PNAS: MERS Pneumonia In A Macaque Model

Photo Credit Wikipedia

 

# 7805

 

 

Two weeks ago, in Nature: Animal Testing Of Drug Combo Shows Potential For Treating MERS, we looked at the the potential role of Interferon-α2b & ribavirin in the treatment of MERS-CoV infection, based on a NIAID led study conducted on rhesus macaques. At the time I cautioned that, while encouraging, the following caveats should be kept in mind:

 

• First, the macaque model is not a perfect substitute for humans, as they tend not to be as severely impacted by the MERS virus. 
• Second, treatment was initiated 8 hours post infection, which is an earlier pharmacological intervention than most humans could hope to see. 
• And third, most severe human infections have been seen in people with co-morbidities like COPD, cancer, diabetes, asthma . . . variables this study does not attempt to replicate.

 

These same group of researchers are back with a another study - published yesterday in the journal  PNAS - that looks at the pathogenesis of MERS-CoV in rhesus macaques.  Once again, caveats 1 and 3 need to be considered.

 

The study is called:

 

Middle East respiratory syndrome coronavirus (MERS-CoV) causes transient lower respiratory tract infection in rhesus macaques

Emmie de Wit^a, Angela L. Rasmussen^b, Darryl Falzarano^a, Trenton Bushmaker^a, Friederike Feldmann^c, Douglas L. Brining^c, Elizabeth R. Fischer^d, Cynthia Martellaro^a, Atsushi Okumura^b, Jean Chang^b, Dana Scott^c, Arndt G. Benecke^b,^e, Michael G. Katze^b, Heinz Feldmann^a,^f,¹, and Vincent J. Munster^a,¹

Significance

The Middle East respiratory syndrome coronavirus (MERS-CoV) is the latest emerged coronavirus causing severe respiratory disease with a high case fatality rate in humans. To better understand the disease caused by MERS-CoV, we developed a rhesus macaque model. Infection of rhesus macaques with MERS-CoV resulted in the rapid development of a transient pneumonia, with MERS-CoV replication largely restricted to the lower respiratory tract. This affinity of MERS-CoV for the lungs partly explains the severity of the disease observed in humans. The MERS-CoV rhesus macaque model will be instrumental in developing and testing vaccine and treatment options for an emerging viral pathogen with pandemic potential.

Abstract

(Excerpt)

Upon a combination of intratracheal, ocular, oral, and intranasal inoculation with 7 × 10⁶ 50% tissue culture infectious dose of the MERS-CoV isolate HCoV-EMC/2012, rhesus macaques developed a transient lower respiratory tract infection. Clinical signs, virus shedding, virus replication in respiratory tissues, gene expression, and cytokine and chemokine profiles peaked early in infection and decreased over time. MERS-CoV caused a multifocal, mild to marked interstitial pneumonia, with virus replication occurring mainly in alveolar pneumocytes. This tropism of MERS-CoV for the lower respiratory tract may explain the severity of the disease observed in humans and the, up to now, limited human-to-human transmission.

 

In simple language, once infected, macaques developed mild to moderate, albeit short-lived pneumonia, with infection and viral replication most prominently seen in the lower lung tissue. This tropism (affinity) of the virus for the lower respiratory tract in macaques does match what we’ve seen in severe human cases, but in macaques the severity and duration of MERS infection was limited.

 

We lack a fully predictive animal model for human medical research. Mice, guinea pigs, and ferrets are often employed because of their small size, low cost, and ease of use.  Rhesus macaques, on the other hand, are more difficult to obtain and to work with, but are viewed as being a closer human analog. 

 

Still, results with these animals must be accepted with a certain degree of caution. The old saying in biomedical research is that `Mice lie, and monkeys exaggerate.’

 

We’ve seen mild MERS infections in humans, primarily in younger patients and those without co-morbidities, and so it may well be that the young, healthy macaques used in this study are mirroring that cohort.

 

What this study does tell us is that this virus prefers the lower respiratory tract (in macaques), and that that may help explain both its severity in humans, and its limited human-to-human transmission to date. 

 

For more on this story, Robert Roos of CIDRAP NEWS wrote an excellent overview last night.

 

Macaque study: MERS-CoV settles deep in lungs

Robert Roos | News Editor | CIDRAP News

Sep 23, 2013

Researchers say the macaque model will be useful in developing and testing vaccines and treatments for MERS.

If rhesus macaques are good stand-ins for humans in studying Middle East respiratory syndrome coronavirus (MERS-CoV), the virus prefers the environment deep in the lungs, a finding that may help explain some features of the disease in humans, according to new research.

The scientists say that in macaques, the virus mainly affects the lower respiratory tract, which may help explain why the human disease is often severe but does not spread very easily from person to person.

(Continue . . .)

The Cytokine Storm Revisited

Credit CDC

 

 

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Cytokines are a category of signaling molecules that are used extensively in cellular communication. They are often released by immune cells that have encountered a pathogen, and are designed to alert and activate other immune cells to join in the fight against the invading pathogen.

 

This cascade of immune cells rushing to the infection, if it races out of control, can overwhelm the patient. Their lungs can fill with fluid (which makes a terrific medium for a bacterial co-infection), and cells in the lungs (Type 1 & Type II Pneumocytes) can sustain severe damage.

 

Previously, in Swine Flu Sequelae and Cytokine Storm Warnings, we looked at some of the severe lung damage detected during the 2009 pandemic that was thought to be due to this overreaction of the immune system.

 

Last night Robert Roos, Editor of CIDRAP NEWS, wrote about a study that appeared this week in the American Journal of Pathology that looked at the lungs from 50 fatal cases of H1N1 during the 2009 pandemic, and their finding of "remarkably" high levels of cytokines in the lung tissue.

 

Robert does a terrific job explaining this research, so I’ll invite you to read his article at the link below. When you return, I’ll have some more background on the cytokine response.

 

Study shows cytokine storm in fatal 2009 H1N1 cases

Aug 16, 2013

Researchers who studied lung tissue samples from 50 people who died of pandemic H1N1 (pH1N1) influenza infections in 2009 say they found clear evidence that the intense immune response known as a cytokine storm played a role in their demise.

 

The scientists found that the peak levels of virus in the victims' lungs correlated with "remarkably" high levels of certain cytokines in the same tissues, according to their report, which was released ahead of print this week in the American Journal of Pathology.

(Continue . . . )

 

The abstract to the study is available at:

Cytokine and Chemokine Profiles in Lung Tissues from Fatal Cases of 2009 Pandemic Influenza A (H1N1

Role of the Host Immune Response in Pathogenesis

Rongbao Gao, Julu Bhatnagar, Dianna Blau, Patricia Greer, Dominique C. Rollin, Amy M. Denison, Marlene Deleon-Carnes, Wun-Ju Shieh, Suryaprakash Sambhara, Terrence M. Tumpey, Mitesh Patel, Lindy Liu, Christopher Paddock, Clifton Drew, Yuelong Shu, Jacqueline M. Katz, Sherif R. Zaki

 

 

While influenza can strike people of any age, it generally exacts its greatest toll on the elderly – those over the age of 65 - whose weaker immune systems (and comorbidities) can render them less able to fight off an infection.

 

Exact numbers are unknown, since influenza is only rarely cited as the primary cause of death. If a cause of death (beyond`natural causes’) is given, comorbidities like COPD, heart disease, asthma are far more likely to listed on a death certificate.

 

Still, estimates are that 90% of seasonal flu mortality occurs in those over the age of 65 (cite CDC Pink book).

 

In 2010, (see Study: Years Of Life Lost Due To 2009 Pandemic), researchers estimated the median age of death due to seasonal influenza-related illness in the United States to be 76.

 

In contrast, pandemic influenza strains, at least during the first few years after their introduction, often produce a dramatic `age shift’ downward in mortality. 

 

The CDC’s estimate of average and median age of death due to the 2009 Pandemic virus reads:

 

Based on two CDC investigations of confirmed 2009 H1N1-related deaths that occurred during the spring and fall of 2009, the average age of people in the U.S. who died from 2009 H1N1 from April to July of 2009 was 40. The median age of death for this time period was 43. From September to October of 2009, the average age of people in the U.S. who died from 2009 H1N1 was 41, and the median age was 45.

 

An even more pronounced `age shift’ was observed during the 1918 Spanish Flu, which exacted its heaviest toll among those aged 25 to 34 – an age group that would normally be expected to weather the illness better than any other.

 

The infamous `W shaped curve’ of the 1918 pandemic clearly shows that the death rates among those in their teens, 20s, and 30s was much higher than was normally seen in previous influenza years. Those over the age of 65, however, saw a reduction in mortality during the pandemic.

 

Similarly, the H5N1 avian flu virus has shown a disturbing predilection for younger victims, as illustrated by the following chart showing the ages of H5N1 cases in China over the past decade (see WHO Perspective Human infections with avian influenza A(H7N9) virus in China: preliminary assessments of the age and sex distribution).

.

 

Although not universally embraced, the Cytokine Storm theory has been adopted by many researchers as the most likely reason why the young, and healthy – those with presumably the most robust immune systems – would suffer disproportionately with some pandemic flu strains.

 

Somewhat surprisingly, we haven’t seen this age shift during the first wave of H7N9 avian flu cases in China this spring.  We’ll have to see if this trend continues if, and when, the virus re-emerges.

 

 

 

As you can imagine, many researchers and doctors are looking for effective ways to safely dampen runaway immune responses as a possible treatment for pandemic influenza.

 

This is particularly important as most of the world would have little hope of seeing a vaccine for a pandemic flu during the first year or two of its arrival.

 

Dr. David Fedson – former Professor of Medicine at the University of Virginia School of Medicine and formerly Director of Medical Affairs, Aventis Pasteur MSD - has long championed the idea that we should be looking at statins for pandemic flu, which he believes may help modulate the immune response.

 

If they can be proved effective, statins have the advantage of being cheap, easy to manufacture and distribute, and have relatively few side effects.

 

The problem is, while some studies on statins and pneumonia have yielded promising results, not all of the research is in agreement. Complicating matters, since many statins are now generic, there is little financial incentive for drug companies to fund expensive research.

 

You can read about the potential for statin therapy in the blogs below.

 

Study: Statins, Influenza, & Mortality

Another Study On Statins And Pneumonia

Dr. David Fedson: The Case For Using Statins In A Pandemic

Statins Revisited

 

There are other approaches under investigation as well. 

 

In 2011, in Study: Calming The Cytokine Storm, we looked at research from The Scripps Research Institute  that found a protein located on the surface of endothelial cells, called S1P1, to be largely responsible for flu-associated cytokine storms.

 

While a specific drug to target this protein is likely a long way off, their discovery provides new avenues for research into dampening the cytokine response.

 

This latest study in the American Journal of Pathology provides some of the strongest evidence we’ve seen on the impact of cytokine production in the pathogenesis of influenza.

 

Results that will likely spur additional interest in finding ways to moderate the cytokine storm.

 

For a better understanding of the pathogenesis of influenza, the innate immune system, and the role of cytokines I would invite you to read my 3-part look at the Baskin study from 2009.

Dissecting the Influenza Pathogenesis Study Pt. 1

Dissecting the Influenza Pathogenesis Study Pt. 2

Dissecting the Influenza Pathogenesis Study Pt.3

Nature: H7N9 Pathogenesis and Transmissibility In Ferrets & Mice

Ideally, the well-protected HCW (Health Care Worker) working in an H7N9 environment would be wearing an N95 mask, gloves, gown and eye protection.

 

 

# 7467

 

The Journal Nature has published two H7N9 studies today, each providing a look at just how well adapted the H7N9 virus is to mammals, and offering clues as to what capabilities it still needs to acquire in order for it to become a genuine pandemic threat.

 

One of the studies was conducted by researchers at the CDC, while the other was conducted by an international team led by Yoshihiro Kawaoka of the University of Wisconsin-Madison and the University of Tokyo.

 

I’ll address the CDC study in this post, and will do the Kawaoka study in later tonight or in the morning. Sadly, much of this study is behind a pay wall, but we do have the abstract, and a fairly detailed summary posted on the CDC’s Website.

 

Pathogenesis and transmission of avian influenza A (H7N9) virus in ferrets and mice

Jessica A. Belser, Kortney M. Gustin, Melissa B. Pearce, Taronna R. Maines, Hui Zeng, Claudia Pappas, Xiangjie Sun, Paul J. Carney, Julie M. Villanueva, James Stevens, Jacqueline M. Katz & Terrence M. Tumpey

(Excerpt)

Here we assess the ability of A/Anhui/1/2013 and A/Shanghai/1/2013 (H7N9) viruses, isolated from fatal human cases, to cause disease in mice and ferrets and to transmit to naive animals. Both H7N9 viruses replicated to higher titre in human airway epithelial cells and in the respiratory tract of ferrets compared to a seasonal H3N2 virus. Moreover, the H7N9 viruses showed greater infectivity and lethality in mice compared to genetically related H7N9 and H9N2 viruses.

 

The H7N9 viruses were readily transmitted to naive ferrets through direct contact but, unlike the seasonal H3N2 virus, did not transmit readily by respiratory droplets. The lack of efficient respiratory droplet transmission was corroborated by low receptor-binding specificity for human-like α2,6-linked sialosides.

 

Our results indicate that H7N9 viruses have the capacity for efficient replication in mammals and human airway cells and highlight the need for continued public health surveillance of this emerging virus.

 

Of particular interest, while the virus did not transmit easily via respiratory droplets between ferrets, once acquired, the virus replicated at a much higher rate than one generally sees with seasonal flu. 

 

And while not a complete surprise, this study also seems to confirm the potential for transocular transmission of the H7N9 virus. 

 

We’ve known for more than a decade that H7 viruses often cause conjunctivitis (see MMWR: Mild H7N3 Infections In Two Poultry Workers - Jalisco, Mexico), and other studies have suggested possibility of acquiring influenza virus infection through the eyes.

 

We looked at transocular influenza transmission studies in both 2010 (see I Only Have Eyes For Flu) and again in  2011 (see PPEs & Transocular Influenza Transmission).

 

The  CDC’s Interim H7N9 Infection Control Guidelines, released last April, called for fitted N95 respirators, gowns, gloves, and eye protection as a minimum level of PPEs (personal protective equipment) for all HCWs who may have contact with potential or confirmed H7N9 patients.

 

Here is the CDC’s summary of the findings:

 

CDC Study Analyzes H7N9 Viruses’ Disease Characteristics and Transmissibility

A study published today in Nature by CDC researchers presents findings from animal studies conducted by CDC to better understand the transmissibility and disease characteristics of influenza A (H7N9) viruses isolated in China in late March. Understanding the properties of H7N9 viruses that contribute to human disease and the capacity of these viruses to spread between people is a critical component of the public health response to this emerging disease threat.

 

The study’s key findings indicate that H7N9 viruses are capable of causing infection in a direct contact animal model, but the viruses would need to undergo additional adaptation to spread more easily by droplets or through the air. Person to person transmission, especially by respiratory droplet transmission (such as through coughs and sneezes) is a necessary precondition for the virus to become capable of causing a pandemic.

 

These findings support the conclusions drawn from China’s investigations of human H7N9 cases so far. China has found no clear evidence of sustained human-to-human spread of the H7N9 virus. Human cases of H7N9 virus infection in China reported have been primarily associated with exposure to infected poultry. Currently no human cases of H7N9 virus infection have been reported in the United States.

 

The paper describes the results of multiple studies conducted on two H7N9 viruses obtained from fatal human H7N9 cases from China. The studies were conducted in ferrets, mice and human epithelial cells. Ferrets are considered the best small mammal for studying flu virus infection and are commonly used as a tool for the risk assessment of emerging flu viruses that may pose a risk to public health.

 

The ferret studies revealed that the H7N9 viruses spread readily among ferrets placed in the same cage. However, the viruses were less capable of respiratory droplet transmission, which the researchers tested by placing infected ferrets in cages adjacent to cages housing naive ferrets. Compared to a human seasonal flu virus from last season, the H7N9 viruses were considerably less capable of transmitting by the respiratory route.

 

Other study findings indicated that the H7N9 virus did not cause severe disease in the ferrets and did not spread systemically to the spleen, kidney, liver, or intestinal tract. The lack of systemic spread by H7N9 is different from H5N1 (another avian influenza virus that can cause severe disease in humans). Systemic spread is considered an indicator of severe disease.

 

In addition to ferrets, CDC researchers also studied the H7N9 virus in mice. Compared with ferrets, the virus caused more lethal illness in the mice, and the virus was more capable of replicating in the lungs of mice compared with other avian and human seasonal viruses tested in the study. Also notable, the H7N9 virus was able to easily infect mice, whereas human seasonal flu viruses typically require prior host adaptation to be able to efficiently infect mice.

 

The mouse studies also revealed that H7N9 virus can pass through the eyes to infect the respiratory tract. As a result, the eyes represent a possible portal of entry for the H7N9 virus. This finding supports CDC’s existing flu recommendations to avoid touching the eyes, nose or mouth to help prevent spread of germs. It also supports the recommendation for health care providers to wear eye protection when caring for patients with confirmed or suspected H7N9 infection.

 

The remaining study findings analyzed the H7N9 virus’s ability to replicate in cells derived from human epithelial cells. Epithelial cells are found in the human respiratory tract and are the primary site where flu viruses replicate in humans. CDC researchers found that the H7N9 virus demonstrated a 20- to 400-fold increase in replication at the two-day mark when compared with a human seasonal flu virus and two other avian flu viruses genetically related to the H7N9 virus. Compared with a human seasonal H3N2 virus, the H7N9 virus exhibited an 80,000-fold increase in replication at 24 hours.

 

The studies in mice and ferrets corroborated this finding, as considerably more H7N9 virus was produced and detected in the respiratory tracts of ferrets and mice compared with the amount of virus produced by seasonal flu virus infection. This suggests the H7N9 viruses have the capacity to reproduce quickly and produce a large amount of virus within the cells of mammals and human airway cells. However, the viruses’ ability to replicate was determined to be better suited to the higher temperatures found in the lower airways (lungs) versus the lower temperatures found in the upper airways of mammals.

The study, entitled “Pathogenesis and transmission of A (H7N9) avian influenza virus in ferrets and mice” is available for online viewing via Nature’s website.

Gastrointestinal Bird Flu Infection In Cats

 

 

 

# 5969  

 

 

An intriguing study from the Journal of Virology this morning that looks at an unusual route of infection  - and resultant pathogenesis – of the H5N1 virus in cats (My thanks to Tetano on FluTrackers for posting this link).

 

The study is called:

 

Marked endotheliotropism of highly pathogenic avian influenza virus H5N1 following intestinal inoculation in cats.

November 2011, doi: 10.1128/​JVI.06375-11

Reperant LA, van de Bildt MW, van Amerongen G, Leijten LM, Watson S, Palser A, Kellam P, Eissens AC, Frijlink HW, Osterhaus AD, Kuiken T.

 

 

Endotheliotropism is simply a 12-dollar word meaning an affinity for endothelial cells which are the cells that line the interior surface of blood vessels throughout the body.

 

 

Photo Credit – Wikipedia

 

From the abstract (the entire study is behind a pay wall), we learn that researchers gave cats enteric coated capsules containing H5N1 infected chicken liver in order to deliver the virus directly to the intestine.

 

(EXCERPT)

Intestinal inoculation of HPAIV H5N1 resulted in fatal systemic disease. The spread of HPAIV H5N1 from the lumen of the intestine to other organs took place via the blood and lymphatic vascular systems but not via neuronal transmission.

 

Remarkably, the systemic spread of the virus via the vascular system was associated with massive infection of endothelial and lymphendothelial cells, resulting in widespread hemorrhages.

 

As the abstract points out, this resulted in a disease process similar to what is seen in terrestrial poultry, and differs greatly from the pathogenesis normally seen from respiratory tract infection.

 

The authors conclude that:

 

The marked endotheliotropism of the virus following intestinal inoculation indicates that the pathogenesis of systemic influenza virus infection in mammals may differ according to the portal of entry.

 

 

The surprise here isn’t that cats (and other mammals) can acquire the H5N1 virus via a non-respiratory route (we’ve known that for some time), it is the discovery of the manner in which the virus spread systemically; via massive infection of endothelial and lymph endothelial cells.

 

While anything that betters our understanding of the H5N1 virus is a good thing, this discovery may eventually have practical applications as well. 

 

Should an outbreak occur, gastrointestinal H5N1 infection (with its atypical pathogenesis) may require a different treatment regimen than is currently used with a respiratory infections.

 

An oral route of infection from the H5N1 virus has been suggested over the years, with several human cases being linked to the consumption of infected poultry.

 

One of the earliest indications that H5N1 could bind and flourish in the human gastrointestinal tract comes from this study involving the deaths of a brother and sister in Vietnam in 2004.

 

Fatal avian influenza A (H5N1) in a child presenting with diarrhea followed by coma.

de Jong MD, Bach VC, Phan TQ, Vo MH, Tran TT, Nguyen BH, Beld M, Le TP, Truong HK, Nguyen VV, Tran TH, Do QH, Farrar J.

 

 

In June of 2007, we got a report (see Atypical Presentations of H5N1)  out of Indonesia, of a child infected with H5N1 but that presented without respiratory symptoms.

 

A year later, in a large review of Chinese bird flu patients (see Clinical Case Review Of 26 Chinese H5N1 Patients), we find several mentions of gastrointestinal involvement as well.

 

Diarrhea was present in only two H5N1 cases at admission, but developed in a quarter of cases during hospitalization. Diarrhea was a common presenting symptom among H5N1 cases in Vietnam  and Thailand , but was reported infrequently among cases in Hong Kong SAR, China and Indonesia.

 

H5N1 virus and viral RNA have been detected in feces and intestines of human H5N1 cases. Whether the gastrointestinal tract is a primary site for H5N1 virus infection is currently unknown.

 

In 2010, we saw a study (see H5N1 Can Replicate In Human Gut) that provided even more evidence that the bird flu virus can thrive in the human gastrointestinal system.

 

We’ve also seen numerous reports over the years of cats infected with the H5N1 virus after consuming infected birds.  The following comes from a World Health Organization GAR report from 2006.

 

 

H5N1 avian influenza in domestic cats

28 February 2006

(EXCERPTS)

Several published studies have demonstrated H5N1 infection in large cats kept in captivity. In December 2003, two tigers and two leopards, fed on fresh chicken carcasses, died unexpectedly at a zoo in Thailand. Subsequent investigation identified H5N1 in tissue samples.

 

In February 2004, the virus was detected in a clouded leopard that died at a zoo near Bangkok. A white tiger died from infection with the virus at the same zoo in March 2004.

 

In October 2004, captive tigers fed on fresh chicken carcasses began dying in large numbers at a zoo in Thailand. Altogether 147 tigers out of 441 died of infection or were euthanized. Subsequent investigation determined that at least some tiger-to-tiger transmission of the virus occurred.

 

In 2006, Dr. C.A. Nidom demonstrated that of 500 cats he tested in and around Jakarta, 20% had antibodies for the bird flu virus.  

 

In 2007 the FAO warned that:

 

Avian influenza in cats should be closely monitored

So far no sustained virus transmission in cats or from cats to humans

 

For an overview of a number of other cases involving cats, see Apparently They Didn't Get The Memo.

 

And it isn’t just the H5N1 virus which as shown some propensity for gastrointestinal involvement.

 

Seasonal A & B Influenza viruses, along with the 2009 H1N1 virus, have been looked at for exhibiting unusual gastrointestinal symptoms, albeit nowhere near as severe as described in today’s study.   

 

In January of 2010, in Influenza’s Gastrointestinal Connection, I wrote about a study that appeared in BMC Infectious Diseases, that looked at seasonal flu in pediatric patients. 

 

 

Influenza virus infection among pediatric patients reporting diarrhea and influenza-like illness

The detection of influenza viral RNA and viable influenza virus from stool suggests that influenza virus may be localized in the gastrointestinal tract of children, may be associated with pediatric diarrhea and may serve as a potential mode of transmission during seasonal and epidemic influenza outbreaks.

 

And lastly, during the 2009 pandemic, the CDC’s Interim guidance on Infection Control for the pandemic H1N1 Virus, warned:

 

Transmission of influenza through the air over longer distances, such as from one patient room to another, is thought not to occur. All respiratory secretions and bodily fluids, including diarrheal stools, of patients with 2009 H1N1 influenza are considered to be potentially infectious.

 

 

More evidence (as if we needed it) to show that influenza is a far more complex, and fascinating, virus than most people give it credit for.

PLoS One: Viremia In The 2009 H1N1 Pandemic Influenza

 

 

# 5868

 

 

Today, a fascinating study  that associates viremia, and a specific mutation (D222G/N) in the 2009 H1N1 virus, to more severe disease presentation.

 

Viremia simply refers to the presence of viruses in the blood stream.

 

While many viruses cause viremia (ie. Dengue, Chikungunya, WNV) – seasonal influenza, being primarily a respiratory disease, isn’t usually one of them.

 

But as we’ve seen demonstrated over the past several years, the pathogenesis of the 2009 H1N1 virus sometimes deviated from what one normally sees with seasonal flu.

 

Recently, in mBio: Lethal Synergism of H1N1 Pandemic Influenza & Bacterial Pneumonia we saw how novel H1N1 infection exacerbated lung damage due to bacterial co-infection, when seasonal flu did not.

 

In April of 2010, in There’s No Flu Like A New Flu, I listed many of the other differences observed between seasonal flu and the novel H1N1 virus, including:

 

• The Age shift to under-65s seeing the greatest number of fatalities (see Study: Years Of Life Lost Due To 2009 Pandemic).

 

• Research out of Hong Kong that discovered that the novel H1N1 virus – unlike seasonal flu – easily infect and replicate in the conjunctival tissues of the eye  (see I Only Have Eyes For Flu).

 

• Novel H1N1’s unusually high rate of gastro-intestinal symptoms (see The Lancet study Clinical characteristics of paediatric H1N1 admissions in Birmingham, UK).

 

• And reports of patients that presented with neurological symptoms including unexplained seizures and altered mental status (see Japan: Influenza Related Encephalopathy).

 

 

Although the H1N1 pandemic virus of 2009 proved to be relatively mild for the vast majority of those infected, for a very small percentage, it produced serious and sometimes life-threatening illness.

 

Add to this the fact that this flu, unlike seasonal flu, was also frequently detected in companion animals, and it certainly appears that something was inherently different about the 2009 H1N1 virus.

 

Today, a new study appears in PLoS One that adds more weight to that argument. The open access study is called:

 

 

Clinical and Virological Factors Associated with Viremia in Pandemic Influenza A/H1N1/2009 Virus Infection

 

Herman Tse, Kelvin K. W. To, Xi Wen, Honglin Chen, Kwok-Hung Chan, Hoi-Wah Tsoi, Iris W. S. Li, Kwok-Yung Yuen

Positive detection of viral RNA in blood and other non-respiratory specimens occurs in severe human influenza A/H5N1 viral infection but is not known to occur commonly in seasonal human influenza infection.

Recently, viral RNA was detected in the blood of patients suffering from severe pandemic influenza A/H1N1/2009 viral infection, although the significance of viremia had not been previously studied. Our study aims to explore the clinical and virological factors associated with pandemic influenza A/H1N1/2009 viremia and to determine its clinical significance.

Methodology/Principal Findings

Clinical data of patients admitted to hospitals in Hong Kong between May 2009 and April 2010 and tested positive for pandemic influenza A/H1N1/2009 was collected. Viral RNA was detected by reverse-transcription polymerase chain reactions (RT-PCR) targeting the matrix (M) and HA genes of pandemic influenza A/H1N1/2009 virus from the following specimens: nasopharyngeal aspirate (NPA), endotracheal aspirate (ETA), blood, stool and rectal swab.

Stool and/ or rectal swab was obtained only if the patient complained of any gastrointestinal symptoms. A total of 139 patients were included in the study, with viral RNA being detected in the blood of 14 patients by RT-PCR.

The occurrence of viremia was strongly associated with a severe clinical presentation and a higher mortality rate, although the latter association was not statistically significant. D222G/N quasispecies were observed in 90% of the blood samples.

Conclusion

Presence of pandemic influenza A/H1N1/2009 viremia is an indicator of disease severity and strongly associated with D222G/N mutation in the viral hemagglutinin protein.

 

The authors propose several theories as to why the virus was detected in the bloodstream, and gastrointestinal tract.

 

The detected viral RNA in blood could either reflect extensive pulmonary damage with phagocytic uptake of virus-infected cells or true infection of monocyte-derived dendritic cells and macrophages [26].

On the contrary, viruses in the stool may originate from swallowed respiratory secretions, although viral replication in the epithelial tissue along the gastrointestinal tract cannot be ruled out entirely.

 

 

The significance of the H222G/N mutation in the 2009 H1N1 virus has been vigorously debated for nearly two years.

 

The `Norway’ or D222G/N (D225G/N in influenza H3 Numbering) mutation cited in this study was first linked to more severe disease by Norwegian Scientists in November 2009, although patients carrying these strains can have mild illness as well. 

 

While we’ve covered this territory a number of times over the past year, a brief (and hopefully simple) review is in order. If you are up to speed on receptor binding, and the history of the D222G/N variant, feel free to skip the next section.

 

This mutation involves a single amino acid change in the HA1 gene at position 222 from aspartic acid (D) to glycine (G) (or asparagine (N)).

 

The pdmH1N1 virus carrying this mutation appears to bind more readily to receptor cells (α2-3) found deeper in the lungs, whereas unmutated seasonal flu strains bind preferentially to the (α2-6) receptor cells found in the upper airway.

 

A virus’s ability to bind to specific cells is controlled by its RBD or Receptor Binding Domain; an area of its genetic code that allows it to attach to, and infect, specific types of host cells.

(A Very Simplified Illustration of RBDs)

Like a key into a padlock, the RBD must `fit’ in order to open the cell to infection.

 

The evidence for the D222G/N  amino acid substitution driving increased virulence has been mixed, with the World Health Organization, the CDC, and the HPA continuing to investigate. 

 

Complicating matters - viruses can have multiple amino acid changes – and it may be the combination of these changes can unpredictably (at least for now) alter the virus’s behavior. 

 

Since the D222G/N mutation has been found in patients showing mild disease, it may be that a second (or third) mutation elsewhere in the virus – in concert with D222G/N – is required to produce greater virulence.

 

There is simply a lot we don’t know yet.

 

During the first week of January, Eurosurveillance  printed a study looking at fatal and non-fatal cases of influenza in the UK (see Eurosurveillance: Analysis Of Fatal H1N1 Cases In The UK). 

 

Ellis et al. reported that almost all of the virus samples tested in fatal and non-fatal cases during the early wave of the 2010/11 influenza season showed aspartic acid (D) at position 222.

 

In other words, no `Norway’ mutation.

Towards the end of January 2011, Eurosurveillance published a letter from an Italian researcher who had found a high percentage of D222G/N mutations in severely ill patients (43%)  – particularly when taking virus samples from the lower respiratory tract (lungs).

 

In a reply, the authors of the original study concede that in many cases, only upper respiratory swabs were available for this analysis, and that when possible, samples from the lower respiratory system would be useful.

 

This scholarly debate wasn’t over, as Ellis et al. state in their reply:

 

The selection and emergence of the D222G mutation as a cause or consequence of more severe lower respiratory tract infection is still to be resolved.

 

Emergence of this mutant is likely to exacerbate severity of disease, but by itself, may be neither necessary nor sufficient to account for a severe disease outcome, which is invariably a balance between virus virulence factors and host immune response capability.

 

And so the debate has continued, with some scientists believing the `Norway’ mutation causes more severe illness, while others are less certain.

 

It will take more samples, more research, and more time to determine the truth in the matter.

 

Still, this study is another step forward in our understanding of the unusual pathogenesis, and genetic evolution, of the pandemic H1N1 virus.

 

And since we’ve seen similar severe lung damage, and scattered reports of viremia, among the small number of H5N1 `bird flu’ cases that have been examined, what we can learn about the 2009 H1N1 virus may provide clues on how to tackle a more severe pandemic in the future.

mBio: Lethal Synergism of H1N1 Pandemic Influenza & Bacterial Pneumonia

 

 

 

CDC PHIL - Photomicrograph of Streptococcus (Diplococcus) pneumoniae bacteria

 

# 5856

 

 

While the vast majority of people who contracted the H1N1 pandemic flu of 2009 recovered without incident, a very small minority saw severe – sometimes fatal – illness. 

 

Often during 2009 we saw reports of severe lung damage. Damage that in some cases was compared to what has been seen in H5N1 bird flu and during the great pandemic of pandemic of 1918.

 

A few of the stories from back then include:

 

In early September of 2009, in Pathology Of Fatal H1N1 Lung Infections, we looked at a report by Helen Branswell that looked early autopsy results.

 

 

Lung damage in fatal swine flu cases more bird flu than seasonal flu: expert

By Helen Branswell Medical Reporter (CP) 

TORONTO — The lungs of people who have died from swine flu look more like those of the victims of H5N1 avian influenza than those of people who succumb to regular flu, the chief of infectious diseases pathology at the U.S. Centers for Disease Control says.

 

Study of about 70 fatal H1N1 cases so far also reveals there may be more incidences of co-infections with bacteria than was earlier thought, Dr. Sherif Zaki told The Canadian Press in an interview.

 

A couple of weeks later in More On The Pathology Of Novel H1N1, we saw a report by Maggie Fox, then Health and Science Editor for Reuters, who brought us more details of this  story, including comments by Dr. Sherif Zaki of the U.S. CDC who  stated that "This is almost exactly what we see with avian flu. This looks like avian flu on steroids."

 

That same month, I wrote about the use of ECMO (Extracorporeal Membrane Oxygenation) in the treatment of severe lung injury in H1N1 victims in The ECMO Option.

 

In early December (see NIH: Post Mortem Studies Of H1N1) the NIH announced the results of a series of autopsies conducted on H1N1 victims in New York City over the summer, which are chronicled in the Archives of Pathology & Laboratory Medicine.

 

The NIH put together a press release, which provided highlights of the study.

 

FOR IMMEDIATE RELEASE
Monday, Dec. 7, 2009

Media Contact: Anne A. Oplinger
(301) 402-1663
niaidnews@niaid.nih.gov

New York Autopsies Show 2009 H1N1 Influenza Virus Damages Entire Airway

In fatal cases of 2009 H1N1 influenza, the virus can damage cells throughout the respiratory airway, much like the viruses that caused the 1918 and 1957 influenza pandemics, report researchers from the National Institutes of Health (NIH) and the New York City Office of Chief Medical Examiner. The scientists reviewed autopsy reports, hospital records and other clinical data from 34 people who died of 2009 H1N1 influenza infection between May 15 and July 9, 2009. All but two of the deaths occurred in New York City. A microscopic examination of tissues throughout the airways revealed that the virus caused damage primarily to the upper airway—the trachea and bronchial tubes—but tissue damage in the lower airway, including deep in the lungs, was present as well. Evidence of secondary bacterial infection was seen in more than half of the victims.

 

The team was led by James R. Gill, M.D., of the New York City Office of Chief Medical Examiner and New York University School of Medicine, and Jeffery K. Taubenberger, M.D., Ph.D., of the National Institute of Allergy and Infectious Diseases (NIAID) at NIH. The findings are reported in the Archives of Pathology & Laboratory Medicine, now available online and scheduled to appear in the February 2010 print issue.

<SNIP>

“This pattern of pathology in the airway tissues is similar to that reported in autopsy findings of victims of both the 1918 and 1957 influenza pandemics,” notes Dr. Taubenberger.

 

While many people continued to insist that swine flu was no worse than seasonal flu, obviously something was different in the way it produced severe lung damage.  

 

A year into the pandemic, I summarized many of the ways that the 2009 H1N1 virus differed from seasonal flu in There’s No Flu Like A New Flu.

 

While the overall incidence of these complications was relatively low, those who suffered from them often experienced extremely severe illness.

 

 

All of which serves as prelude to an open access study, published today in mBio, called:

 

Lethal Synergism of 2009 Pandemic H1N1 Influenza Virus and Streptococcus pneumoniae Coinfection Is Associated with Loss of Murine Lung Repair Responses

John C. Kash^a, Kathie-Anne Walters^b, A. Sally Davis^a, Aline Sandouk^a, Louis M. Schwartzman^a, Brett W. Jagger^a, Daniel S. Chertow^a, Qi Li^a, Rolf E. Kuestner^b, Adrian Ozinsky^b, and Jeffery K. Taubenberger^a

 

 

The entire study is available, and is well worth reading, but briefly:

 

Scientists at NIAID and the Institute for Systems Biology (ISB) infected experimental mice with both seasonal flu and the 2009 H1N1 pandemic flu, and after 48 hours exposed some of them to Streptococcus pneumoniae, one of the main causes of pneumonia.

 

Mice that were exposed only to the two flu strains showed expected flu symptoms, but all survived.

Mice that were exposed to seasonal flu and S. pneumoniae experienced minor lung damage, but once again, all survived.

 

But all of the mice infected with the pandemic H1N1 virus, and S. pneumoniae showed severe weight loss, lung damage, and 100% mortality

 

Excerpts from the press release below explain what else they found:

 

American Society for Microbiology

 

2009 H1N1 pandemic flu more damaging to lungs, opens opportunities for bacterial infection

(EXCERPT)

The lung tissues of the dead mice revealed that the alveoli were severely inflamed and the surfaces of the bronchioles were wiped clean of the protective layer of cells called the epithelium. There was also increased bacterial replication in the lungs of the co-infected mice, a sign that the bacteria were thriving there.

 

Looking at the mouse genes that were expressed during infection revealed more details about how the pandemic influenza virus sets the stage for lethal bacterial infections. Mice infected with the pandemic flu virus and S. pneumoniae had a similar inflammatory response as the other mice, but they lack responses that would repair and regenerate their damaged epithelial cells, those protective tissues that would otherwise keep bacteria from penetrating to deeper layers of tissue.

 

All these factors add up to big problems in the lung: as compared with seasonal flu, infection with the pandemic strain of flu was associated with more extensive damage to the epithelium that requires more extensive tissue repair. This opens the body up to attack from bacterial invaders, including Streptococcus pneumoniae.

(Continue . . . )

 

So not only did this duel infection lead to greater lung damage, and increased bacterial replication, it also disabled the lung’s ability to repair itself.

 

Since it can take 6 months or longer to develop a vaccine for a novel influenza virus, these results may suggest a bigger role for the 23-valent Pneumonia vaccine (PPVSV) during a future pandemic. 

 

More than a year after the end of the 2009 pandemic, scientists are still uncovering basic information about how pandemic flu differs from seasonal flu. 

 

With luck, work like this will provide better ways for us to deal with an outbreak, when the next one arrives.

H1N1 & The Non-Protective Antibody Response

 

 

 

# 5117

 

 

Normally, with seasonal influenza, it is the elderly and frail that make up 90% of the hospitalizations and deaths each year. The average age of death from seasonal flu in the US has been estimated to be about 76.

 

The mean age of death from the 2009 H1N1 virus,  has been calculated to be half that, or 37.4 years (see Study: Years Of Life Lost Due To 2009 Pandemic).

 

Although the 2009 pandemic was `mild’ in terms of the total number of people killed, it was anything but mild in the way it attacked a small percentage of – mostly young adult – patients.

 

A few blogs from the past year on how novel H1N1 presented differently than seasonal flu:

 

Canada: H1N1 Sent More To ICU Than Seasonal Flu

NIH: Post Mortem Studies Of H1N1

Pathology Of Fatal H1N1 Lung Infections

 

While the reasons why were not clear, it was apparent that in a small subset of patients, H1N1 produced severe – sometimes fatal – lung damage.

 

We’ve an intriguing study published today in the journal Nature Medicine that theorizes why those between the ages of 20 and 50 saw more severe illness from the pandemic than those who were either younger or older.

 

The culprit, researchers suggest, was a non-protective antibody response, that they believe attacked the patient instead of the virus.

 

First a link to the study (which is behind a pay wall) & abstract, followed by a few short excerpts from a press release describing some of the findings.  After that, a link to a sciencemag.org story on the study, and lastly, a link to a Nature News feature story about this study.

 

 

Severe pandemic 2009 H1N1 influenza disease due to pathogenic immune complexes

Ana Clara Monsalvo,Juan P Batalle,M Florencia Lopez,Jens C Krause,Jennifer Klemenc,Johanna Zea Hernandez,Bernardo Maskin,Jimena Bugna,Carlos Rubinstein,Leandro Aguilar,Liliana Dalurzo, Romina Libster, Vilma Savy,Elsa Baumeister,Liliana Aguilar, Graciela Cabral,Julia Font,Liliana Solari,Kevin P Weller,Joyce Johnson,Marcela Echavarria,Kathryn M Edwards,James D Chappell,James E Crowe Jr,John V Williams,Guillermina A Melendi& Fernando P Polack et al.

 

The press release (which I’ve only excerpted), comes from Vanderbilt University Medical Center.

 

Over-reactive immune system kills young adults during pandemic flu

(Excerpts)

In a paper published Dec. 5 in Nature Medicine, Fernando Polack, M.D., the Cesar Milstein Associate Professor of Pediatrics at Vanderbilt, and colleagues in Argentina and Nashville provide a possible explanation for this alarming phenomenon of pandemic flu. The study's findings suggest people are made critically ill, or even killed, by their own immune response.

 

"Every time there is an influenza pandemic there is a large proportion of younger, or middle-aged adults who die. We have always explained these deaths, based on presumed virulence of virus, or getting bacterial infection at the same time. We now have vaccines and antibiotics, but still we see middle-aged individuals who die," Polack said.

 

<SNIP>

 

"We have seen this before. Where non-protective antibody responses are associated with an immune-based disease in the lung," Polack said.

 

Polack has previously published evidence that a first-line immune response, primed by an imperfect antibody, can overreact in a violent and uncontrolled fashion. Patients die from lung damage inflicted by their own immune system. A molecule called C4d, a product of this biochemical cascade (the complement system), is a marker for the strength of the response.

 

In adults who died during the 2009 H1N1 pandemic, high levels of C4d in lung tissues suggest a massive, potentially fatal activation of the complement system.

(Continue . . . )

 

 

You can find a pretty good overview of this study in an article that appears today in Science Magazine.

 

How Swine Flu Killed the Healthy

by Kristen Minogue on 5 December 2010, 1:00 PM

But perhaps the most complete summary can be found in this Nature News story, which also contains an interesting caveat about what all of this could mean for the development of `universal’ flu vaccines. 

Exposure to seasonal flu weakened armour against H1N1

Faulty antibodies from previous infections boosted severity of swine flu in the middle-aged.

Study: Receptor Binding Changes With H1N1 D222G Mutation

 

 

 

# 4909

 

 

Although it’s nestled behind a pay wall at the Journal of Virology, the abstract from a study published ahead of print this week in the Journal of Virology gives us a tantalizing glimpse at research conducted on the D222G mutation that has been found in some isolates of the pandemic H1N1 (pdmH1N1) virus.

 

While we’ve discussed the D222G mutation before, this is an obscure enough subject as to make a review helpful.  I’ll keep it simple (essential so that I can follow, as well), so real scientists may wish to skim or skip ahead.

 

The `Norway’ or D222G (D225G in influenza H3 Numbering) mutation first announced by Norwegian Scientists last November has sparked repeated speculation that it might be associated with increased virulence.

 

This mutation had actually been detected months earlier, and in many other countries, but Norway was the first country to announce a possible link between that mutation and greater virulence.

 

This mutation involves a single amino acid change in the HA1 gene at position 222 from aspartic acid (D) to glycine (G).

 

The World Health Organization’s take on this mutation has been pretty consistent.  It is worth following, and studying, but there is no evidence (as yet) that it poses a substantial public health hazard.

 

In January, in a blog entitled WER Review: D222G Mutation In H1N1, I quoted the latest WHO report that stated:

 

`Based on currently available virological, epidemiological and clinical information, the D222G substitution does not appear to pose a major public health issue.’

 

This view is not universally held, however. There are some who have maintained that that the WHO is underestimating the impact of this mutation.

 

In March of this year, researchers from the Norwegian Institute of Public Health in Oslo reported that they found the mutation in 11 of 61 severe illness cases that they analyzed, but that it was not found in any of the 205 mild cases they looked at  (see CIDRAP Report On The H1N1 Mutation Debate).

 

The WHO WER Review reported that the overall prevalence of D222G was <1.8% (52 detections among >2755 HA sequences) in contrast to a rate of 7.1% in fatal cases. The WHO paper also reported on the occurrence of  two other mutations at this amino acid position, D222E and D222N, although their significance is unclear.

 

While this may sound like fairly damning evidence, it should be noted that mild cases have been detected with this D222G mutation in other studies, and most of the severe and fatal cases of pandemic H1N1 that have been examined did not have this mutation.

 

Which brings us to today’s study, which features an impressive pedigree and some very familiar names including Ab Osterhaus and  Ron Fouchier of the Erasmus Medical Center in Rotterdam.

 

This study was also supported by researchers from the Mt. Sinai School of Medicine in New York, the NIH, the University of Cambridge, the University of Maryland . . . among others.

 

First the abstract (hat tip Tetano on FluTrackers) slightly reformatted for readability, then a little discussion.

 

Virulence-associated substitution D222G in hemagglutinin of 2009 pandemic influenza A(H1N1) virus affects receptor binding.

Chutinimitkul S, Herfst S, Steel J, Lowen AC, Ye J, van Riel D, Schrauwen EJ, Bestebroer TM, Koel B, Burke DF, Sutherland-Cash KH, Whittleston CS, Russell CA, Wales DJ, Smith DJ, Jonges M, Meijer A, Koopmans M, Rimmelzwaan GF, Kuiken T, Osterhaus AD, Garcia-Sastre A, Perez DR, Fouchier RA.

Abstract

The clinical impact of the 2009 pandemic influenza A(H1N1) virus (pdmH1N1) has been relatively low. However, amino acid substitution D222G in the hemagglutinin of pdmH1N1 has been associated with cases of severe disease and fatalities.

 

Here, D222G was introduced in a prototype pdmH1N1 by reverse genetics, and the effect on virus receptor binding, replication, antigenic properties, and pathogenesis and transmission in animal models was investigated.

 

pdmH1N1 with D222G caused ocular disease in mice without further indications of enhanced virulence in mice and ferrets. pdmH1N1 with D222G retained transmissibility via aerosols or respiratory droplets in ferrets and guinea pigs.

 

The virus displayed changes in attachment to human respiratory tissues in vitro, in particular increased binding to macrophages and type II pneumocytes in the alveoli and to tracheal and bronchial submucosal glands.

 

Virus attachment studies further indicated that pdmH1N1 with D222G acquired dual receptor specificity for complex α2,3- and α2,6-linked sialic acids. Molecular dynamics modeling of the hemagglutinin structure provided an explanation for the retention of α2,6 binding.

 

Altered receptor specificity of the virus with D222G thus affected interaction with cells of the human lower respiratory tract, possibly explaining the observed association with enhanced disease in humans.

 

 

Testing here was done on mice, ferrets, guinea pigs, and on human cells in vitro, and each demonstrated (sometimes small) pathogenic differences between the D222G-engineered and regular pdmH1N1 virus.

 

In mice and ferrets, the D222G virus showed no increase in virulence with the exception of `ocular disease’ in mice (I’m guessing conjunctivitis, but without access to the full article, I can’t be certain).

 

Given the low incidence of the D222G mutation in the wild (less than 1.8%), it has been suggested that this mutation might render the virus less contagious, but ferret and guinea pig studies showed it retained transmissibility via aerosols and respiratory droplets.

 

The increased binding to type II pneumocytes in the alveoli (in vitro) is a particularly interesting finding, given that this was also observed in the Baskin Study of H5N1 vs human H1N1 viruses.

 

Seasonal H1N1 viruses, when they invade the lungs, are more likely to attack type I pneumocytes which handle the gas exchange (02 and C02) between the lungs and the blood stream.  

 

Type II pneumocytes are responsible for the production of surfactant with antimicrobial, immunomodulatory, and anti-inflammatory properties, and are the lung’s primary mechanism for repairing damaged cells.

 

Damaging them can significantly degrade the lung’s ability to recover from injury.

 

Which brings us to the last major finding, that D222G acquired dual receptor specificity for complex α2,3- and α2,6-linked sialic acids.

 

Familiar territory to regular readers of this blog, but at the risk of repeating myself:

 

A virus’s ability to bind to specific cells is controlled by its RBD or Receptor Binding Domain; an area of its genetic code that allows it to attach to, and infect, specific types of host cells.

 

(Very Simplified Illustration of RBDs)

 

Like a key into a padlock, the RBD must `fit’ in order to open the cell to infection.

 

Avian adapted influenza viruses bind preferentially to Alpha 2,3 receptor cells, which are commonly found in the digestive tract of birds.

 

Human adapted viruses have an affinity for the alpha 2,6 receptor cell, which populate the upper airway and lungs.

 

Humans have some avian-like alpha 2,3 receptor cells, particularly deep in the lungs. 

 

This has been suggested as the reason that when humans contract H5N1, it is usually a deep lung infection.  It has also been postulated that H5N1’s deeper lung infections may reduce human-to-human transmission, as sneezing is a less common symptom.   

 

This duel receptor affinity with the D222G mutation may help explain why some patients that contract it also develop more serious lung infections.

 

The operative word here being `may’. 

 

The bottom line here is that so far, whatever pathogenic differences this mutation may spark, it has had a relatively small effect on the overall mortality and morbidity of this virus. 

 

That could change, of course, if this mutation were to become more common, or if complementary concurrent changes to the genetic structure of the virus were to further enhance its virulence.

 

All in all, a fascinating piece of research, and one that advances our knowledge of this mutation considerably.  No, it doesn’t answer the `big question’, of whether this mutation will end up becoming a significant public health threat.

 

But scientific knowledge is gained incrementally. 

 

So stay tuned.

 

 

For more on the Baskin Study (Early and sustained innate immune response defines pathology and death in nonhuman primates infected by highly pathogenic influenza virus by Carole Baskin et. al.  that appeared PNAS), which looked at the comparative pathogenesis of seasonal H1N1, a 1918-like H1N1, and the H5N1 virus, you may enjoy my 3-part series available at the following links:

 

 

Dissecting the Influenza Pathogenesis Study Pt. 1

Dissecting the Influenza Pathogenesis Study Pt. 2

Dissecting the Influenza Pathogenesis Study Pt. 3

Study: What Makes Avian Flu So Deadly

 

 

 

# 4830

 

 

Avian flu, particularly H5N1, has our attention because unlike regular influenza, it has a very high mortality rate.  Among those we know to have been infected, roughly 60% have died.

 

A rate well over 100 times higher than with regular flu.

 

Roughly 18 months ago we got a look at a study that compared the pathogenesis (disease progression) of non-human primates (macaques) infected with the H5N1 virus, seasonal flu, and with two altered viruses carrying genetic material from the 1918 Spanish Flu.

 

The study, entitled Early and sustained innate immune response defines pathology and death in nonhuman primates infected by highly pathogenic influenza virus by Carole Baskin et. al.  appeared PNAS (The Proceedings of the National Academy of Science).

 

At the time, I wrote a 3-part essay which attempted to put this complex study into layman’s terms. 

 

For those interested in learning more about the human immune system, cytokine production, and the pathogenesis of influenza the Baskin study and these three blogs may be of value:

 

Dissecting the Influenza Pathogenesis Study Pt. 1 (link fixed)

Dissecting the Influenza Pathogenesis Study Pt. 2

Dissecting the Influenza Pathogenesis Study Pt. 3

 

While the Baskin study is fascinating, and gives us considerable insight into what avian flu does to primates, it really doesn’t explain how or why.

 

To help us with those questions, researchers at Baylor College of Medicine and The University of Texas at Austin have studied the molecular structure of the avian flu virus, and have found 4 tiny amino acids dangling from the tip of a protein called NS1 that they believe at least partially explains this virulence.

Their research appears in the latest issue of the Journal of Virology.  You can access the abstract at the link below.

 

J. Virol. doi:10.1128/JVI.01278-10

The ESEV PDZ Binding-Motif of the Avian Influenza A Virus NS1 Protein Protects Infected Cells from Apoptosis through Directly Targeting Scribble

 

Hongbing Liu, Lisa Golebiewski, Eugene C. Dow, Robert M. Krug, Ronald T. Javier, and Andrew P. Rice

 

Admittedly, to non-scientists, this title is more than a little imposing.  

 

Apoptosis is programmed cellular death, while Scribble is a protein the body’s immune system uses to promote the early death (apoptosis) of virally infected cells. 

 

In this way, the immune system can help limit viral replication while it develops defenses (antibodies, cytokines, etc.) against the invader.

 

In the case of H5N1, the virus’s PDZ binding-motif works to  deactivates the host’s apoptosis defense mechanism, giving the virus a decided advantage.

 

Fortunately, for us mere mortals without a virology degree, we have a less technical background piece from the BCM news site which is well worth following the link and reading in its entirety. 

 

 

Avian flu virus protein turns off cell defense

HOUSTON -- (August 23, 2010) -- As the avian influenza A virus seeks to infect its bird hosts, it brings a special weapon to the fray – four tiny amino acids that hang off the end of a viral protein called NS1, said researchers from Baylor College of Medicine (www.bcm.edu) and The University of Texas at Austin in a report that appears in the current Journal of Virology.

 

This collection of molecules known as the PDZ binding-motif help make the avian virus – known to experts at H5N1 – particularly virulent and a threat to human populations everywhere.

(Continue . . . )