Asymptomatic Pigs: Revisited

Credit Wikipedia

 

# 6660

 

A couple of months ago in EID Journal: Flu In Healthy-Looking Pigs we looked at a report indicating that it isn’t always possible to identify pigs carrying an influenza virus based simply on their appearance.

 

A dispatch from the EID Journal reported that nearly 1 in 5 healthy-looking pigs they tested at the Minnesota State Fair during the 2009 H1N1 influenza pandemic were actually infected with a flu virus.

 

This came out during the midst of several swine variant flu outbreaks this summer, involving several hundred people across 10 states. Viruses apparently contracted from pigs on display at local fairs (see MMWR: H3N2v Related Hospitalizations In Ohio – Summer 2012).

 

While fair officials were turning away pigs with overt signs of infection, this report suggested that perhaps those measures might not be sufficient.

 

Today, a pair of studies from Ohio State University -  one that finds a surprisingly large percentage of flu infected swine to be asymptomatic - and another that establishes just how closely linked the human and swine variant strains of influenza this summer really were.

 

In both cases, the lead author is Andrew Bowman, a  Ph.D. candidate in veterinary preventive medicine at Ohio State.

 

First, from the EID Journal, research that found more than 80% of the pigs that tested positive for influenza at the Ohio State fair between 2009 and 2011 showed no signs of illness.

 

Subclinical Influenza Virus A Infections in Pigs Exhibited at Agricultural Fairs, Ohio, USA, 2009–2011

Andrew S. Bowman , Jacqueline M. Nolting, Sarah W. Nelson, and Richard D. Slemons

Author affiliations: The Ohio State University, Columbus, Ohio, USA

Abstract

Agricultural fairs are associated with bidirectional, interspecies transmission of influenza virus A between humans and pigs. We examined pigs exhibited at agricultural fairs in Ohio during 2009–2011 for signs of influenza-like illness and collected nasal swab specimens from a representative subset of these animals.

 

Influenza virus A was recovered from pigs at 12/53 (22.6%) fairs during the 3-year sampling period. Pigs at 10/12 (83.3%) fairs from which influenza virus A was recovered did not show signs of influenza-like illness. Hemagglutinin, neuraminidase, and matrix gene combinations of the isolates were consistent with influenza virus A concurrently circulating among swine herds in the United States.

 

Subclinical influenza virus A infections in pigs at agricultural fairs may pose a risk to human health and create challenges for passive surveillance programs for influenza virus A in swine herds.

(Continue . . . )

 

 

 

Ohio State University has published a lengthy press release that discusses both papers.

 

Studies: Pigs Look Healthy But Test Positive for Flu at Fairs; Flu Transmission Seen Between Pigs and Humans

COLUMBUS, Ohio – More than 80 percent of pigs that tested positive for influenza A virus at Ohio county fairs between 2009 and 2011 showed no signs of illness, according to a new study.

 

Ohio State University researchers tested 20 pigs each at 53 fair events over those three summers and found at least one flu-positive pig at 12 fairs – almost a quarter of fairs tested.

 

The influenza strains identified in pigs in this study include H1N2 and H3N2 viruses – strains that have been circulating in pigs since 1998. In 2011, all of the H3N2 and H1N2 isolates found in pigs at the fairs contained a gene from the 2009 pandemic strain of H1N1, which is similar to the H3N2v strain causing human illness this year.

 

Though this finding alone is no cause for panic, it does show how quickly influenza viruses can change, said Andrew Bowman, lead author of the study and a Ph.D. candidate in veterinary preventive medicine at Ohio State.

 

In a second study led by Bowman, researchers compared the genomic sequences of influenza A viruses recovered in July 2012 from pigs and people. The analysis, showing a greater than 99 percent genetic similarity among the viruses, confirms that pigs and humans were infected with the same virus, indicating interspecies transmission.

(Continue . . .)

 

This second study appears in the journal Emerging Microbes & Infections.

 

Although the timing of the illnesses (and initial sub-typing) in humans and swine at the Ohio State Fair last July strongly suggested interspecies transmission, a >99% genomic match pretty much erases all doubt.

