 infections bring the total number of H3N2v infections during 2017 to 12 and the cumulative total since 2011 to 376.
Early identification and investigation of human infections with novel influenza A viruses are critical to ensure timely risk assessment and so that appropriate public health measures can be taken. Additional information on influenza in swine, variant influenza infection in humans, and strategies to interact safely with swine can be found at http://www.cdc.gov/flu/swineflu/index.htm.
Last October, in MMWR: Investigation Into H3N2v Outbreak In Ohio & Michigan - Summer 2016, we looked at the CDC's investigation into a cluster of 18 H3N2v cases across two states in August of 2016. This was the biggest outbreak of swine variant infections we'd seen since 2012, when more than 300 cases were reported across 10 states.
The `headline' in that report was that 16 of the 18 cases analyzed belonged to a new genotype not previously detected in humans. Swine influenza viruses, like all flu viruses, are continually evolving.
As the state and county fair season continues over the summer and into fall, it would not be surprising to see additional, scattered reports of swine variant infection, as these venues tend to put a lot of people into close contact with pigs.
For more information on swine variant viruses, and how to protect yourself when in contact with farm animals, the CDC provides the following guides.
- Key Facts for People Exhibiting Pigs at Fairs[545 KB, 2 pages]
- Take Action to Prevent the Spread of Flu Between People and Pigs[1.3 MB, 2 pages]
- Educational Posters[389 KB, 1 page]
- Compendium of Measures to Prevent Disease Associated with Animals in Public Settings, 2013.
- Reduce Your Risk (English)[22 KB, 1 page] | (Spanish)[22 KB, 1 page]
- Measures to Minimize Influenza Transmission at Swine Exhibitions, 2016 – NASAHO and NASPHV[97 KB, 8 pages]