Avian Flu Diary: A Variant Swine Flu Review

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# 7421

Last summer, before anyone had ever heard of MERS-CoV (initially dubbed novel coronavirus or nCoV) and the H7N9 avian flu virus, public health officials across the nation were facing large outbreaks from two emerging disease threats; West Nile Virus (WNV) and Swine Variant Influenza.

We’ve discussed WNV several times recently (see Texas: First West Nile Case Of 2013, DVBID: 2012 Record Number Of West Nile Fatalities), but swine variant influenza has been pretty much crowded out of the headlines since late last fall.

With state and county fair season once again upon us (it runs June-November around the nation) – tens of thousands of fairgoers will once again be coming into relatively close contact with farm animals – providing fresh opportunities for swine variant flu viruses to make the jump to humans.

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.

Although the actual number of human variant flu infections that occur each year is unknown, the CDC has reported 1 or 2 cases each year since 2005.

In 2010, that number jumped to 8, and in 2011, to 12.

These cases were generally mild, and have primarily involved children under the age of 10. They have generated enough concern, however, that in late 2011 the CDC announced their intention to work on a candidate vaccine (see H3N2v Vaccine Trials).

Last summer the floodgates opened, with more than 300 confirmed cases, nearly all linked to county or state fair attendance.

Indiana reported the most cases (n=138), followed by Ohio (n=106).

While the H3N2v virus was by far the most commonly reported strain, H1N1v and H1N2v were also detected.

As to why these swine variant viruses suddenly began jumping to humans with vigor last year?

Starting in 2011, the H1N1v virus was found to have acquired the M (matrix) gene from the 2009 H1N1 pandemic virus. Since then, this M gene has been showing up regularly in all three swine variant viruses (H1N1v, H1N2v, H3N2v).

The CDC has speculated that `This M gene may confer increased transmissibility to and among humans, compared to other variant influenza viruses.’

In September of last year, the CDC published MMWR: H3N2v Related Hospitalizations In Ohio – Summer 2012 that provided an overview of 11 patients from Ohio that required hospitalization, including the nation’s only H3N2v related fatality.

The MMWR report provides a summary of the findings, which reads:

What is already known on this topic?

Beginning in the summer of 2012, CDC reported increases in numbers of cases of human infections with influenza A (H3N2) variant (H3N2v) viruses associated with swine exposure at agricultural fairs. Nationwide, 305 cases, 16 hospitalizations, and one death across 10 states have been reported since July 2012.

What is added by this report?

Of 16 patients hospitalized with confirmed H3N2v virus infection, 11 were Ohio residents, including the only H3N2v-associated fatality to date. All but one of the Ohio patients were children, and six were considered high-risk for complications of influenza because they were aged <5 years or had underlying medical conditions; four high-risk persons became ill after indirect contact with pigs. These findings support current CDC recommendations that persons at high risk for complications of influenza should avoid exposure to swine at agricultural fairs this fall.

What are the implications for public health practice?

County and state fairs in the United States continue to occur through the month of October, highlighting the potential for continued cases of H3N2v virus infection. Persons at high risk for complications of influenza should avoid exposure to swine at agricultural fairs. Patients with suspected influenza, including H3N2v, who are hospitalized or at increased risk for influenza complications, should receive antiviral treatment with oral oseltamivir or inhaled zanamivir as soon as possible. Antiviral treatment also is encouraged for outpatients with suspected H3N2v who are not at increased risk for influenza complications.

While fairs have instituted inspections for any signs of illness in livestock – as we discussed last October (see Asymptomatic Pigs: Revisited) - pigs can carry this virus without showing any outward signs of infection.

The CDC offers the following advice for fairgoers and exhibitors.

Preventive Actions

CDC Recommendations For People At High Risk:

If you are at high risk of serious flu complications and are going to a fair where pigs will be present, avoid pigs and swine barns at the fair this year. This includes children younger than 5 years, people 65 years and older, pregnant women, and people with certain long-term health conditions (like asthma, diabetes, heart disease, weakened immune systems, and neurological or neurodevelopmental conditions).

If you are not at high risk, take these precautions:

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.

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.

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, gloves and masks that cover your mouth and nose when contact is required.

To further reduce the risk of infection, minimize contact with pigs and swine barns.

Swine are highly susceptible to flu viruses - can serve as `mixing vessels’, allowing viruses to reassort into new hybrid strains – and were the originating host of the 2009 H1N1 pandemic virus.

The variant viruses that now carry the M gene from the 2009 H1N1 virus are reassortants as well.

The concern with these variant swine flu infections, as it is with any novel flu, is that it gives the virus another opportunity to better adapt to human physiology.

While humans have a long history of exposure to seasonal H3N2 flu viruses, research has shown only limited community immunity to these variant strains (see CIDRAP: Children & Middle-Aged Most Susceptible To H3N2v).

The good news is that while some limited community transmission of these variant flu strains appears to have occurred last summer, sustained and efficient human-to-human transmission did not.

Public health officials will no doubt be alert for any new cases - and more importantly, for any signs that the behavior of the virus has changed - over the coming months.

For more on the flu risks from swine reassortments, I’d heartily recommend Helen Branswell’s terrific piece in SciAm from late 2010 called Flu Factories.

Flu Factories

The next pandemic virus may be circulating on U.S. pig farms, but health officials are struggling to see past the front gate

By Helen Branswell | December 27, 2010 |

And for some of my earlier looks at swine influenza, you may wish to revisit: