Companion Animals & Reverse Zoonosis

 

The undisputed ruler of my house

 

# 6605

 

When we think of zoonotic transmission of diseases – we usually think of a pathogen from moving from animals to humans – but in truth, diseases can go in both directions.

 

Luckily, most viruses are fairly selective about the type of cells they will invade, what organ systems they will attack, and even what species they will infect.

 

This explains why a virus might affect a dog, or a cat, or a bird, yet not affect humans.  This species selectivity is known as a `host range'.

 

 

Most viruses generally have a fairly narrow host range (there are exceptions, of course.  Like rabies). But one of the surprises that came out of the 2009 H1N1 pandemic was that virus’s ability to infect wide range of species.

 

In December of 2009 in a blog called USDA Listing Of Animals With H1N1 we looked at some early reports of pandemic H1N1 infecting a variety of animals. Along with swine  the USDA listed ferrets (5), cats(3), turkeys (5), and a Cheetah (1) as having contracted the virus.

 

(Click to load PDF file)

 

The infection of swine with an H1N1 swine-like virus wasn’t unexpected, nor was the susceptibility of ferrets a big surprise.  Ferrets are often used in influenza research because they are susceptible to the virus.

 

The jumping to cats was less expected, given that the only other flu virus known to affect cats was the H5N1 bird flu. Dogs were not immune (see US: Dog Tests Positive For H1N1), either.

 

In October of 2010 we looked at a study in the EID Journal: Pandemic H1N1 Infection In Cats that found that - while producing less severe symptoms - cats infected with the 2009 H1N1 virus showed similar pathogenic processes to cats infected with the HPAI H5N1 bird flu virus.

 

While it may not happen very often - with flu season upon us - the potential exists for humans pass one of the seasonal flu viruses on to their pets (or to farm animals).

 

Apart from obvious concern over our pet’s wellbeing, the other worry is the possibility that an influenza’s promiscuous behavior could lead to the creation of a mutated or reassorted strain of the virus.

 

 

It is probably more likely that reassortment would occur in swine, birds, or humans – but other species (like dogs, cats, ferrets, skunks, etc.) cannot be ruled out.

 

All of which brings us to a press release today from the University of Oregon, which talks about the need to study `reverse zoonotic’ influenza infections in pets.  I’ve only included excerpts, follow the link to read:

 

 

Onset of flu season raises concerns about human-to-pet transmission

10-3-12

CORVALLIS, Ore. – As flu season approaches, people who get sick may not realize they can pass the flu not only to other humans, but possibly to other animals, including pets such as cats, dogs and ferrets.

 

This concept, called “reverse zoonosis,” is still poorly understood but has raised concern among some scientists and veterinarians, who want to raise awareness and prevent further flu transmission to pets. About 80-100 million households in the United States have a cat or dog.

 

It’s well known that new strains of influenza can evolve from animal populations such as pigs and birds and ultimately move into human populations, including the most recent influenza pandemic strain, H1N1. It’s less appreciated, experts say, that humans appear to have passed the H1N1 flu to cats and other animals, some of which have died of respiratory illness.

 

There are only a handful of known cases of this phenomenon and the public health implications of reverse zoonosis of flu remain to be determined. But as a concern for veterinarians, it has raised troubling questions and so far, few answers.

 

<SNIP>

 

The researchers are surveying flu transmission to household cat and dog populations, and suggest that people with influenza-like illness distance themselves from their pets. If a pet experiences respiratory disease or other illness following household exposure to someone with the influenza-like illness, the scientists encourage them to take the pet to a veterinarian for testing and treatment.

 

<SNIP>

 

The primary concern in “reverse zoonosis,” as in evolving flu viruses in more traditional hosts such as birds and swine, is that in any new movement of a virus from one species to another, the virus might mutate into a more virulent, harmful or easily transmissible form.

 

“All viruses can mutate, but the influenza virus raises special concern because it can change whole segments of its viral sequence fairly easily,” Loehr said. “In terms of hosts and mutations, who’s to say that the cat couldn’t be the new pig? We’d just like to know more about this.”

 

Veterinarians who encounter possible cases of this phenomenon can obtain more information from Loehr or Jessie Trujillo at Iowa State University. They are doing ongoing research to predict, prevent or curtail emergent events.

 

This press release also makes mention of the laboratory interspecies transmission of a canine H3N2 (avian-origin) influenza virus in Korea.  You’ll find my coverage of that story at the link below:

 

Interspecies Transmission Of Canine H3N2 In The Laboratory

»» Read More

PNAS: A Hypothesis On The Effects Of La Niña On Influenza Reassortment

 

 

# 6078

 

 

 

We have an interesting hypothesis being offered today by a pair of well-respected researchers (Jeffrey Shaman of Columbia University's Mailman School of Public Health and Marc Lipsitch of the Harvard School of Public Health), who note that the weather patterns prior to the pandemics of 1918, 1957, 1968 and 2009 all showed the Pacific ocean to be in a La Niña cycle.

 

We know, of course, that correlation doesn’t necessarily imply causation, but an apparent association between two events can often provide a useful starting point for further scientific investigation.

 

And that’s what these researchers are calling for.

 

Whether this correlation is casual, or is simply coincidental, is for now unknown.  

 

For those unfamiliar with the basics of El Niño and La Niña, a very brief overview:

 

The Pacific Ocean cycles between an El Niño pattern (warmer) and a La Niña (colder) than normal water temperatures in the Equatorial Pacific Ocean.

 

These water temperature cycles can have major effects on climate and weather far removed from the Pacific. During La Niña years, for example, the Atlantic Hurricane season is usually more active.

 

 

La Niña (December 2000)

El Niño (December 1997)

Sea surface temperature anomalies (°C)

Photo Credit- NOAA 

 

La Niña's occur every 2 to 7 years, and over the past 62 years 14 have been observed. During that time, we saw 3 pandemics (1957, 1968, 2009).

 

Graph Credit- Wikipedia

 

 

We’ve  the Press Release from Columbia University's Mailman School of Public Health, but after a quick visit to the PNAS journal website I wasn’t able to locate the article online. I imagine it will be online shortly.

 

Does the La Niña weather pattern lead to flu pandemics?

 

Public release date: 16-Jan-2012

 

Worldwide pandemics of influenza caused widespread death and illness in 1918, 1957, 1968 and 2009. A new study examining weather patterns around the time of these pandemics finds that each of them was preceded by La Niña conditions in the equatorial Pacific. The study's authors--Jeffrey Shaman of Columbia University's Mailman School of Public Health and Marc Lipsitch of the Harvard School of Public Health—note that the La Niña pattern is known to alter the migratory patterns of birds, which are thought to be a primary reservoir of human influenza. The scientists theorize that altered migration patterns promote the development of dangerous new strains of influenza.

 

The study findings are currently published online in PNAS.

 

To examine the relationship between weather patterns and influenza pandemics, the researchers studied records of ocean temperatures in the equatorial Pacific in the fall and winter before the four most recent flu pandemics emerged. They found that all four pandemics were preceded by below-normal sea surface temperatures—consistent with the La Niña phase of the El Niño-Southern Oscillation. This La Niña pattern develops in the tropical Pacific Ocean every two and seven years approximately.

 

The authors cite other research showing that the La Niña pattern alters the migration, stopover time, fitness and interspecies mixing of migratory birds. These conditions could favor the kind of gene swapping—or genetic reassortment—that creates novel and therefore potentially more variations of the influenza virus.

 

"We know that pandemics arise from dramatic changes in the influenza genome. Our hypothesis is that La Niña sets the stage for these changes by reshuffling the mixing patterns of migratory birds, which are a major reservoir for influenza," says Jeffrey Shaman, PhD, Mailman School assistant professor of Environmental Health Sciences and co-author of the study.

 

Changes in migration not only alter the pattern of contact among bird species, they could also change the ways that birds come into contact with domestic animals like pigs. Gene-swapping between avian and pig influenza viruses was a factor in the 2009 swine flu pandemic.

 

 

For the record, the Pacific is currently in a La Niña cycle, and the forecast is for it to remain so well into the Northern Hemisphere spring of 2012.

 

 

This is an interesting hypothesis, and should promote some fascinating avenues of investigation.

»» Read More

Iowa DPH Reports 3 Novel trH3N2 Cases

 

Note: This story is updated at  More Details On The trH3N2 Story

 

# 5973

 

Reassortant H3N2 virus detected in Pennsylvania,Indiana & Maine – Source CDC

The Iowa Department of Public Health announced today in a brief press release that they have detected three cases of a novel trH3N2 SOIV (Swine Origin Influenza Virus) described as being similar to the ones reported recently in Indiana, Pennsylvania, and Maine.

 

For more on those earlier cases see:

 

CDC Update On trH3N2 Swine Infections

Maine Confirms A 2nd trH3N2 Case

CDC Update On trH3N2 Cases

A 5th trH3N2 SOIV Report

CDC Update On Recent Novel Swine Flu Cases

MMWR: Swine-Origin Influenza A (H3N2) Virus Infection in Two Children

 

Unlike the majority of cases reported over the past few months, these three cases report no animal exposure, and so limited Human-to-Human spread is suspected.

 

My thanks to Carol@SC on the Flu Wiki for posting a news item that led me on a search to find this news release from the Iowa DPH.

 

 

Flu Activity in Iowa Includes Novel Strain

Posted: Tue, 22 Nov 2011 15:09 CST

Important to cover your cough and stay home when sick

Routine surveillance by the Iowa Department of Public Health (IDPH), the State Hygienic Lab and other partners across the state indicate that a novel strain of the influenza virus has been detected in three children in Webster and Hamilton Counties.

This virus, an influenza A/H3N2 recombinant virus, has also been detected in other states in recent months. Symptoms are similar to the regular seasonal flu and include fever, cough, tiredness, body aches and loss of appetite.This influenza A/H3N2 virus contains components of human, avian, H1N1, and swine influenza.

All spread has been human to human, and spread appears to be limited; no further cases have been identified in the last week. None of the cases have had any animal exposure. Because the virus is unique, IDPH has increased surveillance for this strain at clinics and emergency rooms.

 

“It appears the seasonal influenza vaccine currently available may offer some protection against this novel strain,” said IDPH Medical Director, Dr. Patricia Quinlisk. “However, we continue to stress the importance of personal protective actions. Remember the three Cs: Clean you hands frequently; Cover your coughs and sneezes; and Contain germs by staying home when ill.”

 

No serious illness or death has been reported in connection with this novel influenza A/H3N2 virus, and all cases have recovered. For more information on the virus, visit www.idph.state.ia.us/Cade/Influenza.aspx?pg=FluHome .

 

While unusual, human infections by novel swine viruses are not unheard of.  Over the past 5 years more than 2 dozen (trH1N1 & trH3N2) cases have been detected.  Most are a result of direct exposure to swine, although limited human-to-human transmission appears to have occurred.

 

Since these novel H3N2 infections continue to appear in low levels across the upper Midwest,this is obviously a story we will continue to follow.

»» Read More

The Debate Over Bird Flu Experiments Continues

# 5970  


In an attempt to learn what evolutionary steps are required for the H5N1 bird flu virus to mutate into a pandemic strain, scientists around the world have been working to create new laboratory strains and testing them for biological fitness and virulence.

Last September, one of the best known researchers in the world - Ron Fouchier of Erasmus Medical Centre in Rotterdam - revealed at a scientific conference that he’d managed to turn H5N1 into a virulent, and easily transmissible (among ferrets, anyway) pathogen.

(You can read about this work in Katherine Harmon’s Sci-Am article and in a follow up to this story in New Scientist: Five Easy Mutations.)

While still unpublished, there are growing concerns over the wisdom of conducting research like this, and its eventual publication. Some fear that this knowledge could be used by bioterrorists to engineer a bio-weapon (see NPR: Bio-Terrorism Concerns Over Bird Flu Research).

On Thursday Robert Roos of CIDRAP wrote on this issue in:

H5N1 transmission experiment stirs concern

Robert Roos News Editor
Nov 17, 2011 (CIDRAP News) – A national biosecurity board that monitors "dual use" research is apparently worried about an as-yet-published study in which a mutant form of H5N1 avian influenza virus was found to be easily transmissible in ferrets, which are considered good models for flu in humans.
(Continue . . .)

This morning Helen Branswell of the Canadian Press brings us a detailed look at this growing controversy. Follow the link to read the article in its entirety.

Highly recommended.

Debate rages over new bird flu research; some argue it's not safe to publish


November 19, 2011 - 08:05
Helen Branswell, The Canadian Press
TORONTO - New bird flu research that shows that the dangerous virus can mutate to become easily transmissible among ferrets — and perhaps humans — has embroiled the scientific community in a difficult debate.
(Continue . . . )

A Brief Personal Note:  

I've been called away on a family medical emergency and do not expect to be back at my desk until late Monday (21st) or early Tuesday (22nd).  In the meantime, please avail yourself to the links to bloggers, newsgathers, and flu forums in my sidebar for the latest on flu and emerging infectious diseases.