 

Molecular evidence for interspecies transmission of H3N2pM/H3N2v influenza A viruses at an Ohio agricultural fair, July 2012

Andrew S Bowman¹, Srinand Sreevatsan², Mary L Killian³, Shannon L Page⁴, Sarah W Nelson¹, Jacqueline M Nolting¹, Carol Cardona² and Richard D Slemons¹

 

Evidence accumulating in 2011–2012 indicates that there is significant intra- and inter-species transmission of influenza A viruses at agricultural fairs, which has renewed interest in this unique human/swine interface.

 

Six human cases of influenza A (H3N2) variant (H3N2v) virus infections were epidemiologically linked to swine exposure at fairs in the United States in 2011. In 2012, the number of H3N2v cases in the Midwest had exceeded 300 from early July to September, 2012.

 

Prospective influenza A virus surveillance among pigs at Ohio fairs resulted in the detection of H3N2pM (H3N2 influenza A viruses containing the matrix (M) gene from the influenza A (H1N1) pdm09 virus). These H3N2pM viruses were temporally and spatially linked to several human H3N2v cases.

 

Complete genomic analyses of these H3N2pM isolates demonstrated >99% nucleotide similarity to the H3N2v isolates recovered from human cases. Actions to mitigate the bidirectional interspecies transmission of influenza A virus between people and animals at agricultural fairs may be warranted.

(Continue . . .)

 

 

While the vast majority of the swine-to-human flu transmissions this year have involved the H3N2v virus, as you can see from the following table, small number of H1N1v and H1N2v infections have been reported as well. 

 

 

Given the limits of surveillance, testing, and reporting – we really don’t know what the normal `background rate’ of these types of novel flu infections are in humans.

 

The smattering of reports since 2005 indicate they may be fairly rare, but are certainly not unheard of.

 

The majority of human swine variant flu infections this summer were relatively mild (out of 300+ infections, 16 were hospitalized, and 1 died), but it is always of concern anytime a novel influenza virus jumps from another species to humans.

 

Each time a novel flu jumps from a pig to a human it gives the virus another opportunity to adapt to human physiology. The CDC’s most recent assessment on the H3N2v virus reads:

 

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.

 

So far, the severity of illnesses associated with this virus in people has been similar to the severity of illnesses associated with seasonal flu virus infections. Limited serologic studies indicate that adults may have some pre-existing immunity to this virus while children do not.

 

CDC is closely monitoring human infections with all novel influenza viruses, including H3N2v viruses, and will provide more information as it becomes available.

 

 

With further evidence of asymptomatic influenza infection in pigs, fair officials and public health agencies will need to decide on the best policies to limit future exchanges (in either direction) of flu viruses between people and pigs.

»» Read More

Ontario Confirms H1N1v Case

 

Credit Wikipedia

 

# 6779

 

 

While details are somewhat scant this morning, the Province of Ontario, Canada has announced that they have detected a single of case of H1N1v flu infection in a person who had contact with pigs.

 

First the press release, then I’ll return with a bit more:

 

 

Case of Influenza A H1N1 Variant Detected in Ontario

September 25, 2012 8:00 AM

Today, Dr. Arlene King, Ontario's Chief Medical Officer of Health, issued the following statement on a case of influenza A H1N1 variant detected in Ontario:

 

"An Ontario resident has been confirmed as having been infected with an H1N1 variant (H1N1v) influenza virus. An influenza virus that normally circulates in animals is referred to as a variant virus when it infects humans.

 

This adult male patient became ill after close contact with pigs. He is being treated and closely monitored in a hospital in southwestern Ontario.

 

I would like to reassure Ontarians that this variant influenza virus rarely spreads from animals to humans. Subsequent human-to-human transmission is also rare. I would also like to stress that this is not a food safety issue; the consumption of properly cooked pork continues to be safe.  Proper cooking of meats, including pork, kills all bacteria and viruses.

 

Ontarians should remember that hand washing is the single best infection prevention and control measure against respiratory illnesses such as influenza. Individuals should wash their hands often with soap and running water, or use an alcohol-based hand rub if soap and water are not available.

 

I also would like to remind Ontarians that it is important to get immunized every year with the seasonal flu vaccine when it becomes available each fall. This will protect you against seasonal influenza viruses that are expected to circulate. Everyone six months of age and older should get the seasonal flu vaccine each year.

 

The identification of this case is the result of the strength of our current surveillance system here in Ontario. It is not an unexpected occurrence and there have been a number of human infections with variant influenza viruses in the United States over the past year.

