Posted on
October 27, 2014 in
Dallas’s index Ebola Zaire patient, Thomas Duncan, was at home for four days while he was symptomatic with Ebola. His family were not infected with the virus.
While Duncan infected two nurses at the hospital during his final days (when he was leaking blood from every available orifice) he didn’t infect the people who lived with him when he was very sick—sick enough to have gone to the hospital and been sent away.
One of the commenters on my last Ebola post pointed out that Ebola has a very low basic reproduction number, R0, of about two. R0 is not an inherent characteristic of a virus, but depends on the environment. The R0 for Ebola Zaire has been calculated as 2.7 in some outbreaks, but 2.0 in this one in Africa. As long as R0 is greater than one, the disease will continue spreading. If R0 were intrinsic, Ebola Zaire would continue spreading until eventually everyone got sick. Fortunately, R0 will be lower in a more developed nation than in the Third World.
Given that neither of the people whom we know Duncan to have infected appears to have infected anyone else, R0 for Ebola Zaire in Dallas in 2014 is something less than one (2/3?).
What about the scary transmission through the air? The good thing about that is that Ebola doesn’t make you cough or sneeze. So while an infected person can, contrary to the government’s assertions, transmit the virus through the air, it’s not a mode of transmission of which the virus has evolved to take advantage (contrast a cold or flu virus, which spreads by making you expel virus-laden particles at high velocity through your mouth and nose).
So I’m downgrading my concern about Ebola in the U.S. from “do something now” to “play Whac-A-Mole as cases appear.”
Much better perspective than the Chris Christie/Andrew Coumo approach of “let’s lock up all the do-gooders from Doctors Without Borders.”
I’m still on the fence, Mark.
Yes–its “K” (I like that term, used to describe the rate of fission propagation in a nuclear weapon) is low-ish, certainly not as exciting as, say, flu.
But remember viral evolution; every virus wants to be the common cold. Actually every virus wants to be one of the many incorporated in our very genome…Viral Valhalla. But they’ll settle for cold virus status. (Right–they don’t “want” anything, but selective pressures drive their evolution this way)
Increasing transmission, decreasing virulence. Don’t kill your host. Don’t debilitate your host. Spread quickly and cleanly. THAT’S the way, my boy!
Ebola’s hot and young, impetuous, and voracious. Its “beta” once you’re infected is fantastic; the literature refers to “fulminant viremia”.
Here’s the question–what’ll it learn first? Seems this strain already has acquired a longer incubation; could it be turning down its “K”? Or is it on the way to producing infectious carriers to spread for a while before a joyful coming-of-age party and the host’s death?
Epidemics come in waves, with an initial few cases…delay while incubating their contacts…a second slightly larger wave…humans don’t think well in exponents. We don’t realize just how FAST those numbers grow after the Nth generation.
I’m watching it carefully.
P.S. It’s no secret our bioweapon “defense” programs have been playing with these bugs for a long time; their rationale is “We have to develop them to develop defenses, for surely The Enemy will develop them….”
P.P.S. One of those labs is in Kenema, Sierra Leone–a country not signatory to the bioweapons treaty. Is this bug an accidental release of one of their pets? Shades of Plum Island and Lyme disease…