»» Read More

An Influenza Double Whammy

 

 

 

# 5936

 

 

Although we’ve seen this sort of thing a few times before, the news yesterday that researchers in Cambodia detected two patients with dual influenza infections (back in 2009) has made quite a splash in the media overnight.

 

Some of the headlines include:

 

It's Possible to Come Down With Two Flu Viruses at Once Yahoo! 

Cambodians infected with both swine, seasonal flu The Straits Times

Global flu watch: Report of rare flu coinfection in Southeast Asia hot... PhysOrg.com

 

Like the influenza virus itself, the UK papers tend to go for the throat with their headlines:

 

Britain On Alert For New Super-flu Daily and Sunday Express

Deadly strain of super-flu 'could spread to Britain within 24 hours' Daily Mail

 

 

Before these hyperbolic headlines entice anyone to head down to the bunker, the study on which these stories are based found no `super flu’.

 

In fact, while researchers detected a relatively rare dual infection of seasonal H3N2 and the new pandemic H1N1 virus in a pair of Cambodian patients, in neither case did they find a reassortant virus.

 

The point is, this is the sort of set up that could have produced a new, potentially dangerous hybrid virus.

 

First stop, the study which appears in the American Journal of Tropical Medicine & Hygiene, then we’ll come back and look at the potential ramifications of dual influenza infections.

 

Dual Infection of Novel Influenza Viruses A/H1N1 and A/H3N2 in a Cluster of Cambodian Patients

Christopher A. Myers, Matthew R. Kasper, Chadwick Y. Yasuda, Chin Savuth, David J. Spiro, Rebecca Halpin, Dennis J. Faix, Robert Coon, Shannon D. Putnam, Thomas F. Wierzba and Patrick J. Blair

 

 

The details are behind a pay wall, but as the authors point out in their abstract:

 

This incident confirms dual influenza virus infections and highlights the risk of zoonotic and seasonal influenza viruses to coinfect and possibly, reassort where they cocirculate.

 

 

Earlier this year you may recall we saw a similar co-infection in Canada that actually led to the creation of a unique hybrid reassorted virus (see Webinar: pH1N1 – H3N2 A Novel Influenza Reassortment).

 

In this case, the patient was a 16-month old boy from the Greater Toronto Area who was admitted briefly to a local hospital for respiratory and gastrointestinal symptoms in January of 2011.

 

The child was sent home, and recovered without incident, and no other family members or contacts reported flu-like symptoms.

 

It wasn’t until later, when viral cultures showed a hybrid (reassorted) H1N1-H3N2 virus, did scientists realize that something unusual had occurred.

 

Details of this event were presented in an online webinar on June 16th of this year. 

 

From the abstract:

 

pH1N1 – H3N2: A Novel Influenza Virus Reassortment

Presenter:

Dr. Jonathan Gubbay- Medical Microbiologist, OAHPP

Abstract

Dr. Jonathan Gubbay, medical microbiologist at the Toronto Public Health Laboratory, will present on a new influenza virus that has been discovered by the Ontario Agency for Health Protection and Promotion (OAHPP). It is the first Canadian confirmed finding of a patient with a coinfection of seasonal H3N2 and pH1N1 followed by reassortment.

(Continue . . .)

 

A little more than a year ago, in EID Journal: Co-Infection By Influenza Strains, I wrote about a study in New Zealand during the opening months of the 2009 pandemic that discovered at least 11 co-infections (out of 1,044 samples tested) with the older seasonal H1N1 virus and the newly emergent pandemic H1N1 virus.

 

Pandemic (H1N1) 2009 and Seasonal Influenza A (H1N1) Co-infection, New Zealand, 2009

Matthew Peacey , Richard J. Hall, Stephanie Sonnberg, Mariette Ducatez, Shevaun Paine, Mackenzie Nicol, Jacqui C. Ralston, Don Bandaranayake, Virginia Hope, Richard J. Webby, and Sue Huang

 

 

The authors state that the rate of co-infection could actually be higher, since samples were not checked for any other flu strains such as H3N2 and influenza B.

 

And going back even further, Maryn McKenna wrote – in an article for CIDRAP News – of an Indonesian teen who was found to have been co-infected with an avian (H5N1) and a human (H3N2) influenza strain.

 

Avian, human flu coinfection reported in Indonesian teen

Maryn McKenna Contributing Writer

Mar 17, 2008 – ATLANTA (CIDRAP News) – An Indonesian teenager has been brought forward as a case of simultaneous infection with seasonal and avian strains of influenza—a possibility that health planners have long warned could give rise to a pandemic flu strain.

(Continue . . . )

 

In the Indonesian and New Zealand cases above, no reassortant viruses were detected. Still, this research suggests that humans, like swine, could be `mixing vessels’ for influenza. 

 

While gene swapping is possible under a co-infection scenario, it isn’t by any means assured.

 

And even should a reassortment take place, the resulting virus might not prove biologically `fit’, or if it is `fit’, any worse than either of its parental strains.

 

However, the potential for creating a devastating novel flu strain cannot be discounted.

 

Last August, in Professor Peter Doherty On Bird Flu, we looked at his worries on the possibility that the H5N1 virus might one day swap genes (reassort) with the H1N1 virus and produce an easily transmitted, highly virulent flu strain.

 

And in September we saw research (see Study: Reassorted H1N1-H5N1 Produced Virulent Strain) where a laboratory-created reassortant virus with genes taken from the H5N1 and H1N1 virus produced a highly transmissible and virulent strain.

 

Of course, while the world was waiting for bird flu, in 2009 a reassorted Swine flu virus unexpectedly sparked a global pandemic. We were fortunate that it wasn’t any more severe than it was, but it illustrates that there are many ways a pandemic can evolve.

 

 

In addition to the various clades of human flu strains ( both pdmH1N1 & H3N2) now circulating, and a growing constellation of avian flu strains (H5N1, H9N2, H7N7, etc), we continue to see rare sporadic human infections by reassorted swine viruses as well (Maine Confirms A 2nd trH3N2 Case).

 

Further evidence that nature’s laboratory is open 24/7, and that influenza viruses are constantly mutating and reassorting, looking for an evolutionary advantage.

 

While most of these reassortant viruses are doomed to end up in the evolutionary dustbin, failing to thrive and compete with other viruses, it only takes one fit, virulent, and easily transmissible virus to spark a global pandemic.

 

And that is something that might emerge tomorrow, next month, or perhaps not until years from now.  

 

But history as history has us shown over and over:

 

Pandemics happen.  Count on it.

»» Read More

When Pig Viruses Fly

 

 

# 5860

 

 

Being of swine origin, the pandemic producing 2009 H1N1 virus – to no great surprise – moved easily from human hosts back into pig populations around the globe.

