Viruses and Pangolins and Bats, Oh My!

Why we really need to understand zoonosis and bat feces.

Posted Mar 17, 2020

Besides being deadly, what do coronavirus, rabies, malaria, swine flu, SARS, Lyme disease, ebola, and the Black Plague have in common?  

Turns out that all of those nasty diseases originated in other animal species.  

That’s not true of every communicable disease. According to David Quammen, author of Spillover: Animal infections and the next human pandemic.  Polio and smallpox, for example, are uniquely human afflictions. 

Cover of book being discussed here
Spillover: Animal infections and the next pandemic
Source: Cover of book being discussed here

Why does it matter?  As Quammen explains, diseases that originated in humans are easier to contain, because once scientists develop a vaccine, we can functionally eradicate the disease.  But diseases that naturally inhabit other animal species aren’t so easy to wipe out, because even if you vaccinated every single human being on the planet, the organisms that caused the disease would go on duplicating themselves in those other species. 

David Quammen was recently interviewed by my colleagues Athena Aktipis and Dave Lundberg Kenrick, as part of a fascinating podcast series called Zombified. The series is concerned with biological organisms that hijack our brains, including various amazing microbes, your pet dogs, and even artificially intelligent algorithms. 

Despite its humorous name, Zombified has included serious conversations with prominent biologists, anthropologists, psychologists, and other experts considering parasitism in all its diverse manifestations.

Neil Smith from Zombified website. Used with permission
Zombified interview with Qammen
Source: Neil Smith from Zombified website. Used with permission

I knew of David Quammen because I’d read his fascinating book The Song of the Dodo, which is an outstanding example of good scientific writing, interweaving the story of Alfred Russell Wallace’s 19th century jungle adventures to introduce the field of island biogeography. Russell is the fellow who co-discovered the principles of evolution by natural selection.

Quammen’s interview for the Zombified series was recorded several months before the coronavirus epidemic, but it is eerily prescient regarding the events unfolding this month.  Quammen discusses how many of the most deadly diseases known to man normally live comfortably in various species of other mammals (especially bats, it turns out).  The organisms causing those diseases occasionally get transmitted to humans via a species other than the usual host.

Not coincidentally, the latest guess about the coronavirus is that it originated in bats and may have been transmitted to humans via pangolins, scaly anteaters that are currently threatened with extermination because they are highly valued for their scales and for their meat, which are believed in China to have medicinal properties. 

In the interview, which is quite appropriately titled: “Bat sh*t,” Quammen tells the story of the Hendra virus, a deadly disease you’ve probably never heard of unless you are an Australian interested in horse racing. The virus is called Hendra after the town outside Brisbane where it killed several race horses and was then transmitted to three human beings (two of whom died).  In Quammen’s book, and in the interview, he describes the fascinating biological detective work by which a graduate student named Hume Field traced the origins of the disease to the local fruit bats.

During the conversation, Quammen manifests his ability to introduce complex biological ideas via interesting stories of biologists working on intriguing mysteries. I was particularly impressed with his ability to toss terms like “endogenous retrovirus” into a casual conversation. I didn’t know the distinction between "reservoir hosts" and "amplifier hosts," which Quammen also brought up, but it turns out it’s critical for understanding how pandemics, like the current one, unfold. 

I also wasn’t aware that ebola is still a serious problem in West Africa, or why biologists think we shouldn’t be nearly as worried about ebola as we are about diseases like Covid-19. 

Nor was I even remotely aware that 1 in 5 species of mammals is a bat, or why bats are so frequently the reservoir hosts for deadly epidemics.  

Finally, I was shocked to learn that eight percent of the human genome is DNA that was inserted by viruses, and that some of that viral DNA may even be responsible for the evolution of mammals.  

How all that works is in Quammen’s fascinating interview. He also talks about his formula for writing good popular science along the way.