Extreme Weather Conditions Can Cause Infectious Diseases To Kill In Cooperation

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Main Category: Infectious Diseases / Bacteria / Viruses
Also Included In: Biology / Biochemistry;  Tropical Diseases
Article Date: 25 Jun 2008 - 0:00 PDT

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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
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