Swine variant viruses (H1N1v, H1N2v & H3N2v) are swine flu viruses that have jumped to human hosts, and over the past decade the CDC has recorded just over 380 cases around the country.
The bulk of those (309 cases) all occurred in 2012, and most were linked to swine exhibits at county and state fairs across multiple states.
While undoubtedly more common than we know, most years fewer than a dozen cases are reported. Symptoms are essentially the same as seasonal flu, and without laboratory testing, you wouldn't know the difference.
Of the three swine variant strains reported in the United States, H3N2v has been the most common, making up 94% of all reported cases.
On July 1st, we saw Fluview Week 25: 2 Novel H1N2v Cases Reported (Wisconsin & Minnesota), bringing 2016's total to 4.
Yesterday the Michigan Department of health announced 2 more (see below), both connected to the Muskegon County Fair, and has put out an alert for the possibility of others.
Contact: Jennifer Eisner 517-241-2112
For Immediate Release: August 5, 2016
LANSING, Mich. – Today the Michigan departments of Health and Human Services and Agriculture and Rural Development, along with the Public Health Muskegon County (PHMC) have identified two cases of influenza A H3N2 variant (H3N2v) in Muskegon county residents who were swine exhibitors at the Muskegon County Fair. The fair took place July 25-30, 2016. A sick pig from the fair tested positive for influenza A H3N2 at the National Veterinary Services Laboratories in Ames, Iowa.
PHMC is reaching out to swine exhibitors who attended the Muskegon County Fair to identify any additional illnesses. PHMC has already alerted providers in their jurisdiction to watch for patients presenting with respiratory symptoms who report exposure to swine or visited the swine barn and the fair.
Symptoms of H3N2v infection in people are similar to those of seasonal flu viruses and can include fever and respiratory symptoms, such as cough and runny nose, and possibly other symptoms, such as body aches, nausea, vomiting, or diarrhea. Infections with influenza viruses (including variant viruses like H3N2v) can sometimes cause severe disease, even in healthy people. This can include complications, such as pneumonia, which may require hospitalization, and sometimes death. People who are at high risk of developing complications if they get influenza include children younger than five years of age, people 65 years of age and older, pregnant women, and people with certain long-term health conditions, such as asthma, diabetes, heart disease, weakened immune systems, and neurological or neurodevelopmental conditions.
The incubation period (the time it takes from exposure to illness) for this influenza is similar to seasonal influenza, up to 10 days, and most commonly two days. Currently, there is no vaccine for H3N2v and the seasonal flu vaccine will not protect against H3N2v; however, antiviral drugs, such as oseltamivir and zanamivir, are effective in treating H3N2v virus infections. Early treatment works best and may be especially important for people with a high risk condition.
Below are some steps that you can take to protect yourself and prevent the spread of any illness:
- Avoid close contact with sick people
- Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it
- Wash your hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub
- Do not eat or drink in livestock barns or show rings
- Don’t take toys, pacifiers, cups, baby bottles, strollers, or similar items into pig areas
- Anyone who is at high risk of serious flu complications and planning to attend a fair should avoid pigs and swine barns
- Avoid touching your eyes, nose and mouth. Germs spread this way
- If you are sick, stay home from work or school until your illness is over
- Avoid contact with pigs if you have flu-like symptoms. Wait seven days after your illness started or until you have been without fever for 24 hours without the use of fever-reducing medications, whichever is longer
- Get an annual influenza vaccination
For more information about H3N2v, visit www.cdc.gov/flu/swineflu/h3n2v-basics.htm.
Although a major outbreak is unlikely, based on the experience of 2012, it would not be unexpected if additional cases linked to the Muskegon fair are uncovered, or if additional transmission occurs at other venues this summer and fall.
Since the influenza subtypes that commonly circulate in swine (H1, H2 & H3) are also the same that have caused all of the human pandemics going back 130 years (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?), they are generally regarded as having less far to `jump’ to humans than do many avian viruses.
Which is precisely how the H1N1 pandemic virus emerged in 2009, and why we watch these swine variant viruses so closely.
The CDC's assessment of H3N2v reads:
It's possible that sporadic infections and even localized outbreaks among people with this virus may occur. While there is no evidence at this time that sustained human-to-human transmission has occurred, all influenza viruses have the capacity to change and it's possible that this virus may change and become widespread in people.
Illness associated with H3N2v infection so far has been mostly mild with symptoms similar to those of seasonal flu. Like seasonal flu, however, serious illness, resulting in hospitalization and death is possible. In 2012, for example, of 309 human infections with H3N2v, 16 people were hospitalized and one of these people died. Most of the people who were hospitalized and the person who died had one or more health or age factor that put them at high risk of serious flu-related complications.
People at high risk of serious complications from seasonal influenza and H3N2v include children younger than 5, people with certain chronic conditions like asthma, diabetes, heart disease, weakened immune systems, pregnant women and people 65 years and older. CDC has issued guidance for people attending fairs where swine might be present, including additional precautions for people who are at high risk of serious flu complications. Limited serologic studies indicate that adults may have some pre-existing immunity to this virus while children do not. Most cases of H3N2v infection have occurred in children who have little immunity against this virus.
While North American swine variant viruses are a legitimate concern, globally - particularly in places where surveillance and biosecurity is lax - the risks are arguably even greater.
Last December, in PNAS: The Pandemic Potential Of Eurasian Avian-like H1N1 (EAH1N1) Swine Influenza, we looked at a study by Chinese and Japanese researchers who had isolated and characterized a number of avian-like H1N1 virus variants circulating in Chinese pigs that they believe have considerable pandemic potential.
Our study shows the potential of EAH1N1 SIVs to transmit efficiently in humans and suggests that immediate action is needed to prevent the efficient transmission of EAH1N1 SIVs to humans.
For more on swine variant viruses, both in the United States and around the world, you may wish to revisit:
Eurosurveillance: Seroprevalence Of Cross-Reactive Antibodies To Swine H3N2v – Germany
JID: Evolutionary Dynamics Of Influenza A Viruses In US Exhibition Swine