 

I would like to thank health officials in Ontario who displayed the utmost vigilance in identifying, treating and closely investigating this case. Protecting the health of Ontarians is a priority and we will continue to monitor the situation."

 

 

H1N1v is one of the `viral contenders’ I wrote about several weeks ago in An Increasingly Complex Flu Field, and until just over a year ago, was the most commonly reported variant swine flu virus detected in humans since 2005.

 

In the past twelve months, it has primarily been the H3N2v flu virus that we’ve seen jumping from pigs to humans (300+ cases).  But 2 weeks ago, we saw a single case of H1N1v was reported out of Missouri (see The Return Of H1N1v).

 

This was only the second H1N1v case reported in a year, and it was also the second time that the H1N1v virus had been found to carry the M (matrix) gene from the 2009 H1N1 pandemic virus. 

 

This M gene  has been showing up regularly in swine variant viruses (H1N1v, H1N2v, H3N2v) for more than a year. The CDC has previously stated that `This M gene may confer increased transmissibility to and among humans, compared to other variant influenza viruses.’

 

A couple of cases of H1N1v, hundreds of miles apart, while of concern  .  .  .  does not a pandemic make. 

 

But this is further evidence that these variant viruses (H1N1v, H1N2v, H3N2v) continue to evolve, and spread widely in swine, and on occasion manage to make the jump to humans.

 

The concern is that over time one of these viruses may become a more human adapted virus, and begin to spread more easily among the population.

 

So we watch reports such as this with more than a little bit of interest.

 

For more on the flu risks from swine reassortments, I  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:

 

H3N2v: When Pigs Flu

You Say You Want An Evolution?

The (Swine) Influenza Reassortment Puzzle

»» Read More

FluView Week 37 & Variant Flu Update

 

Variant Flu Numbers are Unchanged This week

 

 

 

# 6569

 

 

The CDC has released their weekly FluView and Variant Flu update, and for the first time in a couple of months, there are no new variant (H3N2v,H1N2v, H1N1v) cases reported to the CDC.

 

Admittedly, there could be some cases out there that are mild, and are going unreported. 

 

But no new cases is a pretty good indication that – as the CDC has been saying all along – these viruses aren’t spreading efficiently among humans.

 

As far as seasonal flu reports are concerned, they remain at very low inter-season levels.

 

2011-2012 Influenza Season Week 37 ending September 15, 2012

All data are preliminary and may change as more reports are received.

U.S. Virologic Surveillance:

WHO and NREVSS collaborating laboratories located in all 50 states and Washington, D.C. report to CDC the number of respiratory specimens tested for influenza and the number positive by influenza type and subtype. Region specific data can be found at http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.

Similarly, outpatient visits to doctors for ILI (Influenza-like Illness) are low as well.

 

Today’s data is current through September 15th, and with schools back in session, and cooler weather on its way, we shouldn’t be surprised to see flu activity pick up in the next few weeks.

»» Read More

The Return Of H1N1v

 

(click to enlarge)

# 6556

 

 

Yesterday’s FluView report, in addition to updating the number of new H3N2v cases, announced the detection of a single H1N1v flu infection in a person living in Missouri. That patient has fully recovered.

 

H1N1v is one of the `viral contenders’ I mentioned two weeks ago in An Increasingly Complex Flu Field, and until just over a year ago, was the most commonly reported variant swine flu virus detected in humans since 2005.

 

 

This week’s announced case brings to 14 the total number of H1N1v cases reported since 2005.  The last reported case of H1N1v infection came from Wisconsin in December of 2011.

 

Of particular interest, this week’s detection is the second time that the H1N1v virus has been found to contain the M (matrix) gene from the 2009 H1N1 pandemic virus. 

 

Here is how this week’s FluView describes it:

 

Confirmatory testing at CDC identified H1N1v with the matrix (M) gene from the 2009 H1N1 influenza virus in specimens collected from this patient. Cases of H1N1v have been detected previously, and the current case marks the second report of H1N1v with the M gene from the 2009 H1N1 virus.

 

This M gene  has been showing up regularly in swine variant viruses (H1N1v, H1N2v, H3N2v) for more than a year. The CDC has previously stated that `This M gene may confer increased transmissibility to and among humans, compared to other variant influenza viruses.’

 

The $64 question is, what to make of all of this? 