 

By the fall of 2009 we’d seen reports of pigs in Canada, the US, Japan, Ireland, Norway, Australia, Argentina, Iceland, and China  showing infection with the humanized H1N1 virus. 

 

Since humans are far more traveled than your average pig, a virus that might have remained confined to swine herds in one region of the world for years soon spread to every continent via international travel.

 

Each year, more than 17 million commercial airline flights transport hundreds of millions of people across the globe (see Pathological Flyers).

 

You can literally travel from just about any two cities (with airports) anywhere in the world in 24 hours or less. No longer are the oceans, or distance, a protection against diseases normally seen only in remote areas of the world.

 

Which is why the pandemic of 2009 spread so quickly around the globe.

 

Given the very limited animal testing and surveillance in the United States and around the world (see Swine Flu: Don’t Test, Don’t Tell) the true scope of the spread of the H1N1 virus back into the pig population remains unknown.

 

The concern is that once `humanized’, and then reintroduced back into the swine population, the virus will have enhanced opportunities to meet up with – and reassort with – other flu viruses. 

 

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

 

 

We’ve already seen multiple reports of pdmH1N1 reassortments, although none have emerged that pose a renewed pandemic threat. 

 

With global pig production growing rapidly to meet the demands of a hungry world, each year we add millions more `mixing vessels’ to natures laboratory.  And the bulk of the predicted growth in hog farming is expected in developing countries where testing is pretty much non-existent.

 

Credit – FAO

 

 

Illustrating the problem is a report yesterday from UCLA on the prevalence of the pandemic H1N1 virus among pigs in Cameroon.

 

In one village, nearly all of the pigs tested showed evidence of current or past infection.

 

 

I’ve a small excerpt from a much longer UCLA Newsroom background article, along with a link to the study.

 

 

UCLA scientists find H1N1 flu virus prevalent in animals in Africa

By Stuart Wolpert September 22, 2011

 

UCLA life scientists and their colleagues have discovered the first evidence of the H1N1 virus in animals in Africa. In one village in northern Cameroon, a staggering 89 percent of the pigs studied had been exposed to the H1N1 virus, commonly known as the swine flu.

 

"I was amazed that virtually every pig in this village was exposed," said Thomas B. Smith, director of UCLA's Center for Tropical Research and the senior author of the research. "Africa is ground zero for a new pandemic. Many people are in poor health there, and disease can spread very rapidly without authorities knowing about it."

(Continue . . . )

 

The study appears (behind a pay wall) in Veterinary Microbiology.

 

Pandemic A/H1N1/2009 influenza virus in Swine, Cameroon, 2010

Kevin Y. Njabo,  Trevon L. Fuller, Anthony Chasar, John P. Pollinger, Giovanni Cattoli, Calogero Terregino, Isabella Monne, Jean-Marc Reynes, Richard Njouom, Thomas B. Smith

 

 

The viruses detected in Cameroon were  reportedly `virtually identical’ to the H1N1 viruses detected early in the pandemic in San Diego. Thomas B. Smith, the senior author of the research is quoted as saying:

 

"When different strains of influenza are mixed in pigs, such as an avian strain with a human strain, you can get new hybrid strains that may affect humans much more severely and can potentially produce a pandemic that can allow human-to-human infection. This is how a pandemic can arise; we need to be very vigilant.

 

 

Of course, it isn’t just the 2009 H1N1 virus in swine that we concern ourselves with. In recent years we’ve seen a variety of reassorted H1N1 and H3N2 viruses in pigs, and on rare occasions these have been passed on to humans.

 

Pigs in Indonesia have also been found to have contracted the H5N1 bird flu virus (see EID Journal: Asymptomatic H5N1 In Pigs).

 

 

Most recently, four cases of a reassorted H3N2 virus with the M gene from H1N1 turned up in children in Pennsylvania and Indiana (see CDC Update On Recent Novel Swine Flu Cases).

 

While the epidemiological investigation continues, so far we’ve no evidence of sustained human transmission.

 

It is likely that limited infection by novel influenza reassortments such as these occur occasionally (and largely unnoticed) all over the world. Since only a tiny fraction of influenza flu viruses are ever sequenced, we really don’t know how often these types of novel infections occur.

 

But it’s probably more often than we think.

 

These rare SOIV infections are important to monitor and analyze, and may give us an early warning about the next pandemic threat. But for now they pose a very low public health threat.

 

Admittedly, it may be years or even decades before another pandemic emerges and threatens the human population. The timing of these events is impossible to predict.

 

But surveillance studies like the one above show that flu viruses will literally go to the ends of the earth looking for new hosts and an evolutionary advantage.

 

 

 

For more on the reassortment potential of avian, swine, and human flu viruses, you can’t do better than  Helen Branswell’s excellent Scientific American article from last December called Flu Factories, or her SciAm Podcast interview.

»» Read More

Study: Reassorted H1N1-H5N1 Produced Virulent Strain

 

 

 

# 5846

 

 

Less than 3 weeks ago, in Professor Peter Doherty On Bird Flu, we looked at his concerns over the possibility that the H5N1 virus might one day swap genes (reassort) with the H1N1 virus and produce an easily transmitted, highly virulent flu strain.

 

Reassorted viruses can result when two different flu strains inhabit the same host (human or otherwise) at the same time. Under the right conditions, they can swap one or more gene segments and produce a hybrid virus.

 

 

 

While a bird flu reassortment has long been a concern, many scientists have assumed that such a genetic merger - with an already human–adapted flu virus - would produce a less virulent flu strain.

 

Something more on par with the (still horrific) 1918 Pandemic virus which killed about 2.5% of those stricken in the United States.

 

Today we’ve research that appears in The Journal of Virology that calls that assumption into question.

 

 

Increased pathogenicity of a reassortant 2009 pandemic H1N1 influenza virus containing an H5N1 hemagglutinin

J. Virol. doi:10.1128/JVI.05582-11

Troy D. Cline¹, Erik A. Karlsson¹, Pamela Freiden¹, Bradley J. Seufzer¹, Jerold E. Rehg², Richard J. Webby¹, and Stacey Schultz-Cherry^1,*

¹ Departments of Infectious Diseases
² Pathology, St. Jude Children's Research Hospital, Memphis, TN 38105

 

 

Using reverse genetics, researchers at St. Jude Children’s Research Hospital created several reassortant 2009 pH1N1 viruses with individual genes borrowed from a 1997 H5N1 virus, and then tested them for replication and virulence.

