Wednesday, July 13, 2016

CDC On Protecting Against Swine Variant Viruses


Two weeks ago the CDC notified us of two recent cases of (swine variant) H1N2v flu infections (see Fluview Week 25: 2 Novel H1N2v Cases Reported in Wisconsin & Minnesota) detected in America's upper Midwest.

While most years we only see a handful of swine variant cases, in the summer of 2012 we saw in excess of 300 cases spread across several states, nearly of which were linked to attendance and swine exposure at state and county fairs. 

With fair season underway, and agricultural exhibits always very popular, the CDC has been promoting basic precautions for fairgoers via their twitter account.

Swine variant viruses include H1N1v, H1N2v, and (most commonly) H3N2v.

First a look at their recommendations, then a bit more on these variant flu viruses - both in the United States, and around the world.  

Take Action to Prevent the Spread of Flu Between People and Pigs at Fairs

Pigs can be infected with their own influenza viruses (called swine influenza) that are usually different from human flu viruses.
While rare, influenza can spread from pigs to people and from people to pigs. When people get swine flu viruses, it’s usually after contact with pigs. This has happened in different settings, including fairs. The Centers for Disease Control and Prevention (CDC) is concerned about a flu virus that has been found in U.S. pigs and that has infected people too. This virus – called H3N2v – may spread more easily from pigs to humans than is usual for swine flu viruses.

CDC Recommendations For People with High Risk Factors:

  • Anyone who is at high risk of serious flu complications planning to attend a fair where pigs will be present should avoid pigs and swine barns at the fair.
  • People who are at high risk of serious flu complications include children younger than 5 years, people 65 years and older, pregnant women, and people with certain long-term health conditions (like asthma and other lung disease, diabetes, heart disease, weakened immune systems, and neurological or neurodevelopmental conditions).

CDC Recommendations for People Not at High Risk:
  • Don’t take food or drink into pig areas; don’t eat, drink or put anything in your mouth in pig areas.
  • Don’t take toys, pacifiers, cups, baby bottles, strollers, or similar items into pig areas.
  • Avoid close contact with pigs that look or act ill.
  • Take protective measures if you must come in contact with pigs that are known or suspected to be sick. This includes minimizing contact with pigs and wearing personal protective equipment like protective clothing and gloves and masks that cover your mouth and nose when contact is required.
  • Wash your hands often with soap and running water before and after exposure to pigs. If soap and water are not available, use an alcohol-based hand rub.
  • To further reduce the risk of infection, minimize contact with pigs in the pig barn and arenas.
  • Watch your pig (if you have one) for illness. Call a veterinarian if you suspect illness.
  • Avoid contact with pigs if you have flu-like symptoms. Wait 7 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. If you must have contact with pigs while you are sick, take the protective actions listed above.

People with high risk factors who develop flu symptoms should call a health care provider. Tell them about your high risk factor and any exposure to pigs or swine barns you’ve had recently. Seasonal flu vaccine will not protect against H3N2v, but prescription influenza antiviral drugs can treat H3N2v illness in people.

We’ve not seen sustained or efficient spread of these swine flu viruses in humans - but like all flu viruses - swine variant viruses are capable of evolving, reassorting, and adapting to their hosts.
Due to their (often) unremarkable presentation, and limited laboratory testing, cases likely occur more often than we know (see CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012).

Last summer we looked at a study that examined two newly  discovered (in 2014) North American swine variant strains (see J. Virol: Novel Reassortant Human-like H3N2 & H3N1 Influenza A Viruses In Pigs).  

They described both of these novel subtypes as “. . . virulent and can sustain onward transmission in pigs, and the naturally occurring mutations in the HA were associated with antigenic divergence from H3 IAV from human and swine’ and goes on to warn that  ``. . . the potential risk of these emerging swine IAV to humans should be considered”.

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.

They wrote:
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.

And just last March, in WHO: H1N1v Cases In China, we looked at recent reports of human H1N1v infection and the WHO's Risk Assessment.

Risk Assessment:

1. What is the likelihood that additional human cases of infection with influenza A(H1N1)v viruses will occur? 
Influenza A(H1N1) viruses circulate in swine  populations in many regions of the world. Depending on geographic location, the genetic characteristics of these viruses differ.  Most human cases are exposed to the A(H1N1) virus through contact with infected swine or contaminated environments. Human infection tends to result in mild clinical illness. Since these viruses continue to be detected in swine populations, further human cases can be expected.

The 2009 H1N1 pandemic showed how it can take years, sometimes even decades, of a virus kicking around in swine herds before it evolves enough to spark a public health threat.

For most swine viruses, it will simply never happen.

But the growing genetic diversity of swine flu viruses are giving researchers pause, particularly since studies have shown only limited community immunity to these variant strains (see CIDRAP: Children & Middle-Aged Most Susceptible To H3N2v).  

For more recent blogs on swine and swine variant influenza, 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
Live Markets & Novel Flu Risks In The United States

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