FluView Week 17: Fatal Swine Variant (H1N1v) Case In Ohio

Credit Wikipedia

 

# 10,048

 

I confess to being a little chagrined that – with our regular flu season essentially over – I didn’t check last week’s FluView report (week 17), else I’d have seen the following notice (h/t Camster on FluTrackers) summarizing the second  swine variant (H1N1v) infection recorded for 2015 (see FluView Wk 3 for 1st report) . 

 

A bit surprisingly, it was not listed in last week’s MMWR table of Notifiable diseases (which I did check).  First the report, then I’ll return with a bit more on swine variant viruses.

 

Novel Influenza A Virus:

One human infection with a novel influenza A virus was reported by the state of Ohio. The person was infected with an influenza A (H1N1) variant (H1N1v) virus and died from complications as a result of the infection. The patient worked at a livestock facility that housed swine but no direct contact with swine was reported in the week prior to illness onset. No ongoing human-to-human transmission has been identified.

Early identification and investigation of human infections with novel influenza A viruses are critical in order to evaluate the extent of the outbreak and possible human-to-human transmission. 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 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.

 

Over the past few years we’ve watched as several swine variant influenza viruses (H1N1v, H1N2v or H3N2v) have made tentative jumps into the human population (see Keeping Our Eyes On The Prize Pig) and each summer the CDC has issued advice on preventing infection at county and state fairs (see Measures to Minimize Influenza Transmission at Swine Exhibitions, 2014).

Of the 374 Swine variant infections detected over the past decade (undoubtedly an undercount given the limited testing), the the vast majority have been of the H3N2v subtype.  Only 18 (5%) were H1N1v, and even less (5) were of the H1N2v variety.

We’ve not seen many reported cases the past couple of years, but during the summer of 2012 more than 300 cases were detected, with Indiana and Ohio accounting for more than 3/4ths of the cases. 

 

Illnesses were usually mild or moderate ( only 1 fatality until now), and infection usually occurred in the summer and fall - associated with attendance of local and state fairs where pigs were being shown.  Of course, some people have contact with swine all year round, and so while uncommon, it isn’t terribly surprising that someone would contract a swine variant virus `out of season’.

 

These swine viruses are important because – unlike many of the avian strains – they belong to the H1, H2, and H3 HA types that have led to all of the known pandemics of the past 130 years.  

 

The progression of human influenza pandemics over the past 130 years has been a fairly unoriginal H2, H3, H1, H2, H3, H1, H1 sequence.

 

While that doesn’t prove that an H5 or an H7 virus couldn’t adapt to humans (or hasn’t in the past), it has led some researchers to wonder whether a non H1, H2, or H3 virus has the `right stuff’ to spark a pandemic (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?).

 
So – while not all that unusual, typically poorly transmitted by humans, and generally producing only mild to moderate illness – we keep a special eye on any swine origin virus that manages to jump to humans. 

 

Two weeks ago, in Waiting For The Next Flu To Drop, we looked at some of these `novel flu contenders’, and with county and state fair season kicking off in some areas next month, I’m sure we’ll be talking about biosecurity measures both for the swine and poultry exhibits frequently over the summer.

USDA IAV-S Surveillance Program Detects Novel H3N1 In US Swine

 

 

# 9081

 

While Ebola and MERS have had the bulk of our attention recently, high up on our perennial list of concerns are the non-human influenza viruses that circulate in birds, pigs, horses and even dogs that – with a little evolutionary help – could make the jump to mankind.  

 

The 2009 H1N1 virus was one such virus that had bounced around swine farms for years before it jumped species and sparked a pandemic.

 

Over the past several years we’ve been watching several swine variant influenza viruses – H3N2v, H1N1v, H1N2v – making tentative jumps into the human population (see Keeping Our Eyes On The Prize Pig) and each summer the CDC issues advice on preventing infection at county and state fairs (see Measures to Minimize Influenza Transmission at Swine Exhibitions, 2014).

 

Today, thanks to a report in the National Hog Farmer (picked up by ProMed Mail) we’ve learned of new version of an older swine flu virus – H3N1 – that has recently been detected in at least two states. 