 

They found that one of these lab-created viruses, with the HA gene from the H5 virus, increased replication over the parental strain and produced virulence in mice comparable to the parent H5N1 strain.

 

They also report that serial passage through human lung epithelial cells "resulted in increased pathogenicity, suggesting that these viruses may easily adapt to humans and become more virulent."

Somewhat surprisingly, the opposite was found when the parent H5N1 strain was passed sequentially through human lung cells, as the virus grew weaker.

 

CIDRAP has a news brief on this study here, and you can read the abstract here.

 

Of course, just because it can be artificially created in the laboratory doesn’t guarantee that it will evolve on its own in the wild. 

 

It just means that it’s possible.

 

The less-than-comforting bottom line from the abstract:

 

Together, these data suggest that reassortment between co-circulating human pH1N1 and avian H5N1 influenza strains may result in a virus with the potential for increased pathogenicity in mammals.

 

For more on the reassortment and mutation potential of influenza viruses, you may wish to revisit some of these earlier blogs:

 

M Is For Mutation

Two Reassortment Studies To Ponder

Hong Kong: Influenza Surveillance In Pigs

EID Journal: Swine Flu Reassortants In Pigs

If You’ve Seen One Triple Reassortant Swine Flu Virus . . .

»» Read More

CDC Update On The Pennsylvania Swine Flu Cases

 

 

# 5821

 

 

The CDC has released a couple of new updates to the big story we’ve been following for a week – the detection of several novel H3N2 swine flu infections among 4 children living in Indiana (1) and Pennsylvania (3).

 

Earlier stories include:

 

Pennsylvania DOH: Updated FAQ On The Novel Swine Flu Cluster

Pennsylvania Reports 2 More Novel Flu Cases

MMWR: Swine-Origin Influenza A (H3N2) Virus Infection in Two Children

 

The epidemiological investigation is ongoing, and there remain many unanswered questions regarding the source, pathogenicity, and transmissibility of this virus. 

 

Alas, good science takes time. 

 

While the CDC continues to investigate, thus far the good news, according to Lyn Finelli - Chief Outbreak Investigator for CDC’s  Influenza Division – is that:

 

“. . . it does not look like there is current spread in the community and so far, illness associated with these viruses has not been especially severe. Two of the patients are fully recovered and the third is recovering.”

 

 

The CDC continues to update this situation on their HAVE YOU HEARD? webpage. You’ll find excerpts from a much longer entry below. 

 

Follow the link to read it in its entirety.

 

 

Number of Swine Origin H3 Infections in Pennsylvania Rises to Three

September 6, 2011 -- CDC laboratory testing has confirmed two additional cases of human infection with swine origin influenza A (H3) viruses in children in Pennsylvania. These additional two cases bring the total number of confirmed cases of human infection with swine origin influenza A (H3) viruses from the Pennsylvania investigation to three. According to the Pennsylvania Department of Health, all three of the children confirmed with swine origin influenza A (H3) influenza infection reportedly attended the Washington County Agricultural Fair the week of August 13-20, 2011, where swine were exhibited.

 

The first case of human infection with swine origin influenza A (H3) in Pennsylvania was reported in an MMWR early release issued on Friday, September 2, 2011 and occurred in a girl younger than 5 years. The two cases confirmed over the weekend also occurred in girls, both younger than 10 years. All three of the patients were in the area where swine were exhibited and one had direct contact with swine.

 

Like humans, pigs can become infected with and spread their own influenza viruses. The symptoms of swine flu in pigs are very similar to the symptoms humans get from human seasonal flu illness and can include coughing, lack of appetite, runny nose and lethargy. Not only do pigs become infected and spread swine influenza viruses, but they can be infected with both human and avian influenza viruses. Though rare, humans also can be infected with swine influenza viruses.

 

“It′s pretty rare to see human infections with swine flu viruses. CDC gets reports of about 5 cases of human infections with swine flu viruses each year,” says Lyn Finelli, Chief Outbreak Investigator for CDC′s Influenza Division. “Most of the time, these cases occur after close contact with pigs and seldom spread onward from the first person infected.” There have been rare cases where human-to-human transmission may have occurred, most recently in Indiana in a case also reported in the September 2, 2011 MMWR early release. “The hallmark of influenza viruses is their ability to change,” cautions Mike Shaw, the Influenza Division′s Associate Director for Laboratory Science. “That is why we watch these types of situations closely, to make sure that the virus hasn′t changed to allow efficient and sustained human-to-human transmission.”

(Continue . . . )

 

 

A second embedded link provides us with some background on the genetics of this new virus, showing how it is the product of reassortment, with 7 gene segments from the H3N2 swine flu virus and 1 gene segment (M) from the 2009 H1N1 virus.

 

Number of Swine Origin H3 Infections in Pennsylvania Rises to Three [508 Image Compliance Text]

The above graphic depicts how the human cases of swine-origin H3N2 influenza virus reported in Indiana and Pennsylvania resulted from the reassortment of two different influenza viruses. The image on this page shows three influenza viruses placed side by side, with eight color-coded RNA segments inside of each virus. Note: All influenza viruses contain 8 RNA segments. These RNA segments are labeled HA (hemagglutinin), NA (neuraminidase), PB1, PB2, PA, NP, M and NS.

 

The virus in the center of the picture represents the human cases of swine-origin H3N2 influenza in Indiana and Pennsylvania. Seven of these viruses’ eight RNA segments are derived from influenza viruses that commonly circulate in pigs. The virus on the left of the diagram, labeled “1998-2011 swine H3N2 triple reassortant viruses,” represents these swine influenza viruses. These swine viruses are called triple reassortant viruses because they contain genetic material from humans, pigs and birds.

(Continue . . .)

 

Anytime a novel influenza virus jumps species and demonstrates the ability to infect humans, it is a matter of both scientific curiosity and concern.

 

We’ve seen a number of novel flu viruses emerge over the past few years, and with the notable exception of the 2009 H1N1 pandemic virus, all have turned out to transmit poorly in humans.

 

Given the limits of testing and surveillance, it is likely that limited transmission of novel flu viruses to humans is far more common than we know.

 

The concern is that another novel virus could evolve that is both pathogenic and easily transmissible among humans.

 

Which is why epidemiologists take investigations of novel swine flu infections like these so seriously.

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Pennsylvania DOH: Updated FAQ On The Novel Swine Flu Cluster

 

 

 

# 5818

 

 

The Pennsylvania Department of Health has updated their FAQ sheet (Q & A: Novel Influenza A Virus) on the recent detections of a reassorted H3N2 swine flu virus in three children who attended a county fair in mid-August.

 

It is still very early in the epidemiological investigation of these cases, and there are a lot of questions yet to be answered.

