Well, I was not expecting to write to you so soon. As
mentioned in my last post, I thought we were at the apex of the flu season and,
as it turned out, that was the case as the incidence of influenza in the North
American season began to diminish soon afterwards. I had hoped to send a note
out now, not on the flu, but on Lyme disease, but some news has changed my
plans.
As you may know, just as our season winds down, our next
year’s flu is beginning to gather steam in the East and in the Southern
Hemisphere. Specifically, China is starting to have flu issues. And as has
occurred before, there is a new strain of avian flu that has infected humans
there, named Avian Influenza A (H7N9). The local bad news is that, to date, 24
or so people have been laboratory confirmed infected with this flu, and 7 or so
have died. This makes catching the flu a highly lethal proposition. (Of course
it is very possible that others had this same flu and have not been laboratory
confirmed and recovered, shifting these numbers, which is a conversation for
another time.) More than likely you will be hearing a great deal about this if
it grows or if the news media picks up the story. What they may not make clear
is what this all means. Allow me to mention a few points I have made over the
past years, so that you have a scaffolding on which to place that information;
I apologize for repeating myself, but it may be useful.
Yes, this does seem to be a novel flu strain to humans. And
yes it does seem to pass from one species to another. However, the main threat
to us, as a population, is not the bird to human spread, but the human-to-human
spread. In other words, while you, a human, may catch it from a bird for
example, and if you do catch it, have
a higher likelihood of mortality, that is not what drives a pandemic. For a
pandemic to occur, human-to-human spread must occur, and must occur easily. The
way I think about this, and the way I have written on this, is thinking of it
as gates that are closed or open. The first gate relates to the ease of the flu
virus transmission from bird to bird. (Here, you can think of bird as a proxy
for another species, such as pig, etc., that can also pass a flu to humans.)
The easier such transfer is, the more open that gate is and more likely for the
virus to spread amongst birds, which is not so good for them, but does not yet
greatly impact people.
The next gate is the bird to human transmission. How easy is
that? If it is easy, then we have a local problem. In other words, the birds
begin to pass the virus to people. And, as you recall our discussion, since the
human’s immune system may not have a great deal of historical experience with
that virus, then those local people may suffer greatly, and some may even die
during that infection.
The next gate is the most important. How likely is it that a
human infected with that virus can pass it to other humans. If that gate is
open, then the likelihood of epidemic is
very high. The last gate is the natural history of that virus. It turns out
that many times a highly lethal virus becomes less lethal as it progresses from
individual to individual. As well, it may become less likely to pass from
individual to individual. This has been noted before in other viruses, and I
believe there are logical evolutionary reasons why this is beneficial to both
virus and host species. (That is also something we can talk about another
time.) However, if the lethality stays or increases, and it is easy to pass
from human to human, then the chance of a pandemic becomes a reality.
Where are we now? We have found this novel virus, that came
from one species to humans, and it turns out that many who catch it die. That
is what we know. Other things we know: Once the virus has been identified,
health authorities began surveillance on family members and others that were
exposed to the individual people that caught/died from the virus. As of now, to
my knowledge, no one has developed this flu. In other words, as of now, it does
not seem as though the human-to-human transmission is easy or being seen at
all, which is good news! That should be one of the most important variables to
track. As well, we may find that over the next weeks the people who catch this
flu have a less lethal version, which would be good news as well, which is what
I expect to see.
That is where we find ourselves, as of now. If you are
likely to hear anything about this virus, it is that some people died in China,
from a flu that is new to humans. A sort of local story that is tragic to those
involved but not to our species. If these variables change or gates open, the
news will just stop there or gather a great deal of steam and hysteria. Until then,
DON’T PANIC if you hear about this news.
Take care,
Paul Herscu ND, MPH