 

While swine H3N1 has been known to circulate in pigs for nearly a decade (see EID Journal 2006 article Novel Swine Influenza Virus Subtype H3N1, United States) this latest variant, which has been reported on several occasions since December 2013, differs in that it has picked up the human seasonal H3 HA protein.

 

First the email sent out from the USDA to all SIV (swine influenza virus) approved NAHLN (National Animal Health Laboratory Network) labs published by the National Hog Farmer, then I’ll be back with a bit more.

 

H3N1 Identified in Swine in Two States

Sep 11, 2014 Source: USDA Animal and Plant Health Inspection Service, Veterinary Services

The U.S. Department of Agriculture IAV-S surveillance program has identified several H3N1s in U.S. swine in at least two states since December 2013. Although this is not the first time H3N1s have been detected in swine in the United States, it is a rare occurrence and needs further examination.

More importantly, two of these H3N1s carry a novel human seasonal HA gene from contemporary human viruses and are distinct from our current swine H3 viruses.

A review of Genbank data indicates there may be more human-like H3 genes (in either H3N1 or H3N2) circulating in U.S. swine subtypes than what the USDA surveillance data has captured. Potential spread of H3N1 or H3N2 that carries the human-like H3 could have significant impact in swine herds due to poor herd immunity as well as potential public health ramifications. Preliminary findings by the USDA-ARS from testing of one of these H3N1 isolates with the human-like H3 gene in swine indicate the virus is fully virulent, causing typical influenza disease.

We are sharing this information to alert producers, veterinarians, and National Animal Health Laboratory Network labs of this occurrence. The surveillance program for IAV-S in swine was established to:

• Monitor the genetic evolution of endemic IAV-S to better understand endemic and emerging influenza virus ecology,
• Make IAV-S isolates and associated epidemiologic data available for research and analysis, and
• Select proper isolates for the development of relevant diagnostic reagents, updating diagnostic assays, and vaccine seed stock products in swine.

The identification of this new human-like H3 in swine subtypes is a key example of how IAV-S surveillance can benefit swine health.

It is anticipated that additional information about swine subtypes carrying the human-like H3 will be captured through the surveillance system to assist in determining how wide-spread the virus is and whether additional actions may be needed by veterinarians, producers and vaccine manufacturers.

The USDA’s surveillance program for influenza A in Swine (IAV-S) began in 2009 with the intent of monitoring the 2009 H1N1 pandemic virus in swine. Since that time their surveillance efforts have broadened to include monitoring all types of influenza circulating in pigs, with the primary goal of tracking the evolution of these viruses.

Since participation is voluntary, and many swine farmers remain reluctant to have their herds tested after the financial beating the industry took in 2009, there are some limitations to this type of surveillance.

 

The following report shows that of the three major swine strains tracked, H1N1, H1N2 & H3N2 incidence has far overshadowed H3N1.

 

USDA Update on Surveillance for Influenza A Virus in Swine

USDA IAV-Surveillance

The following IAV-S surveillance summary data covers data received as of July 1, 2014 and spans November 2009 to June 2014. Note that there can be a monthly time lag in data submission and sequence deposits into GenBank.

Total samples submitted: 61,060 (99.3% from sick pig submissions to diagnostic laboratories)

Accessions submitted: 14,899
Number of positive accessions 5,517
Accessions subtyped 3,633
Accessions with viral isolates 3,100
Number of samples sequenced 2,455
to GenBank

 

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

 

It is far to early to know when, or even if, this novel H3N1 will present a significant human disease threat. But with county and State fair season going into high gear, public health officials will no doubt be keeping a close watch to see if any clusters of influenza are reported associated with fair attendance.

 

Swine are highly susceptible to a variety of flu viruses (human, swine, avian) - and are viewed as excellent `mixing vessels’, allowing viruses to reassort into new hybrid strains, a topic well covered by Helen Branswell a few years ago in a SciAm article called called Flu Factories.