 

Since the outbreak of H3N2v began in earnest in mid July, the CDC and local health departments have stepped up testing for novel or variant flu viruses.

 

And as one might expect, the harder you look, the more you are likely to find.

 

Given the limits of surveillance, testing, and reporting – we really don’t know what the normal `background rate’ of these types of infections are in humans. The smattering of reports since 2005 indicate they are fairly rare, but certainly not unheard of.

 

For now, the H3N2v virus – due to roughly 300 human infections across the Midwest - has captured the bulk of our attention.

 

But these other cases serve to remind us that nature continues to churn out and test new viral variations, and that the next public health threat could come out of left field.

 

The CDC’s assessment on the H3N2v virus reads:

 

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.

So far, the severity of illnesses associated with this virus in people has been similar to the severity of illnesses associated with seasonal flu virus infections. Limited serologic studies indicate that adults may have some pre-existing immunity to this virus while children do not.

CDC is closely monitoring human infections with all novel influenza viruses, including H3N2v viruses, and will provide more information as it becomes available.

 

 

For more on all of this, Robert Roos of CIDRAP NEWS, has an excellent report from last night.

 

Latest variant flu cases include rare H1N1 strain

Robert Roos News Editor

»» Read More

FluView & Variant Flu Update: Week 36

 

 

 

# 6555

 

I’m sitting in on the AMA/IDSA Pandemic Preparedness webinar this morning, so this will be a quick update.

The CDC has released their weekly FluView and Variant Flu update, and the number of new H3N2v flu cases shows only a small increase (n=9) over last week.

 

 

 

This week’s FluView has details on these 9 cases, plus one additional H1N1v case identified in  Missouri.

 

2011-2012 Influenza Season Week 36 ending September 8, 2012

Novel Influenza A Virus:

From July 12 through September 13, 2012, a total of 305 infections with influenza A (H3N2) variant (H3N2v) viruses have been reported from ten states. This is an increase of 9 over last week’s report. Cumulative totals by state since July 15 are: Hawaii [1], Illinois [4], Indiana [138], Maryland [12], Michigan [6], Minnesota [4], Ohio [106], Pennsylvania [11], West Virginia [3], and Wisconsin [20]. Sixteen H3N2v-associated hospitalizations and one H3N2v-associated death have been reported. The vast majority of cases have occurred after prolonged swine exposure, though instances of likely human-to-human transmission have been identified. At this time no ongoing human-to-human transmission has been identified.

 

Public health and agriculture officials are investigating the extent of disease among humans and swine, and additional cases are likely to be identified as the investigations continue. Because of reporting schedules, state totals posted by CDC may not always be consistent with those reported by state health departments. If there is a discrepancy between state and CDC case counts, data from the state health department should be used as the most accurate number.

 

As a result of enhanced surveillance activities for H3N2v, one infection with an influenza A (H1N1) variant (H1N1v) virus has been detected in Missouri in a patient who became ill after contact with swine. The patient has recovered from their illness. Confirmatory testing at CDC identified H1N1v with the matrix (M) gene from the 2009 H1N1 influenza virus in specimens collected from this patient. Cases of H1N1v have been detected previously, and the current case marks the second report of H1N1v with the M gene from the 2009 H1N1 virus. This H1N1v case, in addition to the H3N2v cases outlined above and the H1N2v cases reported previously, brings the total number of variant influenza virus infections detected since July 2012 to 309.

»» Read More

CDC Updates Minnesota H1N2v Cases

Credit Wikipedia

 

# 6542

 

A week ago we learned of three human infections with the H1N2v virus in Minnesota, which - while of swine origin – is a different strain than the one behind the cluster of nearly 300 H3N2v infections we’ve been watching over the summer (see Minnesota Reports Swine H1N2v Flu).

 

H1N2 is one of three swine influenza viruses that are commonly found in pigs, the others are H1N1 and H3N2. Until last week, since 2005, only 2 cases of human infection with trH1N2 (now called H1N2v) had been detected in humans.

 

The three cases reported last week are similar to the 2 previous cases, with the exception that the H1N2v virus – like H3N2v – has picked up the M gene segment from the 2009 H1N1 pandemic virus.

