Re: diseases and immunity

Gerold Firl (
9 Jul 1996 17:06:04 GMT

In article <4rom4t$>, Beth Williams) writes:

|> 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.

There's more to it than that, MB. As gazis-sax wrote:

|> >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.

|> 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.)

Mcneill does mention something like this, discussing a group of
"canadian indians" on their first exposure to TB. He doesn't say when
it happened; I assumed 19th century. He does say that at first
exposure, the infection looked totally unlike TB; not only were the
internal organs attacked, but also the spinal meninges. By the third
generation, the infection settled down into the familiar pulmonary

I have tried to explain this to you before; it's probably useless, but
I'll have another go: the human immune system has enormous
*variability* - that's how it manages to keep ahead of rapidly
mutating pathogens. The immune system must be able to deal with a
large variety of infectious agents, which are constantly changing;
that's why humans are sexually attracted to those with different
immune factors. When TB first appeared as a virgin-soil infection in
the tribe cited above, many of the individuals were carrying an immune
system which had no resistance to TB, so the TB bacilli rapidly spread
throughout their entire body and killed them. Those individuals who
happened to have an immune response which recognized and destroyed the
TB survived, and by the third generation all the children of that
tribe had those immune factors. This is evolution in action. It's very
similar to what happened in europe when syphilis first appeared: the
individuals who were unfortunate enough to have no immunological
response to the syphilis spirochete would die a few days after being
infected. They were eaten alive by the spirochete. Nasty, but that's
the way it works.

|> 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.

You can't see the trees for the forest, mb. Smallpox was the mosd
important killer, but if smallpox hadn't existed, then another disease
would have taken its place. If TB got to an isolated population before
smallpox did, then TB would would kill them off. No one is using TB to
explain the american die-off; the example was cited to illustrate the
vulnurability of previously-unexposed populations to new pathogens.

Disclaimer claims dat de claims claimed in dis are de claims of meself,
me, and me alone, so sue us god. I won't tell Bill & Dave if you won't.
=-=-=-=-=-=-=-=-=-=-=-=-=-=---- Gerold Firl @ ..hplabs!hp-sdd!geroldf