 

Some of my earlier blogs on swine variant influenza include: H3N2v: When Pigs Flu , You Say You Want An Evolution? & The (Swine) Influenza Reassortment Puzzle while last July we looked at J. Virol: Continued Reassortment Of Swine Flu Viruses With Genes From pH1N1 In China

 

EID Journal: H3N2v Swine To Human Transmission At Agricultural Fairs – 2012

 

 

# 8860

 

I hadn’t planned on writing another swine variant influenza-related blog again so soon (see yesterday’s blog CDC: Measures to Minimize Influenza Transmission at Swine Exhibitions, 2014), but today the CDC’s EID Journal has posted an analysis of the 2012 outbreak of H3N2v associated with attendance of agricultural fairs in Ohio in 2012.

 

Although only 19 swine variant flu infections were reported last year,  in 2012 more that 300 cases were reported, with nearly all linked to fairgoers, mostly in Indiana & Ohio.

 

State & local  fairs have instituted inspections for any signs of illness in livestock – but as we’ve discussed previously (see Asymptomatic Pigs: Revisited) - pigs can sometimes carry these viruses without showing any outward signs of infection.

 

The concern with these variant swine flu infections, as it is with any animal flu that jumps to humans, 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 several hundred infections were recorded in 2012, sustained and efficient community transmission was not observed, and for the most part, the virus only caused mild to moderate illness.

 

Today’s study confirms the link between fairs with H3N2v infected pigs, and human cases, and confirms that the strains detected in humans, and those detected in pigs, were > 99.7% identical.  Follow the link below to read:.

 

Swine-to-Human Transmission of Influenza A(H3N2) Virus at Agricultural Fairs, Ohio, USA, 2012

 Andrew S. Bowman , Sarah W. Nelson, Shannon L. Page, Jacqueline M. Nolting, Mary L. Killian, Srinand Sreevatsan, and Richard D. Slemons

Author affiliations: The Ohio State University, Columbus, Ohio, USA (A.S. Bowman, S.W. Nelson, J.M. Nolting, R.D. Slemons); Ohio Department of Health, Columbus (S.L. Page); US Department of Agriculture National Veterinary Services Laboratories, Ames, Iowa, USA (M.L. Killian); University of Minnesota, Saint Paul, Minnesota, USA (S. Sreevatsan)

Abstract

Agricultural fairs provide an opportunity for bidirectional transmission of influenza A viruses. We sought to determine influenza A virus activity among swine at fairs in the United States. As part of an ongoing active influenza A virus surveillance project, nasal swab samples were collected from exhibition swine at 40 selected Ohio agricultural fairs during 2012.

Influenza A(H3N2) virus was isolated from swine at 10 of the fairs. According to a concurrent public health investigation, 7 of the 10 fairs were epidemiologically linked to confirmed human infections with influenza A(H3N2) variant virus. Comparison of genome sequences of the subtype H3N2 isolates recovered from humans and swine from each fair revealed nucleotide identities of >99.7%, confirming zoonotic transmission between swine and humans.

All influenza A(H3N2) viruses isolated in this study, regardless of host species or fair, were >99.5% identical, indicating that 1 virus strain was widely circulating among exhibition swine in Ohio during 2012.

(Continue . . . .)

 

Swine are highly susceptible to a variety of flu viruses (human, swine, avian) - and are viewed as excellent `mixing vessels’, allowing viruses to reassort into new hybrid strains.

 

While a handful of novel swine variant flu infections that don’t appear to transmit efficiently may not sound like a big deal, as the authors of this paper point out, Agricultural Fairs provide a favorable environment for multiple swine flu viruses to get together. They write:

 

Swine-to-human transmission and human-to-swine transmission of influenza A virus are known to occur at fairs (28), highlighting the fact that swine in this setting are potentially exposed to multiple lineages of influenza A viruses simultaneously, making fairs ideal locations for genomic reassortment and novel virus formation.

 

And not only can swine pass flu viruses on to people, people can pass flu viruses on to swine.  Something we saw happen around the world after the 2009 H1N1 pandemic virus emerged and began transmitting in humans. 

 

This bi-directional transfer of influenza viruses allows for even greater mixing and matching of genes, and explains how the H3N2v virus picked up the M (matrix) gene from the 2009 H1N1pdm virus in 2012.