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

 

All of which serves as prelude to today’s update from the CDC on the H1N2v virus:

 

H1N2 Variant Virus Detected in Minnesota

September 7, 2012 -- The Minnesota Department of Health has reported detection of 3 infections with an influenza A H1N2 variant (“H1N2v”) virus with the pandemic M gene from the 2009 H1N1 virus. These cases were reportedly associated with prolonged contact with pigs at a fair. H1N2 viruses normally circulate in pigs, not people, but rare human infections with this virus have been detected in the past. This virus is different from the H3N2v virus that, as of today, is reported to have caused 296 human infections across 10 U.S. states since July 2012. These additional human infections underscore the fact that swine influenza viruses can spread to people after close contact with infected pigs, and support the importance of ongoing surveillance for both human and swine influenza viruses.

 

According to the state of Minnesota, each of the 3 people infected with the H1N2v virus had exhibited pig(s) or spent prolonged time with pig(s) at the Minnesota State Fair. Two of the three people had underlying health conditions that placed them at high risk of serious flu complications; one of the two people with high risk factors was hospitalized, highlighting again the importance of the CDC recommendation that people with high risk factors avoid close contact with pigs and pig arenas at fairs this season. All 3 people have recovered from their illnesses.

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). A full list of high risk factors is available on the CDC seasonal flu site.

 

In addition to avoiding pigs and pig arenas at fairs this year, as always, people with high risk conditions who develop flu-like symptoms should seek prompt medical attention. The H1N2v virus should be susceptible to both currently recommended influenza antiviral drugs [oseltamivir (Tamiflu®) and zanamivir (Relenza®)].

 

CDC has confirmed the Minnesota samples as H1N2v viruses. Sequencing of the viruses indicates these H1N2 variant viruses are very similar to those found in humans previously; with the exception of the addition of the pandemic M gene. This is the first time this virus has included the M gene from the 2009 H1N1 pandemic virus when isolated from a person. Genetic analysis shows that the hemagglutinin (H) of this virus is similar to human seasonal influenza viruses that circulated in people as recently as 2009, so there would likely be protective immunity against this particular virus in the human population.

 

The University of Minnesota Veterinary Diagnostic Lab also isolated an H1N2 virus from swine sampled at the Minnesota State Fair. Sequencing at National Veterinary Services Laboratories in Ames, Iowa, confirmed that it matches the human isolates from Minnesota. According to the USDA Swine Influenza Surveillance program, very similar H1N2 viruses – also containing the pandemic M gene – have been found in pigs since early 2010 in Minnesota and a number of other U.S. states.

 

 

If you missed it, earlier this week in An Increasingly Complex Flu Field, we looked at some of the new `players’ on the viral field, including the H1N2v virus.

 

And for an excellent overview of the risks of new flu viruses emerging from swine operations, I can heartily recommend Helen Branswell’s  Scientific American article from December of 2010 called:

 

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, 2011 

»» Read More

CDC Variant Flu Update & FluView Week 35

Credit CDC – 9/7/12 Update

 

# 6541

 

 

The CDC has updated their case counts of human infections with the swine H3N2v virus, indicating another 8 cases have been confirmed, along with 1 additional hospitalization. 

 

 

This is the second week in a row with a relatively low increase in the number of new confirmed infections, although it should be mentioned that there remain a number of `suspected or probable cases’ that are not in today’s tally.

 

Pennsylvania, for instance, is reporting 11 confirmed cases, but lists another 30 `probable’ on their website this morning.

 

And it is likely that many mild, or sub-clinical cases simply go untested. 

 

The CDC’s Assessment of the situation reads:

 

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. So far, the severity of illnesses associated with this virus in people has been similar to the severity of illnesses associated with seasonal flu virus infections. Limited serologic studies indicate that adults may have some pre-existing immunity to this virus while children do not. CDC is closely monitoring human infections with all novel influenza viruses, including H3N2v viruses, and will provide more information as it becomes available.

 

Even if you consider the gaps in surveillance, and likely under-reporting of infections from this virus, H3N2v obviously isn’t spreading anything like the H1N1pdm09 virus did during its debut in the spring of 2009.

 

To put this into perspective, we are roughly 7 weeks since the first clusters began to appear in the Midwest (July 12th, 2012), and we are (just barely) below 300 confirmed cases across 10 states. 

 

The following blast from the past shows the number (and wide geographic spread) of 2009 H1N1 virus detections being reported to the World Health Organization in early June 2009, roughly 7 weeks after it was first detected. 

