Seroprevalence Study: Avian Flu In Chinese Pigs

 

Since pigs can be infected by more than one flu virus at the same time, the potential exists for two viruses to swap genetic material (reassort), resulting in a new hybrid strain.

 

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Although we tend to think of H5N1 whenever someone mentions `avian flu’, in truth there are many different avian influenza viruses.  If you go back far enough, all influenza A strains – even those thought of today as primarily adapted to humans, equines, or swine – appear to have an avian origin.

 

Influenza A viruses have 8 gene segments (PB2, PB1, PA, HA, NP, NA, M1, M2, NS1, NS2) and are broadly categorized by their HA (hemagglutinin) and NA (neuraminidase) genes.

 

With the recent discovery of H17N10 (see A New Flu Comes Up To Bat), scientists have now identified 17 different serotypes of Hemagglutinin (HA) and 10 serotypes of Neuraminidase (NA), which make many different combinations of HA and NA proteins possible.

Thus far, only about 100 of these combinations have been isolated in nature.

 

But the flu universe is far more diverse than that might lead to you believe, as influenza’s 8 gene segments are largely interchangeable parts. If you were to take two different influenza A viruses (say H3N2 and H5N1) and reshuffle them using reverse genetics, you can come up with 254 possible reassortments.

 

And within each of these HA/NA combinations you can have multiple clades (genetically distinct families), and within each clade, many minor variants – all of which makes for tremendous variety in these viruses.

 

Many of the the H1, H2, and H3 viruses have adapted to human physiology, but we occasionally see infection by other `novel’ strains. Most worrisome, due to its high fatality rate, is H5N1.  But we occasionally see (usually mild) infections by other avian strains.

 

MMWR: Mild H7N3 Infections In Two Poultry Workers - Jalisco, Mexico)

EID Journal: Human Infection With H10N7 Avian Influenza

PLoS One: Seroprevalence Of H9N2 In Poultry Workers – Pune, India

 

Last year scores of dead seals were discovered along the shoreline of New England, predominantly from the North Shore of Massachusetts to the southern coast of Maine.  Investigations showed (see mBio: A Mammalian Adapted H3N8 In Seals) their deaths to be due to a variant of the H3N8 avian flu strain, versions of which are known to also infect horses and dogs.

 

With the propensity of these avian strains to evolve and adapt, scientists are understandably very interested in any avian flu virus that appears to be moving towards `humanization’.

 

While it is possible for a flu virus to jump directly from birds to humans, often it requires an intermediate host to aid in its development. The graphic below illustrates that swine – which are generally susceptible to human and avian flu viruses - are considered excellent mixing vessels’ for influenza viruses.

 

 

The H1N1 `swine flu’ virus of 2009 kicked around in pigs for up to a decade before it adapted well enough to human physiology to spark a human pandemic. Over the past few years we’ve watched attempts by three other swine `variant’ viruses (H1N1v, H1N2v, H3N2v) to jump to mankind. 

 

Which makes the active surveillance of swine a potentially important tool for the early detection of emerging influenza viruses.

 

Unfortunately, while there are some surveillance systems in place, only a tiny fraction of the world’s swine population is actively monitored  (see Helen Branswell’s SciAm Article from late 2010 called Flu Factories).

 

All of which serves as prelude to a new study, recently published in the Journal of Clinical Microbiology, that found low levels of H3, H4, and H6 subtypes of avian influenza in Chinese pigs. Somewhat reassuringly, evidence of infection with the H5N1 virus was not found.

 

These H3, H4, and H6 avian viruses were not seen in a similar study done in 2001, suggesting their arrival into the swine population may be a recent development.

 

 

Seroepidemiological Evidence of Avian Influenza A Virus Transmission to Pigs in Southern China

Shuo Su, Wenbao Qi, Jidang Chen, Wanjun Zhu, Zhen Huang, Jiexiong Xie, and Guihong Zhang

J. Clin. Microbiol. published ahead of print 21 November 2012 doi:10.1128/JCM.02625-12

ABSTRACT

Recently, three novel avian-origin swine influenza viruses (SIVs) were first isolated from pigs in Guangdong Province, southern China, yet little is known about the seroprevalence of avian influenza among pigs in southern China. Here, we report for the first time the seroprevalence of avian H3, H4, and H6 influenza viruses in swine populations and the lack of seroepidemiological evidence of avian H5 influenza transmission to pigs in China.