 

The authors write:

 

The results of this study support previous calls for enhanced surveillance of influenza A viruses among swine, especially at high-risk swine–human interfaces

 
For more on swine variant influenza viruses, and why they matter, you may wish to revisit:

 

J. Virol: Continued Reassortment Of Swine Flu Viruses With Genes From pH1N1 In China

Keeping Our Eyes On The Prize Pig

Study: Novel & Variant Swine Influenzas In Korean Pigs

Seroprevalence Study: Avian Flu In Chinese Pigs

CDC: Measures to Minimize Influenza Transmission at Swine Exhibitions, 2014

Credit Wikipedia

 

# 8857

 

A little over three weeks ago, in Keeping Our Eyes On The Prize Pig, I wrote about the upcoming county & state fair season, and concerns that we could see a resurgence in Swine Variant Influenza infections in fairgoers this year.  Although only 19 such cases were identified in 2013, the previous year more that 300 cases were reported.

 

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.

 

Swine are highly susceptible to a variety of flu viruses (human, swine, avian) - and are viewed as excellent `mixing vessels’, allowing viruses to reassort into new hybrid strains.

Here in North America we’ve been watching the evolution of several swine variant viruses (H1N1v, H1N2v, H3N2v) over the past few years, all of which have reassorted with - and picked up the M gene segment from – the 2009 H1N1 virus.  We’ve also seen similar reassortant viruses emerge in other parts of the world (see J. Virol: Continued Reassortment Of Swine Flu Viruses With Genes From pH1N1 In China).

While most reassortant viruses are evolutionary failures, the concern is that over time another swine variant virus might emerge – as did the 2009 H1N1 virus – and start another human epidemic or pandemic.

 

One strategy to try to prevent that from happening is limiting the number of humans that are exposed to these variant viruses, depriving the virus of opportunities to adapt to human physiology.  To that end, the CDC has issued the following advice for those planning to visit the fair:

 

 

For the past two years the CDC has also provided extended advice to exhibitors of swine, and those in charge of the venues, on their Guidance Associated with Fairs website.

Yesterday the CDC published a 6-page PDF file of Measures to Minimize Influenza Transmission at Swine Exhibitions, 2014, as prepared by the National Assembly of State Animal Health Officials (NASAHO) and the National Association of State Public Health Veterinarians (NASPHV).

 

Follow the link to download and read  the entire file.

 

National Assembly of State Animal Health Officials (NASAHO)
National Association of State Public Health Veterinarians (NASPHV)

Measures to Minimize Influenza Transmission at Swine Exhibitions, 2014

It is estimated that 150 million people visit agricultural fairs each year in North America.  Agricultural exhibitions provide valuable educational venues for the public. Equally important, livestock shows are an important learning opportunity for thousands of 4-H and FFA youth across the United States. For these youth, exhibiting at their county or state fair is the culmination of many months of work dedicated to the care and training of their animal.

Pigs can be infected with human, swine and avian origin influenza A viruses.  While rare, influenza A viruses can spread from pigs to people and from people to pigs. Transmission usually requires close contact between pigs and people.  This has happened in different settings, including livestock shows. When people are infected with swine origin influenza A viruses, it is termed as a variant virus infection and denoted with a “v” after the subtype (e.g. H3N2v).

In the past 5 years, cases of influenza A H1N1v, H1N2v and H3N2v have been associated with swine exhibitions.  Between 2011 and 2013, 340 human cases infected with H3N2v were reported from 13 states.  The largest outbreak occurred in 2012 when a total of 309 human cases of H3N2v flu were identified.

 
(Continue . . . )

 

Although the Public Health risk from these swine variant viruses is considered low at this time, the CDC takes these emerging swine flu viruses seriously, as evidenced by their most recent assessment.

 

CDC Assessment

It's possible that sporadic infections and even localized outbreaks among people with this virus will continue to occur. While there is no evidence at this time that sustained human-to-human transmission is occurring, all influenza viruses have the capacity to change and it's possible that this virus may become widespread. 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, 309 infections with H3N2v were detected. Of these cases, 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 this fair season, 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.