 

Influenza A(H1N1) - update 45

8 June 2009 -- As of 06:00 GMT, 8 June 2009, 73 countries have officially reported 25,288 cases of influenza A(H1N1) infection, including 139 deaths.

There were, by the way, plenty of gaps in testing and surveillance for the H1N1 virus back in 2009 as well.  The numbers reported above are generally considered to be an undercount.

 

While the H3N2v virus may very well develop `legs’ over time - and eventually pose a larger public health threat - right now it obviously isn’t spreading anything like its H1N1pdm cousin did.

 

Today’s FluView Report has a summary of the novel H3N2v activity and the three H1N2v cases reported last week (see Minnesota Reports Swine H1N2v Flu)

 

 

2011-2012 Influenza Season Week 35 ending September 1, 2012

All data are preliminary and may change as more reports are received.

Novel Influenza A Virus:

From July 12 through September 6, 2012, a total of 296 infections with influenza A (H3N2) variant (H3N2v) viruses have been reported from ten states. This is an increase of 8 over last week’s report. Cumulative totals by state since July 15 are: Hawaii [1], Illinois [4], Indiana [138], Maryland [12], Michigan [5], Minnesota [2], Ohio [102], Pennsylvania [11], West Virginia [3], and Wisconsin [18]. Sixteen H3N2v-associated hospitalizations and one H3N2v-associated death have been reported. The vast majority of cases have occurred after prolonged swine exposure, though instances of likely human-to-human transmission have been identified. At this time no ongoing human-to-human transmission has been identified.

 

<SNIP>

As a result of enhanced surveillance activities for H3N2v, three infections with influenza A (H1N2) variant (H1N2v) virus have been detected in Minnesota in patients who became ill after contact with swine. One patient was hospitalized, but all have recovered from their illness. Confirmatory testing at CDC identified H1N2v with the matrix gene from the 2009 H1N1 influenza virus in specimens collected from all three patients. Although cases of H1N2v have been detected previously, the current cases mark the first reports of H1N2v with the matrix gene from the 2009 H1N1 virus.

 

Otherwise, surveillance of flu activity around the country shows very little activity, despite the scattered reports of H3N2v in the Midwest.

 

 

And the 122 Cities Pneumonia & Influenza mortality surveillance continues to indicate deaths are running well below the seasonally adjusted epidemic level.

 

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 35, 5.6% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 6.5% for week 35.

 

 

With cooler weather on the way, another 6 to 8 weeks of state and county fairs (mostly in the south), and schools now going back into session, we’ll be watching closely to see if this two-week decline in new cases is a temporary lull, or a sustained trend.

 

Stay tuned.

»» Read More

An Increasingly Complex Flu Field

 

(Click to enlarge)

 

# 6534

 

 

Up until 1977  it was considered normal that only one strain of influenza A circulated at a time.

 

When a new pandemic strain appeared (as it did in 1918, 1957, and 1968), the existing seasonal strain – for reasons that weren’t well understood – would vanish, and in time the new pandemic virus would settle in as the seasonal flu.

 

But in 1977 something unprecedented happened.

 

The H1N1 flu virus – which had been replaced by the pandemic H2N2 virus in 1957 (only to be replaced by the H3N2 strain 11 years later) - suddenly reappeared after 20 years absence.

 

The theory is that it escaped from a Russian or Chinese lab’s freezer, as it was almost unchanged from a strain not seen since the early 1950s. 

 

It was dubbed the `Russian flu’, and for a while, slammed Emergency rooms and Flu wards in a big way.

 

Most adults had some immunity left over from their exposures before 1957, and so kids under 20 were the hardest hit.  But unlike in 1918, 1957, and 1968 – this new flu didn’t depose the old flu.

 

Instead we ended up with two major Influenza A strains bumping shoulders and jockeying for position.  Some years H3N2 would dominate, and other years it would be H1N1.

 

Further complicating matters we also have Influenza B viruses, which while generally regarded as less serious than influenza A, have divided into two distinct lineages (Yamagata & Victoria.

 

And they too compete each year for dominance.

 

Which leaves us with (currently) four major flu strains to contend with; 

• A/H1N109
• A/H3N2
• B/Victoria
• B/Yamagata

 

These viruses constantly change and evolve over time, and we often have several clades of each strain at any given time. The most recent ECDC: Influenza Virus Characterization found 5 genetically distinct H3N2 strains in circulation across Europe.

