for National Geographic News
Droughts and downpours exacerbated by climate change allowed two diseases to converge and wipe out large numbers of African lions in 1994 and 2001, according to a new study.
Lions regularly survive outbreaks of canine distemper virus (CDV) and infestations by a tick-borne blood parasite called Babesia. But both normally occur in isolation.
In 1994 and 2001, however, a "perfect storm" of extreme drought followed by heavy seasonal rains set up the conditions for the two diseases to converge, the study said.
The effect was lethal: The synchronized infections wiped out about a third of the Serengeti lion population in 1994. The nearby Ngorongoro Crater lion population experienced similar losses in 2001.
(Read a National Geographic magazine online extra about Serengeti and other lions.)
"It was already well known that die offs can be triggered by droughts and floods," Craig Packer, an ecologist at the University of Minnesota in St. Paul, explained in an email from his research site in Tanzania.
"We were able to identify the interacting components of a lethal co-infection that had not previously been considered," he said.
The research is published in today's issue of the journal PLoS ONE.
"Lethal One-Two Punch"
Packer and his colleagues combed through more than 30 years of data on the lion populations to determine the complex combination of factors that caused the mass die offs.
They found that at least five CDV outbreaks swept through the lion populations with no ill effect. The two die offs, which are also tied to CDV outbreaks, were preceded by extreme droughts.
Probing further, the researchers discovered the droughts weakened lion prey, including the Cape buffalo (photo).
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