Keeping Our Eyes On The Prize Pig

Credit Wikipedia

 

# 8792

 

To give you an idea of how rapidly things change in the world of emerging infectious diseases, two summers ago (June 2012), no one had ever heard of the MERS coronavirus, the H7N9 avian flu virus was still 8 months away from breaking out in China, and avian H5N8, H10N8, H6N1 and H5N6 weren’t on anyone’s radar screen.

 

Aside from the perennial concerns over change in transmissibility of H5N1 virus, our primary emerging disease concerns that summer lay in a major outbreak of West Nile Virus (see DVBID: 2012 Record Number Of West Nile Fatalities), and an outbreak of human infection with variant influenza  contracted from show pigs displayed at county and state fairs. 

 

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. During the summer of 2012 more than 300 cases were recorded across the United States, and nearly all were linked to contract with pigs displayed at county and state fairs that summer.

 

Last year we only saw a handful of cases, but with state and county fair season once again upon us (it runs June-November around the nation) the potential exists for seeing cases again this summer and fall. 

 

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

 

Swine are highly susceptible to a variety of flu viruses (human, swine, avian) - and can serve as `mixing vessels’, allowing viruses to reassort into new hybrid strains, a topic well covered by Helen Branswell a few years ago in a SciAm article called called Flu Factories.

 

.

Some of my earlier blogs on swine variant influenza include: H3N2v: When Pigs Flu , You Say You Want An Evolution? & The (Swine) Influenza Reassortment Puzzle.

 

These swine variant strains are – like the 2009 H1N1 pandemic virus – reassortants, that continue to circulate (and evolve) in swine herds.  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.’

 

The concern with these variant swine flu infections, as it is with any animal flu that jumps to humans, 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 during the summer of 2101, sustained and efficient human-to-human transmission did not, and for the most part, the virus only caused mild to moderate illness.

 

But as we’ve seen so often in the past, things can change quickly in the world of infectious diseases.

 

So while Chikungunya, West Nile Virus and MERS will be getting the bulk of the headlines this summer,  public health officials will also be on the lookout for any new swine variant infections - and more importantly - for any signs that the behavior of the virus has changed.

 

In the meantime, the CDC offers this advice for those planning to visit the fair this year:

 

Exhibitors of swine, and those in charge of the venue, will want to consult  Guidance Associated with Fairs.

CID Journal: H3N2v Outbreaks In United States – 2012

Credit CDC

 

# 7808

 

Swine are notoriously prone to influenza infections, and are viewed as potential `mixing vessels’ for flu viruses since they can be infected by swine, avian, and human flu strains. The most common swine flu strains are H1N1, H1N2, H3N1, H3N2, and H2N3.

 

Although predominantly affecting swine, on the rare occasions when they jump to humans, these strains are called variant viruses (e.g. H3N2v).

 

During 2012, a record number (300+) of swine variant infections were recorded in humans, mostly associated with swine exposure at county and state fairs across the Midwest. The concern with these variant flu infections, as with any novel flu, is that each new human exposure provides the virus another opportunity to better adapt to human physiology.

 

While sporadic human-to-human transmission of these viruses was strongly suspected last year, sustained community transmission did not appear to be occurring.   It is likely, however (see CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012)), that the number of confirmed cases under-represents the total number of variant flu infections that occur each year.

 

Today, another study appearing in the CID Journal, conducted by CDC and local Health department researchers, looks at 306 human variant flu infections reported across 10 states last year, and finds the vast majority appear to have contracted the virus from direct exposure to infected pigs, while only about 5% appeared to be the result of H-2-H transmission.

 

