Extreme Weather Conditions Can Cause Infectious Diseases To Kill In Cooperation

Climate
extremes, for instance droughts or floods, can create conditions in
which diseases normally are tolerated in isolation are able to
converge, thus causing massive death of livestock or wildlife. These
findings were published by an international research team in the open
access journal PLoS ONE on June 25, 2008.



This team,
led by scientists at the University of California, Davis, the
University of
Illinois, and the University of Minnesota, specifically examined
outbreaks of canine distemper virus (CDV) in 1994 and 2001 in the lions
of Serengeti National Park and
Ngorongoro Crater in Tanzania. While CDV normally cycles within these
ecosystems, and many epidemics of this kind have occured without a
significant decrease in the lion population, these epidemics resulted
in an unusually high level of mortality. That is, in 1994, the outbreak
the Serengeti study area's popoulation dropped more than 35%. Losses
were similar in 2001 in the Crater.



The
story behind these outbreaks is an involved chain of events. Both of
these outbreak years were preceded by extreme drought conditions, which
considerably hurt the Cape buffalo population, a major source of food
for these lions. The rains returned, and with them serious infestations
of ticks, carrying the parasite Babesia. These
parasites, which
are normally present in the lions at harmless levels, thus had
increased levels of infections in the lions. When the canine distemper
virus outbreak began, the lion population's immunity was already
compromised, and it was the tick-bourne parasite that led to fatalities
in the lion population.



While the populations of lions
recovered quickly, most climate changed models, in light of global
warming, predict increasing frequency of droughts. This study suggests
that the extreme weather conditions caused by these changes could
create a "perfect storm" of infectious outbreaks, triggering enourmous
levels of mortality.



According to the authors, such changes as
climate events can have complex implications on populations. "The study
illustrates how ecological factors
can produce unprecedented mortality events and suggests that
co-infections may lie at the heart of many of the most serious
die-offs in nature," said Craig Packer, Regents Professor of Ecology,
Evolution and Behavior at the University of Minnesota.



Climate Extremes Promote Fatal Co-Infections during Canine
Distemper Epidemics in African Lions.

Munson L, Terio KA, Kock R, Mlengeya T, Roelke ME, et al. (2008)


PLoS ONE 3(6): e2545.

doi:10.1371/journal.pone.0002545

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Written by Anna Sophia McKenney