 

Prime among those is whether this virus has the potential to spread efficiently in humans.

 

For now, evidence of sustained human transmission has not been found.  Of course, the CDC is still investigating, and that could change if more cases show up.

 

But it is important to note, that even if a few more cases were to show up over the next few weeks, that wouldn’t necessarily mean that we are faced with an epidemic or pandemic situation. 

 

For that to happen the virus would need to be adapted well enough to human physiology to have an R₀ number (basic reproductive number) sufficient to sustain an outbreak.

 

The R₀  number signifies the average number of secondary infections caused by one infectious person entering a totally susceptible population. 

 

If less than 1.0, outbreaks are likely to sputter and die out.  If greater than 1.0, the outbreak is more capable of spreading. 

 

And as we’ve seen with roughly 20 other reported novel swine infections since 2005, and with a significant number of H5, H7, and H9 avian flu infections, it is possible to have limited outbreaks of a novel flu virus without it sparking an epidemic.

 

We’ll need to wait for more epidemiological evidence before we can know whether this particular virus has `legs’. If it is spreading efficiently (and that’s still a big `if’), we ought to see evidence of that fairly soon.

 

It is also possible that if this virus isn’t ready for prime time right now, that through further reassortment or mutation, it could become better adapted down the road. The only constant with influenza viruses is change.

 

So this situation deserves ongoing surveillance.

 

But regardless of this virus’s fate, the risks of seeing another novel pandemic virus emerge sometime in the future from either the farm or the wild are genuine.

 

 

A few recent blogs on this possibility include:

 

Professor Peter Doherty On Bird Flu

Two Reassortment Studies To Ponder

Hong Kong: Influenza Surveillance In Pigs

The (Swine) Influenza Reassortment Puzzle

 

 

The CDC’s investigation into these recent novel flu cases in Pennsylvania continues, and hopefully we’ll know more shortly.

 

Below are some excerpts from yesterday’s (9/6/11) updated Health Department FAQ. 

 

 

Questions & Answers: Novel Influenza A Virus

 
About the Flu Virus/Current Vaccination 

• 

What is this novel influenza A virus? 
Influenza A viruses occur in many animals, including humans, swine (pigs) and wild birds.This particular virus is unique from other previous H3N2 human infections in that it also contains a genetic piece of the 2009 H1N1 virus.

  
• Is it possible for humans to transmit it to other humans?  
Currently, it does not appear the virus is spreading from person‐to‐person.  However, we will continue to learn ore as our investigation into this new virus continues.  

•

How serious is this virus?  
We currently know of three cases of this novel influenza virus. One patient has recovered and the other two are recovering. Our investigation will continue to focus on the seriousness of the virus.  Based on what we know about other types of flu, illness can range from very mild symptoms to death in particularly susceptible populations (like older people, young children and those with certain medical conditions).

 

•  What does this mean for this year’s flu vaccines? Will the current vaccine cover both seasonal flu and this new strain of flu?  
The 2011‐2012 vaccine is the same as last year, covering two strains of influenza A pandemic H1N1 and a H3N2 strain that has been circulating for a few years now) as well as a strain of influenza B.  It is too early to tell whether or not this new strain will even need vaccination.  

<SNIP>

Should we be concerned that a flu pandemic is pending?  

A pandemic is a global outbreak of disease.  A flu pandemic happens when a new strain of the flu virus appears for which people have little or no immunity. As a result, it spreads easily from person to person around the world, causing widespread illness and death.

 

Currently, we don’t have any evidence to support that this novel influenza A virus will lead to a pandemic, as we haven’t yet been able to prove that it is being transmitted from human to human.

 

As with any new influenza A virus, public health officials  are working to learn more about the source of this particular strain and to determine how/if it can be spread from person to person. 

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Pennsylvania Reports 2 More Novel Flu Cases

 

 

# 5814

 

 

In a press release this afternoon the Pennsylvania Health Department has announced the detection of two more novel swine flu infections among recent visitors to a county fair held in the southwestern part of the state.

 

This comes on the heels of the announcement on Friday in the CDC’s MMWR of two novel flu infections from a reassortant swine H3N2 virus that contained a gene segment from the H1N1 swine flu virus. 

 

In that announcement we were told of one case in Pennsylvania and another case in Indiana, both of whom had recovered.  All of the cases so far have involved children.

 

Today’s development will no doubt inspire intense state and federal epidemiological investigations to see if this new strain of flu has acquired the ability to spread efficiently from human to human.

 

So far, these appear to be isolated infections with no evidence of secondary transmission of the virus in Pennsylvania, although there are indications that may have occurred in the one case from Indiana.

 

 

 

 

Novel Influenza-A Cases Linked to County Fair; Pennsylvanians Should Continue Flu Prevention Practices and Report Flu-like Illness

HARRISBURG, Pa., Sept. 5, 2011 /PRNewswire/ -- The Pennsylvania departments of Health and Agriculture today announced three cases of a novel influenza A virus have been identified, and are now linked to an agricultural fair in southwestern Pennsylvania.

 

The first individual to become ill, announced on Friday, Sept. 2, has fully recovered from the illness. Two other individuals, confirmed ill over the weekend, are recovering. All three are children who reported attending the Washington County Agricultural Fair the week of Aug. 13-20, 2011.

 

The cases in Pennsylvania are similar to previous, rare human infections with swine-origin H3N2 viruses, but are unique in that they contain a genetic component of the H1N1 virus.

 

A continuing investigation, which is being jointly undertaken by the departments of Health and Agriculture, as well as the Centers for Disease Control and Prevention (CDC), has not yet uncovered how the illness was transmitted to the three individuals.  However, no additional human infections with this virus have been identified to date.

 

Anyone who attended the Washington County Fair and has flu-like symptoms should contact their local health care provider or call 1-877-PA-HEALTH. Symptoms would be similar to that of seasonal influenza, and would include fever, lethargy (extreme tiredness), lack of appetite and coughing. Other influenza symptoms may include a runny nose, sore throat, eye irritation, nausea, vomiting and diarrhea.

 

The Department of Health and the CDC are conducting increased surveillance and tracking in southwestern Pennsylvania, as well as setting up informational booths about influenza at agricultural fairs, while Department of Agriculture is continuing with monitoring the health of animals at all exhibitions.

 

The Department of Health continues to urge the public to take everyday precautions to prevent the spread of respiratory viruses, while the Department of Agriculture reminds residents to remember to wash your hands after coming into contact with animals at fairs and in other public venues.

 

"We're not telling people to avoid public venues or fairs," said Pennsylvania DOH Secretary Dr. Eli Avila. "But, until we complete our investigation, we want to make sure that the public is aware and is taking the proper precautions to protect their health."