 

A copy of the study can be downloaded here.

 

The American Society for Microbiology has published a press release with more information, excerpts of which you’ll find below:

 

 

 

Pigs in southern China infected with avian flu

WASHINGTON, DC – December 19, 2012 -- Researchers report for the first time the seroprevalence of three strains of avian influenza viruses in pigs in southern China, but not the H5N1 avian influenza virus.  Their research, published online ahead of print in the Journal of Clinical Microbiology, has implications for efforts to protect the public health from pandemics.

 

Influenza A virus is responsible both for pandemics that have killed millions worldwide, and for the much less severe annual outbreaks of influenza. Because pigs can be infected with both human and avian influenza viruses, they are thought to serve as “mixing vessels” for genetic reassortment that could lead to pandemics, and pigs have been infected experimentally by all avian H1-H13 subtypes. But natural transmission of avian influenza to pigs has been documented only rarely.

 

In the study, from 2010-2012, Guihong Zhang and colleagues of the College of Veterinary Medicine, South China Agricultural University, Guangzhou, People’s Republic of China, tested 1080 21-25 week old pigs for H3, H4, H5, and H6 subtypes of avian influenza virus, and H1 and H3 subtypes of swine influenza virus. Thirty-five percent of the serum samples were positive for H1N1, and 19.7 percent were positive for H3N2 swine flu virus, and 0.93 percent, 1.6 percent, and 1.8 percent were positive, respectively, for the H3, H4, and H6 subtypes of avian influenza A virus. However, no serum samples collected in 2001 were positive for any of these viruses, indicating that transmission into swine was recent.

 

Given the recent transmission of avian influenzas into swine, “We recommend strongly that the pork industry worldwide should monitor the prevalence of influenza in pigs, considering their important role in transmitting this virus to humans,” says Zhang.

 

Previously, novel reassortant H2N3 influenza viruses were isolated from US pigs, which “were infectious and highly transmissible in swine and ferrets without prior adaptation,” according to a 2009 paper in the Journal of Molecular and Genetic Medicine by Wenjun Ma et al. Those viruses resembled, but were not identical to the H2N2 human pandemic virus of 1957.

 

 

The ability of influenza viruses to evolve, mutate, or reassort in swine hosts has been a frequent topic of discussion in this blog.  For more on this, you may wish to revisit:

 

H3N2v: When Pigs Flu

You Say You Want An Evolution?

The (Swine) Influenza Reassortment Puzzle

»» Read More

The Very Common Cold

 

 

Photo Credit – CDC PHIL

 

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Last Sunday I wrote about this week’s General Meeting of the American Society for Microbiology that was being held in San Francisco, and provided some links to live and archived webcasts (see Webcast: ASM Live San Francisco 2012).

 

As you might expect, a large number of scientific presentations have been made over the past few days - and we’ve seen a number of press releases highlighting that research - including the one that follows, on just how common the `common cold’ really is.

 

 

The surprise here is - that among college students tested over an 8 week period - asymptomatic infections led symptomatic infections by a factor of 4 to 1.

 

Which suggests that simply staying away from people with cold symptoms may not provide much in the way of protection against rhinoviruses, and makes common sense interventions - such as frequent handwashing - probably even more important.

 

A few excerpts from the release, but follow the link to read it in its entirety:

 

 

Asymptomatic rhinovirus infection outnumbers symptomatic infection 4 to 1 among university students

The common cold virus may be more common than previously thought in university students not reporting any symptoms. Rhinovirus, the virus responsible for the common cold was found at some point during an 8-week study period in an estimated 60% of university students that were asymptomatic. Researchers from Canada report their findings at the 2012 General Meeting of the American Society for Microbiology.

