Saturday, July 30, 2005
A possible new kind of vaccination?
The CDC, back in 2001, published a very interesting paper that might change your mind about how and why you get the flu - amongst other things.
Seasonal Variation in Host Susceptibility and Cycles of Certain Infectious Diseases by Scott F. Dowell
is available at
http://www.cdc.gov/ncidod/eid/vol7no3/dowell.htm
It strongly suggests that viruses don't arrive in winter - they were already there, it's just that we get weaker, until a kindling effect can get an epidemic going. He thinks that the photoperiod, and changes in melatonin, are the likely trigger.
He quotes a fascinating observation from 1826, well before jet travel: "...this epidemic affects a whole region in the space of a week, nay, a whole continent as large as North America, together with all the West Indies, in the course of a few weeks, while the inhabitants could not within so short a time have had any communication or intercourse whatever across such a vast extent of country."
But it gets me thinking about an old idea I've kicked around without being able to interest anyone in it.
I wonder if a factor in disease seasonality isn't that the probability of infection vs resistance may depend in part, as well, on the actual number of infectious units initially encountered.
Do we even know whether the gradual exposure to one then 8 then 64 copies of a virus, etc, over days, or weeks might make resistance more likely? That repeated slight exposure might or might not be an effective means of protection generally against infection? (Wouldn't that be nice.)
I mention this because such a mechanism might be expected to logarithmically exaggerate any seasonal effects such as he hypothesizes, mediated by melatonin. Once the snowball got rolling, and exposure came in bunches, it might, to thoroughly mix a metaphor, go like wildfire if the sheer size of the initial exposure is really important. Whereas, during months when everyone's immune system is strong, mild infections of others would expose us only to mild doses of the infectious agent, making the chances of our gaining resistance that much greater as well - if this idea of mine holds at least.
And of course, if repeated or gradually increasing very slight exposures were very likely to produce immunity, this might be quite useful, obviously. We could do that deliberately, as a different sort of vaccination, and one that might be generally applicable as soon as viruses (etc) emerged, without a lot of research and development. Just maybe.
There may well be no such effect of course - but have we ever bothered to find out such a fundamental fact concerning disease transmission? Granted, most in the field would accept that illness-or-resistance is more likely given a large exposure, but the question is, would repeated tiny exposures make developing specific resistance to that disease more likely? Is that part of what's happening during the seasons when viruses or flus aren't virulent?
One interpretation of Dowell's findings might be that he has provided evidence, or at least a hint, that large exposures to infectious agents make resistance more difficult, and less likely.
Even if that's true it doesn't mean that graduated exposure to just any pathogen would be an effective (or wise) countermeasure, but it does get me thinking.
In any case, he's written an impressive and necessary paper, that's very interesting, and might amuse you during flu season.
First published July 30, 2005
Last revised July 30, 2005
Russell Johnston
Seasonal Variation in Host Susceptibility and Cycles of Certain Infectious Diseases by Scott F. Dowell
is available at
http://www.cdc.gov/ncidod/eid/vol7no3/dowell.htm
It strongly suggests that viruses don't arrive in winter - they were already there, it's just that we get weaker, until a kindling effect can get an epidemic going. He thinks that the photoperiod, and changes in melatonin, are the likely trigger.
He quotes a fascinating observation from 1826, well before jet travel: "...this epidemic affects a whole region in the space of a week, nay, a whole continent as large as North America, together with all the West Indies, in the course of a few weeks, while the inhabitants could not within so short a time have had any communication or intercourse whatever across such a vast extent of country."
But it gets me thinking about an old idea I've kicked around without being able to interest anyone in it.
I wonder if a factor in disease seasonality isn't that the probability of infection vs resistance may depend in part, as well, on the actual number of infectious units initially encountered.
Do we even know whether the gradual exposure to one then 8 then 64 copies of a virus, etc, over days, or weeks might make resistance more likely? That repeated slight exposure might or might not be an effective means of protection generally against infection? (Wouldn't that be nice.)
I mention this because such a mechanism might be expected to logarithmically exaggerate any seasonal effects such as he hypothesizes, mediated by melatonin. Once the snowball got rolling, and exposure came in bunches, it might, to thoroughly mix a metaphor, go like wildfire if the sheer size of the initial exposure is really important. Whereas, during months when everyone's immune system is strong, mild infections of others would expose us only to mild doses of the infectious agent, making the chances of our gaining resistance that much greater as well - if this idea of mine holds at least.
And of course, if repeated or gradually increasing very slight exposures were very likely to produce immunity, this might be quite useful, obviously. We could do that deliberately, as a different sort of vaccination, and one that might be generally applicable as soon as viruses (etc) emerged, without a lot of research and development. Just maybe.
There may well be no such effect of course - but have we ever bothered to find out such a fundamental fact concerning disease transmission? Granted, most in the field would accept that illness-or-resistance is more likely given a large exposure, but the question is, would repeated tiny exposures make developing specific resistance to that disease more likely? Is that part of what's happening during the seasons when viruses or flus aren't virulent?
One interpretation of Dowell's findings might be that he has provided evidence, or at least a hint, that large exposures to infectious agents make resistance more difficult, and less likely.
Even if that's true it doesn't mean that graduated exposure to just any pathogen would be an effective (or wise) countermeasure, but it does get me thinking.
In any case, he's written an impressive and necessary paper, that's very interesting, and might amuse you during flu season.
First published July 30, 2005
Last revised July 30, 2005
Russell Johnston
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