 

Everyday preventative actions against influenza include:

• Coughing or sneezing into a tissue, your sleeve or elbow (not your hands);  
• Washing your hands often with soap and water for at least 20 seconds, especially after you cough or sneeze, or using an alcohol-based hand cleaner;
• Keeping your hands away from your face – don't touch your mouth, hands or eyes;
• Keeping frequently used surfaces clean; and
• Staying home from work, school, and social gatherings if you have flu-like and feverish symptoms to help prevent others from catching your illness.

For more information, visit www.health.state.pa.us or call 1-877-PA-HEALTH.

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M Is For Mutation

 

 

 

# 5812

 

 

I usually try to avoid using the word `Mutant’ or `Mutation’ in my blog titles about flu because, strictly speaking . . .

 

All influenza viruses are the product of mutation.

 

Flu viruses are inherently unstable (in particularly, influenza A), and are constantly evolving and changing. Mutating. Which explains why scientists must adjust the flu vaccine nearly every year.

 

Of course, the media loves the word `Mutation’ – I suspect because it conjures up vivid images in the minds of their readers. And to the public, mutations are almost universally perceived as `bad’. 

 

Earlier this week we saw a plethora of `Mutant’ headlines, including:

 

New bird flu virus mutation threatens Vietnam -Thanh Nien Daily

No vaccine yet for mutant bird flu ...  - The Straits Times

Mutant Bird-Flu Strain Spreads in Asia - The Daily Beast

Mutant bird flu strain in Asia prompts call for scrutiny - MSNBC

 

 

While the emergence of this (relatively) new strain of H5N1 is a big story, so far we’ve seen no evidence to suggest that this `mutation’ poses any greater threat to humans than do any of the other dozen or so clades of the bird flu virus.

 

But that isn’t the sort of lede that sells newspapers.

 

Since the `M’ word seems to be on the lips of many people this week, today seems like a good day to go over how influenza viruses mutate.

 

Don’t worry. 

 

I’ll keep this layman simple, mostly so I – a non-scientist - can understand it.  Real scientists, however, may wish to avert their eyes.

 

The genetic sequence of the influenza virus can be represented by a chain of letters identifying the hundreds of amino acids that make up the viral genome.

 

A tiny sub-section of that chain might have an amino acid sequence that looks something like:

 

MKAILVVMLYTFATA

 

As the virus inhabits a cell, and begins to replicate, it makes thousands of copies of itself which then burst out of the cell after a few hours and go on to infect other cells.

 

Those cells, in turn, make copies that go forth to infect more cells and repeat the process.

 

But being a single-strand RNA virus, the influenza virus tends to be sloppy in making copies of itself. As it replicates millions of times, tiny errors sometimes creep in. If in the process of making copies it mixes up just a single amino acid, we can end up with a mutated virus.

 

MKAILVVMLYTFATA

MKAILVVMLYTFATA

MKAIFVVMLYTFATA      -  Voila! A mutation

MKAIFVVMLYTFATA

MKAIFVVMLYTFATA

 

Above, I’ve swapped out the amino acid leucine (L) at position 5 for phenylalanine (F), simulating a replication error.

Assuming the result is a `biologically fit’ and competitive virus (most aren’t), then it may go on to infect other cells, and conceivably, other hosts.

 

Of course, that doesn’t mean it will make the virus more dangerous.  A mutation can make the virus less virulent or less transmissible.

 

Or it may simply have no effect at all.

 

These small mutations in the virus are called drift, and over time the flu virus can accumulate enough changes so that last year’s vaccine is no longer effective.

 

And that is essentially the story behind this new 2.3.2.1 clade of the H5N1 virus. Enough antigenic changes have accumulated in its genome to allow it to evade the poultry vaccines currently in use.

 

Of course, mutations like these are also capable of bringing about other changes, including antiviral resistance, or perhaps increasing the virulence or transmissibility of the virus.

 

So while not necessarily alarming, this week’s bird flu news is certainly worthy of our attention.

 

Bigger changes in the influenza virus generally come about through a process known as reassortment or shift.

 

Reassorted viruses can result when two different flu strains inhabit the same host (human or otherwise) at the same time. Under the right conditions, they can swap one or more gene segments and produce a hybrid virus.

 

 

While far less common than drift, shift can produce dramatic changes in how a virus behaves, and has been responsible for the creation of pandemic viruses in the past. 

 

Again this week, we’ve received news of a pair of `reassortant’ swine H3N2 flu viruses detected in children from two different states (see MMWR: Swine-Origin Influenza A (H3N2) Virus Infection in Two Children).

 

For those of us who were covering the earliest reports of a novel swine flu outbreak in April of 2009, this week’s report admittedly has a tinge of deja flu.

 

But it is important to remember that over the past 5 years (excluding the 2009 H1N1 virus) nearly 2 dozen similar novel swine flu viruses have been detected across the country. It is also probable that a number of other novel infections have escaped notice – yet so far none has been shown to spread efficiently from human-to-human.

 

That could change, of course - as each reassortant is  a new roll of the genetic dice - and so the CDC quite understandably is encouraging enhanced local flu surveillance, and would mount a vigorous response if more cases were to start to appear. 

 

Flu viruses have been quietly mutating and reassorting for thousands of years, but only rarely does that result in a pandemic strain. The vast majority of these mutations end up in evolution’s dustbin.

 

Even though we don’t always know what they signify, today we have the surveillance tools that enable us to watch some of these genetic changes when they start to appear.

 

 

And while that means we are likely to hear about a lot of potential viral threats that never materialize, it also means we may get some invaluable advance warning about the next pandemic virus before it strikes. 

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MMWR: Swine-Origin Influenza A (H3N2) Virus Infection in Two Children

 

 

# 5808

 

 

Earlier today in MMWR: Two Novel trH3N2 Flu Infections I wrote about a bare-bones entry in this week’s MMWR Notifiable Diseases and Mortality Tables on two recently detected novel trH3N2 infections – and expressed the hope that we’d soon see more details on these cases.

 

Well, my hopes were answered this afternoon with the release of a detailed report from the CDC. 

 

Two patients, children from different states, contracted similar swine flu viruses without any apparent epidemiological connection. Only one child had exposure to swine in the weeks prior to falling ill.

 

While similar to eight previously identified swine H3N2 viruses, these two isolates are `reassortants’ – a product of the swine trH2N2 virus with a gene segment taken from the 2009 H1N1 pandemic virus.

 

I’ve posted some excerpts, but this entire report is a fascinating read, and I would encourage you to follow the link to read it in its entirety.