Outbreak of Variant Influenza A (H3N2v) Virus in the United States

Michael A. Jhung1, Scott Epperson1, Matthew Biggerstaff1, Donna Allen9, Amanda Balish1, Nathelia Barnes1, Amanda Beaudoin10, LaShondra Berman1, Sally Bidol7, Lenee Blanton1, David Blythe16, Lynnette Brammer1, Tiffany D'Mello1, Richard Danila8, William Davis1, Sietske de Fijter13, Mary DiOrio13, Lizette O. Durand2, Shannon Emery1, Brian Fowler13, Rebecca Garten1, Yoran Grant6, Adena Greenbaum2, Larisa Gubareva1, Fiona Havers2, Thomas Haupt14, Jennifer House9, Sherif Ibrahim15, Victoria Jiang1, Seema Jain1, Daniel Jernigan1, James Kazmierczak14, Alexander Klimov1, Stephen Lindstrom1, Allison Longenberger11, Paul Lucas4, Ruth Lynfield8, Meredith McMorrow1, Maria Moll11, Craig Morin8, Stephen Ostroff11, Shannon L. Page13, Sarah Y. Park12, Susan Peters7, Celia Quinn3, Carrie Reed1, Shawn Richards9, Joni Scheftel8, Owen Simwale11, Bo Shu1, Kenneth Soyemi4, Jill Stauffer9, Craig Steffens1, Su Su1, Lauren Torso11, Timothy M. Uyeki1, Sara Vetter8, Julie Villanueva1, Karen K. Wong2, Michael Shaw1, Joseph S. Bresee1, Nancy Cox1, and Lyn Finelli1

Abstract

Background. Variant influenza virus infections are rare but may have pandemic potential if person-to-person transmission is efficient. We describe the epidemiology of a multi-state outbreak of an influenza A H3N2v virus first identified in 2011.

Methods. We identified laboratory-confirmed cases of H3N2v and used a standard case report form to characterize illness and exposures. We considered illness to result from person-to-person H3N2v virus transmission if swine contact was not identified within 4 days prior to illness onset.

Results. From July 9—September 7, 2012, we identified 306 cases of H3N2v in ten states. The median age of all cases was 6 years. Commonly reported signs and symptoms included fever (98%), cough (84%), and fatigue (83%). Sixteen cases (5.2%) were hospitalized, and one fatal case was identified. The majority of cases reported agricultural fair attendance (93%) and/or contact with swine (95%) prior to illness. We identified 15 cases of possible person-to-person transmission of H3N2v virus. Viruses recovered from cases were 93% to 100% identical and similar to viruses recovered from previous cases of H3N2v. All H3N2v viruses examined were susceptible to the oseltamivir and zanamivir and resistant to adamantane antiviral medications.

Conclusion. In a large outbreak of variant influenza, the majority of cases reported exposures suggesting swine contact at an agricultural fair was a risk for H3N2v virus infection. We identified limited person-to-person H3N2v virus transmission, but found no evidence of efficient or sustained person-to-person transmission. Fair managers and attendees should be aware of the risk of swine-to-human transmission of influenza viruses in these settings.

 

Compared to last year, reports of swine variant infections this summer are greatly reduced.   Thus far, only 20 cases have been reported to the CDC (see Arkansas Reports Two H1N1v Infections for the latest reports). While we watch these flu strains for any signs they may be changing, for now, the threat to the public from these swine variant viruses appears low.

 

The CDC, in a statement on June 28th of 2013, offered this assessment on H3N2v:

 

CDC will continue to watch this virus closely to make sure there are no changes in the epidemiology of related human infections. That means watching for any changes in the severity of illness caused by infection with this virus and any signs that the virus is becoming more adept at spreading from person-to-person. Like all influenza viruses, it’s possible that mutations could occur that would allow this virus to become more severe or to spread more easily between people.

The risk of this virus triggering a full-blown pandemic is considered relatively low, however, because serology studies have suggested that significant numbers of adults have some existing immunity against this virus. Children younger than about 10 years old, however, have little to no immunity against H3N2v virus. Given this, a more likely scenario if H3N2v were to become more transmissible among people would be localized outbreaks in pockets of the population that do not have immunity against this virus, for example, in day care or school settings.

A few of my recent blogs on Swine variant influenza include:

 

Study: Novel & Variant Swine Influenzas In Korean Pigs

CDC Updates H3N2v County & State Fair Advice

CDC HAN Advisory On H3N2v

And for more information, you may wish to visit the CDC’s Variant (Swine Origin) Influenza Viruses in Humans webpage, or visit these related links.

 

• Key Facts about Human Infections with Variant Viruses (Swine Origin Influenza Viruses in Humans)
• Reported Infections with Variant Influenza Viruses in the United States since 2005
• Influenza A (H3N2) Variant Virus
• What People Who Raise Pigs Need To Know About Influenza (Flu)
• Reports of Human Infections with Variant Viruses