 

The recent emergence of a new – antigenically different – H3N2 strain, along with the recent dominance of the Yamagata influenza B virus, has prompted a major change in this year’s flu vaccine.

 

• The H1N1 component remains essentially unchanged, with the A/California/7/2009 (H1N1)pdm09-like  still recommended.
• But the old A/Perth/16/2009 (H3N2)-like virus now gives way to the A/Victoria/361/2011 (H3N2)-like virus.
• And the Victoria lineage B/Brisbane/60/2008-like virus will be replaced by a Yamagata strain; the B/Wisconsin/1/2010-like virus. 

 

Which makes getting the flu vaccine this fall doubly important, as it is likely that community immunity to both of these strains is low.

 

Beyond these four, keeping researchers up late at night is the fact that there are no fewer than six influenza viruses that – while not well adapted to humans  – keep trying to nudge their way into the human host pool.

 

Most people by now are aware of the concerns over the H5N1 `bird flu’, but less well known are the H7 avian strains, which have managed to jump to humans several times over the past decade.

 

• In 2003 an outbreak of H7N7 at a poultry farm in the Netherlands went on to infect at least 89 people. Most of the victims were only mildly affected, but one person died.
• In 2004 two people in British Columbia tested positive for H7N3 (see Health Canada Report) during an outbreak that resulted in the culling of 19 million birds.
• In 2006 and 2007 there were a small number of human infections in Great Britain caused by H7N3 (n=1)  and H7N2 (n=4), again producing mild symptoms.

 

H9N2 is another avian strain that has, on rare occasions, infected humans and is believed to have some pandemic potential. Over the past dozen years a small handful of cases have been identified – mostly in Hong Kong (see CIDRAP Avian Influenza (Bird Flu): Implications for Human Disease).

 

• In January of 2010, in H9N2: The Other Bird Flu Threat, I wrote about the World Health Organization  recommending the creation of a candidate vaccine virus for H9N2.

• And in November 2010, in Study: The Continuing Evolution Of Avian H9N2, we looked at computer modeling that suggested that the H9N2 virus moving towards becoming more `human-adapted’.

 

And since 2005 the CDC has been reporting a growing number of swine flu variants that have managed – on rare occasions – to jump to humans.

 

The three main flu strains circulating in pigs are:

• H1N1
• H1N2
• H3N2

When one of these swine viruses jumps to a human host, it is then called a `variant’ virus. 

 

Up until last year, it was the trH1N1 swine virus (now called H1N1v) that had been most commonly reported. The numbers were very low – rarely more than 2 or 3 infections each year.

 

Over the past year, the focus has shifted to the H3N2v virus, which emerged in the summer of 2011. After a quiet winter and spring, this summer it has infected several hundred people in the Midwest – most (but not all) appear to have contracted it directly from exposure to pigs.

 

And as an added surprise, on Friday of last week we learned of 1 confirmed and 2 suspected cases of a variant flu strain that had only been reported twice during the previous 7 years, in Minnesota Reports Swine H1N2v Flu.

 

Next week this chart will likely need updating.

 

There are other flu strains out there, of course.

 

Earlier this year, concerns were raised over an H3N8 flu virus that had killed seals off the coast of New England, and which conceivably could infect other mammals as well (see mBio: A Mammalian Adapted H3N8 In Seals).

 

And given the propensity for flu viruses to reassort (swap gene segments), the possibility of seeing an entirely new flu strain emerge can’t be ignored.

 

Nature’s laboratory is open 24/7, and unlike human researchers suffers neither from bureaucratic rules or budgetary constraints.

 

That said, history has shown that pandemic events only happen rarely; just three times during the last century (albeit with a couple of close-but-no-cigar events thrown in to keep us on our toes). 

 

Even with all of these potential threats on the viral horizon we could easily see average flu season.

 

So far, none of these novel viruses has demonstrated the ability to transmit among humans in a sustained and efficient manner while producing significant illness.

And if we get lucky, they never will. 

 

But as schools open, and cooler weather arrives, the conditions conducive for the spread of influenza improve. And that holds true whether we are talking seasonal flu, or one of these upstart strains.

