One of my stated goals for this summer is to read. Reading
is a deep pleasure for me, one I am not able to do as freely as I would like
during the school year, and I have come to realize that if you want to read a
lot, you have to consciously make time for it, thus my summer goal.
I want to share with you today one of the books from the
first half of my summer, and it’s not your typical beach read, though I think
many listeners might find it very interesting. The book is David Quammen’s Spillover:
Animal Infections and the Next Human Pandemic. Quammen is a frequent
contributor to National Geographic, which funded much of the research for this
book, and author of several works of fiction and non fiction, the most well
known of which is probably Song of the Dodo. Spillover is not for
the faint of heart. It takes us on a journey all around the world, and spends
most of its time in equatorial Africa and southeast Asia, tracing the paths of
various diseases, some you have never heard of, others have been in the news
for years. The diseases Quammen catalogs are in the running to be the Next Big
One, and they all employ an ecological strategy that makes them ideal
candidates.
The pathogens that cause diseases including influenza, SARS
(or Sudden Acute Respiratory Syndrome), the very timely Ebola, Hendra, Herpes
B, Rabies, Hanta, Nipah, and Marburg viruses, HIV/AIDS, Bubonic Plague, Lyme
disease, Yellow Fever, Dengue Fever, in fact 60% of human infectious diseases
are what is called “zoonotic”. A zoonotic pathogen, (or zoonosis) is one that
resides in an animal reservoir, causing no harm to that animal species, but
when circumstances are just right, can “spill over” into humans and cause
disease in us (hence the name of the book). In the first example of the book,
Quammen describes the outbreak of a little known (but very lethal) disease that
affected humans and horses in Australia. It became known as Hendra virus, and
after much field work, the reservoir was determined to be flying foxes, a type
of bat, roosting in a tree in a horse paddock. The virus did not affect the
bats at all, presumably it had coevolved with this particular species of bat
over millions of years, but it turned out to be lethal to horses, exposed to
the virus in bat urine and guano raining down from the tree in their paddock,
and to the humans that were caring for the sick horses. The outbreak ended, but
the virus is still there. A certain percentage of these flying foxes still
carry this virus, which is why zoonotic diseases are virtually impossible to
eradicate. We would have to kill literally every infected flying fox to
eliminate this virus. That same story, of an animal host and a certain set of
circumstances that allows for a spill over into humans is repeated for all of
the zoonotic pathogens.
Those pathogens are mostly viruses by the way. Viruses are
barely considered alive, because they can’t replicate themselves, they require
the machinery of a host cell to do that for them. They have relatively short
packets of genetic information, and when they hijack a cell’s DNA reproducing
machinery, they are especially prone to error. Error sounds like a bad thing,
and most of the time it is, mistakes in copying DNA usually lead to death,
death of an individual viron. Occasionally though, an error leads to a new
trait, one that affects the behavior of the viron, perhaps making it more
hardy, more easily transmissible or able to infect a new species. That is
evolution, and it is one of Quammen’s two main points about zoonotic disease.
Ecology puts us in the path of these pathogens. As human behavior causes us to
push further and further into wild habitats and deranges the order of natural
ecosystems, we provide more and more opportunities for spill over. Its not that
these pathogens seek us out, far from it, its just that there are so many of
us, over 7 billion of us. We are getting harder to avoid. Ecology, our
interactions with the world around us creates the opportunity, and evolution
allows the pathogens to adapt to life in a human body.
This book is richly detailed and intensely researched.
Quammen clearly spent years in the field in close proximity to spill over
conditions to bring us this work. Its fascinating but if you are the type of
person to lay awake at night worrying about things beyond your control, you may
want to skip it. I for one, feel that knowledge can be empowering, so I read
this book with gusto. In the end, when the Next Big One does emerge, and there
is no doubt that it will, our actions as individuals actually do make a
difference. We can make choices that these pathogens can’t, and these choices,
along with the knowledge gathered by hundreds of brave scientists will help
dampen the effect of whatever pandemic is coming next.
References:
Spillover: Animal Infections and the Next Human Pandemic,
David Quammen, 2012 W.W. Norton
