Identifying a Pathogen

In his awesome book on pathogens that jump species, Spillover, David Quammen has one section on how the process of identifying a pathogen proceeds. He uses the SARS breakout of 2003 as an example. When it went global starting at Hong Kong, he writes nobody knew what caused it, hence the name:

“Ebola is a virus. Hendra is a virus. Nipah is a virus. SARS is a syndrome.”

 

Most tests in medical labs are designed in a particular way:

“Such tests essentially give you a positive, negative, or approximated answer in response to a specific question: Is it this? Finding an entirely new pathogen is more difficult. You can’t detect a microbe by its molecular signature until you know roughly what that signature is.”

So when trying to identify a new pathogen, scientists try growing it in a culture and then peer at it through a microscope. Then they tried peering through an electron microscope, and thus realized it was a coronavirus, i.e., viral particles “encircled by a corona of knobs”.

 

But could you be sure this was the pathogen you were searching for? After all, it might be some other microbe in the body, not the one related to the disease/syndrome you were trying to figure. To establish causality, they took blood serum from SARS patients which would obviously have antibodies. If you let loose the SARS antibodies on the virus-in-the-lab that you thought was the culprit, there would be war. If not, nothing. The result?

“(It) was like splashing holy water at a witch. The antibodies recognized the virus and reacted strongly.”

And thus it was confirmed that the cause of SARS was the, er, SARS coronavirus, abbreviated to SARS-CoV.