 

 

 

Swine-Origin Influenza A (H3N2) Virus Infection in Two Children --- Indiana and Pennsylvania, July--August 2011

Early Release

September 2, 2011 / 60(Early Release);1-4

Influenza A viruses are endemic in many animal species, including humans, swine, and wild birds, and sporadic cases of transmission of influenza A viruses between humans and animals do occur, including human infections with avian-origin influenza A viruses (i.e., H5N1 and H7N7) and swine-origin influenza A viruses (i.e., H1N1, H1N2, and H3N2) (1). Genetic analysis can distinguish animal origin influenza viruses from the seasonal human influenza viruses that circulate widely and cause annual epidemics. This report describes two cases of febrile respiratory illness caused by swine-origin influenza A (H3N2) viruses identified on August 19 and August 26, 2011, and the current investigations.

 

No epidemiologic link between the two cases has been identified, and although investigations are ongoing, no additional confirmed human infections with this virus have been detected.

 

These viruses are similar to eight other swine-origin influenza A (H3N2) viruses identified from previous human infections over the past 2 years, but are unique in that one of the eight gene segments (matrix [M] gene) is from the 2009 influenza A (H1N1) virus.

 

The acquisition of the M gene in these two swine-origin influenza A (H3N2) viruses indicates that they are "reassortants" because they contain genes of the swine-origin influenza A (H3N2) virus circulating in North American pigs since 1998 (2) and the 2009 influenza A (H1N1) virus that might have been transmitted to pigs from humans during the 2009 H1N1 pandemic.

 

However, reassortments of the 2009 influenza A (H1N1) virus with other swine influenza A viruses have been reported previously in swine (3). Clinicians who suspect influenza virus infection in humans with recent exposure to swine should obtain a nasopharyngeal swab from the patient for timely diagnosis at a state public health laboratory and consider empiric neuraminidase inhibitor antiviral treatment to quickly limit potential human transmission (4).

(Continue . . . )

 

The Summary offered by the MMWR report reads:

What is already known on this topic?

During December 2005--November 2010, 21 cases of human infection with swine-origin influenza were reported, including 12 cases with swine-origin influenza A (H1N1) virus infection, eight cases with swine-origin influenza A (H3N2) virus infection, and one case with swine-origin influenza A (H1N2) virus infection.

What is added by this report?

This report describes two cases of febrile respiratory illness caused by swine-origin influenza A (H3N2) viruses identified on August 19 and August 26, 2011. The viruses identified in these cases are unique in that one of the eight gene segments (matrix [M] gene) is from the 2009 influenza A (H1N1) virus.

What are the implications for public health practice?

Non-human influenza virus infections rarely result in human-to-human transmission, but the implications of sustained ongoing transmission between humans is potentially severe; therefore, prompt and thorough identification and investigation of these sporadic human infections with non-human influenza viruses are needed to reduce the risk for sustained transmission.

 

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Professor Peter Doherty On Bird Flu

 

 

 

# 5794

 

 

With yesterday’s FAO announcement (see FAO Warns On Bird Flu), the H5N1 virus is suddenly back in the news cycle again.

 

Today, the Australian Life Scientist Magazine carries an interview with world renown, 1996 Nobel Prize winning scientist Professor Peter Doherty, who discusses the pandemic potential of this avian virus.

 

Although his comments range from research on GM (genetically modified) flu-resistant chickens to universal flu vaccines, the main thrust of the today’s article centers around the possibility that the H5N1 virus might one day swap genes (reassort) with the H1N1 virus and produce an easily transmitted, highly virulent flu strain.

 

First a link to the article, which is very much worth reading, then I’ll return with more.

 

Bird-swine flu hybrid could be a killer combo

The appearance of a new mutant of bird flu in Asia raises the concern that it might hybridise with swine flu creating a new pandemic threat.

• Tim Dean (Australian Life Scientist)
• 30 August, 2011 17:12

 

 

As we’ve discussed before, influenza viruses change, evolve, or mutate over time via two well established routes; Antigenic drift and Antigenic Shift.

 

Antigenic drift – the more common of the two - causes small, incremental changes in the virus over time.  Drift is the standard evolutionary process by which influenza viruses mutate, and often come about due to replication errors that are common with single-strand RNA viruses.

 

Shift occurs when one virus swap out chunks of their genetic code with gene segments from another virus.  This is known as reassortment. While far less common than drift, shift can produce abrupt, dramatic, and sometimes pandemic inducing changes to the virus.

 

This process has produced pandemic flu strains in the past, and while that obviously doesn’t happen often, virologists are quick to remind us:

 

Shift Happens.

 

 

While reassortment can occur in many species, pigs have long been believed to be an ideal `mixing vessel’ for influenza because they possess both avian-like (SAα2,3Gal) and human-like (SAα2,6Gal) receptor cells in their respiratory tract.

 

That makes pigs susceptible to human, swine, and avian strains of flu. And while it may not happen often, they are capable of being infected by more than one flu virus at a time.

 

This is basically how the 2009 H1N1 pandemic virus evolved, although it took multiple gene swaps over a decade or longer before it finally emerged into the human population.

 

We know that reassortments do happen, but only rarely do they result in a biologically fit virus capable of causing a pandemic.

 

Most hybrid viruses are evolutionary dead-ends, are unable to compete, and die out within the host.

 

But as global pig production grows – particularly in places where biosecurity and surveillance may be lax – it creates increasing opportunities for a new, biologically `fit’  virus to emerge.

 

Source: FAO

 

Lest anyone doubt the ability of pigs to contract the H5N1 virus, a little over a year ago (see EID Journal: Asymptomatic H5N1 In Pigs) we saw research out of Indonesia that showed 52 pigs in 4 provinces were found to be infected with H5N1 between 2005–2007. 

 

While there is justifiable concern over a reassorted H5N1 virus, bird flu isn’t the only pandemic player down on the farm.

 

The H9 and H7 avian viruses, along with various strains of H3 and H1 influenza (and others) are all potential candidates for reassortment.

 

For more on the reassortment potential of avian, swine, and human flu viruses, you can’t do better than  Helen Branswell’s excellent Scientific American article from last December called Flu Factories, or her SciAm Podcast interview.

 

And for good measure, a sampling of a few of my earlier blogs on reassortment:

 

 

Review: Evolution & Adaptation Of The 2009 pdmH1N1 Virus

You Say You Want An Evolution?

EID Journal: Co-Infection By Influenza Strains

EID Journal: Swine Flu Reassortants In Pigs

If You’ve Seen One Triple Reassortant Swine Flu Virus . . .

 

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