Re: diseases and immunity

Gerold Firl (
17 Jul 1996 19:57:19 GMT

In article <4sg1e7$>, Beth Williams) writes:

|> In <4sebpn$> (Gerold Firl)
|> writes:

|> >Here's a simple model of the population dynamics of a pathogen upon
|> >reaching a virgin-soil host population: instead of taking several
|> >years to die, these new hosts die in several days or weeks. They are
|> >also totally open to infection, with no appreciable immune reaction.
|> >This results in a new selection pressure on the pathogen: it needs to
|> >jump to a new host quickly, and it doesn't need to be very picky about
|> >what part of the body is colonized.
|> >
|> >The pathogen thus evolves to become highly contagious, which, in
|> >practical terms, means being able to survive temperature fluctuations
|> >and dessication. Using TB as an example, it also will change so-as to
|> >no longer restrict itself to the lungs. (Bacteria have a varied
|> >repertoir of cell-membrane proteins which attach to different host
|> >tissues; lungs, intestines, blood cells, nerves, cartilage, etc) In an
|> >immunilogically experienced population, TB resides in the lungs; in an
|> >inexperienced host, that restriction is no longer necessary.

|> Wrong, wrong, wrong... Haven't you read _anything_ I've posted? TB
|> does _not_ reside only in the lungs in *immunilogically experienced*
|> populations!

Thanks for clarifying that, MB. You're right. TB does not reside
exclusively in the lungs among immunologically experienced populations.
TB is, however, primarily a pulmonary disorder - unless we're talking
about virgin-soil epidemics.

|> Skeletal TB effects 3-5% of ALL cases of TB, not only in *virgin soil*
|> populations.


|> >As soon as TB invaded amerindian populations, the new environment led
|> >to an evolutionary shift. Highly contagious strains were favored,
|> >since the less-contagious ones died along with their hosts, while more
|> >transmittable strains had already infected a few other people before
|> >their host died.

|> Geez, Gerold, where do you come up with this crap? TB remained *highly
|> contagious* in all densely congregated populations, Indian or white,
|> until the 20th century.

Ya know, MB, it amazes me that someone who apparantly resides at the
UMass anthropology department, and who has done actual physical anthro
fieldwork, could have so little background in biology and evolution. The
lifecycle of parasite-host population ecology is well-known and not at
all complicated. The term "highly contagious" must be evaluated relative
to other diseases, and to other strains of the same disease. Disease
microbes are adapted to a warm, moist, slightly salty environment: the
interior of the human body. It is difficult for them to cross the divide
to a new host. Whereas an endemic pathogen culture has the luxury of
taking years between successfully infecting a new host, an epidemic
pathogen culture has only a matter of days or weeks. This places a huge
premium on transmissibility.

Do you have any idea of the mean lifetime of an 18th or 19th century
european who was infected with TB? One year? Two? Five? It's in that
range. Whereas, in dubos and macneill are to be believed, TB in a
virgin-soil epidemic killed much more quickly. What this means, in an
evolutionary perspective from the PoV of the bacteria, is that it's
absolutely necessary to jump to a new host as quickly as possible.

The lack of immunological defenses among indian populations results in
an increased infection rate even without any changes to the bacteria.
however, the bacteria will not remain passive in such a situation. It
will evolve to maximize it's survival rate, just as the human population
does. That means an increased gene frequency for characteristics which
aid infection, such as dessication-resistance.

|> Go back and read some vital statistics records
|> from New England in the 19th century, and you'll find that
|> *consumption* accounted for nearly 50% of all *natural* deaths between
|> the ages of 18-50, and *lung fever* (rapid pulmonary TB) ranked up with
|> yellow fever, measles and smallpox.

Makes sense to me.

|> >A big factor there is the way people will flee from an epidemic.
|> >Crosby describes how refugees from disease spread it far and wide,
|> >probably accounting for the devastation of the mound builders, far
|> >ahead of any colonization.

|> AH HA HA HA!!!!!! So Europeans were running around North America in
|> the 13th and 14th centuries???? The *moundbuilder* (early
|> Mississipian) cultures, particularly those in the American Bottom
|> region, e.g., Cahokia, dispersed prior to 1400.

Sorry, I used the wrong term then. I was referring to indian inhabitants
of the mississippi/missouri/ohio river valleys in the early 16th
century. I guess they were the successors to the mound builders.

MB, it seems like you are very quick to jump on a minor point
("moundbuilders" or "TB as pulmonary infection") but very unwilling to
come to grips with the major issues. One problem I see with you is your
extreme ethnocentric chauvinism (a characteristic you share with eric
brunner); any fact which could in any way, no matter how remotely, be
construed as indicating amerindian "inferiority" vis-a-vis europeans
provokes an exagerated reaction: whether we're talking about population
density (you claim that the amerinds of the northeast had a population
density equal to england at the time of contact), HLA-mediated immune
response (you claim no genetic difference in disease resistance between
old world populations which had suffered from repeated epidemics and
massive die-offs compared to amerinds who had never in their
evolutionary past seen any exposure) and even our lamentable cannibalism
thread from a few months ago, where you stubbornly denied, in the face
of multifactorial evidence, that your beloved iroquois ate manflesh. How
are you ever going to make it in acedemia with such a closed mind?

I recommend that you pick-up a little background in evolutionary
biology. How can you study Man without understanding evolution?

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