By Stephen Smith
http://www.boston.com/news/science/articles/2006/03/13/a_darwinian_view_of_aids/

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A Darwinian view of AIDS

  By Stephen Smith  |  March 13, 2006

  This is the story of the rabbit and the virus.

  Rabbits were never meant to live in Australia. But a
  19th-century game hunter thought otherwise and imported
  the creatures. Over the decades, they did what rabbits
  do best: multiplied and multiplied, until they became a
  major nuisance.

  So, in the 1950s, Australian authorities introduced a
  viral disease called myxomatosis in a bid to eradicate
  the rabbits. And it worked -- but only briefly. In a
  matter of years, rabbits acquired the ability to resist
  the virus.

  It is a classic tale of evolution -- a story that
  unspools again and again in animals, people included.
  The march of human civilization, measured both by
  survival and suffering, is framed in many respects by
  how well we compete with microscopic organisms.

  By exploring how humans evolve to win the battle with
  diseases and how they are sometimes vanquished by those
  pathogens, scientists hope to find drugs that can mimic
  successes and stave off the worst that viruses and
  bacteria can produce.

  ''It's a constant race between humans and their
  capacity to create new drugs and pathogens and their
  ability to evolve," said Dr. Daniel Cohen, an
  infectious disease researcher at Fenway Community
  Health in Boston, which specializes in AIDS treatment.

  But before researchers can develop new drugs, they must
  understand the evolutionary nature of individual
  diseases and how viruses and bacteria, in turn, shape
  the evolution of humans and other animals.

  Scientists have long known, for example, that in
  regions where malaria is common, most notably Africa,
  humans have developed an intrinsic defense against the
  parasitic illness. And that defense, which involves a
  change in red blood cells, has proved to be a good
  thing for many Africans, making them less susceptible
  to the disease. But the same trait has proved to be a
  bad thing for their descendants in the United States
  and other malaria-free areas, because it results in
  sickle cell disease, a condition that robs organs of
  oxygen, causing debilitating bouts of pain and
  sometimes death.

  There are vital history lessons, too, when it comes to
  HIV.

  As researchers unlocked the secrets of HIV, they found
  a gene mutation they suspect may protect against the
  virus that causes AIDS.

  Human cells have locks on their surface -- scientists
  call them receptors -- and a virus must insert its key
  into these locks to gain entry. One of those is called
  CCR5, and HIV needs to unlock it to be able to infect
  cells. But scientists in recent years discovered that 5
  to 10 percent of people in northern Europe don't have
  CCR5 receptors.

  ''And that's where the story gets interesting," said
  Dr. Calvin Cohen, research director for Community
  Research Initiative of New England, which conducts
  trials of AIDS drugs.

  In contrast, people in Africa and Asia universally
  possess CCR5. So researchers theorized that lower HIV
  rates in northern Europe might be due in part to some
  people lacking the cellular lock.

  But why don't they have it? Right now, it's only an
  informed hunch, but scientists suspect that the
  mutation exhibited by northern Europeans may be an
  artifact of the bubonic plague. The theory goes like
  this: As the plague swarmed Europe starting in the 14th
  century, it wiped out people who possessed CCR5 but
  spared those who lacked it.

  ''What we're talking about is a Darwinian process,"
  Harmit Malik, who specializes in the study of genetic
  conflict at the Fred Hutchinson Cancer Research Center
  in Seattle. ''What was a really rare mutation was what
  survived. Everyone else had fallen prey to this
  particular pathogen."

  And the thing is, people who lack CCR5 receptors appear
  not to suffer any consequences.

  ''So we have an ideal combination," Calvin Cohen said.
  ''HIV needs it, but we don't. What an ideal target for
  drug development."

  That's why drug companies have developed experimental
  medications designed to block CCR5 so that HIV cannot
  enter cells. Cohen's Community Research Initiative is
  currently involved in a study of a Pfizer Inc.
  medication, with several patients enrolled in Boston.

  This and other efforts to use evolution as a weapon
  against HIV are an acknowledgment that even with more
  than two-dozen AIDS medications now available, that's
  still not enough. The AIDS virus is especially adept at
  evolving to escape drugs -- an evolutionary process
  that can take place in weeks and months.

  ''It is essentially an organism that is an example of
  evolution at light speed, constantly, constantly
  changing," said Warner C. Greene, director of the
  Gladstone Institute of Virology and Immunology at the
  University of California at San Francisco.

  Bringing the evolution story full circle, scientists
  continue to explore the history of the viral cousin of
  HIV carried by other primates. They know that HIV is an
  example of a virus that leaped from animals -- monkeys,
  in this case -- to humans. They also know that, with
  the passage of time, the virus ceased to harm monkeys,
  in part to allow its own survival. (So did the virus
  that attacked the Australian rabbits, by the way,
  evolving to be less harmful so more of its hosts could
  survive.)

  ''HIV coming fairly recently into the human population
  has not had a chance to evolve that way," said John M.
  Coffin, a leading AIDS researcher at Tufts University.

  ''Some day it will, but it's a long time away, and none
  of us should want to be a part of that evolutionary
  process."

  Stephen Smith can be reached at stsmith@globe.com.

  Audio  Interview with Brown University biology
  professor Ken Miller
http://www.boston.com/news/special/evolution/kenmiller2.mp3

  Audio  Discussion with Globe Health and Science writers
  on evolution
http://www.boston.com/news/special/evolution/evodiscussion3.mp3

  Pop-up  A brief history of evolution
http://www.boston.com/news/specials/evolution/evolution_timeline

  Pop-up  Evolution of a beak
http://www.boston.com/news/specials/evolution/beaks

  Pop-up  The evolution of Galapagos finches
http://www.boston.com/news/specials/evolution/beaks2

  Message Board  YOUR VIEW: Darwin vs. the Bible
http://boards.boston.com/n/pfx/forum.aspx?nav=messages&tsn=1&tid=2877&am
p;webtag=bc-news

   The science of evolution
http://www.boston.com/news/specials/evolution

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A Darwinian view of AIDS

  By Stephen Smith  |  March 13, 2006
http://www.boston.com/news/science/articles/2006/03/13/a_darwinian_view_of_aids/
  By Stephen Smith