“Nature
answers only when she is questioned.”
--Jacob Henle
We are fast
approaching flu season in the U.S. and it is time for the general public to
start making plans to get vaccinated. It
was time many months ago, however, for the Centers for Disease Control (among
many others) to start planning just exactly what kind of vaccines should be
made available for this year’s version of this ongoing fight against influenza.
 |
| Lots of variations on one basic theme: Ick! Yuck! Phooey! |
We won’t go
into the abhorrent pseudoscience involved in the anti-vaccine movement in this
post (though there is certainly rich material there for many an essay); rather,
we thought this might be a good time to speak about influenza generally, and
avian flu specifically, particularly as it relates to concerns anyone may have
about the possibility of disease spreading through backyard chicken flocks.
Spoiler
alert: Well tended backyard chicken
flocks are actually beneficial in fighting the spread of avian flu. We’ll explain in a bit.
Influenza,
or “flu”, is usually nowhere near so serious an illness as to justify the
enormous amount of attention it gets each year.
Though it is somewhat more severe than the common cold… it is typically
not fatal, and typically lasts for somewhere between a week to two weeks.
The problem,
of course, is that word “usually” – when it does
take a turn for the worse, it takes a nasty
turn for the worse. The most famous
example is the 1918 Spanish influenza pandemic, which took the lives of 50+
million people worldwide. To provide
some context… “only” 16 million people died in World War I over the four years
preceding the pandemic.
Why so much
death from a disease that usually just sends you to bed for a couple of weeks?
The reason
is that the influenza virus is one of the most mutable viruses ever discovered
– most of the time, the dominant strain of influenza is one which may put those
who already have weak health (the elderly, young children, those with
compromised immune systems or who are already wracked by some other illness) in
mortal peril (it is a rare year in which influenza deaths in the U.S. do not
number in the thousands). However, in
most years, those who are reasonably healthy will suffer nothing more than an
uncomfortable couple of weeks of fever, chills, headaches, sore throats, maybe
nausea (depending on strain), general body aches, etc. You know, “being sick”…
In some
years, though, the mutated strain of virus is much more dangerous, and ends up
generating potentially fatal complications like pneumonia, dangerously high
fevers, impaired kidney functioning, etc. in previously healthy persons.
And that is
why all the fuss.
The goal of
immunization is, therefore, not particularly personal.
We bill immunization as an attempt to “keep you healthy” but the reality is that immunization is more about collective than individual health. A population in which a sufficiently large percentage of people have been immunized is much less likely to spread the virus, and is therefore much less likely to play host to the more virulent varieties of the virus. There will still be individuals who get sick even if they get the vaccine. There will simply be fewer of them, which is good for everyone.
So how do
birds relate to all of this?
Glad you
asked. Birds, it turns out, are
frequently the place where the whole story begins. There are various strains of flu associated
with different species, and those which have evolved specifically for human
hosts are almost never particularly dangerous.
The varieties which run amok and kill large numbers of people are viruses
which originally evolved in other kinds of animals. On occasion, those viruses mutate in such a
way that they can cross over and infect humans – this has happened with swine flu before, for example, but avian flu (flu associated with birds) is
by far the most common of these “crossover” diseases.
There are
numerous versions of Influenza A, the
virus which is adapted to birds, the most famous of which in recent years is H5N1.
This variety has been spreading throughout Asia since 2003, reached Europe
in 2005, and the Middle East in 2006.
One case was reported in Canada in January, 2014.
The virus
originated in bird populations, and spread to humans. Which birds?
Well… of the affected populations studied, 84% were domestic populations
composed of chickens, ducks and turkeys, and the remainder were wild
birds. So the domestic populations were
to blame, right?
Wrong. At least, not exactly…
The virus
almost definitely originated in wild birds, and was then transmitted to
domestic flocks via interaction with the wild birds (waste matter dropping into
a pen… wild birds scavenging food or water from the flock… there are a lot of
ways for the birds to comingle). Wild
birds, however, do not live in confined quarters; as a result, they have a much
lower rate of interaction with each other than do domestic birds.
A typical
commercial poultry flock, however, will number thousands of birds in very,
very tight quarters. And will almost
always have insufficiently cleaned ventilation, food and watering appliances. A typical commercial poultry flock is a pathogenic disaster waiting to happen.