 

“A high occurrence of asymptomatic infections indicates that university students can spread infections to classmates, or individuals in the community without knowing they are infected,” says Andrea Granados of McMaster University in Hamilton, Ontario, a researcher on the study. The study was conducted at McMaster University and St. Joseph’s Healthcare in Hamilton, Ontario, Canada as part of the McFlu2 COLD3 clinical trial by Granados and colleagues Emma Goodall, Marek Smieja and James Mahony.

 

Rhinovirus, best known for causing the common cold can also cause bronchitis and trigger asthma attacks.

 

<SNIP details on how the study was done>

 

Based on these findings, the researchers estimate that as many as 60.5% of the asymptomatic student population was infected at some time with rhinovirus over an eight week study period.

 

They also used PCR to determine the viral load in symptomatic and asymptomatic students. Students with asymptomatic rhinovirus infections had significantly less virus than symptomatic infections. Decreased amounts of the virus may be responsible for the lack of symptoms, says Granados, however, larger studies are necessary to confirm this finding.

 

“In this study, we found that university students with rhinovirus infections who lacked symptoms outnumbered by a factor of 4 the number of infected students with symptoms. The virus particles can be spread by aerosols or direct contact with an asymptomatic individual. There is no treatment for the common cold; therefore, frequent hand-washing is important to prevent the spread of the common cold particularly in early fall,” says Granados.

 

 

It’s happened to all of us, I suppose. 

We come down with a cold, wrack our brains trying to remember coming in contact with someone with the sniffles - and come up with a blank - leaving us to wonder just where the heck we caught it.

 

Today’s study provides a plausible explanation.

 

Granted, those with asymptomatic infections showed lower viral loads than those displaying cold symptoms - suggesting that they may be less efficient spreaders of the virus – but we don’t have enough data to know how much of a viral load it takes to spread the virus.

 

The good news here, I suppose, is that we can sometimes (perhaps often) get one of the numerous rhinoviruses that circulate without necessarily enduring the misery of cold symptoms.

The bad news is, we may be spreading those cold viruses to others while looking, and feeling, perfectly healthy.

»» Read More

Webcast: ASM Live San Francisco 2012

 

 

 

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This weekend, and running through Tuesday June 19th, the 112th General Meeting of the American Society for Microbiology is being held in San Francisco. The 306 page Final Program, with details on the participants, schedules, scientific sessions, poster sessions, and other details may be downloaded from ASM2012 Website.

 

For those of us not fortunate enough to be able to attend, today, tomorrow and Tuesday there are live webcasts (almost immediately available on the MicrobeWorld Youtube Channel) featuring interviews with presenters and discussions on some of the hottest topics at this year’s meeting.

 

Clicking on the schedule above will take you to not only this year’s schedule, but an archive of videos from last year’s meeting.

 

The first three sessions - hosted by Stanley Maloy, Chair of the Communications Committee for the ASM - are already completed, and available for viewing. 

 

 

 

Sunday, June 17

 

Watch Now! 10:00 a.m. PDT – ASM Live– Microbial Colonization and the Host: Do the Colonists Reshape the Landscape?

 Katherine Lemon, The Forsyth Institute and Boston Children's Hospital

Karina Pokusaeva, Baylor College of Medicine

Watch Now! 11:00 a.m. PDT – ASM Live – Microbial Analysis of Environmental Surfaces in Hotel Rooms

Katie Kirsch, University of Houston

See ASM Press Release The most contaminated surfaces in hotel rooms for additional information.

 

Watch Now! 12:00 p.m. PDT – When Good Bugs Go Bad: Microbiome Dynamics and Disease

 

Lita Proctor, National Human Genome Research Inst/NIH

Forest Rohwer, San Diego State University

Karen Guillemin, University of Oregon

 

 

The mapping of the Human Microbiome was big news this past week (see NIH: News From The Human Microbiome Project), and so it is not surprising that several of these webcasts will deal with the trillions of microbes that inhabit - and largely co-exist - in our bodies.

»» Read More