While seasonal flu is in full retreat across North America the CDC's weekly FluView report is always worth a look, and today they are reporting on an H3N2v infection from last February in the State of Texas.
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 rare, 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.
First today's report from the CDC's FluView, then I'll return with a bit more.
One human infection with a novel influenza A virus was reported by the state of Texas. The person was infected with an influenza A (H3N2) variant (H3N2v) virus. This H3N2v virus was detected through the Department of Defense Global, Laboratory-based Influenza Surveillance Program.
The patient became ill with respiratory symptoms in February 2017, was not hospitalized, and has fully recovered from their illness. Swine contact at an agricultural event was reported in the week preceding illness onset. This is the first H3N2v virus infection detected in the United States in 2017.
Influenza viruses that circulate in swine are called swine influenza viruses when isolated from swine, but are called variant influenza viruses when isolated from humans. Early identification and investigation of human infections with novel influenza A viruses are critical so that the risk of infection can be more fully understood and 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.
The CDC's Assessment of swine variant viruses states:
Sporadic infections and even localized outbreaks among people with variant influenza viruses may occur. All influenza viruses have the capacity to change and it's possible that variant viruses may change such that they infect people easily and spread easily from person-to-person. The Centers for Disease Control and Prevention (CDC) continues to monitor closely for variant influenza virus infections and will report cases of H3N2v and other variant influenza viruses weekly in FluView and on the case count tables on this website
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.
As the summer state and county fair season gets underway in the next couple of months, we are likely 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]