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Ebola Weakens Progressively with Retransmission

2014-10-29

Here is a comment from NYT that I think explains a lot, but I don’t see how it explains everything:

Donald Kelmers

Fernandina Beach, Florida

I remember reading, at least a decade or two ago following one of the earlier and smaller outbreaks of ebola, an article in The New Yorker magazine written by by a woman who had trained in biology but instead had previously been an anthropologist in the African area where the outbreak occurred. She was included in the medical response team that went to treat the outbreak of ebola because she knew the local language. In Africa, she did not do medical work but instead interviewed patients. She tracked the history of the outbreak from patient zero following patient to patient transmission and mortality as far as retransmission five. What she found that was that infectivity and mortality decreased with each retransmission further from patient zero. After retransmission five away from patient zero, the disease essentially vanished; i. e., the disease burned itself out. She questioned if ebola was natively a human disease or some unknown animal disease that occasionally jumped to humans through a rare mutation but then continued to mutate to weaker forms with each human retransmission until the disease outbreak vanished. I have never seen any followup on her ideas. Could such a weakening with progressive retransmission explain the reported dearth of anticipated patients?

In other words, the virus mutates to become weaker each time it crosses from one patient to the next.  After going through five patients, the virus becomes inactive and no further transmissions occur.  If this were true, it seems to me that the virus would have already burned out; instead, we have ten thousand known victims and five thousand deaths as of this week.  On the other hand, if an index patient were responsible for numerous new patients, for a time the rates would increase rapidly.  The time it takes for a complete cycle would be eight to fourteen days for incubation plus two to three weeks to succumb, at which time one is highly infectious.  Altogether, three to five weeks to cycle from one patient to the next, and less than six months for five generations.

There has to be a non-human source that is starting new index cases for the epidemic to last longer than that, or to grow any longer.  We still do not have definite information on a non-human vector other than possibly a bat.

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