Ten days ago, in Swine Variant Flu Season, we reviewed the history - and recent developments in - swine-variant influenza viruses, and their potential threat to public health.
While rarely reported in humans - infections are most likely to occur in late summer and fall - when county and state fairs are held across much of the country.
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.
In 2012 more than 320 human infections were reported around the nation, while 5 years ago (2016/17) 66 cases were recorded.
Most swine variant infections have been mild or moderate, but the CDC's IRAT (Influenza Risk Assessment Tool) lists 3 North American swine viruses as having at least some pandemic potential (2 added in 2019).
H1N2 variant [A/California/62/2018] Jul 2019 5.8 5.7 ModerateH3N2 variant [A/Ohio/13/2017] Jul 2019 6.6 5.8 Moderate
H3N2 variant [A/Indiana/08/2011] Dec 2012 6.0 4.5 Moderate
The CDC's Assessment of the Risk from these viruses reads:
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
Late yesterday the West Virginia Department of Health and Human Resources (DHHR) reported the detection of swine-variant H3N2v in at least one person after several report of flu-like illness were reported by individuals working closely with swine.
Swine Influenza Detected in Jackson County
DHHR's Bureau for Public Health (BPH) and the Jackson County Health Department are investigating several reports of individuals who have developed influenza-like illness after working closely with swine exhibiting respiratory symptoms and fever at the Jackson County Fair.
DHHR’s Office of Laboratory Services returned presumptive positive influenza A H3N2v on at least one human specimen on Tuesday, August 2. The sample has been forwarded to the Centers for Disease Control and Prevention for confirmation.
“If experiencing symptoms such as fever, runny nose, sore throat, cough or congestion, it is extremely important to let your healthcare provider know if you or your loved one has visited a recent outdoor event with animal livestock, such as pigs, and to be appropriately evaluated,” said Dr. Ayne Amjad, DHHR’s State Health Officer and BPH Commissioner. “These symptoms usually show up 1-3 days after exposure.”
Swine influenza viruses may circulate in pig populations throughout the year and do not usually infect humans. Although influenza viruses can spread between pigs and humans in rare situations, this usually occurs after having contact with a pig in a public setting or by directly working with infected pigs. The same influenza antiviral drugs used to treat seasonal influenza can also be used for treatment of swine flu infection in humans.
State residents are encouraged to take routine precautions when visiting animal exhibits, including washing hands with soap and water before and after exposure to animals, to not take personal items, food or drinks into swine barns or areas with animals, to avoid close contact with animals that are ill, and to avoid contact with pigs if experiencing influenza-like symptoms.
Although we see occasional one-off infections in farm workers, agricultural exhibits at state and county fairs often host thousands of visitors, which can lead to far greater levels of exposure.
While pigs are routinely screened for obvious signs of illness at most of these venues, in 2017's EID Journal Dispatch (Transmission Of Swine H3N2 To Humans At Agricultural Exhibits - Michigan & Ohio 2016), we learned that while widespread illness in pigs was only rarely reported, surveillance revealed an average prevalence of influenza A in fair pigs of 77.5%.
This study cautioned that this suggests `. . . that subclinical influenza A infections in pigs remain a threat to public health (3).'
In other words, healthy looking pigs can carry, and transmit swine-variant viruses. We saw similar findings in a 2012 study (see EID Journal: Flu In Healthy-Looking Pigs).
After two-plus years of pandemic precautions (social distancing, mask wearing, etc.), community immunity to influenza viruses - which includes novel swine and avian viruses - is believed to be very low.
Although the threat from swine variant viruses is currently believed to be low, those attending agricultural venues may want to exercise a little extra caution this summer.
The CDC maintains a comprehensive Swine/Variant Influenza page where you'll find the latest case counts, safety and prevention information, and guidance for health care providers, including: