Scott McPherson's Web Presence

Over at Flutrackers, there is a thread regarding the prevalence of avian influenza in American birds. 

Avian influenza virus (AIV) is an important public health issue because pandemic influenza viruses in people have contained genes from viruses that infect birds. The H5 and H7 AIV subtypes have periodically mutated from low pathogenicity to high pathogenicity form. Analysis of the geographic distribution of AIV can identify areas where reassortment events might occur and how high pathogenicity influenza might travel if it enters wild bird populations in the US. Modelling the number of AIV cases is important because the rate of co-infection with multiple AIV subtypes increases with the number of cases and co-infection is the source of reassortment events that give rise to new strains of influenza, which occurred before the 1968 pandemic. Aquatic birds in the orders Anseriformes and Charadriiformes have been recognized as reservoirs of AIV since the 1970s. However, little is known about influenza prevalence in terrestrial birds in the order Passeriformes. Since passerines share the same habitat as poultry, they may be more effective transmitters of the disease to humans than aquatic birds. We analyze 152 passerine species including the American Robin (Turdus migratorius) and Swainson's Thrush (Catharus ustulatus).
Methods

We formulate a regression model to predict AIV cases throughout the US at the county scale as a function of 12 environmental variables, sampling effort, and proximity to other counties with influenza outbreaks. Our analysis did not distinguish between types of influenza, including low or highly pathogenic forms.

Results

Analysis of 13,046 cloacal samples collected from 225 bird species in 41 US states between 2005 and 2008 indicates that the average prevalence of influenza in passerines is greater than the prevalence in eight other avian orders. Our regression model identifies the Great Plains and the Pacific Northwest as high-risk areas for AIV. Highly significant predictors of AIV include the amount of harvested cropland and the first day of the year when a county is snow free.
Conclusions

Although the prevalence of influenza in waterfowl has long been appreciated, we show that 22 species of song birds and perching birds (order Passeriformes) are influenza reservoirs in the contiguous US.

OK, insightful analysis time.  We always associate bird flu with ducks, or chickens, or turkeys or geese, but rarely do we associate it with songbirds and other smaller birds.  This study makes a clear association between those birds (called "passerines") and bird flu. 

The distribution of those avian flu cases is seen in this map (thanks Laidback Al!):

Now let us look at a map of the principal migratory bird routes over North America:

There is a veritable swarm of migratory bird routes over the Great Plains and Mississippi River delta, and a very strong west coast migratory route.  So it is no coincidence, in my mind, that these migratory superhighways also contain the areas where avian flu has been most strongly detected since 2005.

Now you also notice those "down arrows" leading South of the Border.  This map helps illustrate what happens south of us:

We've got birds encroaching from the south as well as from the north.  This does not just figure into the avian flu equation:  There is this little thing called a major dengue fever epidemic that is raging in many, if not most, South American nations.  And as I mentioned recently, Key West, Florida has enough dengue in it to sicken a man this year.

This all leads into the current status of H5N1 sentinel activity.  With massive budget cuts, waning interest, and competition for attention from swine flu and other diseases, do we have as good a handle on things as we did in 2006 and 2007?  I would like to think so, but I doubt it.

Imagine the encounter:  A researcher goes into his/her supervisor's office, requesting additional funds for H5N1 monitoring.  What, the supervisor says?  You want me to divert $$ from certain necessary projects over to bird flu monitoring?  All while my departmental budget is being cut to ribbons?! No stinking way!

Or words to that effect.  I wish it were not so, but I am pretty certain I am right.

In the midst of all this, the Mexican government recently issued an alert to be watchful for an H5/H1 hybrid virus.  My first impulse was to say, What do they know?  What have they heard?  But is may have been nothing more than speculation.  Nonetheless, vigilance is important, now more than ever.  For H1N1v may not have been the pandemic everyone feared, but it was substantial in terms of its effect on the young; far worse than, say, 1977.  Yet H1N1v, being 1/3 avian, can still hang out with avian flu viruses and reassort.  It is precisely this scenario that should cause us to view this latest report with concern. 

A reader of this Blogsite, Jonathan Singleton, asked me to comment on the recent proMED report regarding Na Tao, Vietnam.  As you may know, Na Tao is at the heart of a possible cluster of human cases of bird flu.  My previous two blogs have covered this developing situation.

The proMED report in question is below.

Influenza A (H5N1) is not transmitted from human to human

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Yesterday afternoon [14 Apr 2010], at a meeting of the National Steering Committee for pandemic influenza control and prevention, Dr Tran Nhu Duong, Deputy Director of the National Institute of Hygiene and Epidemiology confirmed that influenza A (H5N1) has not been transmitted from human to human.

The investigation of the Institute on 2 cases of influenza A (H5N1) in Na Tao village, Nhu Co commune, Cho Moi District, Bac Kan province did not detect human to human virus transmission.

Reports of two investigation teams of the Institute in Bac Kan showed that the two patients were living about 100 meters apart, and they had never been in direct contact with each other.

All 33 people who had contact with the patients, including relatives, visitors, neighbors, nurses, and physicians, were tested and monitored for 16 days. There has been no case with symptoms of the disease. All the test results were negative.

Communicated by:

PRO/MBDS

<promed-mbds@promedmail.org>

As we now know, there are three suspected human cases, not two.  But that is not material to our discussion.  What is material is that two persons, living about a little more than a football field's distance apart, contracted H5N1 bird flu. 

The report seems to conclude that distance alone, coupled with a lack of direct contact of one with another, eliminates the possibility of human-to-human (H2H) transmission.  That sounds logical enough.

But the larger issue -- the proverbial elephant in the room -- is this:  Has the virus itself changed enough in Na Tao, Vietnam, to allow for an easier method of transmission from avian to human respiratory cells?   If so, that disclosure would prove to be almost as big (and ultimately more potentially troublesome) than another H2H cluster.

That is a question that the Vietnamese report does not answer.

Let's consider the facts.  Three persons in one district contract bird flu.  Apparently they all contracted it via contact with diseased poultry.  That tells me that either the virus in that area of Vietnam is more potent, and/or the ability of the virus to favor human epithelial cells as much as it favors chicken epithelial cells.

We all know from reading the research papers that this proclivity toward one species or another is primarily driven by temperature.  The fact that both diseased poultry and diseased villagers have been detected in a cluster bears investigating by the WHO.  For a cluster is a cluster whenever you get multiple persons in a close area, H2H or no H2H.  Three B2H bird flu cases in one hamlet should be significant enough to want to gather many samples and look at them very, very carefully.

The world press is beginning to focus on the province of Bak Kan (or Bac Can), Vietnam.  Bak Kan is in the extreme north of Vietnam, near the Chinese border.  Last week, I blogged on the potential H5N1 bird flu cluster that was threatening to emerge within that province. Just scroll down to read my previous blog.

Following my blog, a second story appeared regarding a second human infection.  It was dated at 6:01 PM, 04/09/2010.  It appears below, and the link to the VOV story is in the headline:

Another A/H5N1 infection case reported in Bac Kan

Yesterday, Vietnam confirmed yet another human bird flu case.  This time, however, this case bears watching, because it could signal something far more disconcerting than just a single human case.

From the proMED report:

The Director of the Bac Kan provincial Health Department, Nong Quoc Chi, confirmed an A (H5N1)-infected case on [5 Apr 2010]. The patient, [male], 22, from Na Tao hamlet, Nhu Co commune, Cho Moi district, is currently in critical condition. He is being treated at the [National Institute of Tropical and Infectious Diseases]. The patient got sick on [30 Mar 2010] with symptoms of high fever and cough. He was admitted to Bac Kan provincial hospital, and then sent to the [National Institute of Tropical and Infectious Diseases] on [3 Apr 2010] where he tested positive for the lethal strain of A (H5N1) virus.

At present, 4 other people in Nhu Co commune show similar symptoms of high fever and cough. They are under quarantine and being treated at Bac Kan provincial hospital.

The patient in question was taken ill on the 30th of March, and then sent to Hanoi when his condition worsened. The four suspected human bird flu cases are currently in quarantine at the provincial hospital in the provincial capital of Bak Kan. (Or Bac Can, as shown on map at left).

There are many unanswered questions.  The most obvious of these is whether these four suspected cases are bird flu, or swine flu?

If these cases are indeed bird flu, has there been human-to-human chain transmission, or were these people all infected during the same timeframe by a single vector?  Were they all infected by sick poultry, or were they sickened by a human infection?

OK, let's assume these four people were all H1N1/swine flu infections.  That is not good news!  That would mean that, once again, bird flu and swine flu had "rubbed elbows" in rural Vietnam.  Search my Blogsite for the earlier known case, back in 2009. 

According to the Vietnamese Department of Preventive Medicine and the Environment, there are no outbreaks of H1N1 anywhere in Vietnam.  From VOA News:

No more A/H1N1 outbreaks in Vietnam