Washington, June 26 : A new study has suggested that droughts and downpours aggravated by climate change allowed two diseases to converge and wipe out large numbers of African lions in 1994 and 2001.
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.
According to a report in National Geographic News, the new study indicated that in 1994 and 2001, a "perfect storm" of extreme drought followed by heavy seasonal rains set up the conditions for the two diseases to converge.
The effect was lethal, with the synchronized infections wiping out about a third of the Serengeti lion population in 1994.
The nearby Ngorongoro Crater lion population experienced similar losses in 2001.
"It was already well known that die offs can be triggered by droughts and floods," said Craig Packer, an ecologist at the University of Minnesota in St. Paul. "We were able to identify the interacting components of a lethal co-infection that had not previously been considered," he added.
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.
When the rains resumed, Babesia-carrying ticks emerged en masse and proliferated in their buffalo hosts. Many of the buffalo died.
The lions feasted on the weakened, parasite-infested buffalo, but the feast left the hunters with unusually high concentrations of Babesia. The subsequent CDV outbreak proved lethal, according to the study.
"CDV is immunosuppressive-like a short, sharp bout of AIDS-thus greatly intensifying the effects of the Babesia," said Packer.
This co-infection, or synchronization of the diseases, caused the mass die offs, Packer and his colleagues concluded.
According to Sonia Altizer, an ecologist who studies wildlife diseases at the University of Georgia in Athens, the research adds to a growing body of evidence showing how extreme climate events can have major impacts on the spread of infectious diseases.
In the case of the lions, Packer noted, wildlife managers may be able to better protect populations by reducing their tick loads immediately following a drought rather than controlling for CDV.