Title:  Human Plague Cases Increasing in Southwest Likely Cause: Global
          Climate Change
Date:   November 19, 1999




  Media contact:                            November 19, 1999
  Cheryl Dybas                               NSF PR 99-70
  (703) 306-1070/cdybas@nsf.gov

  Program contact:
  Scott Collins
  (703) 306-1480/scollins@nsf.gov

  HUMAN PLAGUE CASES INCREASING IN SOUTHWEST
  Likely Cause: Global Climate Change

       Human plague, that dreaded disease of centuries past caused by
       the bacterium Yersinia pestis, is on the rise, at least in the
       southwestern United States.

       Biologists at the National Science Foundation (NSF)-funded
       LongTerm Ecological Research (LTER) site in Sevilleta, New
       Mexico, have found that human plague cases in New Mexico occurred
       more frequently after wetter than average winter-spring time
       periods (October to May).  In fact, during years much wetter than
       normal, a 60% rise in the number of cases of human plague
       resulted.  The scientists report these results in a paper
       published in the November issue of the American Journal of
       Tropical Medicine and Hygiene.

       Plague occurs episodically in many parts of the world, explains
       Robert Parmenter, director of the Sevilleta LTER field research
       station, and lead author of the paper.  "Some outbreaks appear to
       be related to increased abundance of rodents and other mammals
       that serve as hosts for the fleas that then transmit the disease
       to humans."  Increased winter-spring precipitation, say Parmenter
       and his colleague Ken Gage of the Center for Disease Control
       office in Fort Collins, Colorado, enhances small
       mammal food resources (plants and insects), leading to an
       increase in the abundance of plague hosts.  In addition, moister
       climate conditions may act to promote flea survival and
       reproduction, also enhancing plague transmission.  "Our results
       can be used by physicians and public health personnel to identify
       and predict periods of increased risk of plague transmission to
       humans," Parmenter hopes.

       Global climate dynamics are proposed by some scientists as the
       culprit in recent outbreaks of infectious diseases; others warn
       that long-term global warming could increase the risk of
       contracting such diseases.  "The recent El Nino events of the
       1990s have been associated with large increases in rodent
       populations in both North and South America," explains Scott
       Collins, LTER program director at NSF.  "These increases in
       rodent populations have been shown to correlate with numerous
       diseases, including Lyme disease and hantavirus pulmonary
       syndrome.  Climate studies may provide a forecasting tool for
       identifying periods of increased risk of disease transmission."

       Plague was introduced into North America via San Francisco,
       California, in 1899-1900 by shipboard transport of
       plague-infected rats from Asia.  These rats quickly infected
       native mammal populations, especially ground squirrels, and
       plague spread throughout western North America.  Plague is now
       most commonly found in the southwestern United States -- in New
       Mexico, Colorado, Arizona and California.  Major risk factors for
       humans include contact with diseased wild mammals or their
       infected fleas, and exposure to infected fleas carried by pets
       like dogs and cats.

       "If climate conditions become favorable for reproduction and
       survival of either the wild mammal populations or their flea
       populations, then the probability of human infection via
       animal-fleahuman contacts will also increase," write Parmenter
       and his colleagues.

       With known risk of plague transmission following unusually moist
       winter-spring seasons, localized public health warnings and
       heightened medical surveillance can be arranged prior to the peak
       in human cases during the summer, the scientists suggest.  "Local
       physicians and health care professionals can determine if their
       cities and towns have received higher-than-normal precipitation,
       and increase their cognizance for plague patients," the
       researchers write.

  -NSF-

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