|
|
Re: diseases and immunity
Mary Beth Williams (mbwillia@ix.netcom.com(Mary)
7 Jul 1996 15:46:37 GMT
In <31DF65BA.63A0@best.com> Joel and Lynn Gazis-Sax <gazissax@best.com>
writes:
>
>Mary Beth Williams wrote:
>>
>> In <31DB260D.78DE@best.com> Joel and Lynn Gazis-Sax
<gazissax@best.com>
>> writes:
>>
>> >* That Europeans were exposed to many infectious diseases at an
>> >earlier period than the peoples of the Americas.
>> >
>> >* That this exposure weeded out those less able to withstand the
>> >diseases and caused European populations to become more resistant
to
>> >them.
>>
>> Actually, this is both true and false. Yes, the exposure weeded out
>> those more suseptible to these diseases -- they died. However,
those
>> people who actually fell victim to the diseases and survived became
>> *resistant* to such only because of the development of immunity
through
>> prior first-hand exposure, not genetic mutation. Its already been
>> discussed that transfer of maternal immunity only lasts for the
period
>> during breastfeeding (hence, the high mortality of post-weening
>> toddlers.) One of the reasons plague was less *successful* in
>> subsequent epidemics is that it didn't have *virgin* populations
>> through which to pass -- if it hit a pocket of *resistees*, and
>> couldn't thus be transmitted, it died out. This is one of the
reasons,
>> as discussed previously, the smallpox probably didn't often make it
>> across the Atlantic until its vector of transmission (kids and/or
other
>> non-resistees) increased.
>>
>> MB Williams
>> Dept. of Anthro., UMass-Amherst
>
>
>You are right! Immunity is not passed on from generation to
generation. But
>there are other factors which affect how resistant a population is to
>disease. I stand by my original statements simply because my concept
of resistance
>is broader than mere immunity.
>
>We know that when a disease first arrives in a culture, it is
devastating. The
>effects are far worse on the first generation than it is on subsequent
generations.
>Two examples: In the South Pacific, when measles first arrived, it
wiped out
>90% of the population. Measles is a highly infectious disease, but
that does
>not explain why it killed so many people. Mortality rates for the
measles dropped in
>subsequent generations, more to the international norm for this
disease.
>
The reason that measles, and many other highly communicable *childhood*
diseases are so devastating in *virgin* populations is related to the
effects of those diseases on particular age groups, e.g., adults and
very young children experience, for reasons not completely understood
even by the medical field, higher mortality rates than do older
children and pre-teens. In subsequent generations, because adults are
more likely to have contracted the disease and survived, the population
most susceptible to the disease are those not around during earlier
exposures, e.g., children. Young children still have high mortality
rates, but older children have lower, and hence, although there is
mortality, on an average it is much lower than first generation
epidemics.
>Another example is the Ojibway (?) Indians who were first exposed to
>tuberculosis in the early twentieth century. At first, when the
>disease hit, *nobody knew what it was*. It did not act like normal
>tuberculosis which forms tumors in the lungs. In the first generation
>of Ojibway TB victims, tumors formed in the brain, liver, and all over
>the body! It was only by examining the tumors under a microscope that
>the cause was recognized as TB. Again, in subsequent generations it
>resembled the TB we all know and love. (Note that while immunity can
>be formed to TB, TB vaccines have never been as effective as other
>vaccines. The track record is pretty poor.)
Is the case of the Ojibway you reference cited in MacNeil or another
source? (I'd like to look at it first hand, as the groups from the
Upper Midwest have shown indications of TB for centuries, due to their
almost constant contact with Euros from the 16th century, and in fact,
fizzy work done on purported *pre-Contact* TB cases come from that
area, thus I have a difficult time accepting that any group in the
region was first *exposed* to TB within the last century.)
>These cases suggest that something other than immunity must be taken
into account
>when considering the problem of new diseases. European history is
also filled
>with diseases with strange symptoms that came and disappeared, never
to be seen
>again. Or were they? (McNall's Plagues and Peoples is an excellent
>history of disease which takes up these problems.)
Is this
>The point I am making is that there appear to be genetic factors
>beyond immunity that can affect how a disease infects a body. Certain
>forms of a disease are more survivable than others (e.g. TB in the
>lungs has a higher probability of survival than TB in the brain or the
>liver -- the infected may actually live to breed!). The thesis is
>interesting and helpful in explaining the massive depopulation of the
>Americas when the Europeans arrived.
The problem with using TB as an example in explaining the *massive
depopulation* of the Americas is that it really was very
insignificant... TB shows up _after_ the large die-offs, and in fact
may have been only a *secondary* infection, that is, attacking those
individuals whose immunities were weakened by smallpox, measles, etc.
In RI1000, skeletal TB was particularly lethal in the 17-30 age group,
and almost all victims showed evidence of pre-adolescent long-term
trauma, such as the recovery from disease.
Just a few thoughts,
Respectfully,
MB Williams
Dept. of Anthro., UMass-Amherst
|