 

Today is day three of National Preparedness Month, and while most people think of emergency preparedness as something you do for hurricanes and earthquakes, flu epidemics are also worth planning for as well.

 

Preparedness should include practicing good flu hygiene (hand washing-sanitizing, covering cough & sneezes, staying home if sick) all year round, and getting the flu shot early each year.

 

No one can predict with certainty the kind of flu year we will see, and I certainly have no special insight into the matter. The CDC states it pretty succinctly:

 

What sort of flu season is expected this year?

Flu seasons are unpredictable. The CDC and WHO closely monitor flu cases to identify new viruses or potential epidemics or pandemics.

 

The CDC and the WHO obviously take pandemics and epidemics very seriously, which is reason enough for us to take a more in-depth look at pandemic preparedness later this month as National Preparedness Month continues.

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Vietnam:`New’ H3N2 Swine Flu Virus Reported

 

UPDATED: 1500hrs

Henry Niman has posted this afternoon that after further review, he believes this report to be a badly translated repost of a story from December on 10 Cases in the United States we already knew about. 

Today’s story is ambiguous enough to make that a plausible explanation.   Unless and until we can get some confirmation of this story I would advise that you view the following report with caution.

 

# 6131

 

 

This morning Editor & Senior Moderator Tetano on FluTrackers has picked up a series of news articles coming out of Vietnam talking about 10 human cases of infection by a `new’ H3N2 swine flu virus.

 

Two of these articles are machine translated from Vietnamese, and are therefore a bit garbled, but the third is an English Language report from the VOV (Voice of Vietnam). 

 

Assuming the major points of today’s report are correct (not always a given), there is not enough information provided to know how this virus compares to the A/H3N2v virus which has been detected in a handful of cases in the United States (see CDC Releases Updated H3N2v Interim Guidance).

 

Keeping the usual caveats in mind regarding early media reports, here is the story from the Voice of Vietnam.

 

 

New strain of swine flu detected

Updated : 5:16 PM, 09/02/2012

(VOV) - The Heath Ministry has quoted sources from the Ho Chi Minh City Pasteur Institute confirming that a new kind of porcine flu virus, A/H3N1, has appeared, apparently a combination of the pig-related A/H1N1 and A/H3N2 flu viruses.

 

The medical sector has monitored 10 patients infected with the A/H3N2 virus with porcine origin, and found that three of them had not had direct contact with any diseased pigs.

 

Therefore, the sector has not ruled out the possibility of a mutation in the A/H3N2 strain which could lead to transmission between humans, instead of strictly from pigs to humans as previously.

 

However, the situation has not reached an alarming level because the virus has not changed much; it has low toxicity and has shown no sign of drug resistance.

 

Flu vaccines are able to cope with small changes in this kind of virus, said Le Hoang San, Vice Director of the HCMC Pasteur Institute.

 

 

Swine are highly susceptible to the influenza virus, and are capable of serving as `mixing vessels’, allowing them to reassort into new hybrid strains.

 

Reassortment happens when two different influenza viruses co-infect the same host, swap genetic material, and produce a hybrid virus. 

 

That is essentially what happened in 2009, when the H1N1 swine flu virus emerged after bouncing around swine herds for a decade or more, picking up genetic changes along the way.

 

And not surprisingly, this recently emergent `humanized’  H1N1 virus has re-entered the swine population and is once again mixing and matching with other circulating swine flu viruses.

 

As a result we now have a Swine H3N2 virus that has reassorted with the 2009 pandemic H1N1 virus, producing a new hybrid that has – in a limited fashion – begun to emerge into the human population.

 

The article above calls the Vietnamese strain a `combination of the pig-related A/H1N1 and A/H3N2 flu viruses’ – which if we take literally – suggests a different reassortment than the one we’ve seen in the United States.

 

 

As stories in the media often gloss over or confuse crucial scientific details we really need to wait for a more definitive report before we can talk about the origin, genetic makeup, and potential of this new virus.

 

For now, this is simply something new to keep an eye on in the ever changing and always surprising world of influenza.

 

Update:  In a conversation with Sharon Sanders of FluTrackers this morning, she pointed out that this article refers to this new reassortant virus as H3N1 (once) and H3N2 (twice).

I took the first mention (H3N1) as a likely misprint, but until we can get some clarification, I don’t think we can say with any confidence exactly which strain this new virus is.

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