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| Who in their right mind is dumb enough to think this is a good idea? |
The response
of government to the finding of an infected bird is informative in this regard
– when an infected bird is found, the entire flock is killed. They literally have no choice – there is no
way to quarantine an infected bird; if one bird in a chicken farm has it, they all have it. When you are raising birds in a 1’ by 1’ cage
(or “free-ranging” them by allowing 1,000 birds to roam in a 20’ x 50’ barn)
then they are not only breathing the same air, they are quite literally pooping
on each other and living in muck and filth.
And those are the good farms,
where regulations and procedures are being followed.
The sad,
despicable truth, though, is that no one knows exactly how many poultry
operations actually follow the rules.
The USDA does not have enough manpower to cover more than a small
percentage of the regulatory territory to which they are assigned, and even
when inspectors are available to review the health and sanitation of a given
poultry operation… it is frightfully easy for operators to misdirect
investigators away from problem areas.
Salmonella
outbreaks are the most common result of disease-laden poultry farm ventilation
systems… but one can easily envision H5N1 being spread in the same way.
Enter the
backyard chicken flock…
There are a
number of advantages to raising backyard chickens, and we have enumerated many
of them on other occasions; aiding in the fight against avian flu, however, is
one area in which taking birds out of cramped conditions is an underrated
element. Consider:
- The principle dangers associated with poultry farming come from population density, which is not a problem for backyard flocks ranging only anywhere from 4-10 birds, in much larger spaces than are afforded by factory farms.
- Occasional interactions between wild birds and diffuse backyard flocks will still happen… but any one interaction only affects 4-10 birds, not 10,000.
- Human interaction with a flock of 4-10 birds is limited to one household, not the tens or hundreds of thousands (or even millions) who interact with a single poultry farm in factory farming setups.
- While flu can spread via the lungs, it is much easier to transmit via fluids, like, say, blood, which is often smeared all over human workers on a poultry farm, and almost never contacted by backyard birders.
The logic
behind a more diffuse production system for poultry related products is fairly
simple – for the same reason that contagion is more common in dense population
centers, the spread of food-borne pathogens is much higher when the production
of those foods is also performed in dense populations. When the Black Plague hit London, even the
superstitious folk of the pre-Enlightenment era knew to head for the hills,
because there was danger in population density.
The
advantages posed by backyard birding, however, will not be fully felt unless a
sufficient number of folk take up the “hobby” and make it a lifestyle choice. In order to decrease the population density
of
 |
| Much less chance of contagion, and no equipment to clean. |
Barring
having one’s own backyard flock, we would at least encourage consumers of eggs
or poultry meat to consider purchasing from farmer’s markets or other venues
where small producers with free range flocks not raised in pestilential,
overpopulated factory farms make their money.
Otherwise, we will all be vulnerable to the inevitable spread of some
form of influenza from factory farmed bird-to-human, and then from
human-to-human. Once it’s human borne,
it is out of the hands of the backyard birder or responsible consumer.
Which brings
us back to immunization…
We began by
noting that those in charge of manufacturing each year’s vaccine have to plan
months in advance of distribution, owing to the mutability of the virus
(there’s your evolution-in-action laboratory-verifiable example, if you care to
argue with a creationist at any point, though we prefer arguing with brick
walls, as they don’t spout nearly as much nonsense). Because there is so much variability, a flu vaccine
is really usually a vaccination against up to four different virus types.
Which, obviously, takes a lot of planning, based on data gathered from
the previous year’s strains, examples of viruses found in poultry populations,
examples found in other countries with which the U.S. population has a lot of
interaction, and good solid guesses based on historical trends regarding which
strains are “due” for a comeback.
As a result
of all this variability, measuring the effectiveness of flu vaccines is
anything but straightforward. In most
years (for example 16 of the 19 years before a 2007 study), the strains which
actually bloomed during flu season were exactly the strains predicted by
vaccine manufacturers. And even in the
years when they guess wrong, there is still some cross-over protection, given
that not every mutation of the virus is radically different from the previous
version.
There have
been many meta-analyses of the data (basically, reviews of multiple studies)
which suggest that overall, for healthy adults, vaccinations result in roughly
a 75% decrease in the likelihood of getting the bug. Without doubt everyone involved (particularly
those who got the shot but ended up getting sick anyway) would prefer a rate
closer to perfection… but remember, the ultimate objective is not necessarily
to keep any one person healthy, it’s
to keep a pandemic from happening. If a
few people still get sick, but we never see anything like 50 million people
dying from something like the Spanish flu again, it will have been an exercise
well worth it.
So…
Your
assignments for this Fall: Get your flu
shot, raise backyard chickens (or shop at farmer’s markets), try to stay warm
and dry, wash your hands regularly, and…
Happy
farming!
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